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.

Different "photon velocities" ?

In the Velocity section is the sentence..

The Milky Way is moving at around 552 km/s with respect to the photons of the CMB

http://en.wikipedia.org/wiki/Milky_Way#Velocity

It is a fundamental postulate of relativity that the speed of all light is the same in all directions. This quote suggests the EM waves are passing us at different speeds depending on the direction from which they are coming.
May I suggest something like...

The Milky Way is moving at around 552 km/s with respect to the reference frame established by the radiation making up the CMB.

Dave 2346 (talk) 15:06, 24 December 2009 (UTC)

More completely: You confuse the relative speed of a source (the atoms that emitted the photons of the CMB) and a receiver (us, in the MW) of photons with the speed of the photons themselves when received by us. The latter is indeed constant. But the frequency of the photons changes instead, as the relative source/receiver speed changes, and this is what allows us to decide on the 552 km/s speed of the Milky Way: In two opposite directions on the sky (think of North & South Poles), we see frequency changes of +552 and -552 km/s compared to the circle of intermediate directions (think of Equator). Jmacwiki (talk) 04:37, 25 December 2009 (UTC)

Only one frame of reference

In the Velocity section it is stated that there are two different possible "preferred frames of reference", one with respect to the "Hubble flow" and one with respect to the CMB. However, if I understand the reference correctly, these two are actually the same. The velocity of 630km/s of the "first" reference frame is, also according to the reference and CMBR dipole anisotropy, not the galaxy velocity but the Local Group velocity. The galaxy is than again moving within this Local Group giving it a velocity with respect to the CMB (or Hubble flow) of 552 km/s (I did not check this number). There is thus only one "preferred frame of reference" and I suggest to call it just the "reference frame of the CMB". --Jmdx23 (talk) 22:42, 7 January 2010 (UTC)

school project

Hi i am doing a school praject on the milky way can any one help me with head titles or infomation???? —Preceding unsigned comment added by 99.235.238.178 (talk) 05:09, 9 January 2010 (UTC)

If you don't find what you need in the article, please ask a more specific question. —Tamfang (talk) 02:40, 12 January 2010 (UTC)

Here's some information that may help you. You'll get a better grade if you write like this:

Hi. I am doing a school project on the Milky Way. Can anyone help me ...?

HTH. —Tamfang (talk) 02:42, 12 January 2010 (UTC)

Right on, Tamfang! Jmacwiki (talk) 03:38, 21 January 2010 (UTC)

Standard distance units

This article flip-flops between using light years and parsecs as units of distance. I think it would be good if it only used a single unit consistently.—RJH (talk) 20:46, 19 January 2010 (UTC)

Any preference? Mine is for light years as this is far better known to the average lay-reader. Casliber (talk · contribs) 21:02, 19 January 2010 (UTC)

Definitely. Also, it seems far easier to explain -- and therefore for the average reader to understand -- how a light year is defined (distance light travels in a year) than how a parsec is (206,265 * Earth-Sun distance). Jmacwiki (talk) 03:35, 21 January 2010 (UTC)

B Class?

Only B class? Sephiroth storm (talk) 04:03, 22 February 2010 (UTC)

Nominate it for GA if you think it's ready. ScienceApologist (talk) 05:52, 22 February 2010 (UTC)

The article was GA until July 2009 when it was delisted as part of the GA sweeps, see Talk:Milky_Way/GA1. Jdrewitt (talk) 08:15, 22 February 2010 (UTC)

It'd be great to get it back to GA - why not take a look and think about what needs to be done - a to-do list of sorts...Casliber (talk · contribs) 10:46, 22 February 2010 (UTC)

The article as it is looks GA quality, I don't think it would be too much trouble getting it promoted. The main issues from the GA delisting were

1. Copy edit needed.
2. Improve the prose where necessary.
3. Expand the lead.
4. Ensure all areas are cited and replace the {{citation needed}} tags with verifiable sources.

Jdrewitt (talk) 11:55, 22 February 2010 (UTC)

Before copyediting, one should always review comprehensiveness. Are we satisfied the article is fully comprehensive? I haven't looked at it yet myself. Casliber (talk · contribs) 12:52, 22 February 2010 (UTC)

• One thing that is missing in the section about the halo is mention of High velocity clouds and a more complete description of the tidal streams and globular clusters. ScienceApologist (talk) 12:56, 22 February 2010 (UTC)

• The Dark matter halo is interesting and only touched upon in this article, while there is a sizeable segment on the milky way's dark matter halo at Dark_matter_halo#Milky_Way_dark_matter_halo. I'd buff it in this article myself but I am a neophyte at some of these concepts - is the dark matter halo widely accepted? Casliber (talk · contribs) 13:04, 22 February 2010 (UTC)
  • The only evidence we have for it is indirect and there are those observers who would argue that it is not a "part" of the Milky Way per se. Unlike external galaxies, the rotation curve of the Milky Way is notoriously difficult to measure and the mass of the Milky Way is still something of an outstanding question. Evidence for dark matter in the disk of the galaxy coming from the Oort constants has now been thoroughly debunked. However, people who build theoretical models of the galaxy absolutely do consider it vital to its structure and formation and cosmological theories all but demand its existence. Additionally, it's also kinda cutting edge right now to think that the best chance we have for a direct detection of dark matter is looking at the center of the Milky Way where the so-called WMAP haze lies. Yeah, there might some room to discuss dark matter in our galaxy. ScienceApologist (talk) 13:10, 22 February 2010 (UTC)

• • • SA if you want to have a go at incorporating the shtuff to the right level of depth and consensus yada yada (as I have no idea!), I can play with massaging and smoothing the prose and constructing a lead. Of course everyone else is welcome as well :) Casliber (talk · contribs) 23:48, 22 February 2010 (UTC)

• • • • Hmm, I'm not sure I can dig up the appropriate sources to do this and it is seriously something outside of my field of expertise. I'll ask one of my colleagues if they'll have a go at it. ScienceApologist (talk) 23:45, 23 February 2010 (UTC)

Inconsistent mass entries

Twice, this article states that the Milky Way has a mass of 5.8 × 10¹¹ M☉. It then goes on to state that there is about 6 × 10¹¹ to 3 × 10¹² solar masses of dark mater, which far exceeds this previous number. Also, the mass of the Milky Way is routinely said to be comparable to that of the Andromeda Galaxy, given as 1.23 × 10¹² M☉ in its own article. This article also happens to state the Milky Way is 1.9 × 10¹² M☉, which makes a lot more sense. Also, the cited sources for the Milky Way mass seem to be a bit out of date, if I am to understand these recent mass adjustments taking dark matter into account properly.Rip-Saw (talk) 00:25, 20 March 2010 (UTC)

I found an article here that is considerably more current: http://arxiv.org/abs/0801.1232 but I cannot make head or tails of what virial mass means. Seems to give an estimate of 10¹² M☉.Rip-Saw (talk) 00:30, 20 March 2010 (UTC)

What is Going to Happen in the Future to our Galaxy?

I heard our galaxy is going to collide with another galaxy. If someone can prove this is true, I think it'd be nice to put this in the article. --BrandiAlwaysSmiles (talk) 20:15, 7 April 2010 (UTC)

We could link to this article http://en.wikipedia.org/wiki/Andromeda%E2%80%93Milky_Way_collision from the Milky Way article. thx1138 (talk) 21:19, 7 April 2010 (UTC)

Milky Way avoids Serpens?

The list of constellations that the band of the Milky Way passes through includes Aquila, Ophiuchus, Scutum, and Sagittarius. I don't see how it could possibly avoid going through Serpens Cauda - is Serpens missing, or was Ophiuchus a mistake? DenisMoskowitz (talk) 14:13, 2 June 2010 (UTC)

Misuse of sources

Jagged 85 (talk · contribs) is one of the main contributors to Wikipedia (over 67,000 edits, he's ranked 198 in the number of edits), and practically all of his edits have to do with Islamic science, technology and philosophy. This editor has persistently misused sources here over several years. This editor's contributions are always well provided with citations, but examination of these sources often reveals either a blatant misrepresentation of those sources or a selective interpretation, going beyond any reasonable interpretation of the authors' intent. Please see: Wikipedia:Requests_for_comment/Jagged_85. I searched the page history, and found 4 edits by Jagged 85 in May 2008 and 3 more edits in July 2008. Tobby72 (talk) 21:54, 11 June 2010 (UTC)

Number of planets in the Milky Way

I have seen the figure of 10¹² planets in the Milky Way, but I don't understand how this is computed. Thanks, Yann (talk) 13:32, 25 June 2010 (UTC)

I suspect that that number is found by assuming that there are ~10 planets around each of the ~10¹¹ stars in the Milky Way (that is, that every star has a planetary system like our own). I suspect that that estimate may be slightly optimistic, but early results from surveys for exoplanets indicate that there are multi-planet systems around other stars, and a minimum of something like 10-15% of stars in the solar neighborhood host at least one planet. James McBride (talk) 16:03, 25 June 2010 (UTC)

2,500 stars per light year cubed?

How many stars would you say were in a 1 light year volume on the mid arm of a galaxy? I know this would be a decimal, but could someone tell me? --90.218.231.57 (talk) 23:09, 15 July 2010 (UTC)

Number of planets in the Milky Way

I failed to find an answer to that in this article. 88.88.126.66 (talk) 17:24, 16 October 2010 (UTC)

---o

You failed to find that answer because we have no clue. We have only recently been able to identify planets around stars, and of these most are Jupiter sized. So we have 8 planets (poor pluto) around our star and the Milky way is estimated between 100 - 400 billion stars. You can make a really really rough estimate with those numbers. -- TJ —Preceding unsigned comment added by Analystbynature (talk • contribs) 20:41, 16 October 2010 (UTC)

Hmm yes, an estimate would be hard I guess. But in the article about planets, it says 490 in the MW. 88.88.126.66 (talk) 11:42, 17 October 2010 (UTC)

That's 490 discovered planets, but as Analyst above says, there are probably billions of planets in the Milky way.--Roentgenium111 (talk) 22:57, 19 October 2010 (UTC)

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)