North is to the top.
The M10 globular cluster, NGC 6218, is in the constellation
Ophiuchus and was discovered by Charles Messier on May 29, 1764. The
cluster is 14,000 light-years from Earth and has a spatial diameter
of about 83 light-years. The cluster's apparent diameter is about
two-thirds the size of the Moon.
Because M10 is positioned close to the galactic plane, we view it
through a lot of dust and various nebulae. This causes the light to
become reddish, just as the Sun is red at sunset. This effect is
called Galactic Extinction. The top image was calibrated with
foreground stars and shows the cluster with the effects of galactic
The bottom image was color corrected for galactic extinction and
shows the cluster with its intrinsic color. The following color
magnitude correction factors were obtained from the NASA/IPAC
Extragalactic Database (NED).