Back to: Weekend Sky Report
April 24, 2020
Messier 3 is a remarkable globular cluster. It’s over 33,000 light years away, but it’s bright enough to see with a small telescope, which means it’s dense. Around half a million stars exist there. It’s considered by some to be the most beautiful of its kind. But what is a globular cluster?
Globular comes from the Latin globulus, meaning “small sphere.” Small they are not… this one is an estimated 90 light years across. But compared to open clusters, they do seem smaller. Globulars are like open clusters in that they’re a group of nearby stars bound together by gravity, but they form above the galactic plane, or at the outer edge of the galaxy where their collective gravity can hold it together tightly away from the influence of passing bodies, whereas open clusters form further in where the gravity from other stars can disrupt its shape. For this reason, it takes a long time for globular clusters to form.
To find Messier 3, first find bright orange Arcturus. It’ll be in the eastern sky before midnight. One way to find Arcturus is to follow the curve of the handle of the big dipper… arc to Arcturus. Once you’ve found Arcturus, look for a dimmer white star called Cor Caroli (kor CARE-uh-lie). If you’re observing in the evening, it’s above and to the left of Arcturus, next to the handle of the big dipper. Trace a line between Arcturus and Cor Caroli. Point your telescope to the middle of that line and scan slightly downward toward Arcturus until you see what looks like a dim, fuzzy star. That’s Messier 3.
When you find it, you’ll be looking at a globular cluster that’s an estimated 8 billion years old. More than half the age of the universe itself.