User talk:Theindigowombat

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Hi. I'm the user formerly known as As I have noted previously, I happen to have Asperger's Syndrome and an anxiety disorder; because of this, I ask that people excercise the utmost civility and speak with precision and clarity if they wish to talk with me here; this will help ensure clear communication despite my disabilities. Thank you.

Test Page[edit]

I'm going to try an experiment here. As I mentioned on the Milky Way talk page recently, I happen to have a copy of a rewrite of the Milky Way article that was left on my system by an anonymous contributor when I was posting unsecurely through my IP address. I present it below to stimulate discussion and generate ideas. It should be noted that all sources and references cited were not checked out by me personally, but is strictly what was included in the text file left in my documents folder by an unknown editor. This version also does not include my final rewrite and updated sources for the central new statement about nomenclature that the recent debate has centered around. The only change I have made to the text file is to turn off the categories as requested in WP:CFORK. Note: I was incorrect about the source of this alternate version; please see below.

Hi, Theindigowombat. Just a thought - would it be possible to temporarily replace the new text below with the current contents of the article (you could revert it straight away), so that a diff could be performed between the two versions? It seems like most of the major changes are in the first couple of sections and at the end, but there might be other minor changes. Cosmo0 18:51, 12 October 2007 (UTC)
Okay. I'll give that a try at some point today. The other major differences worthy of discussion are the usage of the formal nomenclature in the text of the article. The version currently up in the main namespace represents what I feel is the minimum acceptable concession to the formal nomenclature; the version below reflects my sense of the maximum acceptable concession. I feel the optimum is somewhere in between, but I feel much more discussion is warranted as to what level of concession to the formal nomenclature is appropriate for a Wikipedia article. Theindigowombat 19:51, 12 October 2007 (UTC)
Done. If I made any technical errors in the process, please let me know. It looks like some things that I thought were changes were already in the article, but I had overlooked them somehow. Nonetheless, I hope this is useful. Theindigowombat 20:17, 12 October 2007 (UTC)
Upon a careful review of the comparison between the two versions, I find that in many respects the current version is superior, but there is some additional content in the new version that seems worthy of inclusion in the article. Also, although in most respects re: spelling and grammar the current version is superior, the usage of the formal nomenclature in the below version is closer to what I would prefer (although not perfect). I could probably come up with a way to combine what I see as the best aspects of both, but I don't wish to do so unilaterally. Theindigowombat 03:50, 13 October 2007 (UTC)

Gross factual error on my part[edit]

When I found the below version as a text file in my documents folder, I had no memory of putting it there, and believed it could only have been deposited by a benign intruder. This was incorrect; I have investigated further and now realize that it was a version of the article that I had saved previously, in the midst of my editorial work, then forgotten about. I find it disturbing that I could have forgotten such a thing and that I prematurely accepted an unusual explanation for its presence on my system as fact. It seemed to me to be the most logical, sensible explanation for its presence on my system at the time, and that unsettles me, too. I apologize for any confusion or skepticism that may have been generated by my previous incorrect assumptions about the source of this version. Theindigowombat 06:18, 19 October 2007 (UTC)

Milky Way Galaxy (as written by anonymous contributor alternate version)[edit]

This is an article on our galaxy. For other uses see Milky Way (disambiguation)

360-degree photographic panorama of the entire galaxy.
The Milky Way as it appears in the night sky from a dark location.
The Milky Way in Cygnus

The Milky Way Galaxy (a translation of the Latin Via Lactea, in turn derived from the Greek Γαλαξίας (Galaxias), sometimes referred to simply as "the Galaxy"), is a barred spiral galaxy which forms part of the Local Group. Although the Milky Way Galaxy is but one of billions of galaxies in the universe, the Galaxy has special significance to humanity as it is the home of the Solar System. Democritus (450 BC–370 BC) was the first known person to claim that the Milky Way Galaxy consists of distant stars.

The term "Milky Way" 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. Technically speaking, the term "Milky Way" alone should refer exclusively to the band of light in the night sky, while the term "Milky Way Galaxy" (or "the Galaxy") is the proper description for our galaxy. In practice, however, the intended meaning of the term is often clear from the context in which it is used, and the term "Milky Way" is routinely used to refer to either topic.

The Milky Way 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 250-300 thousand light years in circumference, and outside the Galactic core, about 1,000 light years in thickness. It is composed of 200 to 400 billion stars [1]. As a guide to the relative physical scale of the Galaxy, if it were reduced to 130 km (80 mi) in diameter, the solar system would be a mere 2 mm (0.08 in) in width. The Galactic Halo extends out to 250,000 to 400,000 light years in diameter. As detailed in the Structure section below, new discoveries indicate that the disk extends much farther than previously thought.

The Milky Way's absolute magnitude, which cannot be measured directly, is assumed by astronomical convention to be −20.5, although other authors give an absolute magnitude of −21.3.


The age of the Galaxy is currently estimated to be about 13.6 billion (109) years, which is nearly as old as the Universe itself.[1]

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 Galaxy at 13.6 ± 0.8 billion years.

Composition and structure[edit]

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 overall shape of the Milky Way Galaxy is believed to be a barred spiral. It consists of a bar-shaped core region surrounded by a disk of gas, dust and stars. Within the disk region are several arm structures that spiral outward in a logarithmic spiral shape. The mass distribution within the Galaxy closely resembles the Sbc Hubble classification, which is a spiral-galaxy with relatively loosely-wound arms.[2] It was only in the 1980s that astronomers began to suspect that the Milky Way Galaxy is a barred spiral[3] 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.[4] This argues for a classification of type SBbc (loosely wound barred spiral). In 1970 Gérard de Vaucouleurs predicted that the Milky Way Galaxy was of type SAB(rs)bc, where the "rs" indicates a broken ring structure around the core region.[5]

As of 2006, the Milky Way Galaxy's mass is thought to be about 5.8×1011 M[6][7][8] comprising 200 to 400 billion stars. Its integrated absolute visual magnitude has been estimated to be −20.9. Most of the mass of the Galaxy is thought to be dark matter, forming a dark matter halo of an estimated 600–3000 billion solar masses (M) which is spread out relatively evenly.[8]

Galactic center[edit]

The galactic center in the direction of Sagittarius. The primary stars of Sagittarius are indicated in red.

The galactic disk, which bulges outward at the galactic center, has a diameter of between 70,000 and 100,000 light-years.[9] The distance from the Sun to the galactic center is now estimated at 26,000 ± 1400 light-years while older estimates could put the Sun 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.[10]

The Milky Way 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 the 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 Milky Way Galaxy and most of the Galaxy's star formation activity. Viewed from the Andromeda Galaxy, it would be the brightest feature of our galaxy.[11]

Spiral arms[edit]

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
color arm(s)
cyan 3-kpc and Perseus Arm
sky-blue Norma and Cygnus Arm (Along with a newly discovered extension)
chlorine-green Crux and Scutum Arm
pink Carina and Sagittarius Arm
There are at least two smaller arms or spurs, including:
orange Orion Arm (which contains the solar system and the Sun)

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

As is typical for many galaxies, the distribution of mass in the Milky Way Galaxy 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.[12] 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. Another interesting aspect is the so-called "wind-up problem" of the spiral arms. If one believes that the inner parts of the arms rotate faster than the outer part, then the Milky Way Galaxy will wind up so much that the spiral structure will be thinned out. But this is not what is observed in spiral galaxies. Instead astronomers propose that the spiral arms form as a result of a matter-density wave emanating from the galactic center. This can be likened to a moving traffic jam on a highway—the cars are all moving but there is always a region of slow-moving cars. Thus this results in several spiral arms where there are a lot of stars and gas. This model also agrees with enhanced star formation in or near spiral arms; the compressional waves increase the density of molecular Hydrogen and protostars form as a result.


The galactic disk is surrounded by a spheroid halo of old stars and globular clusters, whose 90% lie within 100,000 light-years,[13] 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.

Recent discoveries have added dimension to the knowledge of the Galaxy's structure. With the discovery that the disc of the Andromeda Galaxy (M31) extends much further than previously thought,[14] the possibility of the disk of the Milky Way Galaxy extending further is apparent, and this is supported by evidence of the newly discovered Outer Arm extension of the Cygnus Arm.[15] 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 Galaxy 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 Galaxy 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 found a huge and diffuse structure (spread out across an area in the sky around 5,000 times the size of a full moon) within the Milky Way Galaxy that does not seem to fit within current models. The collection of stars rises close to perpendicular to the plane of the spiral arms of the Galaxy. The proposed likely interpretation is that a dwarf galaxy is merging with the Milky Way Galaxy. This dwarf galaxy is tentatively named the Virgo Stellar Stream and is found in the direction of Virgo about 30,000 light-years away.

Sun's location[edit]

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 7.62±0.32 kpc from the Galactic Center.[16][17][18][19] The distance between the local arm and the next arm out, the Perseus Arm, is about 6,500 light-years.[20] The 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, is the direction that the Sun travels through space in the Milky Way Galaxy. 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. In addition the Sun oscillates up and down relative to the galactic plane approximately 2.7 times per orbit. This is very similar to how a simple harmonic oscillator works with no drag force (dampening) term.

It takes the solar system about 225–250 million years to complete one orbit (a galactic year),[21] 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.[citation needed]

The Milky Way Galaxy's context in the universe[edit]

The Milky Way Galaxy is orbited by 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. The smallest, Carina Dwarf, Draco Dwarf, and Leo II Dwarf are only 500 light years in diameter. The other dwarfs orbiting our galaxy are the Small Magellanic Cloud; Canis Major Dwarf, the closest; Sagittarius Dwarf Elliptical Galaxy, previously thought to be the closest; Ursa Minor Dwarf; Sculptor Dwarf, Sextans Dwarf, Fornax Dwarf, and Leo I Dwarf.

In January 2006, researchers reported that the heretofore unexplained warp in the disk of the Milky Way Galaxy 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 Galaxy, causing vibrations at certain frequencies when they pass through its edges. Previously, these two galaxies, at around 2% of the mass of the Milky Way Galaxy, were considered too small to influence our galaxy. However, by taking into account dark matter, the movement of these two galaxies creates a wake that influences the larger Milky Way Galaxy. Taking dark matter into account results in an approximately twenty-fold increase in mass for the Galaxy. 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 Galaxy 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 Galaxy.

Current measurements suggest the Andromeda Galaxy is approaching us at 100 to 140 kilometers per second (62 to 87 miles per second). The Milky Way Galaxy may collide with it in 3 to 4 billion years, depending on the importance of unknown lateral components to the galaxies' relative motion. If they collide, it is thought that the Sun and the other stars in the Milky Way Galaxy will probably not collide with the stars of the Andromeda Galaxy, but that the two galaxies will merge to form a single elliptical galaxy over the course of about a billion years.[22]


In the general sense, the absolute velocity 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.)

Many astronomers believe the Milky Way Galaxy is moving at approximately 600 km 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 the Galaxy is moving at 600 km/s, Earth travels 51.84 million km per day, or more than 18.9 billion km per year, about 4.5 times its closest distance from Pluto. The Milky Way Galaxy is thought to be moving towards the constellation Hydra, and may someday become a close-knit member of the Virgo cluster of galaxies.

Another reference frame is provided by the Cosmic microwave background (CMB). The Milky Way Galaxy is moving at around 552 km/s[23] with respect to this frame. 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.

Earth-based observations[edit]

The Milky Way as seen in a very wide angle image showing the whole horizon taken from a very dark sky location (Death Valley).

The Milky Way appears brightest in the direction of the constellation 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. Although the Milky Way has an absolute magnitude of −20.9, it has a relatively low apparent magnitude,which makes it difficult to see from any urban or suburban location suffering from light pollution.

Discovery of "our galaxy"[edit]

See also:Galaxy-Observation history

The Greek philosopher Democritus (450 BC–370 BC) was the first known person to propose that the Milky Way might consist of distant stars. Actual proof of this came in 1610 when Galileo Galilei used a telescope to study the Milky Way and discovered that it was composed of a huge number of faint stars.[24] In a treatise in 1755, Immanuel Kant, drawing on earlier work by Thomas Wright, speculated (correctly) that the Milky Way might be a rotating body of a huge number of stars, held together by gravitational forces akin to the solar system but on much larger scales. The resulting disk of stars would be seen as a band on the sky from our perspective inside the disk. Kant also conjectured that some of the nebulae visible in the night sky might be separate "galaxies" themselves, similar to the Milky Way.[25]

The shape of the Milky Way Galaxy as deduced from star counts by William Herschel in 1785; the solar system was assumed near center.

The first attempt to describe the shape of the Milky Way Galaxy and the position of the Sun within it was carried out by William Herschel in 1785 by carefully counting the number of stars in different regions of the sky. He produced a diagram of the shape of the galaxy with the solar system close to the center.

In 1845, Lord Rosse constructed a new telescope and was able to distinguish between elliptical and spiral-shaped nebulae. He also managed to make out individual point sources in some of these nebulae, lending credence to Kant's earlier conjecture.[26]

In 1917, Heber Curtis had observed the nova S Andromedae within the "Great Andromeda Nebula" (Messier object M31}. Searching the photographic record, he found 11 more novae. Curtis noticed that these novae were, on average, 10 magnitudes fainter than those that occurred within our galaxy. As a result he was able to come up with a distance estimate of 150,000 parsecs. He became a proponent of the so-called "island universes" hypothesis, which held that the spiral nebulae were actually independent galaxies.[27]

Photograph of the "Great Andromeda Nebula" from 1899, later identified as the Andromeda Galaxy

In 1920 the so-called Great Debate took place between Harlow Shapley and Heber Curtis, concerning the nature of the Milky Way, spiral nebulae, and the dimensions of the universe. To support his claim that the Great Andromeda Nebula was an external galaxy, Curtis noted the appearance of dark lanes resembling the dust clouds in the Milky Way, as well as the significant Doppler shift.[28]

The matter was conclusively settled by Edwin Hubble in the early 1920s using a new telescope. He was able to resolve the outer parts of some spiral nebulae as collections of individual stars and identified some Cepheid variables, thus allowing him to estimate the distance to the nebulae: they were far too distant to be part of the Milky Way Galaxy.[29] In 1936 Hubble produced a classification system for galaxies that is used to this day, the Hubble sequence.[30]

Names and mythology[edit]

Jacopo Tintoretto's "The Origin of the Milky Way"

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.

The term Milky Way first appeared in the English literature in a poem by Chaucer.

"See yonder, lo, the Galaxyë
 Which men clepeth the Milky Wey,
 For hit is whyt."

— Geoffrey Chaucer, Geoffrey Chaucer The House of Fame, c. 1380.[31]

In a large area from Central Asia to Africa, the name for the Milky Way is related to the word for straw. It has been claimed that this was spread by Arabs who in turned borrowed the word from Armenian.[32] In several Uralic and Turkic languages and in the Baltic languages the Milky Way is called the "Birds' Path". The Chinese name "Silver River" (銀河) is used throughout East Asia, including Korea. In Japan, "Silver River" (銀河) means galaxies in general and the Milky Way is called the "River of Heaven" (天の川).

There are many creation myths around the world regarding the Milky Way. In particular, there are two similar ancient Greek stories that explain the etymology of the name Galaxias (Γαλαξίας) and its association with milk (γάλα). Some myths associate the constellation with a herd of cattle whose milk gives the sky its blue glow. In Eastern Asia, people believed that the hazy band of stars was the "Silvery River" of Heaven. This is written in hanzi as 銀河.

Akashaganga is the Indian name for the Milky Way, which means Ganges River of the Sky.

According to Greek mythology, the Milky Way was formed by Hera, who spilled milk in the sky after discovering that Zeus had tricked her into feeding young Heracles. In another variant, Hermes snuck Heracles into Olympus to drink from the breasts of Hera who was asleep. Heracles bit Hera's nipple shooting her milk into the skies forming the Milky Way.

In Finnish mythology the Milky Way was called Linnunrata (pathway of the birds). The Finns observed the migratory birds used the galaxy as a guideline to travel south, where they believed Lintukoto (bird home) resided. Only later the scientists indeed confirmed the observation correct; the migratory birds use the Milky Way as a guide and dwell the winters in warm, southern lands. The Milky Way is even today called Linnunrata in the Finnish language.

In Swedish, the Milky Way is known as Vintergatan (winter street), for apparent reasons; it is most visible in the winter in Scandinavia.

Ancient Armenian mythology called the Milky Way the "Straw Thief's Way", relating to one of the gods stealing straw and attempting to flee across the heavens in a wooden chariot, spilling some of the straw along the way.

In Hindu mythology the Milky Way is called the s'is'umara cakra: the dolphin disc. Looking in the night sky one recognized the band of stars as the belly of a dolphin.

In Slovene, the Milky Way is called Rimska cesta, literally "The Roman Road" (or "The Road to Rome", alluding to the ancient pilgrim path). Sometimes, infrequently, it is also called Mlečna cesta, which is a literal translation of its Greek/Latin name. i.e. "Milky Way".

In Spanish, the Milky Way is sometimes called "Camino de Santiago", "The Road to Santiago <de Compostela>", alluding to the ancient pilgrim road to the town of Santiago de Compostela, in Spain.


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External links[edit]

[[Category:Milky Way Galaxy| ]] [[Category:Milky Way Subgroup]] [[Category:Local Group]] [[Category:Galactic astronomy]] [[Category:Barred spiral galaxies]]

af:Melkweg ar:درب التبانة bg:Млечен път ca:Via Làctia cs:Galaxie Mléčná dráha da:Mælkevejen de:Milchstraße el:Γαλαξίας et:Linnutee es:Vía Láctea eo:Lakta vojo fr:Galaxie (Voie lactée) ga:Bealach na Bó Finne ko:우리 은하 io:Lakto-voyo id:Bima Sakti it:Via Lattea he:שביל החלב la:Via lactea lt:Paukščių Takas li:Mèlkweeg hu:Tejút mk:Млечен пат nl:Melkweg (sterrenstelsel) ja:銀河系 no:Melkeveien ug:سامان يولى سىستىمېسى pl:Droga Mleczna pt:Via Láctea ro:Calea Lactee ru:Млечный Путь scn:Jolu di San Jàbbucu simple:Milky Way sl:Naša Galaksija fi:Linnunrata sv:Vintergatan th:ทางช้างเผือก vi:Ngân Hà zh:银河系 zh-min-nan:Gîn-hô-hē

I believe this Milky Way (Galaxy) article to be superior to the current one though the intro could be changed a little for pertinence. -Kain Nihil 04:42, 15 October 2007 (UTC)