Caroline Herschel spent thousands of nights helping her brother William study the stars. She polished the mirrors for his telescopes, helped operate them, recorded his observations, and performed many other tasks. And on her off nights, when William was away, she often made her own observations of the sky. Over the years, she discovered eight comets — the big prizes for astronomers of the day — plus 13 deep-sky objects, which are far beyond our own solar system. The first of those discoveries — made in 1783 — is in view on winter nights, in Canis Major, the big dog. You need help to see it, though. Caroline’s Cluster spans about 15 light-years, and it contains several dozen stars. That’s a bit surprising, because the cluster is more than two billion years old. Over that length of time, most similar clusters are pulled apart by the gravity of the rest of the galaxy’s stars and gas clouds. The individual stars survive, but they go their separate ways. So it’s rare to find clusters of tha
