Messier 67 is a very old open cluster located in the constellation of Cancer. Estimations of the cluster age vary between 3.2 and 5 billion years with recent valuations indicating it to be nearer to 4.0 billion years, making M67 one of the oldest known open clusters. Only a handful of open clusters are believed to be older but none of them are as close to us as M67. As a result of its age, it contains a variety of star types including many Sun like stars, red giants and white dwarfs and is easily the most ancient Messier open cluster. For comparison, the other Messier object in Cancer the great open cluster M44 "The Praesepe" is 600 million years old and brilliant open cluster M45 "The Pleiades" is a very youthful 100 million years of age.
The constellation of Cancer "the Crab" is a faint zodiac constellation that is bordered by much brighter Leo to the east and Gemini to the west. To the north is faint Lynx, with Canis Minor and Hydra located on the southern side. First locate the heart of Cancer, a grouping of four faint stars. They are Asellus Australis (δ Cnc - mag. +3.9), Asellus Borealis (γ Cnc - mag. +4.7), η Cnc (mag. +5.3) and θ Cnc (mag. +5.3) with M44 contained within this grouping. Then identify another faint star in Cancer, α Cnc (mag. +4.3), which is positioned a further 9 degrees to the southeast of M44. M67 is located 1.75 degrees west of this star. Alternatively, M67 can be found about half way along an imagining line connecting first magnitude stars Regulus (α Leo - mag. +1.4) and Pollux (β Gem - mag. +1.1).
M67 was discovered sometime before 1779 by German astronomer Johann Gottfried Koehler. He described the cluster as being rather conspicuous and nebula like in appearance although with his basic telescope, he was unable to resolve it into stars. Charles Messier then independently rediscovered M67, resolved it into stars and cataloged it on April 6, 1780 as a "Cluster of small stars with nebulosity, below the southern claw of Cancer. The position determined from the star Alpha [Cancri].".
M67 is best seen from the Northern Hemisphere during the months of February, March and April.
With an apparent magnitude of +6.1, M67 is at the boundary of naked eye visibility. It's easily seen in 10x50 binoculars, appearing as an elongated "blur" of light with several component stars visible under good seeing. Through telescopes M67 is a beautiful object. A 80mm (3.1-inch) telescope reveals a large concentrated misty patch of light with a sprinkling of bright stars visible. Medium sized scopes fair even better. When viewed through 150mm (6-inch) or 200mm (8-inch) scopes, M67 is resolved into dozens of stars mainly clustered towards the centre, superimposed on a hazy background. Higher magnifications helps to resolve fainter stars. A larger 300mm (12-inch) scope at about 100x magnification displays about 100 stars, at the same time removing the background mist seen in small scopes.
M67 is a rich cluster of at least 200 faint stars in the constellation of Cancer that has a diameter of 30 arc minutes, equivalent to that of the full Moon. It lies at a distance of 2700 light-years from Earth and with an estimated age of 4 Billion years is one of the oldest known and most studied open clusters. Although often overshadowed by M44, its famous neighbour to the north, M67 is a wonderful cluster in its own right that provides a marvelous contrast to the sprawling Beehive cluster.
M67 Data Table
|Object Type||Open cluster|
|RA (J2000)||08h 51m 20s|
|DEC (J2000)||11d 48m 43s|
|Apparent Size (arc mins)||30 x 30|
|Number of Stars||>200|
|Other Name||Collinder 204|