NGC 6231 is an open cluster located near Zeta Scorpii. Zeta 1 (HR 6262) is a member of this star cluster. (Its brighter apparent partner, Zeta 2 (HR 6271), is only 150 ly from Earth and so is not a cluster member.)

This cluster is estimated about 2–7 million years old and is approaching the Solar System at 22 km/s. The cluster belongs to the young Scorpius OB1 association in the neighboring Sagittarius Arm of the Milky Way. Zeta 1 Scorpii (spectral type O8 and magnitude 4.71) is the brightest star in the association, and one of the most radiant stars known in the galaxy

NGC 6231 also includes three Wolf-Rayet stars: HD 151932, HD 152270 and HD 152408.

The cluster was discovered by Giovanni Batista Hodierna before 1654. Hodierna listed it as Luminosae NGC 6231 is an open cluster located near Zeta Scorpii. Zeta 1 (HR 6262) is a member of this star cluster. (Its brighter apparent partner, Zeta 2 (HR 6271), is only 150 ly from Earth and so is not a cluster member.)

This cluster is estimated about 2–7 million years old and is approaching the Solar System at 22 km/s. The cluster belongs to the young Scorpius OB1 association in the neighboring Sagittarius Arm of the Milky Way. Zeta 1 Scorpii (spectral type O8 and magnitude 4.71) is the brightest star in the association, and one of the most radiant stars known in the galaxy

NGC 6231 also includes three Wolf-Rayet stars: HD 151932, HD 152270 and HD 152408.

The cluster was discovered by Giovanni Batista Hodierna before 1654. Hodierna listed it as Luminosae [in his catalogue of deep sky observations. This catalogue was included in his book De Admirandis Coeli Characteribuse published in 1654 at Palermo. It was independently observed by other astronomers after Hodierna.

• 1678 Edmond Halley

• 1745-46　de Chéseaux•

• 1751-52　Lacaille

The cluster forms the head of the "False Comet", a wider collection of stars from Scorpius OB1 running northward from Zeta Scorpii and NGC 6231 roughly halfway toward Nu Scorpii. The tail is formed by two clusters, Collinder 361 and Trumpler 24. Trumpler 24 is surrounded by the emission nebula IC 4628, also known as the Prawn Nebula, where the tail appears to fan out.

From Wikipedia