Messier 21. NGC 6531

Click on the image for a full resolution version

        See this image also on Instagram



Messier 21 is a very young open cluster (just 4.6 million years old), located 3,900 light years away in the constellation Sagittarius. Although it is not bright enough to have naked eye visibility, M21 is a fine object to observe through a telescope (or binoculars). Having only 57 stars, M21 hosts many blue giants. It is believed that its stars belong to the Sagittarius OB1 Association and eight of its ten brightest stars are spectroscopic binaries with periods shorter than six days.


Additional Information


Name(s): Messier 21. M21. NGC 6531

Type: Open Cluster

RA:  18h 04m 12s

Dec: -22º 28’ 54”

Constellation: Sagittarius

Size (arcmin): 14×15 arcmin

Magnitude: +6.5

Distance: 3,900 ly


Date: 2021-06-07 to 2021-07-11

Location:, SSO near Coonabarabran, NSW Australia

Size (arcmin): 41×41 arcmin

Telescope: 17” f/6.8 Reflector (unguided)

Camera: FLI PL16803 (4096x4096pix)

Total exposure: 3 hours (RGB, 1 hour each)

Processing: CCDStack, Photoshop CC 2021


error: Content is protected !!