... The great variety of star colors in this open cluster underlie its name: The Jewel Box. One of the bright central stars is a red supergiant, in contrast to the many blue stars that surround it. The cluster, also known as Kappa Crucis contains just over 100 stars, and is about 10 million years old. ... APOD is Six Years Old Today . ... The most compact cluster of stars known in our galaxy, the Arches cluster, boasts 100 or so massive, young stars contained within a diameter of one light-year. ...