[AZ-Observing] Re: Satellite Galaxies
- From: Wil Milan <wmilan@xxxxxxxxxxxxxx>
- To: az-observing@xxxxxxxxxxxxx
- Date: Sun, 06 May 2001 20:16:32 -0700
At 07:02 PM 5/6/2001, you wrote:
>Thanks. Your site is very nice. I didn't realize these 10 galaxies
>were so close, relatively speaking. I was confused to see them being
>called satellite galaxies of our galaxy in the S&T article. In your web
>site you mentioned that Triangulum is not considered a satellite of
>Andromeda. What criteria is used to classify a galaxy as a satellite
>of another vs. just being part of a local group?
It's mostly on the basis of position and Doppler shift. If a small galaxy
is close enough to another to be in orbit around it and its radial velocity
(as measured via Doppler shift) is consistent with orbital motion, then it
can be considered a satellite. With galaxies that are close in, the
determination isn't hard to make. With galaxies much further out (such as
the Phoenix Dwarf) it's much more iffy. It would be much easier if we could
accurately measure proper motion of galaxies, but that's very difficult to do.
Wil Milan
http://www.astrophotographer.com/
"The heavens declare the glory of God
And the firmament proclaims His handiwork."
-- Psalm 19:1
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