SUNSET: 
0
Photographer:
massimo.difusco
Location of Photo:
Rio Hurtado (Chile)
Date/Time of photo:
09/04/2025 03:00
Equipment:
Data acquired at Telescope Live: Planewave CDK24 @3962mm, Mathis MI-1000/1250 Mount, QHY600M Pro camera, Astrodon R/G/B filters
Description:
Messier 21 (also known as M21 or NGC 6531) is an open cluster located in the southern constellation Sagittarius. It has an apparent magnitude of 6.5 and lies at an approximate distance of 4250 light years from Earth. M21 consists mainly of small, faint stars, but is also home to a few blue giants. It is classified as of Trumpler class I 3 r, which means that is a detached cluster with strong central concentration (I), consists of both bright and faint stars (3), and contains more than 100 stars (r). The stars of M21 are believed to be members of the Sagittarius OB1 Association, a group of massive O and B-type stars that share a common motion, age and origin. The eight of the 10 brightest stars in the cluster are spectroscopic binaries with periods shorter than 6 days.
