M13 is one of the finest globular clusters for northern hemisphere viewers. It passes through the highest part of the sky from springtime to the middle of summer. It is located between the western keystone stars of the Hercules constellation. Under good conditions it can be seen without optical aid. With binoculars, it is clearly recognizable as a fuzzy patch, distinctive among the surrounding stars. In a 10" or larger scope the stars are resolvable into jewels of light all the way to the core. At 25,000 light years away, it is further away from us than most globulars, but with maybe a half million stars spread over 125 light years, it still appears bigger and brighter than most. It is also further above the central bulge of our galaxy than most so it's not dimmed as much by the dust and debris as others. Like most globulars, M13 is old, at least 12 billion years old. It, and most of the 120 or so other globular clusters, had already formed by the time our Milky Way Galaxy was starting to get itself together.

Despite at least a half million stars in M13, the stars you see here are only those that are hundreds to thousands of times bigger and brighter than our sun. Not even the biggest telescopes on earth, or in space, could see a star in this cluster that is the size of our sun. Those we can't see are calculated to be there based on the size and total weight of the cluster, which can be calculated by various means. Then the normal frequency of star sizes that we can see all around us infer the number of stars that are likely to be there, unseen.

10" F6.3 Schmidt Cassegrain Telescope, (1600mm F.L.)  Canon 40D camera placed at the scope's prime focus
12 photos aligned and averaged together, then brightness, color, and contrast enhanced.
Each photo, 100 seconds exposure at ISO 1600