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Acesta este centrul galaxiei , Dumnezeu ,Lumina Lumii ,Adevarul   ,Originea si Finalitatea Fiintei , Viata Vesnica.
Aceasta este CALEA ,( Drumul , Labirintul ) catre SINE (san)- CALEA laCTee (MILKY WAY )
                doCTor - open the DOOR
Precum in CER asa si pre Pamant !!
    Get this widget |     Track details   | eSnips Social DNA    
DOamne !! MARE TI-E gradina !!!
Atitudinea ConTemplativa - ultima si cea mai inalta , prin care creatorul isi admira opera !!O adevarata GioCONda !!!
The galaxy seen as a dolphin, a śiśumãra
Spiral galaxies usually consist of two major components: A flat, large disk which often contains a lot of interstellar matter (visible sometimes as reddish diffuse emission nebulae, or as dark dust clouds) and young (open) star clusters and associations, which have emerged from them (recognizable from the blueish light of their hottest, short-living, most massive stars), often arranged in conspicuous and striking spiral patterns and/or bar structures, and an ellipsoidally formed bulge component, consisting of an old stellar population without interstellar matter, and often associated with globular clusters. The young stars in the disk are classified as stellar population I, the old bulge stars as population II. The luminosity and mass relation of these components seem to vary in a wide range, giving rise to a classification scheme. The pattern structures in the disk are most probably transient phenomena only, caused by gravitational interaction with neighboring galaxies.

Our sun is one of several 100 billion stars in a spiral galaxy, the Milky Way.
The Milky Way Galaxy
A spiral galaxy, type Sbc, centered in Sagittarius

[MW, AAT] The Milky Way is the galaxy which is the home of our Solar System together with at least 200 billion other stars (more recent estimates have given numbers around 400 billion) and their planets, and thousands of clusters and nebulae, including at least almost all objects of Messier's catalog which are not galaxies on their own (one might consider two globular clusters as possible exceptions, as probably they are just being, or have recently been, incorporated or imported into our Galaxy from dwarf galaxies which are currently in close encounters with the Milky Way: M54 from SagDEG, and possibly M79 from the Canis Major Dwarf). See our Messier Objects in the Milky Way page, where details are given for each object to which part of our Galaxy it is related. All the objects in the Milky Way Galaxy orbit their common center of mass, called the Galactic Center (see below).

As a galaxy, the Milky Way is actually a giant, as its mass is probably between 750 billion and one trillion solar masses, and its diameter is about 100,000 light years. Radio astronomial investigations of the distribution of hydrogen clouds have revealed that the Milky Way is a spiral galaxy of Hubble type Sb or Sc. Therefore, our galaxy has both a pronounced disk component exhibiting a spiral structure, and a prominent nuclear reagion which is part of a notable bulge/halo component. Decade-long observations have brought up more and more evidence that the Milky Way may also have a bar structure (so that it would be type SB), so that it may look like M61 or M83, and is perhaps best classified as SABbc. Recent investigations have brought up support for the assumption that the Milky Way may even have a pronounced central bar like barred spiral galaxies M58, M91, M95, or M109, and thus be of Hubble type SBb or SBc.
# More on the structure of the Milky Way

The Milky Way Galaxy belongs to the Local Group, a smaller group of 3 large and over 30 small galaxies, and is the second largest (after the Andromeda Galaxy M31) but perhaps the most massive member of this group. M31, at about 2.9 million light years, is the nearest large galaxy, but a number of faint galaxies are much closer: Many of the dwarf Local Group members are satellites or companions of the Milky Way. The two closest neighbors, both already mentioned, have only recently been discovered: The nearest of all, discovered in 2003, is an already almost disrupted dwarf galaxy, the Canis Major Dwarf, the nucleus of which is about 25,000 light-years away from us and about 45,000 light-years from the Galactic Center. Second comes SagDEG at about 88,000 light years from us and some 50,000 light years from the Galactic Center. These two dwarfs are currently in close encounters with our Galaxy and in sections of their orbits situated well within the volume ocupied by our Milky Way. They are followed in distance by the more conspicuous Large and Small Magellanic Cloud, at 179,000 and 210,000 light years, respectively.

The spiral arms of our Milky Way contain interstellar matter, diffuse nebulae, and young stars and open star clusters emerging from this matter. On the other hand, the bulge component consists of old stars and contains the globular star clusters; our galaxy has probably about 200 globulars, of which we know about 150. These globular clusters are strongly concentrated toward the Galactic Center: From their apparent distribution in the sky, Harlow Shapley has concluded that this center of the Milky Way lies at a considerable distance (which he overestimated by factors) in the direction of Sagittarius and not rather close to us, as had been thought previously.

Our solar system is thus situated within the outer regions of this galaxy, well within the disk and only about 20 light years "above" the equatorial symmetry plane (to the direction of the Galactic North Pole, see below), but about 28,000 light years from the Galactic Center. Therefore, the Milky Way shows up as luminous band spanning all around the sky along this symmetry plane, which is also called the "Galactic Equator". Its center lies in the direction of the constellation Sagittarius, but very close to the border of both neighbor constellations Scorpius and Ophiuchus. The distance of 28,000 light years has recently (1997) been confirmed by the data of ESA's astrometric satellite Hipparcos. Other investigations published consequently have disputed this value and propose a smaller value of some 25,000 light years, based on stellar dynamics; a recent investigation (McNamara et.al 2000, based on RR Lyrae variables) yields roughly 26,000 light years. These data, if of significance, wouldn't immediately effect values for distances of particular objects in the Milky Way or beyond.

The solar system is situated within a smaller spiral arm, called the Local or Orion Arm, which is merely connection between the inner and outer next more massive arms, the Sagittarius Arm and the Perseus Arm; see our Milky Way Spiral Structure page.

Similar to other galaxies, there occur supernovae in the Milky Way at irregular intervals of time. If they are not too heavily obscurred by interstellar matter, they can be, and have been seen as spectacular events from Earth. Unfortunately, none has yet appeared since the invention of the telescope (the last well observed supernova was studied by Johannes Kepler in 1604).

Milky Way pictures are wide-field exposures. Besides being attractive and often colorful, they are often suited to view the Milky Way objects (including nebulae and star clusters) in their celestial surroundings of field stars. Some fields include lots of Messier objects and thus included here:

    * Milky Way central region including constellations Sagittarius, Scorpius, Ophiuchus and Scutum, and map of the Milky Way Central Region, by Bill Keel of the University of Alabama
    * Milky Way in Sagittarius, including portions of Scorpius and Ophiuchus
    * Milky Way around M17, M18, and M24

Our image was obtained by David Malin of the Anglo-Australian Observatory, and shows the many Messier objects around the direction of the Galactic Center. It is copyrighted and may be used for private purpose only. For any other kind of use, including internet mirroring and storing on CD-ROM, please contact the Photo Permissions Department (photo at aaoepp.aao.gov.au) of the Anglo Australian Observatory.
# More information on this image by David Malin
# Old style AAT image

In order to obtain a picture of the whole Milky Way as it appears from Earth, one must either compose a mosaic of many photographs (optionally computer-processed), or create a drawing; fine examples may be accessed below:

    * A good Milky Way photo mosaic
    * Knut Lundmark's drawing of the Milky Way

In the infrared light, the structure of the Milky Way can be better investigated, as the obscurring dust clouds are of better transparency for long wavelength IR than for the visible light. The Cobe satellite has provided an infrared image of the Milky Way's central region.

The central region of the Milky Way, as those of many other galaxies, is more densely crouded with stars than the outer region, and contains a massive central object, Sagittarius A*.

Below we give some data for the Galactic Center (this and all following positions for epoch 2000.0):

Right ascension 17 : 45.6 (h : m)
Declination -28 : 56 (deg : m)
Distance 28 (kly)

The Galactic North Pole is at

Right ascension 12 : 51.4 (h : m)
Declination +27 : 07 (deg : m)

The coordinate data given here were extracted from the online coordinate calculator at Nasa/IPAC's Extragalactical Database (NED) (also available by telnet).

Our Sun, together with the whole Solar System, is orbiting the Galactic Center at the distance given, on a nearly circular orbit. We are moving at about 250 km/sec, and need about 220 million years to complete one orbit (so the Solar System has orbited the Galactic Center about 20 to 21 times since its formation about 4.6 billion years ago).

In addition to the overall Galactic Rotation, the solar system is moving between the neighboring stars (peculiar motion) at a velocity of about 20 km/s, to a direction called "Solar Apex," at the approximate position RA=18:01, Dec=+26 (2000.0); this motion has been discovered by William Herschel in 1783.

Considering the sense of rotation, the Galaxy, at the Sun's position, is rotating toward the direction of Right Ascension 21:12.0, Declination +48:19. This shows that it rotates "backward" in the Galactic coordinate system, i.e. the Galactic North Pole is actually a physical South Pole with respect to galactic rotation (defined by the direction of the angular momentum vector).

    * More info on the Milky Way Spiral Structure
    * Messier Objects in the Milky Way page

More links to Milky Way materials:

    * Milky Way Galaxy images from the Astronomical Picture of the Day archives
    * Milky Way Wide-Angle Photos
    * Multi Wavelength Images of the Milky Way (Nasa ADC)
    * Milky Way page of the MAP space observatory project
    * The Summer Milky Way from S.E. Arizona
    * Milky Way panorama by Axel Mellinger
    * The Milky Way Galaxy within 50,000 light years, A Map of the Milky Way, and The Milky Way's Satellite Galaxies, from An Atlas of the Universe
    * The Structure of the Milky Way Tutorial, Gene Smith
    * Yahoo's index of Milky Way webpages


    * D.H. McNamara, J.B. Madsen, J. Barnes, and B.F. Erickson, 2000. The Distance to the Galactic Center. Publications of the Astronomical Society of the Pacific, Vol. 112, pp. 202-216 (Feb. 2000) [ADS: 2000PASP..112..202M]

General References and Further Reading:

    * The Milky Way, by Bart J. and Priscilla F. Bok. 5th edition. Harvard University Press, 1981.
    * The Guide to the Galaxy, by Nigel Henbest and Heather Cooper. Cambridge University Press, 1994.
    * The Alchemy of the Heavens, by Ken Croswell. Anchor Books, New York, 1995.

Hartmut Frommert
Christine Kronberg

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Last Modification: August 25, 2005
Originea ADN ???
O nebuloasa ciudata in forma de dublu-helix in apropierea centrului Caii Lactee  
Categorie: STIRILE SOFTPEDIA :: Stiinte

  Creata probabil de campul magnetic din centrul galaxiei
By: Vlad Tarko, Senior Editor, Sci-Tech News

Telescopul spatial Spitzer a facut o descoperire fara precedent: o nebuloasa in forma de dublu-helix care se intinde pe o lungime mai mare de 80 de ani lumina, localizata la numai 300 de ani lumina de gaura neagra enorma care este in centrul Caii Lactee. In comparatie, Pamantul este la mai mult de 25 000 de ani lumina de centrul galaxiei.

Nebuloasele sunt nori interstelari de praf, gaz si plasma care au rezultat in urma exploziei stelelor si sunt locurile in care se formeaza noi stele.

"Vedem doua siruri inconjurandu-se unul in jurul celuilalt ca intr-o molecula de ADN", a spus Mark Morris, un profesor de fizica si astronomie la UCLA. "Nimeni pana acum nu a mai vazut asa ceva in spatiul cosmic. Cele mai multe nebuloase sunt fie galaxii spirale pline de stele sau conglomerate amorfe de praf si gaz. Ceea ce vedem insa aici are un grad ridicat de ordine."

Morris si colegii sai de la UCLA studiaza centrul galaxiei pe toate lungimile de unda. Telescopul Spatial Spitzer este un telescop in domeniul infrarosiilor, iar imaginile sale ale cerului au o rezolutie fara precedent. Tocmai aceasta rezolutie si sensibilitate a lui Spitzer sunt lucrurile care au permis astronomilor sa observe cu claritate nebuloasa in forma de dublu helix.

Oamenii de stiinta se intreaba ce anume determina formarea acestei forme neobisnuite. Morris speculeaza ca probabil are de-a face cu campurile magnetice:

"Stim ca centrul galactic are un camp
magnetic puternic, care este foarte ordonat si ca liniile de camp sunt orientate perpendicular pe planul galaxiei. Daca iei aceste linii de camp magnetic si le rasucesti la baza lor, atunci trimiti de-a lungul liniilor de camp o unda numita unda torsionala. Puteti sa va imaginati aceste linii de camp magnetic asemenea unor benzi de cauciuc intinse. Daca invarti de un capat, rasucirea se transmite de-a lungul benzilor."

"Ceea ce vedem este aceasta unda torsionala propagandu-se spre exterior. Nu o vedem efectiv miscandu-se, pentru ca dureaza vreo 100 000 de ani pentru a se misca de la locul de unde credem ca a plecat pana la locul in care se gaseste acum – insa, oricum, se misca repede – cam cu 1 000 de kilometri pe secunda – pentru ca in centrul galaxiei campul magnetic este atat de puternic – cam de 1 000 de ori mai puternic decat aici unde suntem noi, in suburbiile galaxiei."

Datorita faptului ca nebuloasa este facuta din plasma – adica din ioni si electroni – asemenea campuri magnetice influenteaza forma sub care se distribuie materia in spatiu. Pe de alta parte, studiind distributia materiei – forma unor asemenea nebuloase – pot fi obtinute informatii despre campurile magnetice. Morris a argumentat de ani de zile ca in centrul galaxiei exista un camp magnetic extrem de puternic – acest nou studiu, publicat impreuna cu Keven Uchida, un fost doctorand la UCLA si Tuan Do, un doctorand in astronomie la UCLA, ofera indicii puternice in favoarea punctului sau de vedere.

Pentru a se forma o asemenea nebuloasa in forma de dublu helix este nevoie de un camp magnetic puternic, de un corp care sa se roteasca, si ca materialul nebuloasei sa fie pozitionat unde trebuie. Gaura neagra centrala este atat sursa unui camp magnetic puternic cat si un corp care se roteste. Dat fiind ca cele mai multe galaxii au asemenea gauri negre masive in centrul lor, Morris se asteapta ca aceste nebuloase sa fie de fapt destul de raspandite – cu toate ca pana acum nu a mai fost descoperita niciuna (din cauza telescoapelor insuficient de bune).

"Cu siguranta ca ma astept sa vad in galaxiile bogate in nori de gaz [aceasta configuratie] cu toate elementele sale", a spus Morris.

Campul magnetic in centrul galaxiei este de 1 000 de ori mai mic decat campul magnetic al Soarelui, insa ocupa un volum atat de mare incat contine cu mult mai multa energie decat cel al Soarelui. Elergia sa este estimata ca echivaland cu cea a 1 000 de supernove.

Campul magnetic este important pentru ca influenteaza formarea stelelor: campul exercita o forta de "frecare" asupra particulelor, forta care poate sa incetineasca formarea stelelor (forta magnetica este proportionala cu viteza particulelor asupra carora actioneaza).

Photo credit: M. Morris / UCLA; Spitzer telescope (NASA/JPL-Caltech)

Milky Way is a barred spiral[1] galaxy of the Local Group. Although the Milky Way is but one of billions of galaxies in the observable universe (between 1×1010 and 8×1010), the Galaxy has special significance to humanity as it is the home of our Solar System. The Greek philosopher Democritus (450 BC–370 BC) was the first known person to claim that the Milky Way consists of distant stars.

The term "milky" originates from the hazy band of white light appearing across the celestial sphere visible from Earth, which comprises stars and other material lying within the galactic plane. The galaxy appears brightest in the direction of Sagittarius, towards the galactic center. Relative to the celestial equator, the Milky Way passes as far north as the constellation of Cassiopeia and as far south as the constellation of Crux, indicating the high inclination of Earth's equatorial plane and the plane of the ecliptic relative to the galactic plane. The fact that the Milky Way divides the night sky into two roughly equal hemispheres indicates that the solar system lies close to the galactic plane.

The main disk of the Milky Way Galaxy is about 80,000 to 100,000 light-years in diameter, about 250,000 to 300,000 light-years in circumference, and outside the Galactic core, about 1,000 light-years in thickness.[citation needed] It is estimated to contain 200[2] billion stars but this number might reach 400 billion [1] if small-mass stars predominate. As a guide to the relative physical scale of the Milky Way, if the galaxy were reduced to 130 km (80 mi) in diameter, the solar system would be a mere 2 mm (0.08 inches) in width. The Galactic Halo extends outward, but is limited in size by the orbits of the two Milky Way satellites, the Large and the Small Magellanic Clouds, whose perigalacticon is at ~180,000 light-years.[3] As detailed in the Structure section below, new discoveries indicate that the disk extends much farther than previously thought.

The Milky Way's visual absolute magnitude is −20.9[4]
The galactic center in the direction of Sagittarius. The primary stars of Sagittarius are indicated in red.
The galactic center in the direction of Sagittarius. The primary stars of Sagittarius are indicated in red.

    * 1 Age
    * 2 Structure
    * 3 The Sun's place in the Milky Way
    * 4 The Milky Way environment
    * 5 Speed through space
          o 5.1 Future of the Milky Way
    * 6 Name and myths
    * 7 References
    * 8 External links

[edit] Age

It is extremely difficult to define the age at which the Milky Way formed, but the age of the oldest stars in the Galaxy is currently estimated to be about 13.6 billion years, which is nearly as old as the Universe itself.[5]

This estimate is based upon research performed in 2004 by a team of astronomers: Luca Pasquini, Piercarlo Bonifacio, Sofia Randich, Daniele Galli, and Raffaele G. Gratton. The team used the UV-Visual Echelle Spectrograph of the Very Large Telescope to measure, for the first time, the beryllium content of two stars in globular cluster NGC 6397. This allowed them to deduce the elapsed time between the rise of the first generation of stars in the entire Galaxy and the first generation of stars in the cluster, at 200 million to 300 million years. By including the estimated age of the stars in the globular cluster (13.4 ± 0.8 billion years), they estimated the age of the oldest Milky Way stars at 13.6 ± 0.8 billion years.

[edit] Structure
Observed structure of the Milky Way's spiral arms
Observed structure of the Milky Way's spiral arms

The mass distribution within the Milky Way closely resembles the Sbc Hubble classification, which is a spiral-galaxy with relatively loosely-wound arms.[6] It was only in the 1980s that astronomers began to suspect that the Milky Way is a barred spiral[7] rather than an ordinary spiral, which observations in 2005 with the Spitzer Space Telescope have since confirmed, showing that the galaxy's central bar is larger than previously suspected.[8] This argues for a classification of type SBbc (loosely wound barred spiral). In 1970 Gérard de Vaucouleurs predicted that the Milky Way was of type SAB(rs)bc, where the "rs" indicates a broken ring structure around the core region.[9]

As of 2006, the Milky Way's mass is thought to be about 5.8×1011 M☉[10][11][12] comprising 200 to 400 billion stars. Its integrated absolute visual magnitude has been estimated to be -20.9.

The galactic disk, which bulges outward at the galactic center, has a diameter of between 70,000 and 100,000 light-years. [13] The distance from the Sun to the galactic center is now estimated at 26,000 ± 1400 light-years while older estimates could put our parent star as far as 35,000 light-years from the central bulge.

The galactic center harbors a compact object of very large mass (named Sagittarius A*), strongly suspected to be a supermassive black hole. Most galaxies are believed to have a supermassive black hole at their center.[14]

As is typical for many galaxies, the distribution of mass in the Milky Way is such that the orbital speed of most stars in the galaxy does not depend strongly on its distance from the center. Away from the central bulge or outer rim, the typical stellar velocity is between 210 and 240 km/s.[15] Hence the orbital period of the typical star is directly proportional only to the length of the path traveled. This is unlike in the solar system where different orbits are also expected to have significantly different velocities associated with them, and is one of the major pieces of evidence for the existence of dark matter.

The galaxy's bar is thought to be about 27,000 light-years long, running through the center of the galaxy at a 44 ± 10 degree angle to the line between our sun and the center of the galaxy. It is composed primarily of red stars, believed to be ancient. The bar is surrounded by a ring called the "5-kpc ring" that contains a large fraction of the molecular hydrogen present in the galaxy and most of the Milky Way's star formation activity. Viewed from the Andromeda Galaxy, it would be the brightest feature of the Milky Way[16]

Each spiral arm describes a logarithmic spiral (as do the arms of all spiral galaxies) with a pitch of approximately 12 degrees. There are believed to be four major spiral arms which all start at the Galaxy's center. These are named as follows, according to the image at left:
Observed and extrapolated structure of the spiral arms (click to see legend)
Observed and extrapolated structure of the spiral arms (click to see legend)

    * 2 and 8 - 3kpc and Perseus Arm
    * 3 and 7 - Norma and Cygnus Arm (Along with a newly discovered extension - 6)
    * 4 and 10 - Crux and Scutum Arm
    * 5 and 9 - Carina and Sagittarius Arm

There are at least two smaller arms or spurs, including:

    * 11 - Orion Arm (which contains the solar system and the Sun - 12)

Outside of the major spiral arms is the Outer Ring or Monoceros Ring, a ring of stars around the Milky Way proposed by astronomers Brian Yanny and Heidi Jo Newberg, which consists of gas and stars torn from other galaxies billions of years ago.

The galactic disk is surrounded by a spheroid halo of old stars and globular clusters, whose 90% lie within 100,000 light-years [2], suggesting a stellar halo diameter of 200,000 light-years. However, a few globular clusters have been found farther, such as PAL 4 and AM1 at more than 200,000 light-years away from the galactic center. While the disk contains gas and dust obscuring the view in some wavelengths, the spheroid component does not. Active star formation takes place in the disk (especially in the spiral arms, which represent areas of high density), but not in the halo. Open clusters also occur primarily in the disk.

Most of the mass of the Milky Way is thought to be dark matter, forming a dark matter halo of an estimated 600-3000 billion solar masses (M☉) which is concentrated towards the Galactic Center.[12]

Recent discoveries have given added dimension to our knowledge of the structure of the Milky Way. With the discovery that the disc of the Andromeda Galaxy (M31) extends much further than previously thought,[17] the possibility of the disk of the Milky Way extending further is apparent, and this is supported by evidence of the newly discovered Outer Arm extension of the Cygnus Arm.[18] With the discovery of the Sagittarius Dwarf Elliptical Galaxy came the discovery of a ribbon of galactic debris as the polar orbit of Sagittarius and its interaction with the Milky Way tears it apart. Similarly, with the discovery of the Canis Major Dwarf Galaxy, a ring of galactic debris from its interaction with the Milky Way encircles the galactic disk.

On January 9, 2006 Mario Juric and others of Princeton University announced that the Sloan Digital Sky Survey of the northern sky has found a huge and diffuse structure (spread out across an area around 5,000 times the size of a full moon) within the Milky Way that does not seem to fit within our current models. The collection of stars rises close to perpendicular to the plane of the spiral arms of the Milky Way. The proposed likely interpretation is that a dwarf galaxy is merging with the Milky Way. This galaxy is tentatively named the Virgo Stellar Stream and is found in the direction of Virgo about 30,000 light-years away.

[edit] The Sun's place in the Milky Way
360-degree photographic panorama of the entire galaxy, from the viewpoint of our solar system.
360-degree photographic panorama of the entire galaxy, from the viewpoint of our solar system.

The Sun (and therefore the Earth and Solar System) may be found close to the inner rim of the Orion Arm, in the Local Fluff, at a hypothesized distance of 7.94±0.42 kpc from the Galactic Center.[19][20][21] The distance between the local arm and the next arm out, the Perseus Arm, is about 6,500 light-years.[22] Our Sun, and thus the solar system, is found in what scientists call the galactic habitable zone.

The Apex of the Sun's Way, or the solar apex, refers to the direction that the Sun travels through space in the Milky Way. The general direction of the sun's galactic motion is towards the star Vega near the constellation of Hercules, at an angle of roughly 60 sky degrees to the direction of the Galactic Center. The sun's orbit around the galaxy is expected to be roughly elliptical with the addition of perturbations due to the galactic spiral arms and non-uniform mass distributions.

It takes the solar system about 225-250 million years to complete one orbit (a galactic year),[23] and so is thought to have completed about 20-25 orbits during its lifetime or 0.0008 orbit since the origin of humans. The orbital speed of the solar system is 217 km/s, i.e. 1 light-year in ca. 1400 years, and 1 AU in 8 days.

[edit] The Milky Way environment
NGC 7331 is often referred to as "the Milky Way's twin." This is what an observer from another galaxy might see when looking at the Milky Way.
NGC 7331 is often referred to as "the Milky Way's twin." This is what an observer from another galaxy might see when looking at the Milky Way.

The Milky Way and the Andromeda Galaxy are a binary system of giant spiral galaxies. Together with their companion galaxies they form the Local Group, a group of some 50 closely bound galaxies. The Local Group is part of the Virgo Supercluster.

The Milky Way is orbited by two smaller galaxies and a number of dwarf galaxies in the Local Group. The largest of these is the Large Magellanic Cloud with a diameter of 20,000 light-years. It has a close companion, the Small Magellanic Cloud. The Magellanic Stream is a peculiar streamer of neutral hydrogen gas connecting these two small galaxies. The stream is thought to have been dragged from the Magellanic Clouds in tidal interactions with the Milky Way. Some of the dwarf galaxies orbiting the Milky Way are Canis Major Dwarf (the closest), Sagittarius Dwarf Elliptical Galaxy, Ursa Minor Dwarf, Sculptor Dwarf, Sextans Dwarf, Fornax Dwarf, and Leo I Dwarf. The smallest Milky Way dwarf galaxies are only 500 light-years in diameter. These include Carina Dwarf, Draco Dwarf, and Leo II Dwarf. There may still be undetected dwarf galaxies, which are dynamically bound to the Milky Way. Observations through the zone of avoidance are frequently detecting new distant and nearby galaxies. Some galaxies consisting mostly of gas and dust may also have evaded detection so far.

In January 2005, researchers reported that the heretofore unexplained warp in the disk of the Milky Way has now been mapped and found to be a ripple or vibration set up by the Large and Small Magellanic Clouds as they circle the Milky Way, causing vibrations at certain frequencies when they pass through the edges of our Galaxy.[citation needed] Previously, these two galaxies, at around 2% of the mass of the Milky Way, were considered too small to influence the Milky Way. However, by taking into account dark matter, the movement of these two galaxies creates a wake that influences the larger Milky Way. Taking dark matter into account results in an approximately twentyfold increase in mass for the Milky Way. This calculation is according to a computer model made by Martin Weinberg of the University of Massachusetts, Amherst. In this model, the dark matter is spreading out from the Milky Way disk with the known gas layer. As a result, the model predicts that the gravitational impact of the Magellanic Clouds is amplified as they pass through the Milky Way.

[edit] Speed through space

In the general sense, the absolute speed of any object through space is not a meaningful question according to Einstein's Special Theory of Relativity, which declares that there is no "preferred" inertial frame of reference in space with which to compare the galaxy's motion. (Motion must always be specified with respect to another object.)

With this in mind, many astronomers believe the galaxy is moving through space at approximately 600km per second relative to the observed locations of other nearby galaxies. Most recent estimates range from 130 km/s to 1,000 km/s. If indeed the Milky Way is moving at 600 km per second, we are traveling 51.84 million km per day, or more than 18.9 billion km per year. For comparison, this would mean that each year, we are traveling about 4.5 times the distance that Pluto lies from the Earth (at its closest). The Milky Way is thought to be moving in the direction of the constellation Hydra, and may someday become a close-knit member of the Virgo cluster of galaxies. Our galaxy may also collide with the Andromeda galaxy in roughly 4 billion years. See below.

Another reference frame is provided by the Cosmic microwave background (CMB). The Milky Way is moving at around 552 km/s[24] with respect to the photons of the CMB. This can be observed by satellites such as COBE and WMAP as a dipole contribution to the CMB, as photons in equilibrium at the CMB frame get blue-shifted in the direction of the motion and red-shifted in the opposite direction.

[edit] Future of the Milky Way

    Main article: Andromeda-Milky Way collision

Current measurements suggest the Andromeda Galaxy is approaching us at 100 to 140 kilometers per second (100 kilometers per second is exactly 3,600 times faster than typical freeway speed in the U.S. or Canada at 100 km/h or 60 miles per hour) , and that the Milky Way might collide with it in several (3-4) billion years, depending on the importance of unknown lateral components to the galaxies' relative motion. If they do collide, it is thought that our sun and the other stars of the Milky Way will probably not collide with the stars of Andromeda, but that the two galaxies will merge to form a single elliptical galaxy over the course of about a billion years.[25]

[edit] Name and myths

    Main article: List of names for the Milky Way
    Main article: Milky Way (mythology)

There are many creation myths around the world which explain the origin of the Milky Way and give it its name. The English phrase is a translation from Greek Γαλαξίας Galaxias which is derived from the word for milk (γάλα, gala). This is also the origin of the word galaxy. In Greek myth the Milky Way was caused by milk spilt by Hera when suckled by Heracles.

[edit] References

  1. ^ C. Alard (2001). "Another bar in the Bulge". Astronomy and Astrophysics 379 (2): L44-L47.
  2. ^ Sanders, Robert. "Milky Way galaxy is warped and vibrating like a drum", UCBerkeley News, January 9, 2006. Retrieved on 2006-05-24.
  3. ^ Connors, et al.. "N-body simulations of the Magellanic stream", Monthly Notices of the Royal Astronomical Society, January 26, 2007. Retrieved on 2007-01-26.
  4. ^ "The Local Group of Galaxies.", A.A Springer.. Retrieved on 2007-03-14.
  5. ^ 17 August 2004 - Press release, European Southern Observatory
  6. ^ Ortwin, Gerhard (2002). "Mass distribution in our Galaxy". Space Science Reviews 100 (1/4): 129-138. Retrieved on 2007-03-14.
  7. ^ Chen, W.; Gehrels, N.; Diehl, R.; Hartmann, D. (1996). "On the spiral arm interpretation of COMPTEL ^26^Al map features". Space Science Reviews 120: 315-316. Retrieved on 2007-03-14.
  8. ^ 16 August 2005 - New Scientist article
  9. ^ López-Corredoira, M.; Cabrera-Lavers, A.; Mahoney, T. J.; Hammersley, P. L.; Garzón, F.; González-Fernández, C. (2007). "The Long Bar in the Milky Way: Corroboration of an Old Hypothesis". The Astronomical Journal 133 (1): 154-161. Retrieved on 2007-03-15.
  10. ^ Karachentsev, I. D.; Kashibadze, O. G. (2006). "Masses of the local group and of the M81 group estimated from distortions in the local velocity field". Astrophysics 49 (1): 3-18.
  11. ^ The Physics Factbook - entry citing references about the mass of the Milky Way. URL accessed March 16, 2006.
  12. ^ a b The radial velocity dispersion profile of the Galactic halo: Constraining the density profile of the dark halo of the Milky Way, Battaglia et al. 2005, MNRAS, 364 (2005) 433
  13. ^ "The Stars of the Milky Way".
  14. ^ Blandford, R.D. (1999). "Origin and evolution of massive black holes in galactic nuclei". Galaxy Dynamics, proceedings of a conference held at Rutgers University, 8-12 Aug 1998,ASP Conference Series vol. 182.
  15. ^ http://zebu.uoregon.edu/~imamura/123/lecture-2/mass.html
  16. ^ [ 23 April 2006] - http://www.bu.edu/galacticring/new_introduction.htm
  17. ^ 6 April 2005 - Ibata, R. et al, Astrophys. Journal, 634 (2005) 287-313
  18. ^ http://www.solstation.com/x-objects/gal-ring.htm
  19. ^ Reid, M. J. (1993), "The distance to the center of the Galaxy". Annual Review of Astronomy and Astrophysics, Vol. 31, p. 345-372.
  20. ^ Eisenhauer, F., et al (2003), "A Geometric Determination of the Distance to the Galactic Center" Astrophys.J. 597 L121-L124.
  21. ^ Horrobin, M. et al (2004), "First results from SPIFFI. I: The Galactic Center" (PDF). Astronomische Nachrichten, Vol. 325, p. 120-123.
  22. ^ 14 January 2000 - Press release, Canadian Galactic Plan Survey
  23. ^ http://hypertextbook.com/facts/2002/StacyLeong.shtml
  24. ^ 23 October 2006 - ApJ COBE paper
  25. ^ Wong, Janet. "Astrophysicist maps out our own galaxy's end", University of Toronto, April 14, 2000. Retrieved on 2007-01-11.

Milky Way (mythology)
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    "Great Sky River" redirects here. It is also the name of a novel: Great Sky River, by Gregory Benford.
    This article deals with mythology related to the Milky Way Galaxy. For other uses, please see Milky Way (disambiguation).

There are many legends about the origin of the Milky Way, the distinctive bright streak across the sky.

    * 1 Armenian mythology
    * 2 Khoisan mythology
    * 3 Cherokee mythology
    * 4 Eastern mythology
    * 5 Egyptian mythology
    * 6 Finno-Ugric mythology
    * 7 Greek and Roman mythology
    * 8 Hindu mythology
    * 9 Hungarian mythology
    * 10 Māori mythology
    * 11 References
    * 12 See also

[edit] Armenian mythology

Ancient Armenian mythology called the Milky Way the "Straw Thief's Way". According to legend, the god Vahagn stole straw from the Assyrian king Barsham and brought it to Armenia during a cold winter. When he fled across the heavens, he spilled some of the straw along the way.[1]

[edit] Khoisan mythology

The Khoisan Peoples of the Kalahari desert in southern Africa say that long ago there were no stars and the night was pitch black. A girl, who was lonely and wanted to visit other people, threw the embers from a fire into the sky and created the Milky Way.[2]

[edit] Cherokee mythology

A Cherokee folktale tells of a dog who stole some cornmeal and was chased away. He ran away to the north, spilling the cornmeal along the way. The Milky Way is thus called Gili Ulisvsdanvyi "The Way the Dog Ran Away".[3]

[edit] Eastern mythology

Peoples in Eastern Asia believed that the hazy band of stars was the "Silvery River" of Heaven (Chinese: 銀河, Korean: eunha and Japanese: ginga). In one story, the stars Altair and Vega were said to be two lovers who were allowed to meet only once a year on the seventh day of the seventh month, when a flock of magpies and crows formed a bridge over the galactic river. That day is celebrated as Qi Xi, the Seventh Night (Chinese: 七夕; pinyin: qī xī, Korean: chilseok and Japanese: tanabata).

[edit] Egyptian mythology

In Egyptian mythology, the Milky Way was considered a pool of cow's milk. It was deified as a fertility cow-goddess by the name of Bata (later on syncretized with the goddess Hathor).

[edit] Finno-Ugric mythology

Among the Finns and related peoples, the Milky Way was called "The Pathway of the Birds" (Finnish: Linnunrata, Estonian: Linnutee). The Finns observed that the migratory birds used the galaxy as a guideline to travel south, where they believed Lintukoto (bird home) resided. In Estonian folklore it is believed that the birds are led by a white bird with the head of a maiden who chases birds of prey away.[4] Only later did scientists indeed confirm this observation; the migratory birds use the Milky Way as a guide to travel to warmer, southern lands during the winter.[citation needed] The name in the Indo-European Baltic languages has the same meaning (Lithuanian: Paukščių Takas, Latvian: Putnu Ceļš).

[edit] Greek and Roman mythology

The Greek name for the Milky way (Γαλαξίας Galaxias) is derived from the word for milk (γάλα, gala). One legend explains how the Milky Way was created by Heracles when he was a baby.[2] His father, Zeus, was fond of his son, who was born of the mortal woman Alcmene. He decided to let the infant Heracles suckle on his divine wife Hera's milk when she was asleep, an act which would endow the baby with godlike qualities. When Hera woke up and realized that she was breastfeeding an unknown infant, she pushed him away and the spurting milk became the Milky Way.

A story told by the Roman Hyginus in the Poeticon astronomicon (ultimately based on Greek myth) says that the milk came from the goddess Ops (Greek Rhea), the wife of Saturn (Greek Cronus). Saturn swallowed his children to ensure his position as head of the Pantheon and sky god, and so Ops conceived a plan to save her newborn son Jupiter (Greek Zeus): She wrapped a stone in infant's clothes and gave it to Saturn to swallow. Saturn asked her to nurse the child once more before he swallowed it, and the milk that spurted when she pressed her nipple against the rock eventually became the Milky Way.[5]

Older Greek mythology associates the Milky Way with a herd of dairy cows/cattle, where each cow is a star and whose milk gives the blue glow.[citation needed] As such, it is intimately associated with legends concerning the constellation of Gemini, with which it is in contact. The constellation was named for the twins, Castor and Polydeuces, who sometimes raided cattle. In addition, Gemini (in combination with Canis Major, Orion, Auriga, and the deserted area now called Camelopardalis) may form the origin of the myth of the Cattle of Geryon, one of The Twelve Labours of Heracles.

[edit] Hindu mythology
The galaxy seen as a dolphin, a śiśumãra
The galaxy seen as a dolphin, a śiśumãra

In the Hindu collection of stories called Bhagavata purana, all the visible stars and planets moving through space are likened to a dolphin that swims through the water, and the heavens is called śiśumãra cakra, the dolphin disc. The Milky Way forms the abdomen of the dolphin and is called Akasaganga which means "The Ganges River of the Sky".[6]

[edit] Hungarian mythology

In Hungarian mythology, Csaba, the mythical son of Attila the Hun and ancestor of the Hungarians is supposed to ride down the Milky Way when the Székelys (ethnic Hungarians living in Romania) are threatened. Thus the Milky Way is called "The Road of the Warriors" Hungarian: Hadak Útja .[7]

[edit] Māori mythology

To the Māori the Milky Way is the waka (canoe) of Tama-rereti. The front and back of the canoe are Orion and Scorpius, while the Southern Cross and the Pointers are the anchor and rope. According to legend, when Tama-rereti took his canoe out onto a lake, he found himself far from home as night was falling. There were no stars at this time and in the darkness the Taniwha would attack and eat people. So Tama-rereti sailed his canoe along the river that emptied into the heavens (to cause rain) and scattered shiny pebbles from the lakeshore into the sky. The sky god, Ranginui, was pleased by this action and placed the canoe into the sky as well as a reminder of how the stars were made.[8]

The slight bulge of the Milky Way around Scorpius is also sometimes pictured as a whale.[citation needed]

In (certain) Australian aboriginal mythology, the milky way was created as an outpouring of milk, squirted across the heavens.[citation needed]
Pestele - simbol crestin euharistic

• Minunea pescuirii de la lacul Ghenizaret: "Spaima il cuprinsese pe el (Petru) si pe toti cei ce erau cu el, pentru pescuitul pestilor pe care ii prinsesera" (Luca 5, 9).

Sfinta Evanghelie a duminicii a XVIII-a dupa Rusalii ne istoriseste pescuirea minunata ce a avut loc la inceputul SINERGIEI Mantuitorului cu ucenicii Sai. Sfintul evanghelist Ioan mentioneaza ca a avut loc si o a doua pescuire minunata, dupa Invierea Domnului (Ioan 21, 1 - 14). Cum s-a petrecut prima dintre ele? La tarmul lacului Ghenizaret, Iisus a vazut doua corabii (barci) pescaresti. Pescarii (Simon - Petru si Andrei, fratele sau, Iacov si Ioan, fiii lui Zevedeu) isi spalau mrejele. Toata noaptea se trudisera sa prinda peste. Era, deci, intr-o dimineata si Apostolii erau, desigur, suparati ca nu prinsesera nimic. Iisus s-a apropiat de ei si s-a urcat in corabia lui Simon. I-a cerut acestuia sa o indeparteze putin de tarm. "Si sezind in corabie, invata din ea multimile" (Luca 5, 3). Asadar, Hristos foloseste barca lui Petru ca AMVON, de unde arunca "plasa" Evangheliei asupra auditoriului sau. Dupa ce Si-a incetat cuvintul Sau, Iisus s-a adresat lui Petru: "Mina la adinc si lasati in jos mrejile voastre, ca sa pescuiti". Simon asculta cuvintul Domnului. Ascultarea de cuvintul Fiului lui Dumnezeu si-a aratat indata roadele. Pescuirea a fost mai bogata ca niciodata: "..au prins multime mare de peste, ca li se rupeau mrejile" (Luca 5, 5). Esential, nu numai peste pamintesc au obtinut Apostolii atunci. Darul cel cu adevarat mare si de negrait a fost Hristos Insusi: Iata "Pestele" pe care L-au "prins" obositii pescari. Dupa Inviere, Hristos avea sa Se dea Apostolilor, euharistic, ca "peste" (Ioan 21, 9, 13). Astfel, de la inceputurile Bisericii, pestele a devenit primul simbol al lui Hristos si al Sfintei Impartasanii (Euharistii), prin care El se daruieste credinciosilor Sai. Cuvintul grecesc pentru peste - IHTHYS - a fost considerat prescurtarea unui adevarat "crez" hristologic. Fiecare litera a fost identificata ca initiala unui cuvint intreg. In greceste, anagrama "ihthys" s-a tradus: "Iisus Hristos, Theos i Sotirios", adica, in romaneste: "Iisus Hristos, Dumnezeu Mantuitorul". Cu privire la simbolul pestelui, scriitorul crestin Clement Alexandrinul (m. 215) a afirmat: "Iisus Hristos este ca un peste care invata pescuirea oamenilor prin apa" (adica prin Sfintul Botez). Tertulian din Cartagina (m. 220) a conchis, si el: "Noi, pestisorii (latineste: pisciculi), dupa Pestele nostru Iisus Hristos, ne nastem in apa si nu ne mantuim decat ramanand in apa" (adica in darurile Botezului crestin). Multe inscriptii paleocrestine din vestitele catacombe il infatiseaza pe Pestele-Hristos. In perioada persecutiilor, crestinii se recunosteau intre ei prin desenul unui peste. Semnul Sfintei Cruci era prea vizibil pentru persecutori. O inscriptie in versuri, de pe mormintul Sfintului Averchie, episcop de Hierapolis (circa 216 d.Hr.) mentioneaza ca Averchie, ucenicul "Pastorului Cel Sfant" (Hristos), mergind la Roma "sa priveasca Imparatia (Biserica) i s-a dat "in orice loc" ca hrana "Pestele de izvor", adica Hristos cel euharistic din Impartasanie. O alta inscriptie de mormint, numita "a lui Pectorius", descoperita in sudul Frantei, de pe la sfirsitul secolului al II-lea, mentioneaza nu mai putin de patru referiri la "Pestele" mistic (IHTHYS) al crestinilor. Iata inceputul acestei inscriptii: "Neam dumnezeiesc al Pestelui (IHTHYS) ceresc, pastreaza o inima curata, primind printre muritori izvorul cel nemuritor al apei divine; incalzeste-ti, prietene, sufletul tau in apele vesnice ale intelepciuni eterne". (Actele martirice, PSB Bucuresti, 1982, p. 365).

pr. prof. dr. Constantin Leonte
From Wikipedia, the free encyclopedia
Jump to: navigation, search
For other uses, see Laser (disambiguation).
Experiment with a laser (US Military)
Experiment with a laser (US Military)

In physics, a laser is a device that emits light through a specific mechanism for which the term laser is an acronym: Light Amplification by Stimulated Emission of Radiation. This is a combined quantum-mechanical and thermodynamical process discussed in more detail below. As a light source, a laser can have various properties, depending on the purpose for which it is designed and calibrated. A typical laser emits light in a narrow, low-divergence beam and with a well-defined wavelength (corresponding to a particular color if the laser is operating in the visible spectrum). This is in contrast to a light source such as the incandescent light bulb, which emits into a large solid angle and over a wide spectrum of wavelength. These properties can be summarized in the term coherence.

A laser consists of a gain medium inside an optical cavity, with a means to supply energy to the gain medium. The gain medium is a material (gas, liquid, solid or free electrons) with appropriate optical properties. In its simplest form, a cavity consists of two mirrors arranged such that light bounces back and forth, each time passing through the gain medium. Typically, one of the two mirrors, the output coupler, is partially transparent. The output laser beam is emitted through this mirror.

Light of a specific wavelength that passes through the gain medium is amplified (increases in power); the surrounding mirrors ensure that most of the light makes many passes through the gain medium. Part of the light that is between the mirrors (i.e., is in the cavity) passes through the partially transparent mirror and appears as a beam of light. The process of supplying the energy required for the amplification is called pumping and the energy is typically supplied as an electrical current or as light at a different wavelength. In the latter case, the light source can be a flash lamp or another laser. Most practical lasers contain additional elements that affect properties such as the wavelength of the emitted light and the shape of the beam.

The first working laser was demonstrated in May 1960 by Theodore Maiman at Hughes Research Laboratories. Recently, lasers have become a multi-billion dollar industry. The most widespread use of lasers is in optical storage devices such as compact disc and DVD players, in which the laser (a few millimeters in size) scans the surface of the disc. Other common applications of lasers are bar code readers and laser pointers. In industry, lasers are used for cutting steel and other metals and for inscribing patterns (such as the letters on computer keyboards). Lasers are also commonly used in various fields in science, especially spectroscopy, typically because of their well-defined wavelength or short pulse duration in the case of pulsed lasers. Lasers are also used for military and medical applications.

    * 1 Physics
    * 2 History
          o 2.1 Foundations
          o 2.2 The maser
          o 2.3 The laser
          o 2.4 Recent innovations
    * 3 Types and operating principles
          o 3.1 Gas lasers
          o 3.2 Chemical lasers
                + 3.2.1 Excimer lasers
          o 3.3 Solid-state lasers
                + 3.3.1 Fiber-hosted lasers
                + 3.3.2 Semiconductor lasers
          o 3.4 Dye lasers
          o 3.5 Free electron lasers
    * 4 Continuous wave and pulsed lasers
          o 4.1 Continuous wave operation
          o 4.2 Pulsed operation
                + 4.2.1 Q-switching
                + 4.2.2 Modelocking
                + 4.2.3 Pulsed pumping
    * 5 Uses
          o 5.1 Example uses by typical output power
    * 6 Laser safety
    * 7 Related terminology
    * 8 Popular misconceptions
    * 9 Fictional predictions
    * 10 Hobby uses
    * 11 See also
    * 12 Further reading
          o 12.1 Books
          o 12.2 Periodicals
    * 13 References
    * 14 External links

[edit] Physics
Principal components:1. Active laser medium2. Laser pumping energy3. High reflector4. Output coupler5. Laser beam
Principal components:
1. Active laser medium
2. Laser pumping energy
3. High reflector
4. Output coupler
5. Laser beam
A helium-neon laser demonstration at the Kastler-Brossel Laboratory at Univ. Paris 6. The glowing ray in the middle is an electric discharge producing light in much the same way as a neon light. It is the gain medium through which the laser passes, not the laser beam itself, which is visible there. The laser beam crosses the air and marks a red point on the screen to the right.
A helium-neon laser demonstration at the Kastler-Brossel Laboratory at Univ. Paris 6. The glowing ray in the middle is an electric discharge producing light in much the same way as a neon light. It is the gain medium through which the laser passes, not the laser beam itself, which is visible there. The laser beam crosses the air and marks a red point on the screen to the right.
Spectrum of a helium neon laser showing the very high spectral purity intrinsic to nearly all lasers. Compare with the relatively broad spectral emittance of a light emitting diode.
Spectrum of a helium neon laser showing the very high spectral purity intrinsic to nearly all lasers. Compare with the relatively broad spectral emittance of a light emitting diode.

    See also: Laser science and Laser construction

A laser is composed of an active laser medium, or gain medium, and a resonant optical cavity. The gain medium transfers external energy into the laser beam. It is a material of controlled purity, size, concentration, and shape, which amplifies the beam by the quantum mechanical process of stimulated emission, predicted by Albert Einstein while he studied the photoelectric effect. The gain medium is energized, or pumped, by an external energy source. Examples of pump sources include electricity and light, for example from a flash lamp or from another laser. The pump energy is absorbed by the laser medium, placing some of its particles into high-energy ("excited") quantum states. Particles can interact with light both by absorbing photons or by emitting photons. Emission can be spontaneous or stimulated. In the latter case, the photon is emitted in the same direction as the light that is passing by. When the number of particles in one excited state exceeds the number of particles in some lower-energy state, population inversion is achieved and the amount of spontaneous emission due to light that passes through is larger than the amount of absorption. Hence, the light is amplified. Strictly speaking, these are the essential ingredients of a laser. However, usually the term laser is used for devices where the light that is amplified is produced as spontaneous emission from the same gain medium as where the amplification takes place. Devices where light from an external source is amplified are normally called optical amplifiers.

The light generated by stimulated emission is very similar to the input signal in terms of wavelength, phase, and polarization. This gives laser light its characteristic coherence, and allows it to maintain the uniform polarization and often monochromaticity established by the optical cavity design.

The optical cavity, a type of cavity resonator, contains a coherent beam of light between reflective surfaces so that the light passes through the gain medium more than once before it is emitted from the output aperture or lost to diffraction or absorption. As light circulates through the cavity, passing through the gain medium, if the gain (amplification) in the medium is stronger than the resonator losses, the power of the circulating light can rise exponentially. But each stimulated emission event returns a particle from its excited state to the ground state, reducing the capacity of the gain medium for further amplification. When this effect becomes strong, the gain is said to be saturated. The balance of pump power against gain saturation and cavity losses produces an equilibrium value of the laser power inside the cavity; this equilibrium determines the operating point of the laser. If the chosen pump power is too small, the gain is not sufficient to overcome the resonator losses, and the laser will emit only very small light powers. The minimum pump power needed to begin laser action is called the lasing threshold. The gain medium will amplify any photons passing through it, regardless of direction; but only the photons aligned with the cavity manage to pass more than once through the medium and so have significant amplification.

The beam in the cavity and the output beam of the laser, if they occur in free space rather than waveguides (as in an optical fiber laser), are, at best, low order Gaussian beams. However this is rarely the case with powerful lasers. If the beam is not a low-order Gaussian shape, the transverse modes of the beam can be described as a superposition of Hermite-Gaussian or Laguerre-Gaussian beams (for stable-cavity lasers). Unstable laser resonators on the other hand, have been shown to produce fractal shaped beams (Link to original article in Nature Vol. 402, 138 (11 November 1999)) [1]. The beam may be highly collimated, that is being parallel without diverging. However, a perfectly collimated beam cannot be created, due to diffraction. The beam remains collimated over a distance which varies with the square of the beam diameter, and eventually diverges at an angle which varies inversely with the beam diameter. Thus, a beam generated by a small laboratory laser such as a helium-neon laser spreads to about 1.6 kilometers (1 mile) diameter if shone from the Earth to the Moon. By comparison, the output of a typical semiconductor laser, due to its small diameter, diverges almost as soon as it leaves the aperture, at an angle of anything up to 50°. However, such a divergent beam can be transformed into a collimated beam by means of a lens. In contrast, the light from non-laser light sources cannot be collimated by optics as well or much.

The output of a laser may be a continuous constant-amplitude output (known as CW or continuous wave); or pulsed, by using the techniques of Q-switching, modelocking, or gain-switching. In pulsed operation, much higher peak powers can be achieved.

Some types of lasers, such as dye lasers and vibronic solid-state lasers can produce light over a broad range of wavelengths; this property makes them suitable for generating extremely short pulses of light, on the order of a few femtoseconds (10-15 s).

Although the laser phenomenon was discovered with the help of quantum physics, it is not essentially more quantum mechanical than other light sources. The operation of a free electron laser can be explained without reference to quantum mechanics.

It is understood that the word light in the acronym Light Amplification by Stimulated Emission of Radiation is typically used in the expansive sense, as photons of any energy; it is not limited to photons in the visible spectrum. Hence there are infrared lasers, ultraviolet lasers, X-ray lasers, etc. For example, a source of atoms in a coherent state can be called an atom laser.

Because the microwave equivalent of the laser, the maser, was developed first, devices that emit microwave and radio frequencies are usually called masers. In early literature, particularly from researchers at Bell Telephone Laboratories, the laser was often called the optical maser. This usage has since become uncommon, and as of 1998 even Bell Labs uses the term laser.[2]

[edit] History

[edit] Foundations

In 1917, Albert Einstein in his paper Zur Quantentheorie der Strahlung (On the Quantum Theory of Radiation), laid the foundation for the invention of the laser and its predecessor, the maser, in a ground-breaking rederivation of Max Planck's law of radiation based on the concepts of probability coefficients (later to be termed 'Einstein coefficients') for the absorption, spontaneous, and stimulated emission.

In 1928, Rudolph W. Landenburg confirmed the existence of stimulated emission and negative absorption.[3]

In 1939, Valentin A. Fabrikant (USSR) predicted the use of stimulated emission to amplify "short" waves.[4]

In 1947, Willis E. Lamb and R. C. Retherford found apparent stimulated emission in hydrogen spectra and made the first demonstration of stimulated emission.[5]

In 1950, Alfred Kastler (Nobel Prize for Physics 1966) proposed the method of optical pumping, which was experimentally confirmed by Brossel, Kastler and Winter two years later.[6]

[edit] The maser

In 1953, Charles H. Townes and graduate students James P. Gordon and Herbert J. Zeiger produced the first microwave amplifier, a device operating on similar principles to the laser, but amplifying microwave rather than infrared or visible radiation. Townes's maser was incapable of continuous output. Nikolay Basov and Aleksandr Prokhorov of the Soviet Union worked independently on the quantum oscillator and solved the problem of continuous output systems by using more than two energy levels and produced the first maser. These systems could release stimulated emission without falling to the ground state, thus maintaining a population inversion. In 1955 Prokhorov and Basov suggested an optical pumping of multilevel system as a method for obtaining the population inversion, which later becomes one of the main methods of laser pumping.

Townes, Basov, and Prokhorov shared the Nobel Prize in Physics in 1964 "For fundamental work in the field of quantum electronics, which has led to the construction of oscillators and amplifiers based on the maser-laser principle".

[edit] The laser

In 1957, Charles Hard Townes and Arthur Leonard Schawlow, then at Bell Labs, began a serious study of the infrared maser. As ideas were developed, infrared frequencies were abandoned with focus on visible light instead. The concept was originally known as an "optical maser". Bell Labs filed a patent application for their proposed optical maser a year later. Schawlow and Townes sent a manuscript of their theoretical calculations to Physical Review, which published their paper that year (Volume 112, Issue 6).
The first page of Gordon Gould's laser notebook in which he coined the acronym LASER and described the essential elements for constructing one.
The first page of Gordon Gould's laser notebook in which he coined the acronym LASER and described the essential elements for constructing one.

At the same time Gordon Gould, a graduate student at Columbia University, was working on a doctoral thesis on the energy levels of excited thallium. Gould and Townes met and had conversations on the general subject of radiation emission. Afterwards Gould made notes about his ideas for a "laser" in November 1957, including suggesting using an open resonator, which became an important ingredient of future lasers.

In 1958, Prokhorov independently proposed using an open resonator, the first published appearance of this idea. Schawlow and Townes also settled on an open resonator design, apparently unaware of both the published work of Prokhorov and the unpublished work of Gould.

The term "laser" was first introduced to the public in Gould's 1959 conference paper "The LASER, Light Amplification by Stimulated Emission of Radiation".[7] Gould intended "-aser" to be a suffix, to be used with an appropriate prefix for the spectra of light emitted by the device (x-ray laser = xaser, ultraviolet laser = uvaser, etc.). None of the other terms became popular, although "raser" was used for a short time to describe radio-frequency emitting devices.

Gould's notes included possible applications for a laser, such as spectrometry, interferometry, radar, and nuclear fusion. He continued working on his idea and filed a patent application in April 1959. The U.S. Patent Office denied his application and awarded a patent to Bell Labs in 1960. This sparked a legal battle that ran 28 years, with scientific prestige and much money at stake. Gould won his first minor patent in 1977, but it was not until 1987 that he could claim his first significant patent victory when a federal judge ordered the government to issue patents to him for the optically pumped laser and the gas discharge laser.

The first working laser was made by Theodore H. Maiman in 1960[8] at Hughes Research Laboratories in Malibu, California, beating several research teams including those of Townes at Columbia University, Arthur L. Schawlow at Bell Labs,[9] and Gould at a company called TRG (Technical Research Group). Maiman used a solid-state flashlamp-pumped synthetic ruby crystal to produce red laser light at 694 nanometres wavelength. Maiman's laser, however, was only capable of pulsed operation due to its three energy level pumping scheme.

Later in 1960 the Iranian physicist Ali Javan, working with William Bennet and Donald Herriot, made the first gas laser using helium and neon. Javan later received the Albert Einstein Award in 1993.

The concept of the semiconductor laser diode was proposed by Basov and Javan. The first laser diode was demonstrated by Robert N. Hall in 1962. Hall's device was made of gallium arsenide and emitted at 850 nm in the near-infrared region of the spectrum. The first semiconductor laser with visible emission was demonstrated later the same year by Nick Holonyak, Jr. As with the first gas lasers, these early semiconductor lasers could be used only in pulsed operation, and indeed only when cooled to liquid nitrogen temperatures (77 K).

In 1970, Zhores Alferov in the Soviet Union and Izuo Hayashi and Morton Panish of Bell Telephone Laboratories independently developed laser diodes continuously operating at room temperature, using the heterojunction structure.

[edit] Recent innovations
This short section requires expansion.
Graph showing the history of maximum laser pulse intensity throughout the past 40 years.
Graph showing the history of maximum laser pulse intensity throughout the past 40 years.

Since the early period of laser history, laser research has produced a variety of improved and specialized laser types, optimized for different performance goals, including:

    * new wavelength bands
    * maximum average output power
    * maximum peak output power
    * minimum output pulse duration
    * maximum power efficiency
    * maximum charging
    * maximum firing

and this research continues to this day.

Lasing without maintaining the medium excited into a population inversion, was discovered in 1992 in sodium gas and again in 1995 in rubidium gas by various international teams. This was accomplished by using an external maser to induce "optical transparency" in the medium by introducing and destructively interfering the ground electron transitions between two paths, so that the likelihood for the ground electrons to absorb any energy has been cancelled.

In 1985 at the University of Rochester's Laboratory for Laser Energetics a breakthrough in creating ultrashort-pulse, very high-intensity (terawatts) laser pulses became available using a technique called chirped pulse amplification, or CPA, discovered by Gérard Mourou. These high intensity pulses can produce filament propagation in the atmosphere.

[edit] Types and operating principles

    For a more complete list of laser types see this list of laser types.

Spectral output of several types of lasers.
Spectral output of several types of lasers.

[edit] Gas lasers

Gas lasers using many gases have been built and used for many purposes. They are one of the oldest types of laser.

The helium-neon laser (HeNe) emits at a variety of wavelengths and units operating at 633 nm are very common in education because of its low cost.

Carbon dioxide lasers can emit hundreds of kilowatts[10] at 9.6 µm and 10.6 µm, and are often used in industry for cutting and welding. The efficiency of a CO2 laser is over 10%.

Argon-ion lasers emit 458 nm, 488 nm or 514.5 nm.

Carbon monoxide lasers must be cooled but can produce up to 500 kW.[citation needed]

A nitrogen transverse electrical discharge in gas at atmospheric pressure (TEA) laser is an inexpensive gas laser producing UV Light at 337.1 nm.[citation needed]

Metal ion lasers are gas lasers that generate deep ultraviolet wavelengths. Helium-silver (HeAg) 224 nm and neon-copper (NeCu) 248 nm are two examples. These lasers have particularly narrow oscillation linewidths of less than 3 GHz (0.5 picometers),[11] making them candidates for use in fluorescence suppressed Raman spectroscopy.

[edit] Chemical lasers

Chemical lasers are powered by a chemical reaction, and can achieve high powers in continuous operation. For example, in the Hydrogen fluoride laser (2700-2900 nm) and the Deuterium fluoride laser (3800 nm) the reaction is the combination of hydrogen or deuterium gas with combustion products of ethylene in nitrogen trifluoride.

[edit] Excimer lasers

Excimer lasers are powered by a chemical reaction involving an excited dimer, or excimer, which is a short-lived dimeric or heterodimeric molecule formed from two species (atoms), at least one of which is in an excited electronic state. They typically produce ultraviolet light, and are used in semiconductor photolithography and in LASIK eye surgery. Commonly used excimer molecules include F2 (fluorine, emitting at 157 nm), and noble gas compounds (ArF (193 nm), KrCl (222 nm), KrF (248 nm), XeCl (308 nm), and XeF (351 nm)).

[edit] Solid-state lasers
A 50W FASOR, based on a Nd:YAG laser, used at the Starfire Optical Range
A 50W FASOR, based on a Nd:YAG laser, used at the Starfire Optical Range

Solid state laser materials are commonly made by doping a crystalline solid host with ions that provide the required energy states. For example, the first working laser was a ruby laser, made from ruby (chromium-doped sapphire).

Neodymium is a common dopant in various solid state laser crystals, including yttrium orthovanadate (Nd:YVO4), yttrium lithium fluoride (Nd:YLF) and yttrium aluminium garnet (Nd:YAG). All these lasers can produce high powers in the infrared spectrum at 1064nm. They are used for cutting, welding and marking of metals and other materials, and also in spectroscopy and for pumping dye lasers. These lasers are also commonly frequency doubled, tripled or quadrupled to produce 532nm (green, visible), 355nm (UV) and 266nm (UV) light when those wavelengths are needed.

Ytterbium, holmium, thulium, and erbium are other common dopants in solid state lasers. Ytterbium is used in crystals such as Yb:YAG, Yb:KGW, Yb:KYW, Yb:SYS, Yb:BOYS, Yb:CaF2, typically operating around 1020-1050 nm. They are potentially very efficient and high powered due to a small quantum defect. Extremely high powers in ultrashort pulses can be achieved with Yb:YAG. Holmium-doped YAG crystals emit at 2097 nm and form an efficient laser operating at infrared wavelengths strongly absorbed by water-bearing tissues. The Ho-YAG is usually operated in a pulsed mode, and passed through optical fiber surgical devices to resurface joints, remove rot from teeth, vaporize cancers, and pulverize kidney and gall stones.

Titanium-doped sapphire (Ti:sapphire) produces a highly tunable infrared laser, commonly used for spectroscopy as well as the most common ultrashort pulse laser.

Thermal limitations in solid-state lasers arise from unconverted pump power that manifests itself as heat and phonon energy. This heat, when coupled with a high thermo-optic coefficient (dn/dT) can give rise to thermal lensing as well as reduced quantum efficiency. These types of issues can be overcome by another novel diode-pumped solid state laser, the diode-pumped thin disk laser. The thermal limitations in this laser type are mitigated by utilizing a laser medium geometry in which the thickness is much smaller than the diameter of the pump beam. This allows for a more even thermal gradient in the material. Thin disk lasers have been shown to produce up to kiloWatt levels of power.[12]

[edit] Fiber-hosted lasers

Solid state lasers also include glass or optical fiber hosted lasers, for example, with erbium or ytterbium ions as the active species. These allow extremely long gain regions and can support very high output powers because the fiber's high surface area to volume ratio allows efficient cooling. In addition, the fiber's waveguiding properties tend to reduce thermal distortion of the beam. Quite often, the fiber is designed as a double-clad glass fiber. This type of fiber consists of a fiber core, an inner cladding and an outer cladding. The index of the three concentric layers is chosen so that the fiber core acts as a single-mode fiber for the laser emission while the outer cladding acts as a highly multimode core for the pump laser. This lets the pump propagate a large amount of power into and through the active inner core region, while still having a high numerical aperture (NA) to have easy launching conditions. Fiber lasers have a fundamental limit in that the intensity of the light in the fiber cannot be so high that optical nonlinearities induced by the local electric field strength can become dominant and prevent laser operation and/or lead to the material destruction of the fiber.

[edit] Semiconductor lasers

Commercial laser diodes emit at wavelengths from 375 nm to 1800 nm, and wavelengths of over 3 µm have been demonstrated. Low power laser diodes are used in , laser printers, and CD/DVD players. More powerful laser diodes are frequently used to optically pump other lasers with high efficiency. The highest power industrial laser diodes, with power up to 10 kW, are used in industry for cutting and welding. External-cavity semiconductor lasers have a semiconductor active medium in a larger cavity. These devices can generate high power outputs with good beam quality, wavelength-tunable narrow-linewidth radiation, or ultrashort laser pulses.

Vertical cavity surface-emitting lasers (VCSELs) are semiconductor lasers whose emission direction is perpendicular to the surface of the wafer. VCSEL devices typically have a more circular output beam than conventional laser diodes, and potentially could be much cheaper to manufacture. As of 2005, only 850 nm VCSELs are widely available, with 1300 nm VCSELs beginning to be commercialized,[13] and 1550 nm devices an area of research. VECSELs are external-cavity VCSELs. Quantum cascade lasers are semiconductor lasers that have an active transition between energy sub-bands of an electron in a structure containing several quantum wells.

The development of a silicon laser is important in the field of optical computing, since it means that if silicon, the chief ingredient of computer chips, were able to produce lasers, it would allow the light to be manipulated like electrons are in normal integrated circuits. Thus, photons would replace electrons in the circuits, which dramatically increases the speed of the computer. Unfortunately, silicon is a difficult lasing material to deal with, since it has certain properties which block lasing. However, recently teams have produced silicon lasers through methods such as fabricating the lasing material from silicon and other semiconductor materials, such as Indium(III) phosphide or Gallium(III) arsenide, materials which allow coherent light to be produced from silicon. These are called hybrid silicon laser. Another type is a Raman laser, which takes advantage of Raman scattering to produce a laser from materials such as silicon.

[edit] Dye lasers

Dye lasers use an organic dye as the gain medium. The wide gain spectrum of available dyes allows these lasers to be highly tunable, or to produce very short-duration pulses (on the order of a few femtoseconds).

[edit] Free electron lasers

Free electron lasers, or FELs, generate coherent, high power radiation, that is widely tunable, currently ranging in wavelength from microwaves, through terahertz radiation and infrared, to the visible spectrum, to soft X-rays. They have the widest frequency range of any laser type. While FEL beams share the same optical traits as other lasers, such as coherent radiation, FEL operation is quite different. Unlike gas, liquid, or solid-state lasers, which rely on bound atomic or molecular states, FELs use a relativistic electron beam as the lasing medium, hence the term free electron.

[edit] Continuous wave and pulsed lasers

A laser may either be built to emit a continuous beam or a train of short pulses. This makes fundamental differences in construction, usable laser media, and applications.

[edit] Continuous wave operation

In the continuous wave (CW) mode of operation, the output of a laser is relatively consistent with respect to time. The population inversion required for lasing is continually maintained by a steady pump source.

[edit] Pulsed operation

In the pulsed mode of operation, the output of a laser varies with respect to time, typically taking the form of alternating 'on' and 'off' periods. In many applications one aims to deposit as much energy as possible at a given place in as short time as possible. In laser ablation for example, a small volume of material at the surface of a work piece might evaporate if it gets the energy required to heat it up far enough in very short time. If, however, the same energy is spread over a longer time, the heat may have time to disperse into the bulk of the piece, and less material evaporates. There are a number of methods to achieve this.

[edit] Q-switching

Main article: Q-switching

In a Q-switched laser, the population inversion (usually produced in the same way as CW operation) is allowed to build up by making the cavity conditions (the 'Q') unfavorable for lasing. Then, when the pump energy stored in the laser medium is at the desired level, the 'Q' is adjusted (electro- or acousto-optically) to favorable conditions, releasing the pulse. This results in high peak powers as the average power of the laser (were it running in CW mode) is packed into a shorter time frame.

[edit] Modelocking

Main article: Modelocking

A modelocked laser emits extremely short pulses on the order of tens of picoseconds down to less than 10 femtoseconds. These pulses are typically separated by the time that a pulse takes to complete one round trip in the resonator cavity. Due to the Fourier limit (also known as energy-time uncertainty), a pulse of such short temporal length has a spectrum which contains a wide range of wavelengths. Because of this, the laser medium must have a broad enough gain profile to amplify them all. An example of a suitable material is titanium-doped, artificially grown sapphire (Ti:sapphire).

The modelocked laser is a most versatile tool for researching processes happening at extremely fast time scales (femtosecond physics and femtosecond chemistry, also called ultrafast science), for maximizing the effect of nonlinearity in optical materials (e.g. in second-harmonic generation, parametric down-conversion, optical parametric oscillators and the like), and in ablation applications. Again, because of the short timescales involved, these lasers can achieve extremely high peak powers.

[edit] Pulsed pumping

Another method of achieving pulsed laser operation is to pump the laser material with a source that is itself pulsed, either through electronic charging in the case of flashlamps, or another laser which is already pulsed. Pulsed pumping was historically used with dye lasers where the inverted population lifetime of a dye molecule was so short that a high energy, fast pump was needed. The way to overcome this problem was to charge up large capacitors which are then switched to discharge through flashlamps, producing a broad spectrum pump flash. Pulsed pumping is also required for lasers which disrupt the gain medium so much during the laser process that lasing has to cease for a short period. These lasers, such as the excimer laser and the copper vapour laser, can never be operated in CW mode.

[edit] Uses
Lasers range in size from microscopic diode lasers (top) with numerous applications, to football field sized neodymium glass lasers (bottom) used for inertial confinement fusion, nuclear weapons research and other high energy density physics experiments.
Lasers range in size from microscopic diode lasers (top) with numerous applications, to football field sized neodymium glass lasers (bottom) used for inertial confinement fusion, nuclear weapons research and other high energy density physics experiments.

    Main article: Laser applications

When lasers were invented in 1960, they were called "a solution looking for a problem". Since then, they have become ubiquitous, finding utility in thousands of highly varied applications in every section of modern society, including consumer electronics, information technology, science, medicine, industry, law enforcement, entertainment, and the military.

The first application of lasers visible in the daily lives of the general population was the supermarket barcode scanner, introduced in 1974. The laserdisc player, introduced in 1978, was the first successful consumer product to include a laser, but the compact disc player was the first laser-equipped device to become truly common in consumers' homes, beginning in 1982, followed shortly by laser printers.

In 2004, excluding diode lasers, approximately 131,000 lasers were sold world-wide, with a value of US$2.19 billion.[14] In the same year, approximately 733 million diode lasers, valued at $3.20 billion, were sold.[15]

[edit] Example uses by typical output power

Different uses need lasers with different output powers. Many lasers are designed for a higher peak output with an extremely short pulse, and this requires different technology from a continuous wave (constant output) lasers, as are used in communication, or cutting. Output power is always less than the input power needed to generate the beam.

The peak power required for some uses:

    * 5 mW - CD-ROM drive
    * 5-10 mW - DVD player
    * 100 mW - CD-R drive
    * 250 mW - output power of Sony SLD253VL red laser diode, used in consumer 48-52 speed CD-R burner.[16]
    * 1 W - green laser in current Holographic Versatile Disc prototype development.
    * 100 to 3000 W (peak output 1.5 kW) - typical sealed CO2 lasers used in industrial laser cutting.
    * 1 kW - Output power expected to be achieved by "a single 1 cm diode laser bar"[17]
    * 700 terawatts (TW) - The National Ignition Facility is working on a system that, when complete, will contain a 192-beam, 1.8-megajoule laser system adjoining a 10-meter-diameter target chamber.[18] The system is expected to be completed in April of 2009.
    * 1.25 petawatts (PW) - world's most powerful laser (claimed on 23 May 1996 by Lawrence Livermore Laboratory).

[edit] Laser safety
Warning symbol for lasers
Warning symbol for lasers

    Main articles: Laser safety and Lasers and aviation safety

Even the first laser was recognized as being potentially dangerous. Theodore Maiman characterized the first laser as one "Gillette"; as it could burn through one Gillette razor blade. Today, it is accepted that even low-power lasers with only a few milliwatts of output power can be hazardous to human eyesight.

At wavelengths which the cornea and the lens can focus well, the coherence and low divergence of laser light means that it can be focused by the eye into an extremely small spot on the retina, resulting in localized burning and permanent damage in seconds or even less time. Lasers are classified into safety classes numbered I (inherently safe) to IV (even scattered light can cause eye and/or skin damage). Laser products available for consumers, such as CD players and laser pointers are usually in class I, II, or III. Certain infrared lasers with wavelengths beyond about 1.4 micrometres are often referred to as being "eye-safe". This is because the intrinsic molecular vibrations of water molecules very strongly absorb light in this part of the spectrum, and thus a laser beam at these wavelengths is attenuated so completely as it passes through the eye's cornea that no light remains to be focused by the lens onto the retina. The label "eye-safe" can be misleading, however, as it only applies to relatively low power continuous wave beams and any high power or q-switched laser at these wavelengths can burn the cornea, causing severe eye damage.

[edit] Related terminology

In analogy with optical lasers, a device which produces any particles or electromagnetic radiation in a coherent state is also called a "laser", usually with indication of type of particle as prefix (for example, atom laser.) In most cases, "laser" refers to a source of coherent light or other electromagnetic radiation.

The back-formed verb lase means "to produce laser light" or "to apply laser light to".[19]

[edit] Popular misconceptions

The representation of lasers in popular culture, especially in science fiction and action movies, is often misleading. Contrary to their portrayal in many science fiction movies, a laser beam would not be visible (at least to the naked eye) in the near vacuum of space as there would be insufficient matter to cause scattering, except if there were a significant amount of fine shrapnel and other organic particles in that region.

In air, however, moderate intensity (tens of mW/cm²) laser beams of shorter green and blue wavelengths and high intensity beams of longer orange and red wavelengths can be visible due to Rayleigh scattering. With even higher intensity pulsed beams, the air can be heated to the point where it becomes a plasma, which is also visible. This causes rapid heating and explosive expansion of the surrounding air, which makes a popping noise analogous to the thunder which accompanies lightning. This phenomenon can cause retro-reflection of the laser beam back into the laser source, possibly damaging its optics. When this phenomenon occurs in certain scientific experiments it is referred to as a "plasma mirror" or "plasma shutter".

Some action movies depict security systems using lasers of visible light (and their foiling by the hero, typically using mirrors); the hero may see the path of the beam by sprinkling some dust in the air. It is far easier and cheaper to build infrared laser diodes rather than visible light laser diodes, and such systems almost never use visible light lasers. Additionally, putting enough dust in the air to make the beam visible is likely to be enough to "break" the beam and trigger the alarm (as demonstrated on an episode of Mythbusters on the Discovery Channel).

Science fiction films special effects often depict laser beams propagating at only a few metres per second—slowly enough to see their progress, in a manner reminiscent of conventional tracer ammunition—whereas in reality a laser beam travels at the speed of light and would seem to appear instantly to the naked eye from start to end. Some fans claim that the "laser beams" shown in such movies are in fact other type of sci-fi weaponry, such as particle beams or plasma weapons.

Several of these misconceptions can be found in the 1964 James Bond film Goldfinger, which was probably the first film to use a laser in its plot. In one of the most famous scenes in the Bond films, Bond, played by Sean Connery, faces a laser beam approaching his groin while melting the solid gold table to which he is strapped. The director Guy Hamilton found that a real laser beam would not show up on camera so it was added as an optical effect. The table was precut up the middle and coated with gold paint, while the melting effect was achieved by a man below the table with an oxyacetylene torch. Goldfinger's laser makes a whirring electronic sound, while a real laser would have produced a fairly heat-free and silent cut.[20]

In addition to movies and popular culture, laser misconceptions are present in some popular science publications or simple introductory explanations such as laser light is not perfectly parallel as is sometimes claimed; all laser beams spread out to some degree as they propagate due to diffraction. In addition, no laser is perfectly monochromatic (i.e. coherent); most operate at several closely spaced frequencies (colors) and even those that nominally operate a single frequency still exhibit some variation in frequency. Furthermore, mode locked lasers are designed to operate with thousands or millions of frequencies locked together to form a short pulse.

[edit] Fictional predictions

For lasers in fiction, see also raygun.

Before stimulated emission was discovered, novelists used to describe machines that we can identify as "lasers".

    * The first fictional device similar to a military CO2 laser (see Heat-Ray) appears in the sci-fi novel The War of the Worlds by H. G. Wells in 1898.
    * A laser-like device was described in Alexey Tolstoy's sci-fi novel The Hyperboloid of Engineer Garin in 1927: see Raygun#In specific scenarios (scroll down to alphabetical order 'H' in the left column).
    * Mikhail Bulgakov exaggerated the biological effect (laser biostimulation) of intensive red light in his sci-fi novel Fatal Eggs (1925), without any reasonable description of the source of this red light. (In that novel, the red light first appears occasionally from the illuminating system of an advanced microscope; then the protagonist Prof. Persikov arranges the special set-up for generation of the red light.)

[edit] Hobby uses

In recent years, some hobbyists have taken interests in lasers. Lasers used by hobbyists are generally of class IIIa or IIIb, although some have made their own class IV types.[21] However, compared to other hobbyists, laser hobbyists are far less common, due to the cost and potential dangers involved. Due to the cost of lasers, some hobbyists use inexpensive means to obtain lasers, such as extracting diodes from DVD burners.[22]

Cartea d-lui prof .Ioan Manzat poate fi considerata o traducere a BIBLIEI pe intelesul tuturor , sau macar pe intelesul majoritatii , sau o "FOAIE PT. MINTE , INIMA SI LITERATURA " - TOATA STIINTA SI RELIGIA CONDENSATA.
SEMNEAZA cu multumiri si deosebita stima si consideratie : HRISTOS SI PASAREA MAIASTRA SI NU hristOS   si   pasarea MAIastra !!.
Cele 10 porunci dumnezeiesti (Decalogul):

              1.   Eu sunt Domnul Dumnezeul tau; sa nu ai alti dumnezei afara de Mine.
              2.   Sa nu-ti faci chip cioplit, nici alta asemanare, si sa te inchini lor.
              3.   Sa nu iei Numele Domnului Dumnezeului tau in desert.
              4.   Adu-ti aminte de ziua Domnului si o cinsteste pe ea. (Aceasta este Duminica)
              5.   Cinsteste pe tatal tau si pe mama ta, ca bine sa-ti fie tie si multi ani sa traiesti pe pamant.
              6.   Sa nu ucizi.
              7.   Sa nu traiesti in desfranare.
              8.   Sa nu furi.
              9.   Sa nu ridici marturie mincinoasa impotriva aproapelui tau.
              10. Sa nu poftesti nimic ce este al aproapelui tau.
Prin urmare Dumnezeu nu iti porunceste   sa nu fumezi , sa nu servesti cafea , nes si bauturi alcoolice .
De la mitul colectiv la mitul personal
Pentru multe persoane, poate, asocierea dintre psihologie şi mit este una curioasă. Psihologia se doreşte a fi o ştiinţă exactă, modernă; mulţi oameni ajung la psiholog pentru a primi răspunsuri clare, sfaturi sau un diagnostic – ei doresc o certitudine. Fie că îşi expun problema laconic, în câteva cuvinte, fie că recurg la o descriere amplă, bogată în asociaţii şi opinii personale, ei aşteaptă un verdict limpede, fără nuanţe de gri: „Sunt sau nu sunt nebun?”, „Am sau nu am şanse de vindecare?”.
Mitul, pe de altă parte, dăinuie în cugetul omenirii ca o poveste fantastică, o poveste menită să explice anumite fenomene naturale sau istorice pe limba primitivilor sau a copiilor. Mitul nu este considerat a fi un produs obiectiv; este văzut doar ca o plăsmuire a oamenilor din vechime care personificau şi „umanizau” ceea ce pentru ei era încă de neînţeles.  
Psihologia şi psihoterapia analitică se interesează de sensul individului. Într-o terapie, aceasta ar echivala cu aducerea individului, pe cât posibil, în acord cu sine însuşi şi reconectarea sa la propriile resurse interioare. Experienţa sensului, potrivit lui Joseph Campbell, antropolog ca formaţie, profesor de literatură ca vocaţie, poate fi trăită citind mituri. „Ele ne învaţă că ne putem întoarce spre interior şi [atunci] începem să înţelegem mesajul simbolurilor. Citiţi miturile altor popoare, nu pe acelea ale propriei religii, deoarece pe acelea tindem să le interpretăm în termeni istorici – dar dacă le citiţi pe ale celorlalţi, începeţi să înţelegeţi mesajul.”
Prin urmare, miturile ne apropie de simbol, expresia acelui ceva necunoscut şi inexprimabil din noi şi, mai departe, de sensul propriei existenţe. Miturile prind viaţă în fiecare dintre noi. Şi, pentru fiecare dintre noi, ele au un înţeles propriu.
Prin intermediul acestor rânduri vă propun o călătorie – de la miturile colective, universal umane, spre mitul personal al fiecăruia.
Dacă unul dintre capetele drumului pare a fi cunoscut – un basm cu uriaşi, elemente învolburate ale naturii, incercări de tot felul, eroi şi eroine, al doilea este învăluit oarecum în mister. Căci, pentru fiecare dintre noi, primul pas către descoperirea mitului personal este călătoria pe mare – adică întoarcerea către sine, interiorizarea, căutarea înăuntrul fiinţei, a ceea ce în zadar am aşteptat până acum să apară din afară.  
Spre deosebire de punctul de vedere antropologic, pentru care mitul reprezintă o simplă producţie a minţii umane şi care încearcă să explice similitudinea dintre miturile unor popare diferite prin fenomene precum migraţia sau schimburile comerciale şi culturale, pentru psihologia analitică mitul este expresia inconştientului colectiv al umanităţii. Mitul reprezintă proiecţia conţinuturilor arhetipale, inconştiente. Psihicul uman este conştient şi inconştient deopotrivă sau luminos şi întunecat, tenebros. În viziunea jungiană, inconştientul comportă două aspecte: inconştientul personal, populat de complexe şi inconştientul colectiv, populat de arhetipuri. Carl Gustav Jung definea arhetipurile, în lucrarea sa, O Abordare Psihologică a Dogmei Trinităţii, „factori şi teme ce aranjează elementele psihice sub forma anumitor imagini, considerate a fi arhetipale, şi care pot fi recunoscute numai după efectele pe care le produc.” Printre astfel de efecte pot fi citate miturile. Jung a ajuns la această concluzie observând fantasmele pacienţilor nevrotici şi psihotici. Ele conţineau, în mod uluitor, elemente mitice, fără ca pacienţii respectivi să fi avut acces în mod conştient la acestea.
Miturile sunt interpretate, astfel, ca produse ale inconştientului colectiv. Personajele lor, născute din necesitatea arhetipurilor de a se manifesta în lumea conştientă, sunt cunoscute ca imagini arhetipale. Astfel, dacă în primul caz mitul apare ca un produs subiectiv, ulterior ritului, psihologia analitică îi conferă atributul obiectivităţii. Deşi exprimat într-o manieră subiectivă, mitul înfăţişează realitatea obiectivă a psihicului uman. De aici, o nouă deosebire între concepţia antropologică şi aceea jungiană: conform primeia, mitul narează realităţi exterioare; conform celei de a doua, mitul dezvăluie ceea ce se află în spaţiul interior al omului.
Exprimând conţinuturi inconştiente cu ajutorul fenomenelor naturii, mitul este un element de legătură între realitatea exterioară şi realitatea interioară. Pentru primitiv, acestea erau una. Eul primitivului, ca şi acela al copilului, este identificat cu Sinele. Pentru acesta – spune Jung, explicarea obiectivă a unor lucruri cunoscute prezintă puţin interes, în schimb el, sau mai bine zis inconştientul său, simte o nevoie irezistibilă de a asimila orice experienţă senzorială externă unor procese psihice. Toate fenomenele naturii mitizate, cum ar fi vara şi iarna, fazele lunii, anotimpul ploilor – continuă Jung -   nu sunt alegorii ale unor experienţe obiective, ci expresii simbolice ale dramei intime şi inconştiente a sufletului, care devine accesibilă conştiinţei umane pe calea proiecţiei, adică oglindită în fenomenele naturii. Miturile nu sunt inventate de sufletul primitiv, ci trăite nemijlocit. La fel ca şi copilul, primitivul înţelege şi interpretează lumea exterioară prin intermediul propriilor trăiri: în drumul soarelui pe cer, el vede călătoria unui erou, plecat de lângă părinţii săi într-un car de aur, înfruntând tot felul de obstacole, pentru ca noaptea să piară şi a doua zi să reînvie; întunericul nopţii este populat de monştri, precum inconştientul este populat de lucruri stranii, înspăimântătoare. Ori, miturile îşi au originea în această lume fantastică, magică, care asocia atât de naiv (cu simplitate, într-un mod direct) susul cu josul, exteriorul cu interiorul.
Născute într-o vreme în care conştiinţa umană se afla încă în stadiul de pruncie, miturile se situează la acelaşi nivel de conştiinţă cu visele şi fantasmele. Fiind din aceeaşi plămadă, miturile reprezintă un real sprijin pentru interpretarea produselor inconştientului şi pentru aducerea lor în conştiinţă. Visele sau elementele de vis care ne frapează prin asemănarea lor cu motive mitologice fac referire, de obicei, la arhetipurile principale: cel al mamei, al copilului, al eroului, al umbrei, al animei / animusului – iar în terapie, analogia cu mitul facilitează cunoaşterea şi integrarea acestora, permiţând lărgirea sferei conştiinţei.
Miturile omenirii sunt ţesute în jurul acestor arhetipuri, sau elemente structurale ale psihicului inconştient „formatoare de mituri”, cum le mai numeşte Jung. Fiecare dintre acestea vorbeşte despre condiţia psihică a omului la un moment dat pe parcursul vieţii: naşterea conştiinţei, desprinderea de complexele parentale, lărgirea conştiinţei cu acele conţinuturi respinse iniţial şi proiectate asupra celor din jur (Umbra), proiecţia animei / animusului şi îndrăgostirea, apoi transformarea interioară, echivalentă cu moartea eului. Arhetipurile nu pot fi niciodată înţelese sau descifrate pe deplin de conştiinţa omenească. Întotdeauna, conştiinţa va fi mai restrânsă decât inconştientul, existând, astfel, mereu aspecte care îi vor scăpa. Arhetipurile nu pot fi interpretate sau golite de sens; doar circumambulate. Asocierea liberă, în acest caz, nu este utilă, căci va duce într-un impas, într-un punct mort. Circumambularea implică o mişcare circulară, o „dănţuire” în jurul imaginii arhetipului – reflectarea sa din   mai multe puncte de vedere. La fel ca şi visul, a cărui interpretare este contextuală, arhetipul îşi dezvăluie sensuri diferite pe diferite nivele de interpretare, fără, însă, a le epuiza niciodată.
Ceea ce enunţă un arhetip este în primul rând o asemănare din punctul de vedere al limbii. Dacă vorbeşte despre soare şi îl identifică cu leul, regele, comoara apărată de balaur şi „puterea vindecătoare” sau dătătoare de viaţă a omului, el nu este nici unul, nici celălalt, ci terţul necunoscut, care se exprimă mai mult sau mai puţin potrivit prin toate aceste asemănări, dar care – fapt ce este constant o supărare a intelectului – rămâne necunoscut şi neformulabil.
Intuind că mitologia reprezintă una dintre căile către dezvăluirea psihicului uman, Jung s-a dedicat studiului acesteia. Travaliul său din vremea aceea s-a finalizat cu volumul Simboluri ale Transformării. Apariţia acestuia a constituit nu numai despărţirea de Freud, ci şi începutul unei noi etape în viaţa lui Jung. Personalitate introvertă, Jung obişnuia să se ghideze după impresiile pe care le primea din interiorul fiinţei sale. În acea perioadă, într-o stare a conştiinţei pe care a perceput-o a fi de o deosebită claritate, Jung a sintetizat, într-o clipă, trecut, prezent şi viitor, înţelegând drumul parcurs până în acel moment şi având viziunea celui ce urma să vină:
Acum ai în posesia ta o cheie către mitologie şi ai posibilitatea să deschizi cu ea toate porţile spre psihicul omenesc inconştient. Dar îndată am auzit şoptindu-se în mine: De ce să deschizi toate porţile? Şi s-a şi iscat întrebarea: oare ce realizasem de fapt? Explicasem miturile unor popoare din trecut, scrisesem o carte despre erou, despre mitul în care omul a trăit dintotdeauna. Dar în ce mit trăieşte omul astăzi? În mitul creştin, s-ar putea spune. Tu trăieşti în el? - a răsunat mai departe întrebarea în mine. Ca să fiu sincer, nu! Nu este mitul în care trăiesc eu. Atunci, nu mai avem nici un mit? Nu, e evident că nu mai avem nici un mit. Dar care-i oare mitul tău? Mitul în care trăieşti tu? Deodată, dialogul deveni neplăcut şi am încetat să mai gândesc, ajunsesem la un impas.

Jung îşi punea aceste întrebări la începutul secolului XX. Iată un bun moment pentru a ne opri şi a reflecta asupra propriului mit. Oare noi mai trăim astăzi în mitul creştin? Să fi subscris, unui alt mit colectiv? Care este, oare, mitul nostru, al fiecăruia?

Într-adevăr, pentru omul modern mitul creştin şi-a pierdut din strălucire, din numinozitate. Citându-l pe Nietzsche, „Dumnezeu a murit”. Şi, dacă un mit nu mai este viu, nu mai poate face legătura între cele două lumi – interioară şi exterioară sau spirituală şi fizică. Astfel, funcţia sa principală este anihilată. Mitul devine, în acest caz, o simplă legendă. El nu mai este în stare să provoace trăiri deosebite sau revelaţii. Simbolurile pe care le utilizează devin simple elemente culturale, laice, lipsite de mister, aşa cum pentru multe persoane au devenit crucea, icoanele, aşezămintele creştine.
Pentru civilizaţia occidentală, cel mai apropiat este mitul creştin. Acesa este structurat în jurul arhetipului infans sau puer aeternus – copilul, care prin însăşi venirea sa pe lume, vesteşte schimbarea. Întotdeauna, o astfel de „reînnoire” este privită ca primejdioasă de eu, acesta presimţindu-şi pieirea. După cum ne amintim, Irod, regele iudeu, a poruncit uciderea tuturor pruncilor – gest ce ne duce cu gândul la Cronos, ce şi-a mâncat fiii, sau la basme în care copiii nedoriţi sunt fie ucişi, fie abandonaţi în pădure, fie lăsaţi în grija unor persoane de rang inferior. Irod, simbol al eului, al conştiinţei, se vede ameninţat de naşterea copilului Iisus. În ciuda acestuia, copilul supravieţuieşte şi ajunge la vârsta la care începe să răstoarne vechile moduri de gândire şi de acţiune (distrugerea templului). Dumnezeu, imagine arhetipală a Sinelui, nu putea fi cunoscut în mod nemijlocit, nu putea fi văzut, iar numele său nu putea fi rostit – oamenii se aflau într-o stare de identificare inconştientă cu Sinele. Spre deosebire de acest Dumnezeu ambivalent, răzbunător, imprevizibil, şi de zeii romanilor, capricioşi şi iraţionali – în mod evident imagini dezechilibrate, omnipotente, Iisus întruchipează unirea conştientă a contrariilor, cel care „aduce spada” propovaduind iubirea, cel care tratează cu aceeaşi consideraţie duşmanii şi prietenii, cel care se lasă răstignit, unind în fiinţa sa cele patru funcţii psihice.
Dacă ce se întâmpla până atunci în psihicul colectiv poate fi echivalat cu starea copilului, în acelaşi timp omnipotent dar şi supus voii părinţilor, naşterea lui Iisus simbolizează trezirea conştiinţei.
Mitul creştin este unul colectiv. În câteva sute de ani, el a fost îmbrăţişat de un număr mare de oameni, de pe toate continentele, care au sfârşit prin a crea în jurul său una dintre cele mai puternice religii. Riturile sale sunt trăite în colectivitate: slujbele, sărbătorile pascale, Crăciunul. Credincioşii se roagă şi se bucură alături de ceilalţi, împărtăşesc împreună trăirile înălţătoare şi veneraţia. Timp de aproape două mii de ani, mitul creştin a funcţionat, a fost viu în sufletul europenilor. Este şi acum viu în unele zone rurale sau în sufletul populaţiei de culoare.
Pentru omul modern, însă, „Dumnezeu a murit”. În 1928, Jung definea omul modern ca omul conştient de prezentul imediat. Omul modern este acela care a depăşit etapele anterioare ale conştiinţei, care este vigil şi eficient. Omul modern este atemporal – poate fi modern în secolul 16, ca şi în secolul 21. Aceştia sunt însă puţini. Pentru marea majoritate a oamenilor care nu mai trăiesc în mitul creştin, Sinele se proiectează asupra unor vedete, persoane carismatice, asupra unor organizaţii politice sau asupra obiectelor unor dorinţe care, odată atinse, îşi dovedesc lipsa de sens.
Dacă ivirea pe lume a lui Iisus a reprezentat naşterea conştiinţei, o a doua venire a sa este echivalentă cu „ieşirea din copilărie”, maturizarea şi desprinderea definitivă de complexele parentale. Colectivitatea, grupul, se înscriu pe linia simbolisticii materne. Dacă mitul nu mai este viu, se cere, probabil, o nouă circumambulare a lui, în căutarea unui nou sens:
Dacă arhetipurile nu pot fi negate sau făcute cumva inofensive, fiecare treaptă culturală a diferenţierii conştiinţei este confruntată cu sarcina de a găsi o nouă interpretare, corespunzătoare treptei, pentru a lega viaţa trecută, încă existentă în noi, cu viaţa prezentă care ameninţă să dispară. Dacă aceasta nu se întâmplă, ia naştere o conştiinţă fără rădăcini, care nu mai este orientată în trecut, care sucombă neajutorată tuturor sugestiilor, adică, practic, devine predispusă epidemiilor psihice.    
Conştiinţa dezrădăcinată, orfană, se vede astfel pradă bolilor psihice, dar şi delirului indus sau regresiei la stadii inferioare.

Ideea de mit personal sugerează unicitatea, reprezentând, într-un fel, drumul individuării. O dată cu naşterea eului, în copilăria mică, se conturează, de obicei, şi mitul personal – ca predilecţie spre constelarea anumitor arhetipuri sau a anumitor istorii exemplare. Fiecare dintre noi a avut în copilărie o poveste preferată, fiecare şi-a dorit să devină ceva „când va fi mare”. Cu timpul, claritatea mitului personal păleşte sub impunerile lumii exterioare, ale părinţilor, ale mediului, necesităţii adaptării conştiinţei la normele sociale. Individul îşi uită mitul, sau îl ascunde într-un colţ al sufletului, ruşinat de visurile sale copilăreşti şi devenind, astfel, un sclav al timpului – precum în basme şi legende, eroii sunt vrăjiţi să-şi uite ţara de origine, drumul pe care porniseră (vezi Ulise, vrăjit de Circe) sau aleasa / alesul inimii.
Pentru Jung, devenirea personalităţii, găsirea sensului vieţii, descoperirea şi trăirea mitului personal sunt expresii ale aceluiaşi conţinut. Sensul vieţii este individual. În zadar îl căutăm în modele, în norme sau valori colective. De multe ori, mitul personal ne determină să ne ridicăm împotriva acestora. Este o înfruntare legitimată de propria conştiinţă şi nu doar un gest de rebeliune, născut din eterna luptă inconştientă a contrariilor. În stilul său tranşant în privinţa mediocrităţii, Jung numeşte „personalitate” doar acel individ „care poate spune conştient da puterii vocaţiei sale interioare ce îi vine în întâmpinare; acela însă care sucombă acestei puteri devine sclavul cursului orb al evenimentelor şi este distrus.” A fi în mitul personal aduce după sine curajul de a-ţi asuma propriile decizii, curajul de a te comporta conform propriilor valori, chiar atunci când acestea vin în contradicţie cu normele general acceptate, curajul de a spune „am greşit” şi de a o lua de la capăt. Nu este o cale lipsită de sacrificii. Pentru Jung, imboldul de a-şi urma mitul personal a reprezentat renunţarea, timp de câţiva ani, la cariera universitară.
De asemenea, drumul mitului personal implică pericole. Atunci când eul individului nu este suficient de puternic, el poate fi copleşit de conţinuturile arhetipale puse în joc, dezintegrându-se în psihoză.
Invitaţia de a-şi descoperi mitul personal se adresează tuturor acelora care nu mai trăiesc într-un mit colectiv, fie ei oameni moderni (conform accepţiunii jungiene) sau „conştiinţe dezrădăcinate”, alienate.
Campbell, Joseph, Bill Moyers, The Power of Myth, New York, 1991
inclus în volumul C.W. 11
Jung, C.G., Opere Complete vol.1, în Despre Arhetipurile Inconştientului Colectiv, Bucureşti, 2003
Jung, C.G., Amintiri, Vise, Reflecţii, Bucureşti, 2001
Jung, C.G., Opere Complete vol.1, în Despre Psihologia Arhetipului Infans, Bucureşti, 2003
Jung, C.G., Opere Complete vol.17, în Privitor la Devenirea Personalităţii, Bucureşti, 2006
Cele patru mituri fundamentale ale lumii
      Miturile memoriale sunt pastratoarele faptelor ancestrale si se poate presupune ca ele au inregistrat fie psihoze colective provocate de evenimente de mari proportii cu caracter insolit (ipostezele cunoasterii focului, revolutia agrara), fie incercarea empirica de a explica diverse fapte neobisnuite, petrecute de obicei la confluenta existentiala a doau populatii de nivel spiritual foarte diferit. Aici se pot subclasifica mai multe manunchiuri mitologice, pe care le-am putea numi :(a) interferenta erelor (miturile varstei de aur a salbaticiei arcadice, adica preagrare, dar si miturile animalelor fabuloase, de la popoarele de maimute vorbitoare-poate hominizii, pana la balauri si dragoni -descriind primele contacte ale omului cu regnul animal in genere sau infatisarea, vazuta hipertrofic, a unor fosile pe atunci inca vii, cunoscute azi din paleontologie) ; (b) omul primordial (primele grupuri umane care au inceput a se socoti superioare animalelor si chiar hominizilor coexistenti dar - constranse de mutatia agrara, apoi de cea neolitica sa paraseasca raiul liber al cadrului salbatic -si-au exprimat regretul izgonirii din acel rai sau dintr-un teritoriu edenic parasit in urma altei constrangeri ; (c) revelatia initiala (descoperirile inteligentei primordiale : iubirea, familia, cunoasterea de sine si cunoasterea cadrului- de unde si impactul intre moral si amoral, definint prima data notiunea de imoralitate, ca si ciocnirea inevitabila intre inteligenta si candoare, intre cunoastere si ignoranta, iar in simbol- intre spiritul divin si spiritul luciferic) ; (d) evenimentele insolite (categoria dintre viziunea profetului Iezechil si prabusirea fiului solar Phaethon) ;(e) inventia uneltelor (armele si mecanismele magice, vehiculele pendente de imblanzirea calului, corabiile salvatoare de la potop, carele ceresti) ; (f) modificarile conditiei umane (revolutiile succesive :pastoreasca, agrara, neolitica, metalurgica-implicand, odata cu inchegarea treptata a societatii umane, si schimbarea structurala a modului de trai, de relatii si interese, ca si a tipului de alimentatie, odata cu inventarea satului, cetatii, statului si a ordinii sociale) ; (g) razboaiele ceresti (conflictele de dimensiuni apocaliptice, intre categoriile de divinitati adverse, traducand fie impactul omului cu dezlantuirile extraordinare de forte naturale, fie observarea empirica a unor dereglari astrofizice) ; (h) potopul si reconstructia universului postdiluvian (invaziile acvatice sau solare, urmate de repunerea in ordine a regiunilor afectate, uneori poate la scara sincronic planetara).

  Miturile fenomenologice privesc fenomele de nivel cosmic, alcatiund naratiuni explicative in jurul marilor intrebari omenesti asupra existentei omului si a cadrului sau vizibil si nevazut : (a) actul cosmogonic ( facerea lumii mai ales din haosul primordial, adesea acvatic, sau din intalnirea principiului feminin cu cel masculin, sau prin pornirea timpului inert ; (b) antropologia (crearea omului, ca pereche arhetipala sincronica sau diacronica, printr-un singur act definitiv sau in cateva etape experimentale ; (c) escatologia (vizand ideea de moarte- unica sau periodica, naturala sau prin accident catastrofal- a insului si a universului sau) ;(d) repetitia manifestarilor naturii (succesiunea zilelor si a noptilor, anotimpurilor, erelor terestre si cosmice) ; (e) regnurile fabuloase (formand indeobste structura unora dintre cele mai vechi mituri ale omenirii, care poarta intre ele formele rudimentare de conceptie ambientala din animismul initial ori din ciclul formelor totemice de cult ale epocilor prevanatoresti si vanatoresti carora li s-a adaugat cadrul alegoric din epoca domesticirii animalelor, a cultivarii plantelor, a descoperirii pietrei utilizabile si apoi a metalelor, ca si unor reactii chimice naturale) ; (f) cadrul astral (astrele fiind, in conceptia mitologica, nu corpuri ceresti ci ,,luminatori'' pendenti de vointa patronala a anumitor zei, locuinte divine, iar uneori chiar formele vizibile de intruchipare a zeilor) ; (g) elementele (apa in toate ipostazele sale inerte sau active, focul viu si apoi cel tehnic, focul cosmic si cel meteorologic, pamantul static si dinamic, fertil si distrugator, aerul ca forma de miscare cereasca si ca regenerator perpetuu al vietii, alteori ca tampon intre pamant si cer, in fine mai rar, eterul, element al straturilor ceresti divine, constituind inca in observatia primitiva un ansamblu de conditii esentiale ale existentei cosmice).

  Miturile cosmografice includ intregul cadru divin, adica pe zei si locuintele lor universale : (a) teogonia (poate cel mai straniu dintre actele mitice, intrucat zeii insisi se autocreeaza sau sunt creati, multiplicarea lor apartinand unei conceptii ulterioare, influentate probabil de endogamia tribala si apoi de diviziunea profesionala a indeletnicirilor) ; (b) panteonul (sau totalitatea zeilor- cu numar variabil dupa epoca si zona geogafica- fluctuand intre monoteismul rigid, unde zeii si sfintii devin accesorii tehnice sau divinitati subalterne ale unui singur zeu teologic admis ca suprem, si amplitudinea elastica a politeismului numarand, de pilda, in religia romanilor peste 30.000 de zeitati) ; (c) lumile coexistente (de obicei trei fundamentale :cerul, pamantul si subpamantul, adica lumea divina, cea umana si cea demonica, dar in unlele mitologii si mai multe :la scandinavi noua ;de asemenea, si anumite lumi paralele, parahumane, neconfirmate insa de vreuna din teologii si conservate mai cu seama in folclorul mitologic).

  Miturile transcedentale, consacrate de omul primitiv elucidarii contradictiile existentiale aparente, pe care el nu le accepta decat ideal : (a) eroul arhetipal (nu stramosul totemic, ci modelul de la care porneste sirul, un model absolut si deci inegalabil, de aceea si divinizat) ;(b) suprastructura demonologica (reprezentand transferul in mitologie a credintei animiste in duhurile si in demonii care ar guverna universul -integral ca si in detaliila palpabile) ; (c) destinul (ca lege in sine sau sistem de legi implacabile si intrepatrunse, supunandu-si intregul univers, pana la detalii, omul, omenirea si chiar zeii) ; (d) universul dual (conceptul diviziunii lumii in principii antagonice, care completeaza in mod general intregul :lumina-intuneric, caldura-frig, miscare-repaos, mascul-femela, viata-moarte si in ultima amaliza bine-rau) ;(e) simbolurile conditiei umane (aspiratie omului de a-si depasi conditia, de obicei prin imitarea unor valori ambientale : de pilda zborul icaric, care nu este decat traducerea alegorica a invidiei omului fata de pasare, dar nu si intelegerea deosebirii structurale) ;(f) viata si moartea (ca antiteza acuta suprema in care miturile nu admit totusi termenii antitezei, preferand ideea de stari diferite ale aceeleiasi existente, intrucat thanatofobia conceptuala, care trabuce instinctul de conservare, nu scuteste de suferinta intrebarii nici o fiinta ganditoare) ; (g) aria timpului (timpul uman mensurabil si timpul divin, deci numenal, inaintea acestora si dupa ele, unele mituri admitand si absenta timpului).
Crestinarea in epoca formarii poporului a impiedicat constituirea timpurie a unei mitologii unitare , iar inceputul sincretizarii miturilor sub influenta credintelor popoarelor asiatice navalitoare si sub constrangerea crestinismului a faramitat sip e alocuri a pulverizat o mitologie probabil autonoma , judecand dupa miturile pastrate in traditiile unor sarbatori populare enigmatice (unele numite sarbatori babesti ) , in folclorul epic (balade , basme ) fantastic si eroic ,intr-o anumita categorie de superstitii in descantare , in ritualurile magice ale inmormantarii (Vrancea) , in memoria oieritului transhumant .Miturile biblice , auzite la biserica , sunt sincretizate spontan prin injectarea nervurii mitice locale.(Adam si Eva morti la varsta de 700 ani , au poruncit sa fie inmormanatati in muntele Alelei ).Dar exista variante cosmogonice stranii cu f. vechi radacini (ca acelea din folclorul bucovinean ;la inceput nu era nimic pe lume , decat un munte mare purtat de vanturi , din varful lui iesea foc , iar din foc s-a nascut o femeie neinsufletita ,al carui trup a fost purtat de vanturi ;din varful lui iesea foc , iar din foc s-a nascut o femeie neinsufletita , al carui trup a ajuns la Vantul-cel-de-sus , care i-a dat viata ;de acolo femeia coboara pe munte unde , gasind doua bucati de fier , le inghite , ramane insarcinata si naste doi copii:unul schiop si destept , altul teafar si prost ; muntele neavand decat fier si fratii avand nevoie de lut , cel prost aduce lut din adancul marilor , iar cel destept confectioneaza un cal fara viata si intra amandoi pe rand in cal fara sa-l miste , facand apoi si o caruta ;fiindca numai fratele prost izbutise sa miste calul ramane sa traga el toata viata acest mit folkloric precizeaza ca in vremea aceea “Dumnezeu era necunoscut “.Nucleul mitului nu e sigur ca e migrant , chiar daca fenomene vulcanice recente n-au existat pe teritoriul Romaniei ;iar fierul , ca germen fecundator e dintr-un strat mitic mai tarziu .M.R.in formele cognoscibile azi nu cuprinde zei , numai duhuri (de tip animist ),divinitati secundare de origine totemica (Sfanta Vineri ,Pasarea Maiastra ),animale oraculare (Oaia Nazdravana , Calul Nazdravan ),demoni (dracul , Talpa-Iadului), Ielele, Martolea, Muma-Padurii), divinitati luciferice(Catelul Pamantului), monstri zoomorfi (balaurii)sau fapturi nefaste parahumane (zmeii),Giganti ,(Uriasii, Novacii )si eroi miraculosi ,in parte eroi civilizatori (Fat-Frumos ,Voinic de Plumb),dar si numeroase zane (de tipul Ileana Cosanzeana) bune sau rele ;si divinitati sincretice ale naturii (Sanpetru , santilie);exista si instrumente magice (caciula fermecata , BusteanulIelelor ), lumi paralele (cele doua taramuri, frecvent fiind Taramul Celalat care nu este infernul ci o lume parahumana din alt univers.)In fine , duhuri semifaste , uneori incarnate , ca Pica , divinitatea fumatului .
Trasaturi caracteristice ale mitologiei romanesti)
- Lumea e populate de duhuri rele si viclene , care pot fi insa pacalite de inteligenta omeneasca , desi omul nu se angajeaza in lumea duhurilor decat sau din insarcinare imparateasca sau din vocatie eroica , sau provocat de ele .
- Destinul e implacabil (sensul oracular al Mioritei) , unde oracolul nu e prevenire , ci anuntarea obiectiva a unui fenomen natural ce nu mai poate fi modificatt ;tot asa cand Fat Frumos ,ratacit la rascruce, intreaba o baba adesea pe Sfanta Vineri , incotro s-o ia I se raspunde invariabil :’De vei apuca la dreapta , te vei cai , de vei apuca la stanga iarasi te vei cai”).
-       Credinta intr-un taram second , paralel (Taramul celalat ) unde exista o viata parahumana pagana , libera , incantatoare si eterna.; de obicei acest al doilea taram e locuit sau numai pazit de zmei;rareori are character infernal , si niciodata unul paradisiac in sens biblic(influentele bisericesti nu au patruns in acest mit ).
- Convingerea ca exista undeva , (de obicei pe taramul celalalt ) Tineretea fara batranete si viata fara de moarte , la care totusi unii eroi ajung , dar de unde invariabil pleaca , absorbiti de Dorul de casa , sic and se intorc constata ca acolo timpul se scurgea mult mai incet , iar aici ei imbatranesc si mor imediat , pierzand magia care-I tinuse tineri(timpul) ,desi tema e universala , varianta romaneasca a mitului e tratata   in categoria ideala.:tragicul fara lacrima , neputinta optiunii ;
- Actele esentiale savarsite miraculous de eroii mitici (obtinerea apei vii si apei moarte , omorarea balaurilor , rapirea Ilenei Cosanzene , razboaiele cu fapturile fabuloase sau magice ), de obicei condensati in eroul arhetipal Fat-Frumos , sunt tot ideale , nefiind urmarite in interes personal , caci Fat-Frumos nu e un cavaler supus pana la evlavie suveranului sau , el nu are stapan , e suveran el insusi , posesor liber al inteligentei , dreptatii si fortei , care si ele sunt ideale; singurul care il ajuta real e calul sau nazdravan , dar totdeauna un paradox il sileste sa se supuna altui destin decat al sau. (finalurile fericite fiind interpolari folclorice tarzii ) , intrucat Fat-Frumos este un semizeu luciferic.
      Capodopera absoluta a literaturii noastre populare, dovada geniului artistic al poporului roman, este rezultatul unui proces de creatie seculara, textul baladei armonizand un numar variabil de motive poetice cu existenta independenta in folclor.
"Miorita" sintetizeaza o experienta de viata milenara, pentru a o ridica, prin transfigurare artistica la rang de valoare general-umana.
Datarea genezei baladei este de fapt imposibila, pentru ca ea este rezultatul unei contaminari succesive intre temele majore ale folclorului nostru.
Tema baladei "Miorita" o constituie o drama din viata pastoreasca, din timpul transhumantei.
Subiectul este simplu: conflictul se naste intre trei ciobani: "Unu-i moldovan/Unu-i ungurean/Si unu-i vrancean". Cel moldovean, mai vrednic: "are oi mai multe/Mandre si cornute/Si cai invatati/Si caini mai barbati". Ceilalti doi, cu sufletul cotropit de invidie, si-au pus in gand sa-l omoare pe cel moldovean.
O miorita nazdravana il instiinteaza pe baci de complotul pus la cale. Se pune astfel in evidenta o prima semnificatie a operei: infruntarea dintre bine si rau. Deznodamantul nu ne este cunoscut; nu stim daca ciobanul a fost omorat, dar ii cunoastem gesturile, atitudinea, gandurile in fata mortii.
Partea lirica, urmand celei epice, contine testamentul baciului si rugamintea adresata mioritei de a alina durerea maicutei sale.
Din intreaga poezie izbucneste navalnic, ca un fluviu, vitalitatea dintotdeauna a omului din popor, dragostea oierului fata de indeletnicirea sa, fata de arta, de viata, de natura si, mai ales, iubirea filiala fat pentru mama sa.
In structura compozitional a baladei se pot distinge doua mari parti: una epica, in care sunt narate faptele, si una lirica si dramatica, in care se exprima gandurile si sentimentele ciobanasului aflat in fata mortii.
Motivele fundamentale pe care se sprijina balada sunt:
1• motivul transhumantei
2• motivul complotului
3• motivul mioarei nazdravane
4• motivul testamentului
5• motivul maicutei batrane
6• motivul alegoriei moarte-nunta
In text, cele sase motive se distribuie in trei parti. Prima parte corespunde motivelor transhumantei si complotului, cea de-a doua apartine celui de-al treilea motiv, iar ultima parte celor trei motive finale. Cele trei parti sunt legate sintactic prin conjunctiile "dar" si "iar" cu valoare adversativa sau copulativa.
Prima parte, o adevarata expozitiune, are un caracter epic, ce reprezinta imaginea cadrului natural in care se succed faptele. Astfel, personajele sunt plasate in spatiul romanesc, intr-o atmosfera de calm si seninatate specifica inceputurilor. Metaforele ne introduc intr-o natura de basm, intr-un loc al fericirii in care pastorul se simte linistit.
Ciobanii sunt prezentati vag la inceput, fiind incadrati in coordonatele spatio-temporale carora apartin, pentru ca din primele versuri se deduce si timpul desfasurarii actiunii. E toamna, tarziu, cand turmele coboara la iernat, intr-o miscare mereu repetata numita transhumanta.
In secventa urmatoare, epicul devine intunecat de gravitatea complotului. Echilibrul se strica. Se creaza un contrast puternic intre atmosfera paradisiaca din primul tablou si dramatismul situatiei, sugerat de complot-intriga.
Hotararea de omor este determinata de cauze economice, de invidia determinata de averea mai mare a ciobanului moldovean, care e mai "ortoman". Faptele cu valoare informativa sunt enumerate cu o detasare obiectiva. Poetul anonim se abate de la acest ton o singura data cand, printr-un dativ etic ("ca sa mi-l omoare"), marcheaza participarea sa afectiva la cele relatate, dar si dramatismul situatiei in care se afla ciobanasul.
Partea a doua a baladei, desfasurarea, este dramatica in totalitate ca urmare a comportamentului mioritei.
Autorul staruie mai intai asupra nelinistii oii nazdravane, evidentiind zbuciumul ei puternic si rau prevestitor "Dar cea miorita/Cu lana plavita/De trei zile-ncoace/Gura nu-i mai tace/Iarba nu-i mai place". Dramaticul are acum ca modalitate fundamentala de expresie dialogul. Prin dialog se releva relatia stransa dintre animalul credincios si stapan, reciprocitatea sentimentelor dintre ei, perfecta armonie dintre om si profesiunea sa.
Acum intervine elementul fabulos, de basm, prin personificarea mioarei, ce ii aduce la cunostinta ciobanului hotararea de omor. Tensiunea dramatica este gradata. Printr-un limbaj afectiv, oita isi indeamna stapanul:
"Da-ti oile-ncoace" sau "Iti cheama s-un cane". Complotul este comunicat abia la sfarsit, cu grija de a nu speria: "Ca l-apus de soare/Vreau sa mi
Autorul popula utilizeaza diminutivele exclusiv in momentele de mare intensitate lirica ("bolnavioara", "fluieras", "draguta", "ciobanel"), pentru a spori substanta dramatica a baladei.
Raspunsul baciului, construit in partea a trei a baladei, da contur confruntarii omului cu moartea, capacitatii acestuia de a patrunde tainele universului. Acum se structureaza motivul testamentuluisi al alegoriei moarte-nunta.
De aici incolo, creatorul popular converteste totul intr-un emotionant monolog liric, prin care ciobanasul isi exprima ultimele dorinte inaintea presupusei morti.
Sentimentul de profunda dragoste fata de viata este oglindit de atasamentul fata de indeletnicirea sa. Ciobanul nu isi poate imagina despartirea, chiar si dupa moarte, de stana, oile sau cainii sai.
Folosirea paralelismului, evidenta in pasajul fluierelor, este un procedeu caracteristic intregii poezii folclorice. Stihurile sunt acum un fel de refrene, laitmotive ce apar la intervale egale, puse in evidenta anaforica (repetarea unor cuvinte la inceputul versurilor) a diminutivului "fluieras" si a adverbului "mult".
Dramatismul creste, pe fondul unei seninatati a confruntarii omului cu moartea, sentiment izvorat din intelegerea profunda a alcatuirii universului, din experienta mitica, retraita, a baciului moldovean, atingan culmile tragismului in metafora totala, absoluta "cu lacrimi de sange".
Urmatorul motiv, cel al alegoriei moarte-nunta, adevarat punct culminant, este si partea cea mai concentrata ca substanta poetica.
Dorinta ciobanului este ca lumea sa afle ca petrecera sa din viata a fost o nunta, la care insa "a cazut o stea" (semnificand inchiderea perspectivei fericirii). Se mai realizeaza aici si o incarcatura poetica maxima, constand in incifrarea alegorica a unei realitati etnografice: mortilor tineri, necasatoriti ("nelumiti") li se organizeaza inmormantarea ca o nunta.
Apar acum si simbolorile nelipsite din ceremonialul nuptial: mireasa, nasii, preotii, lautarii si nuntasii, ca si obiectele rituale traditionale (cununa, lumanarile), ce sunt figurate prin elemente al cadrului natural (brazi, paltinasi, munti, pasari) si cosmic (soarele, luna, stelele). Contopirea cu natura, in virtutea unei vechi credinte traditionale, este sugerata de enumerarea de elemente naturale.
Apare insa aici si sentimentul tragic izvorat din neputinta de a stabili dupa moarte legaturi cu mediul uman, reprezentat de mama. Motivul maicutei batrane da glas dragostei si grijei pentru mama pe care nu vrea s-o indurereze. Cunoscand bine semnificatiile, ea nu trebuie sa afle despre caderea stelei, amanunt care i-ar dezvalui imediat realitatea petrecuta.
Momentul, dramatic prin excelenta, prilejuieste o descriere portretistica deosebita, ce sporeste lirismul. Poetul popularo evoca pe maicuta intr-o chinuitoare cautare. Gesturile sale: "Din ochi lacrimand/Pe camp alergand/Pe toti intreband/Si la toti zicand" sunt expresia iubirii materne. Nu este vorba aici de o mama anume, ci de personificarea dragostei plina de ingrijorare si sacrificiu a mamei eterne.
Imaginea mamei este conturata numai printr-un epitet ("batrana") si un detaliu vestimentar ce indica lumea oierilor ("cu braul de lana"). Zbuciumul fiintei indurerate este foarte bine evidentiat de cele patru verbe la gerunziu, aflate in rima, care prin grupul sonor
"-and", sugereaza un lung geamat dureros. Efectul este impresionant din punct de vedere stilistic-eufonic si da motivului o functie estetica.
Portretul ciobanul, de o frumusete parca ireala, este comunicat in text prin intermediul stilului direct, transfigurat de sentimentele mamei. El exprima idealul de cuceritoare barbatie pe care si l-a format, de-a lungul veacurilor, poporul nostru: "Mandru ciobanel/Tras printr-un inel;/Fetisoara lui/Spuma laptelui/Mustacioara lui/Spicul graului/Perisorul lui/Pana corbului/Ochisorii lui/Mura campului". Frumusetea fizica a ciobanasului este o completare a frumusetii morale. Iubirea de natura, dragostea de viata, de munca zilnica, grija cu care se gandeste la soarta oilor si a mamei sale sunt calitati sufletesti pe care poetul popular tine sa le puna in evidenta.
Balada se incheie simetric prin repetarea alegoriei moarte-nunta, ce accentueaza caracterul liric.
"Miorita" face loc, dupa ultimul vers, meditatiei asupra sensului ei adanc, mai indepartat, un sens filozofic. Privind moartea ca pe un fenomen natural, ciobanul se gandeste la destinul lui si al celor apropiati (oile, mama) in eventualitatea mortii. El este preocupat de savarsirea tuturor oranduielilor traditionale, pentru implinirea lui ca om (nunta cosmica) si pentru a-si asigura prezenta postuma in mediul pastoral, atat de familiar.
Originea "Mioritei" nu este cunoscuta. Ea poate sa fi pornit de la un fapt real, ori sa fi fost, la inceput, doar un bocet, un colind, sau chiar rezultatul intreg al fictiunii. Cert este ca "Miorita" este numai a noastra, a romanilor.
Balada este o specie a genului epic popular in versuri, cunoscuta si sub denumirea de cantec batranesc, cu un subiect fantastic, legendar, istoric sau familiar, ale carui versuri se canta sau sunt recitate, acompaniate la un instrument. (balade: fantastice, vitejesti, istorice, haiducesti, pastoresti, familiale)
BIBLIOGRAFIE:Dictionar de mitologie generala , Victor Kernbach , Ed. Albatros , Bucuresti , 1983