M31 - the Andromeda Galaxy

The inner part of the Andromeda Galaxy, Messier 31 (NGC 224), shown from a 10-second red-light exposure (during twilight) with a Tektronix 2048x2048 CCD at the prime focus of the 4-meter Mayall telescope of Kitt Peak National Observatory. North is at the top and east to the left, for direct comparison with a chart or eyepiece view. The image has been block-averaged to 512x512 for this presentation, which uses a logarithmic intensity transformation to preserve information across a wide dynamic range. The field is 14.3 arcminutes square (about 3200 parsecs = 10,300 light-years at the 780-kiloparsec distance of M31). The bright nucleus is readily apparent, recently shown to be in fact double (see the HST image and caption ) as well as the possible site of a supermassive black hole.

Paul Hodge's Atlas of the Andromeda Galaxy from 1981 lists 27 catalogued globular clusters in this area, all of which can be identified on this image. I list them below with their (x,y) coordinates on the 512x512 picture, in which each pixel subtends 1.68 arcseconds on the sky. These coordinates take (0,0) at the lower left corner, a convention which is common in scientific and mathematical application, although some image-processing routines like to count the y-axis down from the top. (Thanks for Jorma Koski for pointing this out, along with a missing cluster). You may want to consult for comparison the beautiful HST image of the brightest globular cluster in M31, Mayall I; this cluster lies well beyond the area shown in my image. Note as well the intricate detail in the dust clouds of the innermost spiral pattern.

For additional context, here's a view of M31 and its companions M32 and M110 taken with the 20-inch astrographic refractor at Lick Observatory. This shows an area over a degree across.

Last changes: 9/2001      © 2001