The Pleiades star cluster catches the eye of the late night skywatcher as we transition into September. Is there a surer sign of winter’s slow approach than the return of this little dipper of stars to the eastern sky? I saw the bunch last night struggling to clear the treetops around 11 p.m. By midnight it stood apart – a beautiful sight with both the naked eye and binoculars.
I love watching the Pleiades (PLEE-uh-deez). There’s nothing quite like it in the heavens. Most stars are single and separate from each other, but the Pleiades packs more than a handful into a single compact shape that stands apart from nearly everything else in the sky.
You’ve probably noticed that the cluster looks a little fuzzy. That’s due in part to seeing so many stars – some visible and many below the naked eye limit – so close together they blend and blur the same way billions of faint stars in the Milky Way do to create a hazy, speckled band across the sky. That’s not all. The Pleiades stars are caught up in a dim cloud of stellar dust or nebulosity that further softens their appearance.
Each bright “Pleiad”, as they’re called, is named after a daughter of the Greek god Atlas, whose job it was to hold up the sky, and Pleione, a protectress of sailing. Say hi to Maia, Electra, Alcyone, Taygete, Asterope, Celaeno and Merope. Oh, and don’t forget the parents – they’re included too.
The Pleiades is one of brightest and closest star clusters in the sky. It contains some 3,000 stars and lies about 400 light years from Earth. From side to side the group spans 13 light years or about halfway from Earth to the bright star Vega. Like a school of fish, all the Pleiads move together as a gravitationally-bound swarm through space. Within the cluster, you’ll also find double and multiple stars including Alcyone (al-SY-oh-nee), a fine quadruple splittable in just about any telescope.
Time exposure photos reveal hazy clouds of stardust swaddling the cluster. This was originally thought to be gas and dust left over from the Pleiades’ formation. Recent studies now show that the group just happens to be passing through a random cloud of interstellar dust. Starlight reflecting off minute dust grains light up the cloud a chilly blue-white, the same color as the hottest, most brilliant Pleiads.
So how many Pleiades can you see? Atlas, Alcyone, Merope, Electra and Maia are easy. Pleione and Taygeta are tougher, and only the very keen-eyed can spot Asterope and Celaeno. When the group rides high in the south just before dawn in a dark sky you might spot additional outliers using averted vision (looking to the side and around an object instead of staring straight at it). I’ve heard reports of some observers seeing 15 to 20!
Take a look at this stellar treat the next night you’re out late. Enjoy the fact that you don’t have to freeze while doing so. Come November, when the Seven Sisters appear in the east as soon as it’s dark, you’ll need a warm coat and hat when you venture out for a look.