Caldwell 87

This image of the globular star cluster Caldwell 87 (or NGC 1261) combines observations made by Hubble’s Wide Field Camera 3 in visible and ultraviolet light along with infrared observations from its Advanced Camera for Surveys. The observations helped astronomers track the motions of the cluster’s stars and better understand the stars’ chemical abundances.

In the past, astronomers thought that all the stars in a globular cluster had similar ages and similar chemical abundances. However, recent studies suggest that this might not be true. It seems as though many globular clusters contain stars with varying chemical abundances, suggesting the stars are different ages. Hubble’s observations of Caldwell 87 have allowed astronomers to investigate this further.

Discovered in 1826 by the Scottish astronomer James Dunlop, Caldwell 87 is located roughly 50,000 light-years from Earth in the constellation Horologium. It has an apparent magnitude of 8.3, and a small telescope is needed to spot it in the night sky. The cluster is best observed in the late spring from the Southern Hemisphere (or in the late autumn from southern latitudes in the Northern Hemisphere).

Apparent Magnitude - The brightness of an astronomical object as seen from Earth, influenced by the object's distance from Earth, its absolute magnitude, and even gas and dust that lie between the object and Earth.

Globular Cluster - A spherical group of stars that are gravitationally bound to each other, with most of the stars concentrated at the cluster’s center.