Right Ascension	18 : 04.6 (h:m)
Declination	-22 : 30 (deg:m)
Distance	4.25 (kly)
Visual Brightness	6.5 (mag)
Apparent Dimension	13.0 (arc min)
Discovered by	Charles Messier June 5th, 1764

M21 is a cluster which shows quite a strong concentration toward its center.

According to Burnham, S.N. Svolopoulos, in 1953, has demonstrated the membership of 57 stars (making it Trumpler type I 3 m), the brightest of which are giants of spectral type B0. This implies that this cluster is very young: the Sky Catalog 2000 gives an estimated 4.6 million years, and states that this cluster is part of the Sagittarius OB1 stellar association.

As it is situated close to the Trifid Nebula M20 (the outlayers of which show up in our image at the upper left edge), many images showing the Lagoon-Trifid region do also show M21.

"Star cluster close to the previous one ( M20 )." Charles Messier

Courtesy www.seds.org