Ptolemy’s Cluster - Messier 7 (Massimo Di Fusco)

Ptolemy’s Cluster - Messier 7

Messier 7 (M7), also known as Ptolemy’s Cluster or NGC 6475, is a bright open cluster in Scorpius constellation that lies at an approximate distance of 980 light years from Earth.
With a visual magnitude of 3.3 and an apparent diameter of 80 arc minutes (more than twice the apparent size of the full Moon), Ptolemy’s Cluster is an easy naked-eye target.
The cluster is the southernmost Messier object in the sky, which makes it a challenging object for those in northern latitudes as Scorpius constellation never rises very high above the horizon.
M7 is one of the most prominent open clusters in the sky, known since antiquity. It was named Ptolemy’s Cluster because it was first recorded by the Greek astronomer and mathematician Claudius Ptolemy in the 2nd century. Ptolemy listed the cluster in his Almagest as object Number 567 and described it as a “nebula following the sting of Scorpius” in 130 AD.
Italian astronomer Giovanni Batista Hodierna counted 30 stars in the cluster before 1654 and Charles Messier included the cluster as the seventh entry in his catalogue on May 23, 1764.

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