and Planetary Nebula NGC 2438
There are three images shown below. The first is taken with Kopernik's 20-inch telescope. The second is another image of the cluster taken with our 80mm Brandon refractor. The third is another version of the 80mm refractor image that shows a wider field.
This is a 10 minute exposure taken with a Canon DSLR camera thru a Brandon 80mm APO refractor. North is at the top.
(February 19th, 1771) ''Cluster of very small stars..... The stars can not be distinguished except in a good telescope. The cluster contains a little nebulosity.''
''Beautiful circular cloud of small stars about a half-degree in diameter.''
Quote from Dreyer's New General Catalog(NGC) for NGC 2437:
"Remarkable! Cluster, very bright, very rich in stars, very large, involved planetary nebula; = M46"
Quote from: "Messier's Nebulae and Star Clusters" by Ken Jones:
"When atmospheric conditions are suitable, M-46 is a fine sight, being at least a half-degree in diameter and very rich in faint stars which are condensed in the central area of the cluster. The brighter stars streach away to the north and east...... The Planetary Nebula NGC 2438 lies within the boundary of the cluster about 10 arc minutes northeast of the center, and being fairly large and diffuse it needs the very best conditions.... Its annular form can just be made out in an 8-inch......"
The best distance estimate from the Hipparcos satellite is 7,250 light years. Recent data shows that the planetary nebula NGC 2438 may be about the same distance. However, its radial velocity is about twice that of the open cluster. Generally planetary nebulae are old objects while open clusters are young. It would seem that NGC 2438 is not an actual part of M-46.
George Normandin, KAS
April 10th, 2005, revised March 7th, 2008