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The Butterfly Cluster is an open cluster in the constellation of
Scorpius.
It is visually the closest Messier object (in angular distance) to the center
of the galaxy in Sagittarius.
Ptolemy may have seen the butterfly cluster with the naked eye while observing
its neighbor Ptolemy's Cluster (M7).
Giovanni Battista Hodierna is the first astronomer to explicity record the
butterfly cluster, before 1654. Charles Messier cataloged it in 1764.
It was not till the 20th century that star counts, distance,
and other properties were measured.
Estimates of the cluster's distance have varied over the years with a mean
value of around 1,600 light years, giving it a spatial dimension of
some 12 light years.
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