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Saturday, December 3, 2016

How Many Galaxies Can You Find

Back in the early '90s, I would go out with my 6" Newtonian reflector telescope and challenge myself to see how many galaxies I could find with it. One clear night in October of 1990, I was out with the Criterion RV6 and saw a target galaxy on my Sky Atlas 2000 that I had never observed before. NGC 7331 (also known as Caldwell 30) is an unbarred spiral galaxy about 50 million light-years away in the constellation Pegasus that is one of the brighter galaxies not included in Charles Messier's famous 18th-century catalog. It was discovered by William Herschel in 1784. NGC 7331 is the brightest member of the NGC 7331 Group of galaxies. 

Galaxies in Pegasus Image Credit & Copyright: Péter Feltóti
Galaxies in Pegasus Image Credit & Copyright: Péter Feltóti.

The other members of the group are the lenticular or unbarred spirals NGC 7335 and 7336, the barred spiral galaxy NGC 7337, and the elliptical galaxy NGC 7340. These galaxies lie at distances of approximately 332, 365, 348, and 294 million light-years, respectively. In both visible light and infrared photos of the NGC 7331, the core of the galaxy appears to be slightly off-center, with one side of the disk appearing to extend further away from the core than the opposite side.

I was able to find the 10th magnitude celestial object almost immediately and took time to sketch it over a half hours time. After examining the sketch the next morning, I referred to "The Universe from Your Backyard" by David J. Eicher. The photo in the book was very similar to my sketch. Of course, back in the 1990s backyard astrophotography was limited compared to today's technology, therefore the detail in the image was limited.

The galaxy is similar in size and structure to the Milky Way, and is often referred to as "the Milky Way's twin". However, discoveries in the 2000s regarding the structure of the Milky Way may call this similarity into doubt, particularly because the latter is now believed to be a barred spiral, compared to the unbarred status of NGC 7331.

What inspired me to write this post was the Astronomy Picture of the Day (APOD) that is posted today. Not only does it consist of an incredible image of the galaxy, but it also contains a disturbed-looking group of galaxies at the lower left which is the well-known Stephan's Quintet. About 300 million light-years distant, the quintet dramatically illustrates a multiple galaxy collision, its powerful, ongoing interactions posed for a brief cosmic snapshot. On the sky, the quintet and NGC 7331 are separated by about half a degree. Not only do you see NGC 7331 and Stephen's Quintet in the image, but you also can spot several other smaller and fainter galaxies if you zoom in on this spectacular image.

How many galaxies can you find?

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