M31


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Image on left is LRGB, while the image on the right adds 6hrs of pure Ha.

M31 is a large spiral galaxy, very similar in appearance to, and slightly larger than, our own Galaxy, and our closest normal-galaxy companion (the very close Magellanic clouds are classified as irregular galaxies). In fact, from a distant vantage point, Andromeda and the Galaxy would appear as a pair, a binary or double galaxy system, if it were not for the rather smaller, though still significant, spiral galaxy M33. As our nearest neighbor, Andromeda is extremely large on the sky. M31 is visible to the naked eye, although we can only see the bright inner bulge, and it has therefore been known since at least the year 964AD, when Persian astronomer Al-Sufi described it as a `little cloud'. We can see that the western (right) side of M31 is closer to us, by the fact that the dark dust lanes belonging to the inner spiral arms show up in silhouette against the nucleus on that side only. At the very center of the Andromeda Galaxy is a brilliant point of light, which is a very tightly packed star cluster.

The entire galaxy is rotating in space, with the lower portions approaching while the upper parts recede. The rotation is not completely smooth, showing `bumps' where the spiral arms occur, which are probably due to the spiral density wave that maintains the arms. By applying gravitational theory to this rotation, we can `weigh' M31, and when we do it seems that there may be ten times as much material as we can see in the visible portions of the galaxy, distributed in a huge dark halo. 

(Text taken from www.noao.edu)
 

Equipment

Telescope:                 FSQ106N by Takahashi (f5)
Mount:                      Paramount ME by Software Bisque
Instrument:               STL11000M CCD Camera by SBIG, CFW-L

Exposure:                  Ha + LRGB 6hrs:3hrs:1hr:1hr:1hr
Capture Software:       CCDSOFT V5, CCDAutopilot V4
Processing:                Maxim DL/CCD, Photoshop CS, CCDStack

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