Discovered 1771 by Charles Messier.
M46 is a very rich open cluster of approximately 500 stars of which some 150 are of magnitude 13 or higher. From relatively dark sky locations, M46 is easily visible with the aid of binoculars. The age of the cluster is about 300 million years. The cluster spans an angular diameter of about 27 minutes of arc. This is almost the size of the full Moon and at the cluster’s distance of 5,400 light years equates to a diameter of 30 light years. A special feature of the cluster is the planetary nebula NGC 2438 which appears near the top of the image above. This nebula is actually a foreground object and is not part of the cluster. Planetary nebulae are the final “gasps” of aging and dying stars. They are fleeting celestial objects and most fade in a matter of a few 10s of thousands of years.