Messier 7 Ptolemy’s Cluster (L. Fernando Parmegiani)

Celestial hemisphere: Southern · Constellation: Scorpius (Sco) · Contains: M 7 · NGC 6475

Messier 7 Ptolemy’s Cluster, L. Fernando Parmegiani

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Messier 7 Ptolemy’s Cluster

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Messier 7 Ptolemy’s Cluster

Messier 7 (M7), also known as Ptolemy’s Cluster, is a bright open cluster in Scorpius constellation.

The cluster lies at an approximate distance of 980 light years from Earth. It has the designation NGC 6475 in the New General Catalogue. 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.

Messier 7 can be seen near the stinger of the celestial scorpion. 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.

The best time of year to observe M7 is in the summer months (North Hemisphere) or winter months (South hemisphere). Because of its large size, the cluster is best seen in binoculars.

Messier 7 can be found 4.75 degrees northeast of the star Lambda Scorpii, also known as Shaula.

Shaula marks the scorpion’s stinger and is the second brightest star in Scorpius constellation, fainter only than the red supergiant Antares.

Object: Cluster

Type: Open

Designations: Messier 7, M7, Ptolemy’s Cluster, NGC 6475, Collinder 354, Lac. II.14

Distance: 980 light years (300 parsecs)

Age: 220 million years

Number of stars: 80

Apparent magnitude: 3.3

Apparent dimensions: 80′

Radius: 25 light years

Tidal radius: 40.1 light years

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Messier 7 Ptolemy’s Cluster

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