In the constellation of Cancer you can observe one of the oldest open clusters, Messier 67, which is over 3 billion years old, and was catalogued by Charles Messier in 1780. Normally, open cluster stars have long since dispersed. Only a few clusters have kept a certain amount of cohesion for such a long time.
M67 is visible to the naked eye as a spot equivalent to the area of the full Moon. This cluster interests many astronomers because its age is close to that of the solar system and its stars have a chemical composition identical to that of the Sun. It is therefore an ideal field of investigation for studying the evolution of stars of the solar type.
M67. Credit Sloan Digital Sky Survey