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Great Globular Cluster in Hercules (M13)
Eugene Park


The largest and richest globular cluster in the Northern Hemisphere. Globular clusters are distinguished from galactic clusters because of their age, size, and location. They are interesting targets for any sort of optical aid, binoculars or telescopes.The Great Hercules cluster (Messier 13) is considered to be the finest globular cluster in the northern half of the heavens. It’s found in a star pattern called the Keystone – a lopsided square within the constellation Hercules – between the two brightest stars of summer, Vega and Arcturus. Barely perceptible to the unaided eye, this cluster is best enjoyed with a telescope. (McClure)

Looks like there is thousands of stars orbiting the collective center of mass of the the cluster. Although the cluster appears extremely dense, but we can assume the distance between individual stars is actually large. However, it looks very pretty with different color stars spotted at the one specific region, which reminds me of colony of bees and hive. Near stars have reddish bright light as it gets closer to the center of the cluster and as it goes further the stars color changes to blue and fade away. According to this information we can predict this cluster is a very old age cluster, because blue color menas high temperature and yellow means less temperature, and by looking at the H-R diagram we can tell the blue color stars are the main sequence and yellowish stars are the supergiants. Therefore having a cluster that contains main sequence stars changing to supergiant stars, we can predict it is an old age cluster.

The distance to this object is estimated to be 25,100 light yers (wikipedia); we find maximum angular size of 289.51 acrseconds, which corresponds to a linear size of 35.23 degree.


McClure, Bruce. "M13: Great Cluster in Hercules." EarthSky. 2010 Feb. 10. Accessed 12 April. 2011. <>

Gaherty, Geoff. "Spot the Great Cluster in Hercules." Space. 15 July. 2009. <>.

Right Ascension (J2000) 16:41:42
Declination (J2000) +36:28:00
Filters used B (Blue), C (Clear), R (Red), V (Green)
Exposure time per filter B, V, R, C (all 60s)
Date observed March 29 2011, 1558 UT



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