NGC 2204

NGC 2204是一个位于大犬座的疏散星团，于1785年被威廉·赫歇尔发现。

NGC 2204 is an open cluster of stars in the constellation Canis Major. It was discovered by the German-English astronomer William Herschel on 6 February 1785. The cluster has an integrated visual magnitude of 8.6 and spans a diameter of 10.0′. Resolving the individual member stars is a challenge with a 10 to 12-inch amateur telescope. It is located at a distance of approximately 13,400 light years from the Sun. The cluster shows a mean radial velocity of +91.38±0.30 km/s relative to the Sun, and is orbiting the inner galactic disk region about 1 kpc below the galactic plane.

This is a rich but diffuse cluster with a Trumpler class of III 3m, spanning a physical diameter of about 55 ly (17 pc). It is an older cluster with an estimated age of 2.0±0.3 billion years. The metallicity is correspondingly poor, showing an abundance of iron about 59% of that in the Sun. There is a prominent giant branch clump on the HR diagram. The cluster has a significant population of blue stragglers, an indicator of past stellar mergers. It has a pair of candidate chemically peculiar stars, and five variable stars have been discovered, including four eclipsing variables.