Open cluster M 67

M 67 — an open cluster in the constellation Cancer, discovered by Johann Gottfried Köhler in 1779. It is located 2° west of Acubens (α Cancri). It is best seen in winter. It covers an area in the sky comparable to the full Moon.

Its age is estimated at 3.2–5 billion years — making it one of the oldest and also nearest open clusters to us. Its mass is approximately 1080–1400 solar masses, but its initial mass was 10 times greater. It contains about 100 Sun-like stars, many red giants, and roughly 150 white dwarfs; in total, over 500 stars.

In 2014–2016, four planets (hot Jupiters) were discovered in the cluster orbiting the stars SAND364, YBP1514, YBP1194, and YBP401.

Among the old open clusters in the Messier and NGC catalogs, only NGC 188 and NGC 6791 are older. In M 67, mass segregation has occurred: massive stars have concentrated in the center, while lighter stars have left the cluster.