Messier 93, NGC2447, was discovered on this day in 1781. This binocular object is an open cluster about 3,600 light years away, spanning approximately 10 light years, in the constellation Puppis. It was the last open cluster to be discovered by Charles Messier himself. M93 contains a good collection of blue giant stars, as well as quite a few red giants, possibly in clusters of their own. It’s hard to say how many stars a cluster contains, mainly because they get in each other’s way when you try to count them. This one has at least 80 identifiable members, but may well turn out to be several hundred strong.