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Padawan
2004-May-18, 09:37 AM
i'm wondering... how many arms does the milky way galaxy have, how large are they, and how many satellite galaxies does it have?


A link to some sorta article about this would be great. :)

Kullat Nunu
2004-May-18, 10:21 AM
i'm wondering... how many arms does the milky way galaxy have, how large are they, and how many satellite galaxies does it have?


A link to some sorta article about this would be great. :)

I think you would like to see this site (http://anzwers.org/free/universe/).

Ari Jokimaki
2004-May-18, 10:42 AM
Just this morning there was a news article in finnish newspaper that a new arm of Milky way has been found. It is composed mostly of hydrogen, but rest of the details I've forgotten.

Kullat Nunu, that's a great webpage! I just wonder why they haven't included closeup of the solar system there.

Ut
2004-May-18, 02:14 PM
Wow, we're up to six or seven now, eh? It wasn't that long ago that every book I picked up only listed 4...

Kullat Nunu
2004-May-18, 02:41 PM
Wow, we're up to six or seven now, eh? It wasn't that long ago that every book I picked up only listed 4...

It's hard to say, since Milky Way is not such a "Grand Design" galaxy like M51. There are probably some gaps along the arms. Orion Arm is not likely a true arm, just a branch between Sagittarius and Perseus Arms. And some arms may have double names, they just look different arms from here. Making a decent map of the Milky Way is really a very difficult to do.

dgruss23
2004-May-18, 02:45 PM
The Milky Way is classified as an SBbcI-II. NGC 3992 (http://www.gralak.com/Astro/M109-ChrisL-LRGB.jpg) has the same classification - although the MW may have more arms.

ngc3314
2004-May-18, 04:08 PM
The Milky Way is classified as an SBbcI-II. NGC 3992 (http://www.gralak.com/Astro/M109-ChrisL-LRGB.jpg) has the same classification - although the MW may have more arms.

De Vaucouleurs wasn't embarrassed to go further, assigning the Milky Way a ring/bar transitional class SAB(rs)bc! That suggests looking something like NGC 1232. There's a nice VLT image (if rather too green on my monitor), at http://www.vt-2004.org/outreach/press-rel/pr-1998/pr-14-98.html.

It was long thought that the little barred companion made this a dead ringer for the MW+LMC system, until the other galaxy's redshift was found to rudely not match NGC 1232 (as I risk drift into another forum).

Ari Jokimaki
2004-May-18, 04:17 PM
Here (http://www.newscientist.com/news/news.jsp?id=ns99994959) is more detailed info about the new arm I mentioned earlier. It seems that this is old news, because when I googled this, I found some newspages which were from december 2003. I quess news still travel slow to these remote places of Earth.

dgruss23
2004-May-18, 05:34 PM
The Milky Way is classified as an SBbcI-II. NGC 3992 (http://www.gralak.com/Astro/M109-ChrisL-LRGB.jpg) has the same classification - although the MW may have more arms.

De Vaucouleurs wasn't embarrassed to go further, assigning the Milky Way a ring/bar transitional class SAB(rs)bc! That suggests looking something like NGC 1232. There's a nice VLT image (if rather too green on my monitor), at http://www.vt-2004.org/outreach/press-rel/pr-1998/pr-14-98.html.

That is a spectacular picture. Its been one of my favorites since it came out.


It was long thought that the little barred companion made this a dead ringer for the MW+LMC system, until the other galaxy's redshift was found to rudely not match NGC 1232 (as I risk drift into another forum).

Its ironic that you mention that because I spent a considerable amount of time the last few days on that example. NGC 1347 (http://www.ngcic.org/dss/n/1/n1347.jpg) provides another example of a rude companion. But as you say, to say more takes us to another forum.

Dgennero
2004-May-18, 07:46 PM
Also somewhat similar is NGC 3953: http://www.astro.princeton.edu/~frei/Gcat_htm/Sub_sel/gal_3953.htm
However, I'm not sure if the central "bar" is as sharply outlined as in all the examples or if it is just of a somewhat oval shape (like M63) and the MW can still be classified as plain old Sbc.
Edge-on NGC 4565 is a good lookalike.
There'd be no question as to how many arms, would we live in a grand design spiral like M81, but our galaxy has a more mottled and filigrane structure, somewhat between the extremes of M81 and the very mottled and somewhat chaotic "Silver Dollar": http://www.koyote.com/users/bobm/ngc253.htm