Since writing last month about the Milky Way, our home galaxy, I’ve wanted to take you deeper into its heart. That’s where you’ll find M4 — a beautiful and interesting object you can see with binoculars and your unaided eyes.
It’s a globular cluster — the name doesn’t sound beautiful, I know. These are groups of stars that are gravitationally bound to each other and form a compact spherical shape. That may sound a lot like a galaxy, but it’s different. M4 orbits the Milky Way and is much smaller than our galaxy. And while a globular cluster might include 100,000 stars, the Milky Way has about 300 billion.
A pair of binoculars can be a big help on a search for M4, and for viewing the night sky in general. With them, the number of stars you can see jumps from about 2,500 to over 100,000, and objects too dim for your eyes alone become visible. But one problem with binoculars is that they’re difficult to hold steady. Even the smallest of movements is amplified at the eyepieces, resulting in a shaky image. You’ll greatly improve your sky watching if you steady the binoculars. Camera tripods work well if your binoculars have an attachment point. But you can improvise a tripod with a shovel handle and some duct tape. Or you can rest the binoculars on a tree branch, deck railing, or anything else that gives some stability.
To find your way to M4, first look for a bright red star low in the southwest. Once your view is stabilized, the star, called Antares, should come into view. The ancient Greeks named Antares, calling it the “rival to Ares,” the god of war, whom the Romans called Mars. The planet Mars also appears as a red star; and due to the whims of orbital mechanics, Mars sometimes looks brighter than Antares, and other times dimmer: thus, the rivalry. You’ll have a chance to compare the two later in the summer, when both are visible.
Now let’s move on to the more difficult target. If you have binoculars, find Antares and get it sharply focused. Then look for a faint, fuzzy blob just to the right of it. You may be tempted to adjust the focus, but don’t — that blob is M4.
Why is it fuzzy? Because M4 is not a single star, but rather about 20,000 stars packed so closely together that from our vantage point, 7,200 light years away, they appear as a single diffuse object. I guess saying these stars are close together is a relative term. M4 spans about 75 light years, or 440 trillion miles. But the effect is similar to the way the Milky Way looks like a faint glow across the sky. (Large amateur telescopes can resolve a globular cluster’s stars, a beautiful sight.)
The name M4 is short for Messier 4. In 1764, the French astronomer Charles Messier compiled a list of 110 objects that could be mistaken for comets, now called the Messier catalog. If you’re feeling even more formal, you can call it NGC 6121, M4’s official designation.
You can find M4 without any optical aid. But it’s going to be easier once you’ve found it through a pair of binoculars. You’ll need a dark site, away from house and street lights. Give your eyes at least 10 minutes to adjust. Put away your smartphones; one glance at a text will ruin your night vision.
When you’re ready, find Antares. Then direct your attention just a tiny bit to its right — about the distance of the width of your finger held out at arm’s length. There you’ll see M4, a patch of hazy white, a little bigger than a star. If you have trouble, try covering Antares with your outstretched finger to block its light.
M4 is elusive, like a ghost, to the unaided eye; one moment you may think you see it, but when you look directly at it, it vanishes. That’s because our eyes are more sensitive to low light away from the center of our field of vision. Try using the old astronomer’s trick of averted vision: while keeping your mind on M4, direct your eyes just next it. It’s a difficult trick to play on yourself, but when you get the hang of it, it works.
There are undoubtably planets around most of M4’s stars. I like to imagine how, if one of them were to harbor intelligent life, those beings would look up at a night sky very different from our own.
From within a globular cluster it’s hardly night at all; bright stars fill the sky, creating a twilight sky that never grows truly dark. What kind of mythology would that inspire? What kinds of stories would they spin about the bright gems that illuminate their sky? And what would they think of us when they look out at the lonely stars of the Milky Way’s spiral arms? Would they pity us for our dark nights?