Messier 18, NGC 6613

Messier 18 (NGC 6613) is an open cluster containing a few dozen bright stars. Charles Messier discovered M 18 in June of 1764.

Messier 18 is situated between the Omega Nebula (M 17) and the Sagittarius Star Cloud (M 24). It is an irregular group of 30 stars of 9th magnitude and fainter in an area 9' across. The stars are surrounded by faint nebulosity that could not have been detected by Messier's modest instruments.

M 18's distance is estimated to be about 4,900 light years, giving it a linear diameter of 17 light years. Its absolute magnitude is -5, a luminosity of 8,300 times that of our Sun. The hottest stars in M 18 are of spectral type B3, so this cluster is quite young; its age is estimated at 32 million years,