Discovered by Charles Messier in 1764.
M10, also designated NGC 6254, is a dense cluster of stars. This type of astronomical object is classified as a globular cluster and typically is composed of hundreds of thousands of stars. The size of M10, as observed from the Earth, is about two thirds the diameter of the full Moon. This includes outlying, gravitationally bound, stars. The bright core, as seen through moderate sized amateur telescopes, is much smaller. The cluster lies in the constellation of Ophiuchus and its estimated distance is about 14,300 light-years.