Messier 46 and Messier 47
Object Type: Star Cluster
Scope: APO 80mm
Exposure 35 minutes
Messier 46 (also known as M 46 or NGC 2437) is an open cluster in the constellation of Puppis. It was discovered by Charles Messier in 1771. Dreyer described it as "very bright, very rich, very large." M46 is about 5,500 light-years away. There are an estimated 500 stars in the cluster, and it is thought to be some 300 million years old.
The planetary nebula NGC 2438 appears to lie within the cluster near its northern edge (the faint smudge at the top center of the image), but it is most likely unrelated since it does not share the cluster's radial velocity. It is an example of a superimposed pair possibly similar to that of NGC 2818.
M46 is located close by to another open cluster, Messier 47. M46 is about a degree east of M47 in the sky, so the two fit well in a binocular or wide-angle telescope field.
Messier 47 (Messier Object 47, M47, or NGC 2422) is an open cluster in the constellation Puppis. It was discovered by Giovanni Batista Hodierna before 1654 and independently discovered by Charles Messier on February 19, 1771. It was later independently discovered again, under the current name NGC 2422.
There is actually no cluster in the position indicated by Messier, which he expressed in terms of its right ascension and declination with respect to the star 2 Puppis. However, if the signs of Messier's coordinate differences are changed, the position matches that of NGC 2422.Until the equivalency of M47 with NGC2422 was found, M47 was considered a lost Messier Object. The discovery that M47 and NGC2422 were the same cluster only came in 1959 with a realization by Canadian astronomer T. F. Morris.
M47 is at a distance of about 1,600 light-years from Earth with an estimated age of about 78 million years. There are about 50 stars in this cluster, the brightest one being of magnitude +5.7. M47 is located relatively close in the sky to Messier 46, which is much older and much further away.