Messier 41, NGC 2287

Messier 41 (NGC 2287) is a large, bright, open cluster located in Canis Major. This cluster is easy to find, as it appears 4 degrees almost exactly south of Sirius, and is visible to the naked eye. It is reported that Aristotle mentioned it in 325 BC as one of the mysterious "cloudy spots" in the sky.

Discovery and History

Messier 41 was possibly recorded by Aristotle around 325 B.C.; this would make it the faintest object recorded in classical antiquity. However, his identification is uncertain; Aristotle may have simply been describing the Milky Way near Sirius.

Giovanni Batista Hodierna was the first to catalog the cluster, some time before 1654. It became generally known after John Flamsteed's independent rediscovery in 1702, who remarked: "Near this star (12 CMa), there is a cluster." The cluster was independently found again by Le Gentil in 1749, and also apparently by Charles Messier, who added it to his catalog in 1765.

Amateur Observation

Messier 41 has a visual magnitude of 4.5. It contains about 100 stars, scattered over an area 38' in diameter. The brightest, situated near the cluster's center, is of magnitude 6.9.

On clear dark nights, M 41 is visible to the naked eye as a hazy patch virtually the size of the full moon. Binoculars partially resolve it, and it is a fine object at low power in small telescopes. Some of the star chains form together to compose a backward question mark. Other bright cluster members lie in the shape of a parallelogram.

Physical Properties

Messier 41 lies approximately 2350 light years away. Its true size is around 25 light-years, and its true luminosity about 8000 suns. The cluster's brightest star, located near the center, is a yellow-orange K3 giant about 700 times as luminous as the Sun. Its hottest star is of spectral type A0. Several more K-type giants are contained in the cluster, and have chemical compositions very similar to that of our Sun. The age of M 41 is estimated to be somewhere between 190 and 240 million years.

The 6th-magnitude star 12 Canis Majoris, mentioned by Flamsteed, is about 1100 light years away - roughly half the distance to the cluster - and thus not a member. However, M 41 is at almost the same distance as another nearby (but less conspicuous) open cluster, Collinder 121. This cluster appears 4.6 degrees away, so the linear distance between them is only about 60 light-years; thus, they may be physically related.