Messier 25

Content sourced from Wikipedia, licensed under CC BY-SA 3.0.

Messier 25 is an open star cluster in the southern sky, in the constellation Sagittarius. It sits about 2,000 light-years away and is around 67.6 million years old. The cluster spans roughly 13 light-years and contains about 1,937 solar masses, with about a quarter of that being gas and dust. It shines at an apparent magnitude of 4.6 and covers about 36 arcminutes of the sky.

A dark lane of dust runs near the center. The cluster includes the variable star U Sagittarii (a Delta Cephei-type Cepheid) and two red giants, one of which is in a binary system. New research suggests Messier 25 may be part of a ternary cluster with NGC 6716 and Collinder 394.

Messier 25 was first seen by Philippe Loys de Chéseaux in 1745 and was added to Messier’s list in 1764.