Collinder 204

Collinder 204 is an old, rich open star cluster in the constellation Cancer, also known as NGC 2682, Messier 67.It is about 2,700 to 3,400 light-years away. It is very rich: Gaia identified 1,526 members, with over 1,000 main-sequence dwarfs, a well-populated subgiant and red giant branch, white dwarfs, sub-subgiants, X-ray sources and cataclysmic variables. A recent study counts over 150 white dwarfs. It stands out for its age: about 4 billion years, similar to the Sun, though estimates range from 3.2 to 5 billion. That makes it one of the oldest open clusters known and, as the closest of the old ones, one of the best-studied in almost every wavelength, a benchmark for stellar evolution and solar twins. It contains about 28 to 30 blue stragglers, whose origins (mergers and mass transfer) are still not fully understood. Its metal content is solar, and a hot Jupiter has been found around one of its stars. Johann Gottfried Koehler discovered it in 1779.