Starry, starry night
Messier 10 is a ball of stars that lies about 15,000 light-years from Earth, in the constellation of Ophiuchus (The Serpent Bearer). Approximately 80 light-years across, it should therefore appear about two thirds the size of the moon in the night sky. However, its outer regions are extremely diffuse, and even the comparatively bright core is too dim to see with the naked eye.
Hubble, which has no problems seeing faint objects, has observed the brightest part of the center of the cluster in this image, a region which is about 13 light-years across.
This image is made up of observations made in visible and infrared light using Hubble’s Advanced Camera for Surveys. The observations were carried out as part of a major Hubble survey of globular clusters in the Milky Way.
Image Source: http://www.nasa.gov/mission_pages/hubble/science/cluster-m10.html