Messier 21

Object:   M21  (NGC 6531) Date:               2018 August 1
Type:  Open cluster
Constellation:           Sagittarius Time & altitude:          21.45 UT      16º
Catalogue data: Seeing (5 high):                               2/5
            R.A:                18h 05m Transparency (5 high):                   2/5
            Dec:                -22º 30 Telescope:     0.5m f4.1  Dob.
            Magnitude     5.9 Eyepiece       17mm Ethos              x120
            Size (mins)    13 Filters:            None


Observed at culmination but low altitude even so. Many aircraft contrails are making the sky milky and there’s a lot of turbulence after another sunny day.

This is a loose clump of stars, difficult to say where the cluster ends and the rest of the sky starts. There is a slightly more compact group of maybe 20 stars on the E side of what is probably the cluster. This group fits in a circle of say 5 arc minutes.

There doesn’t seem to be any faint stars in the cluster, down to the limit of visibility. It doesn’t seem to contain stars of a wide range of brightness.