Matt Springer is a graduate student of physics at Texas A&M university. He is also an occasional writer and tinkerer, and he is probably too curious for his own good.
when you order from Amazon, and a fraction of the purchase price will be sent to me at zero cost to you. Much obliged, and thanks for your patronage.Before we figured out that the universe was a very large open space with lots of stuff scattered about, the ancients had some interesting ideas on how the sky worked. Roughly speaking, celestial phenomena came in three kinds. There are the stars, which remain a constant, fixed background. There are the planets, which move about the sky in complicated but predictable patterns. And finally there were other transient phenomena - nova, supernova, comets, meteors, and the rest. These last were often seen as particularly significant by virtue of their rarity.
If you go outside tonight and look toward the western sky, you'll see tonight's Earth and Sky's "Sky Tonight" object of interest: the Pleiades. It's an open cluster of stars that many people initially mistake for the Little Dipper. It's little, and it's in about the same shape as the dippers. There's six prominent stars visible, and many more dimmer stars visible in binoculars or a telescope. They are not a coincidental alignment of unrelated stars, but are in fact a gravitationally bound cluster with associated nebulosity that can be photographed with a good telescope. Though they won't look so dramatic to the naked eye, photographed with a long exposure they look like this:
It's more than a little odd that there's only six bright stars. The Pleiades are the seven sisters in Greek mythology. Where's the other one?
Nobody knows. Maybe one of the dimmer stars used to be brighter, or maybe a brighter star was obscured by some other astronomical phenomenon in the cluster. Or maybe the Greeks were just using creative license and figured that six bright stars plus some dim ones were close enough to seven to work. But if it really did change at some point, it may well be the earliest recorded instance of one of the "permanent" features of the starry sky changing. It would have been a watershed moment in the history of physics, astronomy, and cosmology. They just wouldn't have recognized it at the time.
Physical Science
Comments
If one star did in fact disappear, wouldn't there be evidence? Either of a black hole or supernova?
Posted by: Kobra | March 30, 2009 11:16 AM
The car maker Subaru uses a depiction of the Pleiades as their logo. "Subaru" is the Japanese name for the Pleiades.
Posted by: Eric Lund | March 30, 2009 11:23 AM
The "associated nebulosity" is kind of half-associated. The stars in the cluster just by coincidence happen to be passing through a particularly dusty part of space. Thus, there's a reflection nebula, but the dust that's reflecting doesn't share an origin with the stars providing the light.
Posted by: Emory Kimbrough | March 30, 2009 3:30 PM
Maybe the seventh star was Pleione. It is variable, and might have been visible at some time, if you looked hard. The Greeks stared a lot at the Pleiades, because they were used as an agricultural calendar. Besides, the athmosphere was less dirty in those times.
On the other hand, in Indian mythology there are only six stars in Krittika. Maybe the Greeks just made up the seventh. Somebody had forgotten how to mark the number six with the ancient letter system and rounded it up...
Posted by: Lassi Hippeläinen | March 30, 2009 4:36 PM
Back in the day when the sky up here was dark and I had decent vision, the Pleiades appeared to have seven stars, the close pair of the seventh and eigth brightest could be imagined as a seventh star.
We used that "seventh" star, and the double star in the big dipper handle as a criteria for clear viewing and good seeing conditions.
I have not seen a truely dark sky now for several decades. Even in Northern Ontario the horizon has the glow of artificial light now. Many people alive today will never see a dark sky, (unless the economy gets REALLY bad!)
Posted by: Peter | March 30, 2009 5:29 PM
From a naive view (seriously - I don't even know what the constellation's supposed to be composed of), and using
Posted by: dreikin | March 30, 2009 7:00 PM
Apparently forgot to close a tag - let me try again: From a naive view (seriously - I [didn't] even know what the constellation's supposed to be composed of), and using this as a reference for names, I thought initially the Pleiades were composed of Pleione, Atlas, Alcyone, Maia, Taygeta, Electra, and Merope. Pleione might be more visually significant because of its position and brightness, moreso than either alone would make it, anyway.
If the resolution's not enough to tell them apart, then could Sterope and neighbor blend together to make the seventh?
Posted by: dreikin | March 30, 2009 7:10 PM
I seem to remember from HS Astronomy that the seven sisters in a Greek myth were the names of the seven stars of Pleiades; as I believe drelkin goes into more detail with in the comment above. I think that you are just not able to see all seven anymore due to light pollution and air pollution...?
Posted by: KAS | March 30, 2009 9:52 PM
Wikipedia claims that there are nine named stars in the cluster, and that they correspond to the seven sisters, plus Atlas and Pleione, the parents of the seven. I found it rather convincing.
Posted by: Carl Brannen | March 30, 2009 11:29 PM
This article has been added to the Astronomy Link List.
Posted by: Astronomy Link List | March 31, 2009 5:15 AM
The answer can already be found in the cave of Lascaux. There the Pleiades are depicted, and seemingly there are six stars here too.
However, one star might be double. It's the uppermost one in this picture:
http://www.spacetoday.org/images/SolSys/Earth/LascauxCavesStarMap.jpg
That pair of stars corresponds to Atlas and Pleïone, the parents of the daughters.
Note also:
=> Aldebaran (eye of the bull) with the Hyades
=> The girdle of Orion, curiously with 4 stars
=> the (somewhat misplaced) cross before the eye of the bull, corresponding to the autumnal equinox point, that permits to date this painting (16.700 BC, give or take a couple of centuries).
Paper is forthcoming in 'Natuurwetenschappen en Techniek' (in Dutch).
Posted by: Jos Verhulst | April 2, 2009 2:20 PM
I ama conservative creationist, but you got me on this one. Nice post! great photo.
Posted by: defender | April 4, 2009 7:04 PM
This ancient Japanese star chart which is believed to date from 65 BC shows 7 stars.
http://www2.gol.com/users/stever/kitora.htm
Posted by: starman | April 19, 2009 6:55 PM