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Astronomical Observatory: Cool Images

Astr110 Photography Projects, Fall 2006

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The Great Globular Cluster in Hercules (M13), Thea Fitzpatrick

The Great Globular Cluster in Hercules

A globular cluster is most easily explained as "a spherically symmetric collection of stars which share a common origin. The cluster may contain up to millions of stars." This particular cluster, known as the Great Globular Cluster in Hercules or M13, is located, with no surprise, in the constellation Hercules. It was discovered in 1714 by astronomer Edmund Halley. Although the cluster is located about 25,100 light years away, Halley was able to notice the cluster with his naked eye when the sky was dark enough.

M13 contains over hundreds of thousands of stars within itself; this numerous count of stars is held together by the mutual gravitational attraction present among the stars upon each other. This can be most easily noticed by the concentration of stars seen in the center of the cluster and the gradual dispersion of stars that occurs further from the center. The diameter of this cluster is about twenty arc minutes. There is a bluish tint present in this photo which is due to the young blue star that is present within the cluster (Barnard 29).

Also, as you can see from the picture, outside of the very white center, there are other stars that are bright as well. The brightest seem to have a yellowish hue, while the remaining stars are not as bright and contain a blue tint. According to Blackbody laws, these yellow stars are supposed to be colder due to the color being shown. Therefore, the fact that they appear brighter than the hotter blue stars proves that the yellow ones must be enormous. Stars such as this are known as super giants.


Frommert, Hartmut and Kronberg, Christine. "Messier 13." Students for the Exploration and Development of Space.

Mimi Studio. "Globular Cluster."

Right Ascension (J2000) 16:41:42
Declination (J2000) +36:28:00
Filters used blue(B), green(V), red(R), and clear(C)
Exposure time per filter 20x10 seconds in C, B, V, and R
Date observed

October 13, 2006 (CBVR)




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