NGC 2360
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NGC 2360 (also known as Caroline's Cluster<ref name="simbad">Template:Cite simbad</ref> or Caldwell 58) is an open cluster in the constellation Canis Major. It was discovered on 26 February 1783<ref name=hoskin05>Template:Cite journal</ref> by Caroline Herschel, who described it as a "beautiful cluster of pretty compressed stars near 1/2 degree in diameter".<ref name="o'meara"/> Her notes were overlooked until her brother William included the cluster in his 1786 catalogue of 1000 clusters and nebulae and acknowledged her as the discoverer.<ref name=hoskin05/> The cluster lies 3.5 degrees east of Gamma Canis Majoris and less than one degree northwest of the eclipsing binary star R Canis Majoris; it has a combined apparent magnitude of 7.2.<ref name="o'meara">Template:Cite book</ref> It is 13 arc minutes in diameter.<ref name="seds">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> By the western edge of the cluster is the unrelated star, 5.5-magnitude HD 56405.<ref name="streicher">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
American astronomer Olin J. Eggen surveyed the cluster in 1968, concluding that the brightest star in the field, magnitude-8.96 HD 56847, is likely to lie in the field and not a true member of the cluster. He also identified one or possibly two blue stragglers.<ref>Template:Cite journal</ref> These are unexpectedly hot and luminous stars that appear younger than surrounding stars, and have likely developed by sucking matter off companion stars.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Four are now recognised to be in the cluster.<ref>Template:Cite journal</ref> By analysing the masses of the smallest stars that have evolved into red giants—namely, stars of 1.8 or 1.9 solar masses—Swiss astronomers Jean-Claude Mermilliod and Michel Mayor were able to date the age of the cluster at 2.2 billion years.<ref name="Mermilliod">Template:Cite journal</ref> The cluster has a diameter of around 15 light-years and is located 3700 light-years from Earth.<ref name="o'meara"/>
| File:Sirius Mirzam M41.jpg Sirius and M41 (lower right), M50 (upper left), and NGC 2360 (lower left) |
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