NGC 2682

Messier 67 (NGC 2682) is one of the oldest and best-studied open star clusters in the sky, located approximately 2,500 light-years away in the constellation Cancer. It was possibly first noted by Johann Gottfried Koehler before 1779; Charles Messier catalogued it on April 6, 1780. NGC 2682 was long celebrated as possibly the oldest known open cluster, with early estimates placing its age at up to 10 billion years; modern measurements have revised this to around 3.5–4 billion years — still remarkably old for an open cluster, most of which dissolve within a few hundred million years. The cluster contains approximately 500 stars within a diameter of about 12 light-years.

NGC 2682's advanced age makes it a uniquely valuable laboratory for stellar evolution. A cluster this old has evolved past the main-sequence turnoff point where solar-mass stars like our Sun have already spent their lives — meaning M67 is populated by red giant stars, sub-giants, and white dwarfs that represent the endpoint of solar-type stellar evolution, all at the same known age and distance. Astronomers have identified blue straggler stars within the cluster — stars that appear unusually blue and luminous for their age, thought to be the rejuvenated products of stellar mergers or mass-transfer in close binary systems. M67 has also been surveyed extensively for exoplanets, with several confirmed around cluster member stars.

Binoculars show M67 as a faint, slightly hazy spot near the stars of Cancer; a small telescope resolves a hundred or more members of mixed brightness spread across a field about the size of the full Moon. This full-color image was assembled from nine BVR exposures taken in January 1997 at the Burrell Schmidt telescope of Case Western Reserve University's Warner and Swasey Observatory on Kitt Peak.