Messier 25, also known as IC 4725, is an
open cluster of
stars in the southern
constellation of
Sagittarius. The first recorded observation of this cluster was made by
Philippe Loys de Chéseaux in 1745 and it was included in
Charles Messier's list of nebulous objects in 1764.[6] The cluster is located near some obscuring features, with a dark lane passing near the center.[7]
M25 is at a distance of about 2,000 light-years away from
Earth and is 67.6 million years old.[2] The spatial dimension of this cluster is about 13 light-years across. It has an estimated mass of 1,937
M☉, of which about 24% is interstellar matter.[4] A
Delta Cephei type
variable star designated U Sagittarii is a member of this cluster,[8] as are two
red giants, one of which is a binary system.[9]
^Wampler, J.; et al. (May 1961), "Cepheids in Galactic Clusters. VIII. a Reinvestigation of U SGR in M25 (= IC 4725)", Astrophysical Journal, 133: 895,
Bibcode:
1961ApJ...133..895W,
doi:10.1086/147092.
^Mermilliod, J. C.; et al. (September 1987), "Membership of cepheids and red giants in 8 open clusters : NGC 129, 6067, 6087, 6649, 6664, IC 4725, LY 6, RU 79", Astronomy and Astrophysics Supplement Series, 70: 389–407,
Bibcode:
1987A&AS...70..389M.