| NGC 2360 | |
| Class: | Open Cluster |
| Epoch: | J2000 |
| Ra: | [1] |
| Appmag V: | 7.2 |
| Size V: | 13 |
| Constellation: | Canis Major |
| Names: | Caroline's Cluster, Caldwell 58, Cr 134, Mel 64 |
NGC 2360 (also known as Caroline's Cluster[2] or Caldwell 58) is an open cluster in the constellation Canis Major. It was discovered on 26 February 1783[3] by Caroline Herschel, who described it as a "beautiful cluster of pretty compressed stars near 1/2 degree in diameter". 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.[3] 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.[4] It is 13 arc minutes in diameter.[5] By the western edge of the cluster is the unrelated star, 5.5-magnitude HD 56405.[6]
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.[7] These are unexpectedly hot and luminous stars that appear younger than surrounding stars, and have likely developed by sucking matter off companion stars.[8] Four are now recognised to be in the cluster.[9] 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.[10] The cluster has a diameter of around 15 light-years and is located 3700 light-years from Earth.[4]