M25 (open cluster)
See also: M25
M25 (or IC 4725 ) is a open Amas located in the Constellation of the Sagittarius. He was discovered by Philippe Loys de Chéseaux in 1745, and Charles Messier has includes it in its catalogs in 1764.
The cluster counts at least 86 star S, including two giant stars of spectral Type G, as well as a variable Céphéide named U Sagittarii , discovered in 1956 and one 6,74 days period. The radial speed of the stars which compose the cluster is on average of +4 km/s. It is also possible to observe two giants of the type M there, but the radial velocity measurements showed that they did not form in fact not part of M25, those being there visually only by one visual effect.
M25 is located at roughly 2000 light-years Solar system, which taking into account its apparent Diamètre of 40 minutes of arc gives a total extent for approximately the 23 light-year old cluster.
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