M 47

M47 was discovered before 1654 by Hodierna who described it as "a Nebulosa between the two dogs"; this fact, however, remained secret until 1984 when his book came to light. So Messier discovered this cluster independently on February 19, 1771, but did a sign error when computing the position so that it was a missing object until Oswald Thomas identified it in 1934. As a consequence of Messier's error, William Herschel also independently rediscovered it in 1785, and gave it the number 38 H VIII.

Open cluster M47 is a bright cluster which can be glimpsed with the naked eye under good conditions as a dim nebulosity. It is a coarse cluster of bright stars, and contains about 50 stars in a region 12 light years in diameter; in the central portion, the stellar density is about 60 stars per cubic parsec. The brightest star is of spectral class B2 and mag 5.7, the overall population resembles that of the Pleiades. It also contains two orange K giants with luminosity of about 200 times that of the Sun each. The Sky Catalog 2000 gives an estimated age of 78 million years for this stellar swarm which is receding from us at 9 km/sec.

The bright star nearest to the center of our photo is the fine double Sigma 1121, with components of mag 7.9 both and separated by 7.4 arc seconds.

Right ascension	07 : 34.3 (hours : minutes)
Declination	-14 : 22 (degrees : minutes)
Distance	1600.0 (light-years*10^3)
Visual magnitude	4.5