Photographing Spiral Galaxy NGC 7331

Using the 0.6-meter telescope at Williams College on the evening of 11/10/03, I took three five-minute-long exposures, each in a different part of the visible spectrum. I made the color image below by compositing those three exposures with the help of ImageJ and Photoshop. While not scientifically precise, the colors shown approximate the real visible color of the objects. The reddish area around the main galaxy is emitted by hot gas clouds which get their energy from the radiation of stars in the galaxy. The relative color between objects is especially reliable; for instance, the stars in the image range along a very noticeable scale from reddish to bluish (this is due to their differing temperatures).

The image field I photographed is just northwest of the great square in the constellation Pegasus (the winged horse). The main spiral galaxy visible in my image is catalogued as NGC 7331 and is estimated to be 46 million light-years away. (The light that was used to make this photograph had been travelling through space for 46 million years!) Although the galaxy is tilted somewhat away from Earth, the spiral structure is fairly easy to see. The galaxy is not bright enough to make out with the naked eye; it was first discovered in 1784. A supernova appeared in the galaxy in 1959. There are several more galaxies in the same region of the sky as NGC 7331; the fuzzy object to the upper left is NGC 7335, and to the lower left is NGC 7337. In three dimensions, however, NGC 7331 is probably nowhere near them.

You can download desktop picture versions:
1024x768 (standard)
1280x854 (wide)

There is also a nebula photograph I manipulated.

Information sources:,,
A really nice photo of NGC 7331