M 25

Although a conspicuous cluster, even in the smallest telescopes, M25 has only obtained an IC number.

Two giants of spectral type M and two of type G can be found in this cluster, where the G type giants appear to be actual members (the M's not). It moreover contains the Cepheid variable U Sagittarii, which has a period of 6.74 days, a typical period for these variables "in our neighborhood," as Cecilia Payne-Gaposhkin put it. It was discovered by J.B. Irwin in 1956, its membership was confirmed by radial velocity measurements conducted by M.W. Feast of Radcliffs Observatory (the common RV of the cluster members is +4 km/sec).

The occurance of the Cepheid is consistent with the fact that it is not a very young cluster, its age may be about 90 million years (the Sky Catalog 2000 gives 89 million).

This cluster contains at least 86 probable members, according to Ake Wallenquist.

Right ascension	18 : 28.8 (hours : minutes)
Declination	-19 : 17 (degrees : minutes)
Distance	2.0 (light-years*10^3)
Visual magnitude	6.5