Observing Project 14A The Great Andromeda Galaxy and Friends

Early October brings the Great Square of Pegasus high overhead. This asterism, part of the fabled winged horse, is one of the most easily identifiable patterns in the autumn sky. From here we can hop from star to star across to M31.

After locating the Great Square, begin at the star on the northeast corner (top left if you are facing south and the Square is at the zenith). This is Alpheratz (spectral type B9, magnitude +2.0) and from here we'll begin to journey to M31.Alpher-atz (Alpha Andromedae) is also the westernmost member of a three-star arc that runs off towards the northeast. The center star is called Mirach (Beta Androme-dae), a magnitude +2.1, type M0 red giant. From Mirach,scan north-northwest just under four degrees to magnitude +3.8 Mu Andromedae. Extending the line from Mirach to Mu Andromedae about another four degrees brings us to M31.

Galaxies, particularly spirals like M31 stand up well to high power in the telescope, but M31 is very large so that wisdom does not necessarily hold here. With M31 we want to see as much we can so use your widest field eyepiece and a tele-compressor if you have one. Start with M31's nucleus and spend some time looking at this area. Andromeda, like the Milky Way, is a very active star-forming galaxy. If you look carefully and your optics and sky are both in optimal condition, you might see a faint dark lane strewn across the nucleus. This could be as we illustrated before a lane of dust, or it could be a dynamic double nucleus. Whatever it is, once you have found this, try following the dark lane away from the nucleus in either direction. The dust shows the directions of the spiral arms around the galaxy. If your skies are dark and your optics clean and well aligned you may be able to see the faint glow of the arm stretching away in telescopes as small as 6 inches. Any light pollution will render the arms almost impossible to see. In larger telescopes

Figure 14.3. The core of M31. Meade DSI and Celestron Super C-8 Plus at f/6.3. One-minute exposure. The stars are in the foreground. Image by author.

Figure 14.3. The core of M31. Meade DSI and Celestron Super C-8 Plus at f/6.3. One-minute exposure. The stars are in the foreground. Image by author.

the arms show up very nicely. Don't forget to use averted vision and if you are in a light-polluted area a light-pollution filter. While they do not enhance the light of galaxies, they will suppress the unwanted wavelengths of light pollution.

In a wide field eyepiece, just about any telescope will show a second soft glow near the nucleus of M31. This is the dwarf elliptical galaxy M32, a companion galaxy that sits within 130,000 light years of the M31 nucleus. The galaxy is sufficiently close that the two are significantly disrupting each other. M32 has lost an enormous amount of mass to the halo of its host galaxy. Don't waste too much energy looking for the detail in M32. It is a typical elliptical consisting mostly of much older Population II stars, though as we mentioned earlier it is contaminated with a large number of younger stars. On the opposite end of M31 is another small elliptical galaxy, M110. This galaxy is also an old elliptical galaxy that is somewhat farther from the center of M31. If you compare it to M32, you will notice that it is much more elongated in shape than is M32. M32 is a Shapely type E1 galaxy while M110 is an E4. A telescopic field of view of just over one degree should show all three galactic cores in a single field of view.

M31 also makes a pretty photographic subject without using complicated imaging techniques. Try a few long-exposure images using various lenses on your 35-mm SLR camera. Remember that larger lenses will require longer images. The image on page 201 was made with a 35-mm camera and stock lens. I used ISO 400 film and a five-minute exposure. Unfortunately the image is smeared because someone with the same initials as myself accidentally kicked the tripod during the exposure (oops). For the next picture, try attaching the camera to the telescope at prime focus with the telecompressor and make images of M31's nucleus area. If your telescope has a modern drive and is precisely aligned, you should be able to leave the shutter open for several minutes and get a nice exposure of the nucleus. If the telescope has a short enough focal length, you may also be able to image the core of M32 as well. If you own a CCD camera and telescope combination capable of "auto-mosaic" (such as a Meade imager with an LX-200), use it to make a nine-image sequence of the core area. This technique allows you to create an image with a much wider field than the miniscule area available to the camera. Do this on a regular basis when M31 is visible because many of these stars in the core area are much older Population II stars that may be nearing an iron-core collapse and trigger a supernova explosion. The last (and only) supernova in Andromeda was discovered on August 20,1885 so it may be that this galaxy is long overdue to spring one. Pay careful attention to that area as you visit and revisit it over the years. Remember that when you are imaging, patience is a virtue. You will make many mistakes, smear many frames of film and even take some exposures of empty space when you thought there was a galaxy there. Time and practice will reduce your mistakes. Don't get mad about bad pictures. The only way you will learn to take good pictures is to take many bad ones.

Looking through a spectroscope, you will notice something else about Andromeda. Its spectrum looks much like many typical stars, but the emission lines of the spectrum are shifted slightly towards the blue end of the spectrum. This indicates that Andromeda and company are moving towards us and it is in fact on a collision course with the Milky Way. When Andromeda and the Milky Way meet several billion years from now, someone way across the cosmos will have a spectacular view of the collision.

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