NGC 2360 (also known as Caroline's Cluster or Caldwell 58) is an

open cluster An open cluster is a type of star cluster made of up to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way galaxy, and ...

in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

Canis Major Canis Major is a constellation in the Southern Celestial Hemisphere, southern celestial hemisphere. In the second century, it was included in Ptolemy's 48 constellations, and is counted among the 88 modern constellations. Its name is Latin fo ...

. It was discovered on 26 February 1783 by

Caroline Herschel Caroline Lucretia Herschel (; 16 March 1750 – 9 January 1848) was a German born British astronomer, whose most significant contributions to astronomy were the discoveries of several comets, including the periodic comet 35P/Herschel–Rigolle ...

, 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 William is a male given name of Germanic origin.Hanks, Hardcastle and Hodges, ''Oxford Dictionary of First Names'', Oxford University Press, 2nd edition, , p. 276. It became very popular in the English language after the Norman conquest of Engl ...

included the cluster in his 1786 catalogue of 1000 clusters and nebulae and acknowledged her as the discoverer. The cluster lies 3.5 degrees east of

Gamma Canis Majoris Gamma Canis Majoris (γ Canis Majoris, abbreviated Gamma CMa, γ CMa), also named Muliphein , is a star in the constellation of Canis Major. It is unclear exactly why this relatively faint star was given the ' gamma' designation, but p ...

and less than one degree northwest of the

eclipsing binary A binary star is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separate stars, in wh ...

star R Canis Majoris; it has a combined

apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...

of 7.2. It is 13 arc minutes in diameter. By the western edge of the cluster is the unrelated star, 5.5-magnitude HD 56405. 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 straggler A blue straggler is a main-sequence In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams ...

s. These are unexpectedly hot and luminous stars that appear younger than surrounding stars, and have likely developed by sucking matter off companion stars. Four are now recognised to be in the cluster. By analysing the masses of the smallest stars that have evolved into

red giant A red giant is a luminous giant star of low or intermediate mass (roughly 0.3–8 solar masses ()) in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius large and the surface temperature around or ...

s—namely, stars of 1.8 or 1.9 solar masses—Swiss astronomers Jean-Claude Mermilliod and

Michel Mayor Michel Gustave Édouard Mayor (; born 12 January 1942) is a Swiss astrophysicist and professor emeritus at the University of Geneva's Department of Astronomy. He formally retired in 2007, but remains active as a researcher at the Observatory ...

were able to date the age of the cluster at 2.2 billion years. The cluster has a diameter of around 15 light-years and is located 3700 light-years from Earth.

Notes

External links

* {{DEFAULTSORT:NGC 2360 Canis Major

2360 In contemporary history, the third millennium of the anno Domini or Common Era in the Gregorian calendar is the current millennium spanning the years 2001 to 3000 ( 21st to 30th centuries). Ongoing futures studies seek to understand what is ...

Open clusters 058b Astronomical objects discovered in 1783