M15
is one of the best globulars in
the northern sky. It was
discovered by Maraldi in 1746
and included in Messier's
catalogue in 1764. At 12
billion years it's one of the
oldest known globulars and is a
very easy visual target at
magnitude 6.2 and 18' in
diameter. M15 is also one
of the small number of globulars
to contain a planetary nebula
(Pease 1). Pease 1 is very
difficult to see. It's
located just to the top of the
bright centre in this image.
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