This group of galaxies will delight owners of large telescopes.
The Stephen Quint is a cluster of five galaxies that you can see this time of year, provided you’re looking with a large telescope.
Credit: Tony Halas
- The Stephan Quintet, discovered in 1877 by French astronomer Edouard Stephan in the constellation Pegasus, is an example of enhanced detail seen through large astronomical apertures.
- The group consists of five galaxies: NGC 7317 (magnitude 14.6), NGC 7318A (magnitude 14.3), NGC 7318B (magnitude 13.9), NGC 7319 (magnitude 14.1), and NGC 7320 (magnitude 13.2).
- Four of these galaxies (NGC 7317, NGC 7318a, NGC 7318b, NGC 7319) constitute the first compact galaxy cluster ever discovered, while NGC 7320 belongs to the Pegasus Spur galaxy cluster.
- While the 6-inch telescope shows only a faint, faint glow, the 11-inch instrument is necessary to identify the individual members, with magnifications in excess of 200x recommended to resolve the colliding pair NGC 7318a and NGC 7318b.
One of the mantras of amateur astronomy is the “aperture rule”. This means you will see more detail when you observe with larger telescopes. Few celestial bodies demonstrate this better than Stephen’s Quintet. So, fair warning, this post is for those of you who have access to larger hobbyist equipment.
The cluster was discovered by French astronomer Edouard Stephan in 1877 in the constellation Pegasus the Winged Horse. The five galaxies now have the designations NGC 7317 (magnitude 14.6), NGC 7318a (magnitude 14.3), NGC 7318b (magnitude 13.9), NGC 7319 (magnitude 14.1), and NGC 7320 (magnitude 13.2).
Four of these galaxies – excluding NGC 7320 – form a compact galaxy cluster, discovered for the first time. NGC 7320 belongs to the Pegasus Spur, a group of about three dozen galaxies, the brightest of which is magnitude 9.5 NGC 7331.
Although you can “see” Stephen’s quintet through a 6-inch scope, a magnification of 50x will show you only a faint, sticky glow beyond 30. On the other hand, an 11-inch telescope lets you identify individual members.
At the southwestern edge of the quintet is NGC 7317, located next to the 13th-magnitude foreground star. The colliding pair NGC 7318A and NGC 7318B lie 2′ to the east. You will need high magnification – above 200x – to “separate” them.
The brightest and largest member, NGC 7320, lies to the southeast and includes a 13th-magnitude foreground star in its halo. This galaxy shines at 12.5 intensity. NGC 7319, located at the northeastern end of the group, is another test for visual observers.
Choose a moonlit night with a steady wind, stay relaxed and be patient. May you be successful!
