Rough neighborhood

In keeping with the stargazing topics that have been our focus this week, today we're going to start with my favorite naked-eye astronomical object: the Pleiades.

[Image is in the Public Domain courtesy of NASA/JPL]

It's also known as the Seven Sisters; in Greek mythology, the seven brightest stars (about all you can see without a telescope, even if you have good vision) represented the seven daughters of the Titan Atlas and the Oceanid nymph Pleione.  Where I live they're visible in the winter; I love seeing them glittering in the black sky on cold, clear nights.

The Pleiades are mostly hot type-B stars, and the whole group is about 444 light years from Earth, making it one of the closest star clusters.  Stars of this class are so energetic that they have relatively short life spans.  It's estimated that the Pleiades formed about a hundred million years ago from a cloud of gas and dust similar to the Orion Nebula; already the energy output of the individual stars is blowing away the shroud of material from which they were formed, resulting in the halo-like "reflection nebulae" you see surrounding them.

They're also moving away from each other, leaving the "stellar nursery" in which they were born.  In another couple of hundred million years, they will have separated widely enough that future astronomers (assuming there are any around) will have no obvious way to know they started out in the same region of space.  Plus, the biggest and brightest of them will already be approaching the ends of their lives, exploding in the violent cataclysm of a supernova, leaving behind a rapidly-rotating stellar remnant called a neutron star, spinning like a lighthouse beacon to mark the spot where a star died.

The reason all this comes up is some recent research into the composition of the stellar nursery where the Sun formed.  Because it, after all, was born the same way; along with a number of siblings, it coalesced in a massive cloud of hydrogen and helium, with a few heavier elements thrown in as well.  When you look up into the night sky, any of the stars you see could be one of the Sun's sibs.  It's impossible, from where science currently stands, to tell which ones.  They've all undoubtedly traveled a long way away from their point of origin in the 4.6 billion years since they formed.

But the research, which appeared in the Monthly Notices of the Royal Astronomical Society, uncovered a bit more about what our star's stellar nursery was like.  These formations do have some significant differences -- some are small and quiet, with only enough material to form a few stars, while others are enormous and violently active (such as the aforementioned Orion Nebula).  In particular, the models of stellar formation suggest that the two different environments would influence the quantities of heavier elements like aluminum and iron.  By measuring the amounts of these elements in meteorite fragments that are thought to be leftover material from the formation of the Solar System, the researchers concluded that the Sun formed in a high-energy intense environment like the Orion Nebula, swept by gales of dust and hammered by the shock waves of supernovae.

What a sight that would have been.  (From a safe distance.)

So next time you see the Pleiades or Orion's Belt, think about the fact that our calm and stable home star was born in a rough neighborhood.  Lucky for us, it's grown up and settled down a little.  As beautiful as the Pleiades are, I don't think I'd fancy living there.

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The legend of the lost sister

The difficult thing about any sort of historical research is that sometimes, the evidence you're looking for doesn't even exist.

In my own field of historical linguistics, for example, we're trying to determine what languages are related to each other (creating, as it were, a family tree for languages), figuring out word roots, identifying words borrowed from other languages, and reconstructing the ancestral language -- based only on the languages we now have access to.  There are times when there simply isn't enough information available to solve the particular puzzle you're working on.

The further back in time you go, the shakier the ground gets.  You'll see in etymological dictionaries claims like "the Proto-Indo-European word for 'settlement' or 'town' was *-weyk," but that's an inference; there aren't many Proto-Indo-Europeans around these days to verify if this is correct.  It's not just a guess, though,  It was reconstructed from the suffixes -wich and -wick you see in a lot of English place names (Norwich, Warwick), the Latin word vicus (meaning "a village in a rural area"), the Welsh gwig and Cornish guic (which mean approximately the same as the Latin does), the Greek word οἶκος (house), the Sanskrit viś and Old Church Slavonic vĭsĭ (both meaning "settlement"), and so on.  Using patterns of sound change, we can take current languages (or at least ones we have written records for) and backpedal to make an inference about what the speakers of PIE four thousand years ago might have said.

Still, it is only an inference, and the inherent unverifiability of it sometimes leaves practitioners of "hard science" scoffing and quoting Wolfgang Pauli, that such claims "aren't even wrong."  I think that's unduly harsh (but of course, given that this is basically what my master's thesis was about, it's no surprise I get a little defensive).  Even so, I think we have to be careful how hard to push a claim based on slim evidence.

That was my immediate thought when I read an article by Jay Norris, of Western Sydney University, in The Conversation.  It was about the mythology associated with my favorite naked-eye astronomical feature -- the Pleiades.

[Image licensed under the Creative Commons Rawastrodata, The Pleiades (M45), CC BY-SA 3.0]

Norris and another astronomer, Barnaby Norris (not sure if they're related, or if it's a coincidence), have authored a paper that will appear in a book next year called Advancing Cultural Astronomy which looks at a strange thing: in cultures all over the world, the Pleaides are associated with a collection of seven individuals.  They're the Seven Sisters in Greece, and also in many indigenous Australian cultures, for example.  And Norris and Norris realized two things that were very odd; first, that even on a clear night, you can only see six stars with the naked eye, not seven; and in both the Greek and Australian myth, the story involves a "lost sister" -- one of the seven who, for some reason or another, disappeared or is hidden.

So they started looking in other traditions, and found that all over the world, in cultures as unrelated as Indonesian, many Native American groups, many African cultures, the Scandinavians, and the Celts, there was the same tradition of associating the Pleiades with the number seven, and with one of the group who was lost.  

They then went to the astronomical data.  They found that the stars in the Pleiades are moving relative to each other, and that a hundred thousand years ago there would have been seven stars visible to the naked eye in the cluster, but in the interim two of them moved so close together (from our perspective, at least) that they appear to be a single star unless you have a telescope.  That, they say, is the "lost sister," and is why cultures all over the world have a tradition that the group used to have seven members, but now only has six.

And this, they said, was evidence that the myth of the Pleiades is one of the oldest stories humans have told.  At least fifty thousand years old -- when the indigenous Australians migrated across a grassy valley that (when the sea level rose) became the Bay of Carpentaria -- and perhaps as much as a hundred thousand years old, when the common ancestors of all humans were still living in Africa and (presumably) shared a single cultural tradition.

It's a fascinating claim.  I have to admit that the commonalities of the myths surrounding the Pleiades in cultures all over the world are a little hard to explain otherwise.  Still, I can't say I'm a hundred percent sold.  I know from my work in reconstructive linguistics that chance similarities are weirdly common, and can lead to some seriously specious conclusions.  (Long-time readers of Skeptophilia might recall my rather brutal takedown two years ago of a guy named L. M. Leteane, who used cherry-picked chance similarities between words to support his loony claim that the Pascuanese -- or Easter Islanders -- were originally from Egypt, as were the Olmecs of Central America, and both languages were descended from Bantu.)

So as far as the claim that the story of the Seven Sisters is over fifty thousand years old, count me as unconvinced.  I think it's possible; it's certainly intriguing.  But to me, it's too hard to eliminate the simpler possibility, that the "loss" of one of the stars in the Pleaides was noted by many ancient cultures -- separately, and much more recently -- and became incorporated into their legends, rather than all the legends of the Pleiades and the lost sister coming from a single, very ancient ancestral story.

But it'll give you something to think about, when you see the Pleiades on the next clear night.  Whatever the origins of the myths surrounding it, it's awe-inspiring to think about our distant ancestors looking up at the same beautiful cluster of stars on a chilly, clear winter's night, and wondering what it really was -- same as we're doing today using the tools of science.

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I've always loved a good parody, and one of the best I've ever seen was given to me decades ago as a Christmas present from a friend.  The book, Science Made Stupid, is a send-up of middle-school science texts, and is one of the most fall-out-of-your-chair hilarious things I've ever read.  I'll never forget opening the present on Christmas morning and sitting there on the floor in front of the tree, laughing until my stomach hurt.

If you want a good laugh -- and let's face it, lately most of us could use one -- get this book.  In it, you'll learn the proper spelling of Archaeopteryx, the physics of the disinclined plane, little-known constellations like O'Brien and Camelopackus, and the difference between she trues, shoe trees, and tree shrews. (And as I mentioned, it would make the perfect holiday gift for any science-nerd types in your family and friends.)

Science education may never be the same again.

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