“If it were worth the while to settle in those parts near to the Pleiades or the Hyades, to Aldebaran or Altair, then I was really there, or at an equal remoteness from the life which I had left behind, dwindled and twinkling with as fine a ray to my nearest neighbor, and to be seen only in moonless nights by him.” –Henry David Thoreau
Two weeks ago, I asked if you knew your brightest stars. And there are some spectacular ones, of course.
But our nearest major star, alpha centauri, the yellow guy (below, found near the Southern Cross) is over four light years away from us.
But not every star is as lonely as ours is! Stars, as you may know, don’t form one-at-a-time, in isolation. They form in large groups, or clusters, all throughout the spiral arms of galaxies. In fact, looking at a distant galaxy, everywhere you see these “pink” regions, those are regions where the galaxy is forming stars!
Well, obviously we can’t see that well in our own galaxy, but we do have regions just like that! We call them open star clusters, like Messier 11, below.
Some open star clusters are farther away, like this beautiful one in the Small Magellanic Cloud, NGC 265, as imaged by the Hubble Space Telescope.
But perhaps the most famous open star cluster is the Pleiades, or the Seven Sisters, or simply Messier 45.
Of course, none of these are actually the closest to us; the Pleiades is simply the brightest star cluster in the night sky.
But if you can learn how to find the Pleiades, you can find our closest star cluster! Here’s how it goes.
For a few more days, you’ll be able to see Orion in the night sky. Follow the belt across to the bright cluster of blue stars; that bright blue cluster (if you have good vision, you may even be able to make out seven separate stars) is the Pleiades.
But now, I’m going to ask you to look between Orion and the Pleiades.
There’s a bright, giant orange star there: Aldebaran, which just missed my list of brightest notable stars, coming in at the 13th brightest in the Sky. You’ll also notice four other dimmer, but still pretty-bright stars, that help form a big “V” in the sky. They’re part of the constellation Taurus the Bull, and we can take a close look at that region thanks to Lynn Laux‘s photo, below.
Those four other stars are located about 151 light years away, and are some of the brighter stars in our closest star cluster, the Hyades!
If this is the closest one to us, you ask, why is it so dim compared to the Pleiades? After all, there are hundreds of stars located in a pretty dense cluster!
The answer is its age. Most star clusters only live a few hundred million years, but the Hyades is almost ancient, at 625 million years old!
How do we know?
Stars form on this curved line: the bluer ones are the hotter, brighter, more massive ones. But they also burn through their fuel the most quickly! When a star cluster is first formed, it makes all the different types of stars, from the bright, blue, ultra-massive O-stars to the dim, red, barely-burning-their-fuel M-stars. But after just a few million years, the O-stars are all gone. (Even the Pleiades is out of O-stars!)
The Hyades is out of B-stars, but contains many more A-stars and F-stars than our neighborhood does; it even contains 8 white dwarf stars, which are the corpses of B-stars that weren’t quite massive enough to make it to a supernova!
At 625 million years, it’s an oldie but a goodie. And at just 151 light-years away, it might be an ideal place to find a young world to colonize someday! But you’d better move fast, because these stars won’t stay bound together for long. Why not? Break out your red/green 3-D glasses if you’ve got them, because you’ll want to see this animation.
The Hyades are flying apart! Open star clusters don’t live very long because, when you get a large number of massive objects together like that, gravitational interactions periodically kick stars out, eventually dissipating the cluster and just leaving a large number of mostly single, binary or trinary star systems. But for right now, there are hundreds of them pretty tightly packed together, including an unusual concentration of stars more massive than our own!
So next time you’re looking at the night sky, know that just 151 light years away, there are three or four hundred stars, all the same age, just waiting for you to discover them. But don’t be fooled by Aldebaran; the orange giant is much closer, at only 65 light years away! Behind it? That’s your nearest star cluster, the Hyades!