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Spiral Galaxy

NGC7331 is a spiral galaxy. A galaxy, basically described, is a collection of matter in space, contained by its own gravity. Visual markers of a galaxy include a galactic bulge (located in the center) which appears to flatten to form a galactic disk. What classifies NGC7331 as a spiral galaxy is the visible nature of the matter located outside the galactic bulge. The matter contains spiral arms that wrap around the center much like our own Galaxy, the Milky Way. Early in its discovery, NGC7331 was classified as a spiral nebula but was later defined as one of the brighter galaxies that were not included in the 18th century catalog by Charles Messier.

We are able to say that NGC7331 is a spiral galaxy because of the arms that we can observe in the image above. We can also see that the spiral arms are not symmetrical from the left side of the image to the right. Dust in front of the object has obscured our view of the arm, creating a black streak which is not part of the original galaxy. As we look further at the image of the arms, we are able to see a slight blue tint as the arms seem to dissipate into space. We are able to understand that the blue tint signifies that the outer rim stars are very hot and, based on the fact that hot stars do not last very long, we are able to conclude that the material is very new. Under Hubble's Galaxy Classification system as an Sb galaxy. 'S' denoting spiral and b representing the size of its central bulge. Hubble's scheme uses the letters a-c to notate size which leads to the conclusion that NGC7331 lies in the middle of this classification. In this image, four other galaxies can be observed, each of them can recognized in this photo as blurry oblong objects with a central core. Together with NGC7331, these galaxies form a group otherwise known as the Deer Lick Group. The distance from NGC7331 to our planet is estimated to be 12 mpc, and using that data we are able to estimate that its angular size is 31.55 kpc.


1. Chaisson, Eric, and Steve McMillan. Astronomy Today. 7th ed. San Francisco: Person Addison-Wesley, 2011. 604. Print.

2. Chaisson, Eric, and Steve McMillan. Astronomy: A Beginner's Guide to the Universe. 5th ed. Upper Saddle River, New Jersey: Person Prentice Hall, 2007. 376. Print.

3. Astronomy Picture of the Day, NASA <>

Right Ascension (J2000) 22:37.05.10
Declination (J2000) +34:25:12.9
Filters used B (Blue), C (Clear), R (Red), V (Green)
Exposure time per filter B, V, r, and C (60s)
Date observed October 12, 2011



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