Located in the constellation Sagittarius, M21
is an open cluster of about 40 stars varying in magnitude from 9
to 12. The cluster is located about 3,000 light-years from Earth
and has a diameter of about 10 light-years. M21 has a total
visual magnitude of about 5.9, which makes it an impressive
sight in any small telescope. It can also be easily located with
binoculars just a short distance from M20, the Trifid Nebula.