Talk:Milky Way

View From Earth

The astrological direction of slow motion of the Center of the Milky Way is a good paragraph.

A way to visually understand galactic rotation is that the angle between the Andromeda Galaxy and the Center of the Milky Way is slowly increasing. At the present time the galactic longitude of Andromeda is 121.17 degrees. (Andromeda is about -20 degrees in galactic latitude and south of the galactic equator.) If the angle is watched carefully for a thousand years it should increase by six arc-seconds or so. In 35 million years it will be a radian, 57 degrees. Galactic coordinates behave like ecliptic coordinates - their zero slowly migrates around the sky. In the past several thousand years the Spring equinox migrated from Aries well into Pisces, at least thirty degrees.

Minor suggestion for the text above the "Contents" box - Intro

In the introduction above the contents box there is a minor issue but I couldn't edit it.

It says in the first sentence; "The Milky Way Galaxy, commonly referred to as just the Milky Way, or sometimes simply as the Galaxy, is the galaxy in which the Solar System is located."

To clarify, it should say "in which our Solar System is located." There are other solar systems in the Milky Way and I believe this sentence is trying to indicate it is where our solar system is located. —Preceding unsigned comment added by Analystbynature (talk • contribs) 20:31, 16 October 2010 (UTC)

Designation?

Does the Milky Way have an astronomical designation? I've checked both lists on Wikipedia, neither the Messier list (no surprise there) nor the NGC contains it.--Amitakartok (talk) 00:37, 17 October 2010 (UTC)

I doubt it, because those designations are for objects you can see from the earth. You can't see the whole Milky Way from the earth since we're inside it, so it wouldn't have its own designation. thx1138 (talk) 23:22, 19 October 2010 (UTC)

Values for Milky Way thickness inconsistent

The observation table says that the Milky Way has a thickness of about 1,000 light years, but the section on "Size" says that the estimated value for the Milky Way's thickness is 12,000 light years, an order of magnitude greater. Is this inconsistency just caused by data coming from two different sources? Which one do I value as more accurate? And can this inconsistency be changed? 24.7.113.93 (talk) 03:54, 26 October 2010 (UTC)

• 12,000 refers to the gaseous disk — strictly speaking twice the scale height of free electrons in diffuse warm ionised medium (ref). I would assume 1,000 ly refers to the scale height of thin stellar disk. Thick stellar disk is kinematically and chemically a different component, and is—yes—thicker (scale height around 1 kpc, or 3 kly). The bar/bulge is thicker, too, perhaps 1 kpc. The shape of the Galaxy is a difficult topic, and will remain uncertain untill Gaia flies. Random astronomer (talk) 14:24, 2 November 2010 (UTC)

Please revert 2 edits by annon IP 16:35 UTC

Edits are hidden. My cellphone browser can't undo it. Thanks! निओ (talk) 17:42, 18 January 2011 (UTC)

Unsourced etymology

I've removed some unsourced material, which reads like a list dump. I would prefer to add a short summary of the list and mythology articles, but both are in poor shape and unsourced. The Harvard ref I've added properly summarizes the subject, so perhaps the section can be expanded from there. Removed material below: Viriditas (talk) 23:19, 23 February 2011 (UTC)

Slovene has a peculiar expression Rimska cesta (The Roman Road) for the Milky Way, which is not attested in any other language. The name is derived from an old notion that the pilgrims followed it when travelling to Rome.

In a large area from Central Asia to Africa, the name for the Milky Way is related to the word for "straw". This may have originated in ancient Armenian mythology, (Յարդ զողի Ճանապարհ hard goghi chanaparh, or "Trail of the Straw Thief"), and been carried abroad by Arabs. In several Uralic, Turkic languages, Finno-Ugric languages and in the Baltic languages the Milky Way is called the "Birds' Path" (Linnunrata in Finnish), since the route of the migratory birds appear to follow the Milky Way. (The Qi Xi legend celebrated in many Asian cultures references a seasonal bridge across the Milky Way formed by birds, usually magpies or crows.) The Chinese name "Silver River" (銀河) is used throughout East Asia, including Korea and Japan. An alternative name for the Milky Way in ancient China, especially in poems, is "Heavenly Han River"(天汉). In Japanese, "Silver River" (銀河 ginga) means galaxies in general and the Milky Way is called the "Silver River System" (銀河系 gingakei) or the "River of Heaven" (天の川 Amanokawa or Amanogawa). In some of the Iberian languages, the Milky Way's name translates as the "Road of Saint James" (e.g., in Spanish it is sometimes called "El camino de Santiago").

This is fine to remove, we have dedicated articles List of names for the Milky Way and Milky Way (mythology) where this information can go, if sources are found. Polyamorph (talk) 08:27, 24 February 2011 (UTC)

200 billion ≠ 1×10¹¹

 Number of stars   200–400 billion (1–4×1011)

200 billion is not equal to 1×10¹¹. The above should read: 200–400 billion (2–4×10¹¹) or 100–400 billion (1–4×10¹¹). Please correct me if I'm wrong. --George Makepeace (talk) 01:33, 25 February 2011 (UTC)

You are correct, the references cited say 200-400 billion so I have fixed the text. Polyamorph (talk) 10:38, 25 February 2011 (UTC)

Isn't 4×10¹¹ four houndred thousand million stars? 400 billion is 400,000,000,000,000 or 4×10¹⁴ — Preceding unsigned comment added by 188.80.245.124 (talk) 15:33, 7 December 2011 (UTC)

See Long and short scales. Thanks. Regards, RJH (talk) 16:58, 7 December 2011 (UTC)

Age undue synthesis

The figures given in the section Milky_Way#Age is improperly referenced with references that claims "nothing of that kind!" The text claims that an age of 13.2 Ga for HE 1523-0901 gives a lower limit of the age of the MW. It of course does not. If f.ex. MW was formed by the merger of diverse dwarf galaxies, then HE 1523-0901 could have originated in one of those dwarf galaxies, to join the newly emerged MW at the creation year zero, while the HE-star itself was already say 3 Ga old. Rursus dixit. (^mbork³!) 13:58, 25 April 2011 (UTC)

space.com, tertiary source, claims 13.6±0.8 Ga. Using space.com or similar as a source is better, since then we're not doing the WP:SYNTH, just referring to a claim. Rursus dixit. (^mbork³!) 14:06, 25 April 2011 (UTC)

panorama desription

"Part of the Milky Way arches across this 360-degree panorama of the night sky above the Paranal platform, home of ESO’s Very Large Telescope. The image was made from 37 individual frames with a total exposure time of about 30 minutes, taken in the early morning hours. The Moon is just rising and the zodiacal light shines above it, while the Milky Way stretches across the sky opposite the observatory."

Is it nessasry to have all this infommation under the panorama? I think it could be cut down to "Part of the Milky Way arches across this 360-degree panorama of the night sky above the Paranal platform, home of ESO’s Very Large Telescope."
Let me know what you think
-Sic dicit Defectu tui omnis iam = So Says your failure is always present 15:17, 2 June 2011 (UTC)

Remark on page popularity

This article is currently ranked 17th on the list of the Wikipedia most popular astronomy article views, but it only has a 'B' rating. It might be worth bringing up to GA status. Regards, RJH (talk) 19:05, 12 August 2011 (UTC)

picture taken in southern hemisphere please

someone please add a picture of the night sky taken from the southern hemisphere here, without the galaxy going off the horizon as it does in the north. Okay? — Preceding unsigned comment added by 75.87.138.107 (talk) 23:50, 2 September 2011 (UTC)

Age (again) link

These guys claims to have made an adjustion to the isochrones of stars due to debated gravitational settling (atomic diffusion) in the interior of old solar-type stars, and instead of the notorious 16-14 Gyr old age of Milky Way got 10-12 Gyr. In my opinion this only demonstrates that the concluded age of 13.6 (or so) Gyr is very insecure. Slight modifications of star models can cause vast variations in the age determination, and added to that, the age estimates varies also due to the asserted criteria for birth, whether it equals to the birth of the bulge and the globular clusters which might have occurred 2 Gyr before the birth of the disk and spiral arms... Rursus dixit. (^mbork³!) 15:37, 15 September 2011 (UTC)

Unverified statement

• The Milky Way has a relatively low surface brightness due to the interstellar medium that fills the galactic disk, which prevents us from seeing the bright galactic center.

The above statement is unverified and looks to be wrong since it seems to imply that removing the dust lanes would increase surface brightness. It wouldn't, the areas behind the dust lanes would be just as bright as the visible areas. I have seen statements in some texts that the galactic core would be a much brighter object if it was not obscured by dust lanes, but that is a different concept. Fountains of Bryn Mawr (talk) 16:27, 16 September 2011 (UTC)

Galactic centre distance and Galactic mass

I made a few alterations to the article, bringing the stated distance to the Galactic centre in line with more recent data and papers -- in particular removing references to Eisenhauer et al 2005 which has been superseded by Gillessen et al 2009 (identical data plus further observations, similar author list, systematic uncertainties better understood). I also added a more recent estimate of the total Galactic mass (based on many data sets, rather than just the one). — Preceding unsigned comment added by Trefusius (talk • contribs) 15:44, 16 November 2011 (UTC)

Supermassive black holes

There have been a few edits regarding the wording of this sentence: "Most normal galaxies are presumed to have supermassive black holes at their centers." I think that "presumed" is incorrect: this is an observation, not a presumption (or assumption). The first sentence of the abstract of the cited paper says "Beyond all reasonable doubt, black holes are commonly found in the nuclei of most normal galaxies."

Also, Supermassive_black_hole#Supermassive_black_hole_hypothesis (though not a reliable source, it was cited in this edit) says "Astronomers are confident that our own Milky Way galaxy has a supermassive black hole at its center, 26,000 light-years from the Solar System, in a region called Sagittarius A*[10] because:..."

Both statements are pretty unambiguous; all the evidence points to the presence of a supermassive black hole at the center of the Milky Way and most normal galaxies. I think that words like "presumed" weasel inappropriately. Obviously, nothing is universal, hence the qualifiers "most" and "normal".

Thoughts? (Commenting here rather than edit warring.) —Alex (ASHill | talk | contribs) 02:31, 31 January 2012 (UTC)

Commenting since I did the edit. "Sagittarius A*... is a supermassive black hole" and "Most normal galaxies have supermassive black holes at their centers" are absolute statements[4]. "Beyond all reasonable doubt" and "Astronomers are confident" are not absolute statements. One cannot become the other per WP:V. Things can be de-weaseled but they cannot be converted into absolutes to do that. Fountains of Bryn Mawr (talk) 03:23, 31 January 2012 (UTC)

I edited the paragraph again; I hope this sticks to the facts without inserting the sentiment "presumed" that is not in the referenced works. —Alex (ASHill | talk | contribs) 03:31, 31 January 2012 (UTC)

Reworded a little more to remove an absolute statement. Theoretical physics is by definition theoretical, as are black holes. Not sure if you are trying to apply WP:WEASEL but expressing theories in some form is not "weasel-y". "Presumed" is "suppose that something is the case on the basis of probability"[5]: we have referenced probability so "presumed" is not a weasel word. Fountains of Bryn Mawr (talk) 15:49, 31 January 2012 (UTC)

"Presumed" is an informal assessment by somebody, so to me is bordering on weasel. "Observed" does not require direct observation. See neutrinos for example. Regards, RJH (talk) 17:07, 31 January 2012 (UTC)

The statement "Supermassive black holes are located near the center of most normal galaxies" is incorrect per WP:NOR re: going beyond what is expressed in the source. The wording "Beyond all reasonable doubt" in the paper cited, and what is found in secondary sources re: "we now believe to be" (The Galactic Supermassive Black Hole - Forward[6]) "expected to exist" (Introduction to Black Hole Physics, page 11[7]) does not become the statement "are". Feel free to reword. Fountains of Bryn Mawr (talk) 20:55, 31 January 2012 (UTC)

BTW WP:WEASEL only applies to unsupported attributions, we are talking about supported attributions here. Fountains of Bryn Mawr (talk) 21:11, 31 January 2012 (UTC)

Since we do know with reasonable certainty that there are supermassive concentrations at the cores of galaxies, even if we can not yet unarguably confirm that they are SMBHs, perhaps it would be better to say something like, "Compact, supermassive concentrations are located near the centers of most normal galaxies"? Regards, RJH (talk) 21:20, 31 January 2012 (UTC)

That's the sentiment I was trying to get across with my last edit to the page, which now says "The concentration of mass around Sagittarius A* is best explained as a supermassive black hole.[47][48][49] Supermassive black holes are located near the center of most normal galaxies.[50]." I don't think saying "concentration of mass" two sentences in a row is necessary, though, given that there's essentially no debate left in the literature (including the two cited ApJ papers, ref 48 and 49 as of now) about the existence of supermassive black holes. I think that some form of the verb "to be" is a better representation of phrases like "beyond all reasonable doubt" and "it is known" than some form of the verb "presumed". —Alex (ASHill | talk | contribs) 22:41, 31 January 2012 (UTC)

It seems to my eyes that fewer new papers on super massive black holes are using the sort of "beyond all reasonable doubt" language that was once more common. For one example, see the intro or abstract of this paper about a cloud of gas on the way towards Sgr A*, which opens with "The Galactic center is one of the most extreme and puzzling places of the Milky Way. Harboring a supermassive black hole (SMBH) with a mass of MBH = 4.31e6 M_\sun� ..." Or, for SMBHs more generally, this paper about simulations of super star clusters around SMBHs opens with "It is known, nowadays, that many galaxies harbor a supermassive black hole (SBH) in their innermost regions." These are just a couple of recent sources that suggest that "presumed" or comparable language is unnecessary. James McBride (talk) 21:44, 31 January 2012 (UTC)

(de-indent) The papers have a context, that context being theoretical physics i.e we are still dealing with theories, not facts. Even the last papers quoted have phrases like "agree well with models" "mimics the situation observed". Its not our job to weigh the numbers of papers or jump to conclusions in any one sentence, but to match secondary sources (provided). Fountains of Bryn Mawr (talk) 14:43, 1 February 2012 (UTC)