M31 - the Andromeda Galaxy


M31 = Andromeda Galaxy core region

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.

G148 432 202 G187 236 102
G158 383 388 G189 216 312
G161 372 59 G190 211 203
G165 358 342 G194 198 400
G167 348 17 G198 158 391
G168 349 140 G199 133 464
G169 348 403 G203 104 427
G170 341 75 G204 101 304
G174 334 333 G205 91 470
G175 327 156 G207 88 354
G177 327 202 G208 71 275
G182 284 78 G212 61 106
G184 264 154 G215 51 109
G185 259 227 G218 32 91

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.

Blue-light photo of M31


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Last changes: 9/2001      © 2001