Messier 7

Messier 7, or the Ptolemy Cluster, is a bright open star cluster in Scorpius. Its stars formed together and remain loosely bound by gravity.

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Scorpius: Scorpius is a zodiac constellation representing a scorpion, prominent in the southern summer sky. Messier 7 lies within this constellation, near the Scorpion’s tail.
Open cluster: An open cluster is a loose group of stars formed from the same molecular cloud. Messier 7 is an example of this cluster type.
Claudius Ptolemy: Claudius Ptolemy was a second-century Greek astronomer, mathematician, and geographer. His star catalogue recorded the hazy object later identified with Messier 7.
Apparent magnitude: Apparent magnitude measures how bright a celestial object appears from Earth. Its brightness helps explain why Messier 7 is visible to the unaided eye.
Milky Way: The Milky Way is the barred spiral galaxy that contains the Solar System. Messier 7 is a Galactic cluster seen against the Milky Way’s star-rich background.
Ptolemy Cluster: The Ptolemy Cluster is the traditional name for the open star cluster catalogued as Messier 7. This familiar name links the cluster to its ancient recorded history.
Stellar association: A stellar association is a sparse grouping of young stars that are not gravitationally bound. Unlike an association, Messier 7 is a gravitationally bound open cluster.
Al-Sufi: Al-Sufi was a tenth-century Persian astronomer who described stars and celestial objects in the Book of Fixed Stars. His work includes an early account of the cluster’s appearance.
Declination: Declination is the angular distance of a celestial object north or south of the celestial equator. Messier 7’s southern declination makes it best placed for southern observers.
Galactic plane: The galactic plane is the plane in which most of a spiral galaxy’s stars and gas orbit. Messier 7 appears close to the Milky Way’s crowded central band.