Talk:Milky Way

Contents

1 Perseus Arm 2 Sag A* 3 Arms? 4 We don't look at the sky all night anymore 5 This doesn't sound right 6 Barred Spiral 7 Local Bubble/Fluff 8 orbital velocity vs deistance from galactic centre 9 Milky Way: Galaxy vs silvery river in the sky

Perseus Arm

I removed the statement that the distance between the local arm and the Perseus arm is 2000 lyrs. It is not supported by the given reference, http://www.ras.ucalgary.ca/CGPS/press/aas00/pr/pr_14012000/pr_14012000map1.html and in fact, given that the galaxy's diameter is 10^5 lyrs, the map given there suggests that the distance is much larger. AxelBoldt 01:40 Jan 11, 2003 (UTC)

Sag A*

A logged-out user posted "The centre of the Milky is a region called Stagitarius A*." - is this correct, besides the spelling? The interesting choice of spelling leads me to wonder if it was a troll attempt. --Pakaran 05:49, 4 Dec 2003 (UTC)

http://en.wikipedia.org/wiki/Sagittarius Lirath Q. Pynnor

Arms?

Seven arms in the galaxy? Is that correct? That seems like an extraordinarily large number. -- Decumanus 23:02, 8 Feb 2004 (UTC)

IIRC, the Milky Way is more specifically a barred-spiral galaxy, rather than a spiral one. This would imply two arms. See the beginning of the galaxy article for a reference. -- Anonymous

Correct, the Milky Way is a barred spiral but a barred spiral has more than two arms, since the bar splits up into several arms. The diagram in the article is very misleading. A more accurate, scientific diagram can be found here: Svanimpe 16:20, 17 jul 2004 (CET)

We don't look at the sky all night anymore

Most pages on the Milky Way, like this one, fail to confirm my suspicion that the river of stars rotates as the night progresses. I think that is what I am told in Chinese poetry, the translation of which is my main business, but I always like to check facts like that. We are so caught up in the views that modern technology gives us that we forget to remember what the ancients saw and wrote about.

Yes, too true. Because the earth rotates, the stars of the Milky Way (and just about everything else in the sky) appear to move from east to west (rotating counterclockwise around Polaris, and rotating clockwise around the Southern Cross). You cancel this rotation by slowly turning your head or the telescope in the opposite direction. Many telescopes have a equatorial mount, designed to make this easier to do. Then you can see that the stars of the Milky Way (except for the sun) and the stars of all other galaxies appear to stay perfectly motionless. Because this view has been almost exactly the same over the last few millenia, astronomers get tremendously excited when there is even the tiniest amount of change. So they spend lots of time talking about these changes (the Zodiac is the sun's yearly motion relative to the stars; the motion of the planets and the asteroids; supernova; rotating binary stars; satellites; etc.). --DavidCary 22:03, 12 Aug 2004 (UTC)

I'm confused, why should the galaxy itself be visible from earth? even if we're looking at the disk 'the long way' it's still several orders of magnitude larger than we are.. no matter what the distance...

This doesn't sound right

...the Earth's axis of rotation is highly inclined to the normal to the galactic plane...

This needs to be changed. "To the normal to the.." doesn't make sense. --Viriditas 09:20, 25 Sep 2004 (UTC)

Well, it does sound right, but is a bit awkward. I'm trying to think of a better way to express it. ✏ Sverdrup 09:50, 25 Sep 2004 (UTC)

Are you trying to say that that the inclination of the galactic equator to Earth's equator is 62.9°? --Viriditas 11:29, 25 Sep 2004 (UTC)

Umm.. no. I realize now that it should really be "plane of orbit" not "axis of rotation". I don't think "normal to the galactic plane" is wrong, just awkward. I'm editing the article, please change what you don't agree with.✏ Sverdrup 12:05, 25 Sep 2004 (UTC)

Thanks, but I didn't say I didn't agree. I just said that the term, "normal to the galactic plane" is not commonly used in English, TTBOMK. Can you replace the word "normal" in that context? That's all. --Viriditas 12:18, 25 Sep 2004 (UTC)

See the disambig page normal; in geometry/maths, a normal is a vector/line perpendicular to another line or a plane. (I think) I solved it by not using the word normal in the article. ✏ Sverdrup 14:09, 25 Sep 2004 (UTC)

What do you think of this:

This reflects the fact that the highly inclined ecliptic plane of the Earth is normal to the galactic plane. That reads well and preserves the meaning you intended. Or not? --Viriditas 00:27, 26 Sep 2004 (UTC)

No, it's not neccessarily true. A normal is exactly perpendicular to the galactic plane, while the accuracy in the original is just "highly inclined". ✏ Sverdrup 00:32, 26 Sep 2004 (UTC)

That makes sense. What about linking to ecliptic: This reflects the fact that the Earth's plane of orbit is highly inclined to the galactic plane. --Viriditas 02:53, 26 Sep 2004 (UTC)

Yes, absolutely. ✏ Sverdrup 13:03, 26 Sep 2004 (UTC)

Having started the confusion in the first place by using the jargon normal without a definition (I wanted to avoid any need for a formal definition of the angle between two planes), I have now tidied this up. Note that the Earth's equatorial plane and the plane of the ecliptic are inclined by 23.5 degrees (occasionally rising to 24+ due to nutation IIRC). I think the local standard orientation for the solar system is the plane of Jupiter's orbit (the ecliptic, Earth's plane of orbit, is pretty close), as I recall reading that its orbital angular momentum is 60% of that of the solar system (which should not be that hard to check on the back of an envelope). Maybe the Uranians, with their 98 degree axial tilt, are the ones closest to alignment with the galaxy and the rest of us are out of step :-) -- Alan Peakall 18:14, 13 Dec 2004 (UTC)

Barred Spiral

I thought that the structure of the Milky Way was disputed, as in, no one is sure yet whether it's Sbc or SBb? Has the fact that it is a barred spiral been confirmed recently? bob rulz 02:37, Nov 13, 2004 (UTC)

Local Bubble/Fluff

The recent change from Local Bubble to Local Fluff, although technically correct, is not necessarily an "either-or" The Sun is still well within the Local Bubble. The Local Fluff is also known as (perhaps more within the field) as the Local Interstellar Cloud (LIC). Recent evidence suggests the LIC is not alone (surprise) and the acronym CLIC has also started to be used for "Complex/Cluster of Local Interstellar Clouds". --mh 21:28, Feb 8, 2005 (UTC)

orbital velocity vs deistance from galactic centre

These 2 sentences appear to contradict each other:

"The orbital speed of stars in the Milky Way does not depend much on the distance to the center: it is always between 200 and 250 km/s for the Sun's neighbours [1] (http://zebu.uoregon.edu/~imamura/123/lecture-2/mass.html). Hence the orbital period is approximately proportional to the distance from the star to the Galaxy's center (without the power 1.5 which applies in the case of a central mass)."

I think you might be missing the change in term from orbital speed to period. If speed is constant, since the orbital path length increases linearly with R, the period is also linearly proportional to R.--mh 04:37, Apr 17, 2005 (UTC)

Milky Way: Galaxy vs silvery river in the sky

I'm wondering whether this article should be split in two, one being the milky river bit, with the attendant history, and another purely about our Galaxy. They would be Milky Way and Milky Way Galaxy, so that Milky Way can be used by regular people wanting to know about the glowing river in the sky, and its nebulous characteristics, but not about astrophysics or whatnot. The other can be about the characteristics of our galaxy. 132.205.15.43 01:56, 15 Apr 2005 (UTC)

That'd be silly. It's like having one article on the big yellow really bright thingy that's up in the sky during the day, and anther article on the star at the center of our solar system --Ctachme 05:36, 17 Apr 2005 (UTC)

It's separated in the Japanese Wikipedia. It would be akin to the separation as Sun versus Solar System. Or Alpha Centauri versus the various components (A,B,C (Proxima)), or Eta Carinae versus Carina Nebula; besides, the Milky Way is a much more non-astronomical way of thinking of the sky versus the Milky Way Galaxy. The great swath of light above our heads is a significant feature that is not equivalent to the Galaxy which it is part of. 132.205.15.43 01:44, 19 Apr 2005 (UTC)