OF THE ROGER N. CLARK
OF THE ROGER N. CLARK
OF THE ROGER N. CLARK
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VISUAL ASTRONOMY <strong>OF</strong> <strong>THE</strong> DEEP SKY<br />
A VISUAL ATLAS <strong>OF</strong> DEEP-SKY OBJECTS<br />
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NGC 7331, SPIRAL GALAXY IN PEGASUS<br />
R.A. 22 h 37.1m, Dec. 34° 26' (2000.0)<br />
T hoical. NGC 7331 is a spiral galaxy<br />
tid about 15° to 20° from edge-on. It is<br />
. ilar in structure to M3l, but at about 50<br />
gm . .<br />
.<br />
'llion light-years It IS some 20 times more<br />
IS<br />
about 140 billion times the mass of our<br />
;1 ta nt. T.be mass of NGC 7331 is estimated<br />
as<br />
S n and its luminosity as some 50 billion<br />
u , . h<br />
times the Sun's hg t.<br />
Visual. NGC 7331 has a total magnitude of<br />
lO.4 and an angular size of 10 by 2.4 arcminutes,<br />
for a mean surface brightness of22.5<br />
magnitudes per square arc-second. Under<br />
good skies the galaxy is visible in small<br />
amateur telescopes as a fuzzy patch. Through<br />
the 8-inch under good skies, it appears as an<br />
oval extending north-south with a small,<br />
bright nucleus. The west side is closest to us,<br />
as the photograph shows; dark dust patches<br />
here are silhouetted against the galaxy's<br />
bright inner part. This side had a sharp<br />
boundary as seen through the 8-inch at magnifications<br />
of 117 X to l88x. No other detail<br />
was detected. But large amateur telescopes<br />
and good skies may bring out some detail,<br />
such as dark patches and some of the faint<br />
surrounding galaxies.<br />
A half degree to the south-southwest are<br />
five galaxies in a tight group known as<br />
Stephan's Quintet. These galaxies and their<br />
magnitudes are: NGC 7317 (14.5), NGC<br />
73l8A (13.8), NGC 73l8B (13.5), 7319<br />
(13.5) and NGC 7320 (13.1). None could be<br />
found with the 8-inch during the observing<br />
session for NGC 7331. However, in the clear<br />
skies of the Colorado Rockies, all but NGC<br />
7317 were detected in the 8-inch at magnifications<br />
of l17x and l88x. There the limiting<br />
magnitude was 14.6.<br />
238<br />
239
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