M10

Credits: Keith Turnecliff, Long Itchington

Messier 10 or M10 (also designated NGC 6254) is a globular cluster of stars in the equatorial constellation of Ophiuchus. The object was discovered by the French astronomer Charles Messier on May 29, 1764, who cataloged it as number 10 in his catalogue and described it as a "nebula without stars". In 1774, German astronomer Johann Elert Bode likewise called it a "nebulous patch without stars; very pale". Using larger instrumentation, German-born astronomer William Herschel was able to resolve the cluster into its individual members. He described it as a "beautiful cluster of extremely compressed stars". William Parsons, 3rd Earl of Rosse thought he could distinguish a dark lane through part of the cluster. The first to estimate the distance to the cluster was Harlow Shapley, although his derivation of 33,000 light years was much further than the modern value.

Facts about M10 by Keith Turnecliff

It is roughly 15,000 light-years from Earth and has an apparent magnitude of 6.4. This cluster can be spotted using a pair of binoculars and is most easily observed during July. It contains roughly 100,000 stars.
M10 is notable for its high population of blue stragglers — stars that appear to be far younger than their neighbours. The stars in globular clusters are thought to have formed and aged together, so they should all be roughly the same age. These anomalous, bluer stars were created either by collisions between stars or other stellar interactions. Such events are easy to imagine in densely populated globular clusters, in which up to a few million stars are tightly packed together.