Ptolemy’s Cluster

Ptolemy’s Cluster, also known as Messier 7, is a star-rich cluster that extends over about 20 light-years. Most of the stars shine very brightly, and the brightest cluster member is a yellow giant. The age of the cluster is estimated as 220 million years, making it just one-twentieth the age of the Sun.

This beautiful glittering object is 800–1000 light-years away from us. It is approaching the Solar System at a speed of 50 000 kilometres per hour.

This small stellar city harbours some truly extraordinary stars. Four of them for example exhibit unusual characteristics such as exceptionally strong magnetic fields and a high abundance of exotic rare earth elements, such as europium.

Easily seen with the unaided eye, this brilliant open cluster was first referenced in AD 130 by the Greek astronomer and mathematician Claudius Ptolemaeus (also known as Ptolemy). He denoted the cluster as Object Number 567 in his Almagest, describing it as "a nebulous cluster following the sting of Scorpius", which accurately illustrates its position in the sky towards the constellation of Scorpius (the Scorpion). Many years later, around 1654, the Italian astronomer Giovanni Battista Hodierna observed Ptolemy’s Cluster. In 1764, Charles Messier re-discovered it independently and reported it as the seventh entry in his catalogue (Messier 7).