M25 Open Star Cluster

M25 is a magnitude 4.6 galactic star cluster that is about 26 arc-minutes in diameter. It has the rare distinction of containing a cepheid varible star as one of its members. U Sagittarii is a cepheid and a member of M25. The presence of this star is unusual, because cepheid varible stars are extremely rare in galactic star clusters. M25 was discovered by de Cheseaux in 1746. Charles Messier observed this cluster in 1764. This cluster is also distinctive in that, as a result of some error, it was not mentioned in the NGC catalogue, and did not receive an NGC number. Instead it received a number in the Index Catalogue of 1908, which was published as a supplement to the NGC catalogue. M25 is one of only three objects on the Messier List that did not receive an NGC number. The other two are M40 (a double star) and M45 (The Pleiades).

This is an RGB color composite CCD image taken with a Takahashi FCT-150 using an ST-8XE.

M25 (IC 4725)
Constellation: Sagittarius
RA: 18h 32m 10s Dec: -19d 06' 46"
April 27, 2006
Image by Sid Leach
Scottsdale, Arizona

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