Talk:Andromeda Galaxy/Archive 1

Archive 1

Archive 2

Collision

"The Andromeda Galaxy is approaching the Milky Way at an average speed of about 140 kilometres per second; therefore it is one of the few galaxies to exhibit a blue shift. However, this doesn't mean it will collide with the Milky Way, since the galaxy's tangential velocity is unknown."

According to HubbleSite.org (http://hubblesite.org/discoveries/cosmic_collision/cosmic-movie.shtml), an apparent NASA web site, "Andromeda is hurling toward us at 300,000 MPH....The impact will tear these two giant galaxies apart." Subversive 04:28, 6 December 2005 (UTC)

Andromeda's tangential velocity is still unknown, so the above quotation is still valid. Your link presumes that Andromeda is in a direct collision course.--Jyril 08:45, 6 December 2005 (UTC)

---

"With a mass of about 1.5 times more than the Milky Way". Better write, if that is what is meant: "With a mass of about 1.5 times that of the Milky Way".
S.

I've just done a brief google searching, and quite a lot of sources say that M31 is less massive than the Milky Way. Maybe more research is needed before adding that info. [1][2] --Lorenzarius 10:28 Jan 27, 2003 (UTC)

Someone has just edited this page and changed some data regarding the distance of the Andromeda galaxy. Is this vandalism or is it correct? --ChicXulub 21:35 July 20, 2004 (UTC)

There is a good deal of uncertainty in the mass of any galaxy, but the SEDS page linked in the article sites a fairly recent paper that claims the mass of M31 is substantially less than that of our own galaxy. I will probably go through and correct that and a few other issues later once I look at some more sources.

Oh, and the distance change is probably correct. Just so you know for other astronomical objects: a satellite (Hipparchus) went up and information from it has caused astronomers to change the distances for many objects, so if you see a lot of changes in entries it could be because of that.

I just added a Hubble pic of M31, and moved the Obs. data down, so that they wouldn't have right align/float problems. Hope that's ok.  :) --Etacar11 00:36, 12 Jan 2005 (UTC)

Unfortunately, that image is neither from Hubble nor in the public domain. You need to contact the authors and ask them about releasing a version under GNU FDL. See Wikipedia:Image_use_policy#Copyright_(images) for more info. I just removed a prior image on this page recently from another source who did not want his image used. It was also incorrectly credited to NASA. Please be careful to check the source!

As an aside, Hubble would need a huge mosaic of exposures to cover the large (relatively speaking) area of the sky that M31 covers. I don't believe this has been done. There are some shots of globular clusters and the nucleus of M31 from Hubble, however. --mh 02:58, Jan 14, 2005 (UTC)

Hmmm, you're right, guess I got confused by it being on the Hubble website. The size part slipped by me. Sorry! --Etacar11 04:04, 14 Jan 2005 (UTC)

I found another M31 image here: NOAO, and I think its ok to use by NOAO conditions of use. Any objection? --Etacar11 01:10, 15 Jan 2005 (UTC)

I wouldn't personally have any, but the conditional use clauses aren't completely compatible with GNU FDL since they don't grant unrestricted permission through use and reuse (e.g. commercial use requires special permission). They are not public domain, unfortunately. --mh 20:52, Feb 1, 2005 (UTC)

Yeah, I didn't upload it. But someone did put a nice GALEX pic in the article, though. --Etacar11 21:50, 1 Feb 2005 (UTC)

Update

While updating the infobox style, I had to make a few choices I wasn't sure about, so I'll note them here.

• It seems absurd to be giving two significant digits to measurements where we aren't even sure about the first digit. (That's a feature of the infobox template, not the page before my editing.) Is the "3-4 × 10¹¹" style too ugly? If so, what can we use in its place, to indicate that there's that much uncertainty? "3 × 10¹¹ — 4 × 10¹¹"?? That's ugly and long.
• I wanted to go with some estimates of its mass and radius, rather than leave them "unknown", so I used some of the values from the linked SEDS page. I chose to go with the mass of the galaxy itself, excluding its halo (& presumed dark matter); if there's a standard for using the halo mass for these, the mass should be 2.45 ×10⁴², 1.23 ×10¹² (and don't ask me how many significant digits that actually deserves!).
• I have no idea what the colour scale is when referring to a galaxy rather than a star. Somebody go find out. ;) Meanwhile, I leave it "unknown".
• Absolute magnitude should be easy enough to figure out, and if no one else finds a value really quickly, I'll put one in. But it seems kind of meaningless for this kind of thing, anyway, I would think. But again, that's a critique of the infobox template.

--John Owens (talk) 00:29, 2005 Mar 23 (UTC)

John, the visible image you added near the bottom is copyrighted, and I don't think the author has given rights for it to be used under the GNU FDL. You should probably remove it. I notice the image itself is slated for deletion soon anyway. --mh 21:27, May 5, 2005 (UTC)

Are you sure the date on the first photograph is accurate (caption says photographed in 1899)? It's an extremely high resolution, especially considering photography in its simplest state had only been invented some 70 years before. -Mike

Andromeda Galaxy THREE times bigger than the Milky Way??

News Flash!(May 30)

http://www.reuters.com/newsArticle.jhtml?type=scienceNews&storyID=8643726

This is already accounted for in the article. Nandesuka 19:39, 4 Jun 2005 (UTC)

Andromeda in Other Cultures?

I know that the Milky Way is called Akashaganga in Indian mythology. What about Andromeda? Does it have any other names? Thanks. --Brasswatchman 02:03, 18 September 2005 (UTC)

Andromeda Galaxy is visually rather dim, so it's unlikely that it has been mentioned in any mythology.--Jyril 19:22, 8 November 2005 (UTC)

I seem to recall that the only celestial object other than the Sun, the Moon, planets out to Saturn, and stars, and the galaxy that has been featured in mythology is the Coal Sack nebula, which is far more prominent than Andromeda. Considering that the Magellanic Clouds got short-changed, Andromeda wouldn't get attention. Michaelbusch 19:05, 2 November 2006 (UTC)

The Magellanic Clouds are only visible south of about 20deg N, whereas Andromeda is visible from almost all inhabited areas of the world, so I would not put too much faith in that particular line of thought. 85.8.12.78 (talk) 11:03, 20 June 2008 (UTC)

Accurate distance to Andromeda Galaxy measured

A new, Cepheid-independent distance measurement derived from the lightcurve of an eclipsing binary yields a distance of 2.5 million light years. [3]--Jyril 19:22, 8 November 2005 (UTC)

Milky Way / Andromeda mass

I've added a references section to include a BBC News article that says that the Milky Way does indeed contain more mass than Andromeda if dark matter is taken into account.

Here's the article: http://news.bbc.co.uk/2/hi/science/nature/4679220.stm

The relevant information can be found near the bottom of the article.

Nivedh 01:40, 6 February 2006 (UTC)

The opening section is now contradictory. The statements "the Milky Way contains more dark matter and may be the most massive in the grouping" or "2006 estimates put the mass of the Milky Way to be ~80% of the mass of Andromeda" seem to be mutually exclusive. Spherical Time 03:24, 6 March 2007 (UTC)

Dark matter isn't the same as mass, it accounts for gravitational force.

Wait, actually "The dark matter component has vastly more mass than the "visible" component of the universe." You're right.WalrusMan118 18:13, 8 April 2007 (UTC)

Approach towards Milky Way

"The Andromeda Galaxy is approaching the Milky Way at about 300 kilometres per second, so it is one of the few blue shifted galaxies. Given the motion of the Solar System inside the Milky Way, one finds that the Andromeda Galaxy and the Milky Way are approaching one another at a speed of 100 to 140 kilometres per second."

Is there a grammar error or typo in here? As I understand this, the two are approaching each other at both 300 kilometres per second and 100-140 kilometres per second. This can't be, is it perhaps that M31 is approaching the solar system at one of these speeds, not the galaxy?

Niroht 16:48, 15 February 2006 (UTC)

Yes that section of text had me puzzled as well. The velocity of the Sun within the Milky Way is 220 km/sec., so perhaps the author meant the motion of the Andromeda galaxy relative to the Sun? It needs an authoritative reference to straighten that out. I'll see if I can find something... :) — RJH 15:51, 17 April 2006 (UTC)

--> The NED[4] entry lists 300 km/sec. as the heliocentric radial velocity. — RJH 17:22, 17 April 2006 (UTC)

On my reading of the article, there is no mention of this in the text. Does this mean, as I have read elsewhere, that Andromeda and the Milky Way are on collision course? If so when is the likely date of the collision? I have seen figures, but am away from my library at present. John D. Croft 05:36, 6 February 2007 (UTC)

I also found this sentance confusing. Perhaps the Andromeda Galaxy is approaching the Milky Way at about 300 kilometers per second and the Milky Way is traveling towards the Andromeda Galaxy at a unmentioned speed, and if you add the two speeds you find that the two galaxies are approaching each other at a speed of 100 to 400 kilometers per second? Maybe the motion of the solar systems inside the Milky Way gave soem indication of the speed at which our galaxy is approaching the Andromeda Galaxy? Vsst 06:38, 26 March 2007 (UTC)

This sentence is screwed up. I will try to revise it. Dr. Submillimeter 08:48, 26 March 2007 (UTC)

Someone fixed it before Vsst's last comments. I will leave it unchanged. Dr. Submillimeter 16:34, 26 March 2007 (UTC)

Andromedan stars

I have some questions about M31VJ00443799+4129236:

• I understand M31 in the name, but what does the VJ mean, what do the proplus no.s mean, and the postplus no.s mean?
• Is there any other stars in M31 that is confirmed that it is in M31? Is there the same question in another galaxy.

(I could say that M31DM0009702+1234567 is a star in M31, but do I have proof!)

The only reason I ask these questions is because i'm interested in this, yet I can't find a site with this info (plus i'm lazy).
— Hurricane Devon ( Talk ) 01:25, 24 February 2006 (UTC)

My wild-arsed, off-the-cuff guess is the J means the J2000 epoch, V is for (eclipsing) variable, and the numbers refer to a coordinate. I wish I could read the full paper to find out for sure. :) — RJH 19:05, 18 April 2006 (UTC)

It looks like the numbers are in the form: HHMMSS.SS+DDMMSS.S, giving the star's position at R.A. 00^h 44^m 37.99^s and Declination +41° 29′ 23.6″. Compare to the general coordinates of Andromeda: they're in the same ballpark. — RJH 14:29, 5 May 2006 (UTC)

Missing content?

Here are some thoughts I had regarding possible additions to this article:

• A more complete discovery/observation/R&D history.
• Interaction between M31 and M32, including the effects on spiral structure and the displacement of the neutral H from the stars.
• More on globular clusters in M31, including Mayall II.
• An expanded section on the core bulge/disk.[5]
• Perhaps some material on stellar populations/age, cepheid variables, black holes, and novae observed in the galaxy, and comparisons with our own galaxy.

Any others? Thanks. :) — RJH 19:49, 18 April 2006 (UTC)

• • Some of your comments are now in the main article (more on G1 and the displacement of the neutral H from te stars — DaMatriX 23:31, 21 May 2006 (UTC)

Some questions

Andromeda's satellites

Name	Type	Distance from Sun (million ly)	Magnitude	Year discovered
M32	dE2	2.9	+9.2	1749
M110	dE6	2.9	+9.4	1773

Why does that table show the distance from the Sun? That's incredibly arbitrary. How about the distance from the center of the Andromeda Galaxy? Seeing as how we're calling them satellites of Andromeda, that makes a lot more sense. And also, what is the mass of the Andromeda Galaxy (at least in comparison to the Milky Way?). The article doesn't seem to know. --Cyde Weys 09:27, 9 May 2006 (UTC)

Distance from the Sun is used because all measurements have been made here. It is easy to measure apparent distances between the objects in the sky, but radial distances are much tougher. For example, a short while ago the error bars in the distance to the Andromeda Galaxy were probably comparable to distances between it and its satellite galaxies. In fact, I don't know if those distances are even known in any reasonable accuracy.--Jyril 10:13, 9 May 2006 (UTC)

There is an estimate for the Andromeda halo (which includes Andromeda plus dark matter) within the article. See also the reference listed--it has a link to the paper with the mass estimate. :-) — RJH 20:34, 11 May 2006 (UTC)

Good Article nomination has failed

The Good article nomination for Andromeda Galaxy/Archive 1 has failed, for the following reason:

There is a cleanup tag, headings are wrongly capitalised, and there are links to the Wikipedia namespace from the article namespace. Worldtraveller 16:13, 8 June 2006 (UTC)

Issues addressed. Thanks, I'll post the nom. this time. — RJH (talk) 21:45, 8 June 2006 (UTC)

Can anyone nominate an article for "Good Article" or are there specific rules involved?DaMatriX 21:21, 9 June 2006 (UTC)

All the details are on Wikipedia:Good articles/Nominations. Worldtraveller 21:38, 9 June 2006 (UTC)

I was just letting anybody reading the page know that it's been reposted so they wouldn't need to bother. If a page is still undergoing a Peer Review, though, it seems to make sense to wait until the review is wrapped up before going for a G.A. But perhaps it doesn't matter. Thanks. :-) — RJH (talk) 16:25, 16 June 2006 (UTC)

Put link in External links

I moved this link form the name of templete(where it's title was Andromeda Galaxy) to external links. I don't see any reason for it being in the templete.--Scott3 23:45, 14 July 2006 (UTC)

John Herschel coming back from the dead to discover an Andromeda satelite galaxy?

How come he's listed as discovering a satellite galaxy after his own death?Ed Sanville 20:00, 30 July 2006 (UTC)

It looks like that was a typo. Two of the numbers in the year had been transposed. Good catch! — RJH (talk) 16:17, 21 August 2006 (UTC)

Hoskins

In the paragraph on the "Great Debate" between Shapley and Curtis, there is mentioned one "Hoskins". Who is this? Is it an error for Curtis? Zaslav 01:33, 11 September 2006 (UTC)

Yes, it should have said Curtis. Hoskins supposedly published a record of the debate in 1976, although I haven't had much luck tracking it down. Thanks. — RJH (talk) 14:41, 11 September 2006 (UTC)

New developments

In case the editors of this article haven't seen this, there were some major developments yesterday on the scientific view of how Andromeda was formed, see this and google news. If you update the article in time, a case could be made that something should go up on WP:ITN/C. Mikker ^(...) 04:34, 20 October 2006 (UTC)

Yes I saw an article about that on a science news web site. It's a pretty nice piece of research. But it's not about how Andromeda was formed, but rather how it has been reshaped due to an interaction with M32.[6] I went ahead and added in a paragraph to cover this topic. Thanks. — RJH (talk) 14:17, 20 October 2006 (UTC)

angle

All the pictures of this galaxy are from edge-on. Are there any good pictures from a different angle that you can include in this article? —The preceding unsigned comment was added by 63.245.145.78 (talk • contribs).

• Umm, that would involve moving the entire Milky Way Galaxy to another position. We can only view it from one angle! --Etacar11 13:47, 2 November 2006 (UTC)

A rectified image could probably be produced using software, but it would not be completely accurate since the galaxy has some depth. Also the resolution would be better along one axis than another. — RJH (talk) 17:00, 2 November 2006 (UTC)

Ditto. You'd have to move the entire Milky Way Galaxy (that's the galaxy we're currently in). We can't send a probe there because it's so far away, even at the speed of light, it would take 2.5 million years to reach! It's not like in Star Trek where you can do some sort of magical "scan" and see the entire object from any angle. "Mr. Data, let's see the other side of that ship." "Yes, captain. Just let me break a few laws of physics first." "Onscreen!" Stop watching Star Trek and get into a real Science Fiction like Star Wars or The Matrix.Nick Warren 18:55, 2 November 2006 (UTC)

Not sure those count, but that is not for here. We can make a rectified imaged, but as RJHall noted, it would be pretty ugly. We can't even do that with our own galaxy with any great accuracy. We don't actually need to be on the other side of the galaxy to make a good image: we just need to know where everything is. Something like the Gaia spacecraft or someone standing at Alpha Centauri with a small telescope would do the job, because of parallax. Michaelbusch 19:00, 2 November 2006 (UTC)

Hhmmmm....So this might actually be partially possible? Interesting. Nick Warren 19:07, 2 November 2006 (UTC)

Possible in the sense that there is nothing in the laws of physics that forbid it, impossible in that the Gaia mission will only get good distances for the stars in the Milky Way and maybe parts of the LMC and we'd need order-of-magnitude improvements. Then there are little annoyances like the fact that the dust lanes are optically thick across a good portion of the spectrum. Don't expect this to be possible anytime soon.—The preceding unsigned comment was added by Michaelbusch (talk • contribs).

• I doubt someone at Alpha Centauri would have a noticeably different view...only 4.3 light years away, whereas M31 is 2.5 million light years distant. There won't be much of a parallax! --Etacar11 21:27, 2 November 2006 (UTC)

The parallax would be roughly the same as the parallax of Alpha Cen from the Earth (2 AU/4.3 ly ~ 4.3 ly/2.5 million ly). We can measure angles to better than a thousandth of that, so we could map out the galaxy in three dimensions. Of course, putting something at Alpha Cen is a long-term project anyway. Michaelbusch 22:02, 2 November 2006 (UTC)

Are you saying that the shift in M31's inclination would be that big when viewed from Alpha Cen? I find that hard to believe... :) --Etacar11 23:36, 2 November 2006 (UTC)

It would. But remember that the parallax is very small: ~1/4000 of a degree. Consider: if we moved 2.5 million ly along a circle with M31 at the center, the orientation would change by a radian. Then to change the angle by 1/4000 of a degree, we need only move ~1/240000 the distance to M31. This is ~10 ltyr. These are very rough, order-of-magnitude, numbers, but should convey the idea. Michaelbusch 23:43, 2 November 2006 (UTC)

OK so if ya can do it do it then!

Collision Question

Hypothetically, what would happen to the lifeforms (if any exist/still exist at such a point in time) in the galaxies if such a collision actually happens? Some theories suggest none of the stars would collide, so would the "collision" affect any life or not? And depending on the answer to this question, does such information merit a mention in the article? Also, feel free to move this up to the collision section if it would fit there better.Jupiterzguy 03:21, 7 December 2006 (UTC)

The lifeforms probably would not notice. Stars and planetary systems do not actually collide with other stars and planetary systems in such mergers; they just fly past each other. If they were near the star formation regions that formed when interstellar clouds from the two galaxies collided with each other, then they may be affected by the ionizing light from the hot blue stars formed in the regions. Anyhow, please do not create an article on this topic, as it would constitute original research and violate Wikipedia policy. Dr. Submillimeter 08:13, 7 December 2006 (UTC)

LINER comment

I cut this comment from the "Structure" section:

Andromeda is also a LINER-type galaxy (Low-Ionization Nuclear Emission-line Region), the most common class of active nuclei galaxies.

This statement (if it can be referenced properly, although I think it's true) clearly belongs in the "Nucleus" section. However, I cannot figure out how to put the comment in the nucleus section without rewriting the whole section, which I am not inclined to do at this time. Therefore, I am leaving the comment here for the time being. Dr. Submillimeter 00:05, 4 January 2007 (UTC)

Andromeda Galaxy five times larger than previously thought

This Space.com article says that astronomers have discovered metal-poor giant stars far from the bright disk of the galaxy making it at least a million ly in diameter.--JyriL ^talk 00:04, 8 January 2007 (UTC)

The disks of most galaxies do not terminate aabruptly but instead taper off. Realistically, it is impossible to apply a "hard break" to galaxy radii. However, the convention used by most astronomers is the D25 isophote, which is the location at which the surface brightness drops to the 25 magnitude per square arcsec. It is worth mentioning the halo stars in the Andromeda galaxy, but the diameter of the galaxy in the infobox should not be changed. Dr. Submillimeter 09:37, 8 January 2007 (UTC)

Well, I didn't suggest it should be changed. I posted the link because press releases such as this are sometimes hilarious. If someone finds stars gravitationally bound to the Andromeda Galaxy a million ly from the center, there would probably be a press release claiming that the galaxy is two million ly in diameter. The actual point of the astronomers seems to be that this discovery explains why Andromeda's halo stars are so metal-rich: they aren't since the stars originally thought to be halo stars actually belong to the extended disk. I wonder how large Milky Way's disk is if even the most remote stars are counted.--JyriL ^talk 12:33, 8 January 2007 (UTC)

Sorry, but I could not identify the difference between this comment and the typical strange comment from the average amateur astronomer (e.g. Collision question above). The American Astronomical Society is currently meeting, so it is the time for wild astronomy-related press releases. Dr. Submillimeter 14:34, 8 January 2007 (UTC)

Just to note that the WP article already mentions that, "The stars in the extended halos of M31 and the Milky Way may extend nearly 1⁄3 the distance separating the two galaxies," in the last paragraph of the "Structure" section. The original paper (from Dr. Jason Kalirai et al) on which the space.com article may be based is already referenced in this article.[7] Thanks. — RJH (talk) 16:32, 8 January 2007 (UTC)

"the full angular diameter of the galaxy is seven times that of the full moon." If that's true, why aren't the nearby stars that we can see with naked eye in front of the galaxy on photos? If it really was that big on the sky, it would almost reach Cassiopeia (four full moons from M31). Why don't we see Schedar in Cassiopeia next to the Andromeda galaxy on photos? Are you sure it's not 7 times that of the full moon, but only 1/7? We see the little core, and the galaxy is larger than that, one seventh of the full moon, right? 7x the full moon would be larger than the Big Dipper. Silly. —Preceding unsigned comment added by 213.114.121.203 (talk • contribs)

7 times is consistent with the size given in the infobox. I think you are overestimating the size of the moon - it's only half a degree. The Big Dipper is much longer than 3.5 degrees - in fact, the "pointer stars" which point to the North Star, Polaris, are 11 full moons apart. The moon looks larger, but it's purely an optical illusion. It's actually quite small. --Tango 11:48, 20 September 2007 (UTC)

Naming consistency?

The article seems to randomly use Andromeda and M31 to refer to the galaxy. Wouldn't it be better to stick with one? I found it a little annoying while reading. Personally, I'd favor using only Andromeda past the introduction. AoS1014 17:44, 21 May 2007 (UTC)

Very repetitive use of the same words can also be annoying to some readers. Personally I like to vary the text by the use of synonyms. — RJH (talk) 19:44, 21 May 2007 (UTC)

I did a little cleanup and addressed this. "Andromeda" is a constelation and should not be used alone as a name for this object (confusing). I have used the name M31 and "Great Andromeda Nebula" for the sections that reference this object before the discovery that this was, in fact, a galaxy. Could probably be cleaned up a bit more. Halfblue 13:34, 25 August 2007 (UTC)

Misuse of "Redshift"

In the Observation Data box, the entry "Redshift 301+/- 1 km/s" seems to be a misuse of the term "Redshift". Isn't the cited value the relative velocity between M31 and Sun and not "z" or Redshift? This same construct appears in other articles about galaxies such as M33. (I am certainly NOT an astronomer and I did NOT stay at a Holiday Inn Express last night, so this question may be all wet! —Preceding unsigned comment added by 69.151.153.195 (talk • contribs)

This issue was brought up at Wikipedia_talk:WikiProject_Astronomical_objects#Galaxy_template. Both z and radial velocity are measured by means of the redshift, so either is considered suitable. Supposedly we're using km/s for nearby galaxies and the dimensionless z for more distant objects. — RJH (talk) 20:13, 29 May 2007 (UTC)

"-301 +/- 1 km/s" isn't a redshift, it's a velocity. It's a velocity found by measuring redshift (or rather, blueshift), certainly, but it is a velocity. We should either change the heading to "Radial velocity" (my preference) or write it as a redshift, which would be a dimensionless negative number. --Tango 21:12, 29 May 2007 (UTC)

In casual speech among professional astronomers, redshift is used to refer to velocities, but technically, anything measured in km/s is a heliocentric velocity and not a redshift. Interestingly, a search for any nearby object using the NASA/IPAC Extragalactic Database turns up radial velocity and redshift being used almost interchangably; see the entry for the Andromeda Galaxy as an example. Perhaps the solution is to change the "redshift" line in the infobox into a "velocity/redshift" line? Dr. Submillimeter 08:23, 30 May 2007 (UTC)

There is a one-to-one relationship between redshifts and velocities, so they can be interchanged, but if you are using redshifts, you should say "redshift", if you are using velocities, you should say "velocity". I think the best option is to have a redshift and a velocity heading in the table and put both on all articles - redshift is useful if you are actually doing any calculations, but velocity is better for giving a layman a sense of what the object is doing, so why not give both? Tango

Velocities for high-redshift objects are not physically meaningful, and z values for nearby objects are not very useful. (Would z=-0.001 mean anything to anyone?) It would be best just to give one (either the velocity or the z value). Dr. Submillimeter 11:15, 30 May 2007 (UTC)

Strictly speaking, relativistic redshifts aren't actually related to velocities, it's true, but in laymans terms we do talk about galaxies "moving" away from eachother, and that "movement" happens at an easily calculable "velocity". I don't think the magnitude of "z" is very important - is z=-0.001 really any less meaningful than z=6? They're just numbers. --Tango 14:04, 30 May 2007 (UTC)

Yes, the numbers matter. Most professional astronomers use km/s to discuss the redshifts/velocities to nearby objects, so z=0.001 has much less meaning than 300 km/s to the average astronomer. However, objects at higher redshifts are discussed by professional astronomers in terms of z, so z=0.2 is more meaningful than 60000 km/s. Also, for amateur astronomers and the general public, redshifts/velocities expressed in z are going to be much more difficult to understand than those expressed in km/s (although this represents a problem with using z for any objects, including high redshift objects). Dr. Submillimeter 14:45, 30 May 2007 (UTC)

Your last point is exactly why I'm suggesting we give both. Yes, including the redshift for nearby objects probably isn't very useful, but it doesn't do any harm and makes the articles more consistent, so why not? --Tango 10:04, 31 May 2007 (UTC)

I suppose listing both z and km/s would be OK, although I expect that z could cause a lot of confusion for the average reader, and I expect that km/s for high-redshift objects could cause confusion as well. Since the galaxy infobox template is used in hundreds of articles, the change will need to be made with the AutoWikiBrowser, although I could potentially do that. (I would prefer the change to the infobox to be made on a Monday, as I could do this more easily during the work week at work.) I suggest asking for additional comments at Wikipedia Talk:WikiProject Astronomical objects to make sure that everyone else who works on astronomy articles will accept the change. Dr. Submillimeter 12:17, 31 May 2007 (UTC)

Paper on Milky Way/Andromeda collision

I found a this paper at astro-ph which describes a collision between the Milky Way and Andromeda. Keep in mind that this has only been submitted (not accepted) for publication; it has not yet passed through a scientific reviewing process. This paper might be useful for a discussion on the Milky Way - Andromdea merger. Dr. Submillimeter 10:52, 1 June 2007 (UTC)

There's also a summary that's been making the astronomy news circuit about the possible fate of the Sun. But the Earth will probably be uninhabitable by then anyway. — RJH (talk) 22:36, 1 June 2007 (UTC)

Apparent magnitude

The article quotes an apparent magnitude of 4.4 (V) with a reference I find hard to follow and an obscure "note" quoting 4.36. Perhaps [8] is intended giving V_T 3.44, U_T 4.86 and B_T 4.36 if I am extracting the appropriate values. I can certainly find support for this elsewhere on the web, e.g. [9] (4.5). However, List of Messier objects#31-40 gives 3.5 and there looks rather more support for this figure, e.g. [10], [11] (3.4). The last reference confusingly says "B= apparent visual magnitude" but I presume the others are V (see apparent magnitude which says V is usually implied). Is there a generally accepted figure? I realise that there are difficulties in measurement and definition for an extended object with satellite galaxies. Thincat 09:26, 6 June 2007 (UTC)

The B and V magnitudes correspond to apparent magnitudes in blue and yellow (visible) light, respectively. In general, it is much easier to find B magnitudes than it is to find V magnitudes, so B magnitudes are generally used in the infoboxes. However, the infoboxes are set up with "(V)" hardwired into them. It might be better just to set up the infoboxes so that the wave band may be specified in the inserted text rather than in the template. (Also, the SEDS.org website is an unreliable reference. They often use out-of-date, unreferenced, or incorrect information.) Dr. Submillimeter 09:56, 6 June 2007 (UTC)

Double nucleus

Why is the theory that the double nucleus of Andromeda a result of cannibalising another Galaxy untenable? John D. Croft 01:37, 29 August 2007 (UTC)

Categorization

This article is currently listed in the category "unbarred spiral galaxies," but recent observations indicate that M31 is a barred spiral.--Nat 23:37, 4 October 2007 (UTC)

The article is going by the NED reference, which has M31 categorized as SA(s)b LINER. Do you have a more up to date scientific reference that corroborates the bar? Thanks. — RJH (talk) 17:44, 6 October 2007 (UTC)

Discovery

The articles states Abd Al-Rahman Al Sufi observed andromeda in 906, but he was only 2 years old according to his article. The statement is referenced to Kepple, George Robert; Glen W. Sanner (1998). The Night Sky Observer's Guide, Volume 1. Willmann-Bell, Inc., 18. ISBN 0-943396-58-1 so this needs to be checked. Tim! 09:05, 13 October 2007 (UTC)

!!New Discovery 1/5/09!! Mark Reid of Harvard University just released data from a study stating that the Milky Way is 50% bigger than previously found. This new discovery was made with radio telescopes. The data was reported at the January 5th (2009) meeting of the American Astronomical Society. Someone change this article