By Chris Fellows, Serenity Mobile Observatory
Planets are cool, nebula are fine, distant galaxies can be fun to track down and squint at for hours, but for my money there is nothing in the night sky like a globular cluster. These little islands of stars are nearly galaxies in their own right. Made up of thousands if not millions of stars and orbiting the core of the Milky Way, a globular cluster is a tightly compacted ball of strangely ancient stars that swarm around our galaxy like bees around a hive. From our vantage point here on Earth, we have discovered around 150 of these objects. There are probably more that are obscured by the core of the Milky Way, but there are plenty in plain sight to wonder at.
These beauties are common in the universe. As mentioned above, our galaxy has well over 100 that we know about, but around Andromeda, the next large galaxy in our neighborhood, we can see over 500, and in M87, a huge elliptical galaxy, we can make out over 1300 globulars.
Globular clusters are a bit of an enigma. They seem to contain some of the oldest stars in the universe. Measuring the spectra from the stars in a typical globular cluster indicates that most constituent stars are at least 10 billion years old and contain a lot of metals. Current theory indicates that the stars in a globular most likely formed as the first stars in galaxy formation, but that is a process not yet well understood, so there is a bit of a mystery here. The cores and disks of most of the galaxies we see contain vast star forming nurseries when new stars are born, but these are absent in globular clusters. They are like the Florida of galaxies, where older stars go to hang out in retirement.
First observed and cataloged in 1665 by amateur astronomer Abraham Ihle, what is now known as M22 puzzled him. The faint fuzzy ball was clearly there but he couldn’t tell what it was made of or guess at its nature. It wasn’t until 1764 when famous astronomer Charles Messier observed M4 through his improved optics and noticed it was composed of millions of individual stars that were tightly bound by gravity into spheres.
Globulars are, in my opinion, some of the best visual targets you can look at in a small telescope. Several are fairly easy to find by star hopping, and several are bright enough to see with a decent pair of binoculars from a dark sky location. Summer time is globular cluster season and there are several good targets up in the night sky right now.
One of the biggest and brightest is M13, the great globular cluster in Hercules. It is pretty easy to find: If you go out after full dark, say around 10:30 p.m., and look high in the sky towards the southwest, you should be able to spot Hercules. First spot Vega, one of the brightest stars in the summer night sky, and then look farther southwest. You should spot the trapezoid or “keystone” shape of fairly bright stars that make up Hercules’ body. About three-quarters of the way between the southwest-most two stars that make up this trapezoid you will find M13. It is often said that M13 lies in Hercules’ arm pit.
Discovered by the also famous Edmond Halley in 1714, this cluster contains several hundred thousand stars, is around 145 light years in diameter, and is located about 22,000 light years from Earth. It appears as a fuzzy ball of light in smaller instruments, but if you are lucky enough to have a look through a 4-inch or larger telescope you can easily make out individual stars in the cluster.
Globular clusters are one of my favorite targets. It was M3, also in the sky this time of year, that initially got me hooked on astronomy. These glistening balls of glitter dot the night sky and are worth the hunt to spot one. Let me know if you are successful on your hunt and tell me about your experience in the comments.
Till next time!
Chris Fellows, Serenity Mobile Observatory
Find Chris on Facebook (or, if you’re lucky, at your campground). (Editor: Check out his amazing photos on his Facebook page!)