- M 13 The Great Hercules Cluster
M 13 (NGC 6205) is probably the best-known globular cluster. Lying in the late Spring constellation of Hercules, this intensely glowing ball of tiny stars is a truly beautiful sight in even small telescopes. M 13 has a physical diameter of 160 LY and lies at a distance of 25,890 LY. It contains on the order of a million stars. M 13 was discovered by Edmond Halley in 1714. Charles Messier observed it in June of 1764. While he noted that its center was brighter than its borders, it was William Hershel in 1784 who first observed it to be composed of individual stars.
As seen in my image, M 13 is framed by two lovely 8th-magnitude stars, one reddish (HD 150998) and the other white (HD 150679). These stars were noted by Messier in his observations. Along the upper left edge of my image is the small but bright galaxy NGC 6207. Another tiny galaxy (IC 4617) is just visible lying next to a small star about halfway between NGC 6207 and M 13. With a visual magnitude of 5.7, M 13 can be seen with the unaided eye on dark, clear nights, as was noted by Halley.
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