M10

Discovered 1764 by Charles Messier.

Messier 10 (M10, NGC 6254) is one of the bright globulars populating constellation Ophiuchus.

This 7th mag globular cluster appears at about 8 or 9 arc minutes diameter when observed visually in smaller instruments. Average photos show it at about 15.1 arc minutes diameter, and deep photos show it to reach out to about 20 arc minutes, or 2/3 of the diameter of the Full Moon. At its distance of 14,300 light years, this corresponds to a linear diameter of 83 light years. Its brighter core which can be seen visually is only less than half as large, about 35 light-years. It is receding from us at 69 km/sec.