And how they'll finally outrun that jerk Orion.
The Pleiades star cluster. Image: NASA, ESA, AURA/Caltech, Palomar Observatory
Every week, Becky Ferreira, your hostess with the cosmostest, hones in on the most important science and history topics the hit show Cosmos glosses over. Previously: What the World Actually Looked Like on the Day Creationists Say It All Began.
Last night's episode of Cosmos was called “Sisters of the Sun," a title that works on a few levels. The most obvious interpretation refers to the stars born in the same “litter” as the Sun, whose fates astronomers have been trying pin down for years. Needless to say, rooting these stars out is like finding needles in a galactic haystack, and the search may be inherently quixotic.
On a less literal level, Cosmos finally elevated the work of female astronomers like Annie Jump Cannon, Henrietta Swan Leavitt, and Cecelia Payne-Gaposchkin. It doesn't make up for the glaring omission of Caroline Herschel back in the fourth episode, but it was a great snapshot of the Harvard College Observatory's sisterhood of astronomers.
Even so, there is no doubt that the real stars of this episode were the Pleiades—the ultimate stellar sisters. Bright, distinctive, and visible in both the Northern and Southern hemispheres, the Pleiades have had an enormous impact on human cultures across the globe. You'd be hard-pressed to find a constellation with more mythological gravitas, not to mention that the legends behind the cluster often have important astronomical observations embedded in their details.
For example, the most famous story associated with the constellation—and the one for which it is named—is a Greek myth about the seven daughters of Atlas and the ocean nymph Pleione: Maia, Electra, Alcyone, Taygete, Asterope, Celaeno, and Merope. As Neil deGrasse Tyson explained in last night's episode, the sisters were having a merry old time until the hunter Orion showed up and started chasing them around like the perv he was. Zeus intervened by transforming the women into a dole of starry doves, but because he was as much of a sadist as Orion, he placed the hunter in the skies too, eternally on their heels.
Elihu Vedder's "The Pleiades." Image: Metropolitan Museum of Art
There are a couple of variations of this myth, which explain not only the relative position of the Pleiades with Orion, but with other objects too. In one telling, the sisters are part of the entourage of the moon goddess Artemis, and it is she who beseeches her daddy Zeus to aid them. Her father ensures that the star cluster frequently crosses paths with Artemis's lunar chariot, allowing her time to catch up with her girls. Artemis also convinces her brother Apollo to punish Orion by siccing a giant scorpion on him, explaining away the position of constellation Scorpio.
It seems many cultures independently decided that the Pleiades were a group of tight-knit women, often evading unwanted attention. Tyson outlined the Kiowa tribe's story, in which bears chase the sisters down, only to be thwarted by the formation of Devil's Tower. There's also an aboriginal Australian myth in which the Moon is not their ally, but a would-be rapist.
My favorite Pleiades-as-women myth, however, is that of the Mono tribe. In this origin story, the Pleiades are a group of women who eat onions nonstop. Their stinky breath irks their husbands so much that they exile the women from their homes. By the time the men realize they miss their wives, it's too late—the onion-lovin' ladies have wandered into space to become to the Pleiades. Let that be a lesson to all who defame onions.
In addition to making celestial observations, dozens of cultures have also used the Pleiades as a yardstick for terrestrial phenomenon. As Tyson mentioned, the rise of the cluster at dusk coincided with the Celtic holiday of Samhain, which has evolved into modern day Halloween. Suspended between the autumnal equinox and the winter solstice, the sight of the Pleiades signaled that it was time to slaughter livestock for the winter, and think morbid thoughts. South American and African cultures also regarded the Pleiades as a signal of the harvest, and the Aztecs amazingly based their entire calendar on the movements of the star cluster.
There are even myths describing the “Lost Pleiad,” which may refer to the variable luminosity of one of the cluster's members. To explain why this star flickered in and out of visibility, the Greeks claimed that one of the sisters, usually Electra or Merope, was overcome by grief after the fall of Troy, and simply peaced out so she wouldn't have to watch anymore tragedy befall her relatives on Earth.
A sculpture of the Lost Pleiad covering her face. Image: A Gude/Flickr
We are beneficiaries of the many weird and wonderful stories about these recognizable star systems, invented to explain the mysteries of the skies and Earth. Not only are do they make for great entertainment, they give us a good idea of how astronomically sophisticated ancient civilizations were. The burgeoning field of archeoastronomy is devoted to interpreting these tales and their related artifacts and landmarks.
“Sisters of the Sun” showed how evocative and useful these stories were, but the episode's real triumph was adding its own science-based myth to the corpus of the Pleiades' canon. We now know the true nature of the cluster, and we can accurately predict how the famous legend will end. From our perspective, Orion will continue to give chase to the star cluster, gaining ground until the giant stars that make up the hunter will explode one by one. Free from their pursuer, the Pleiades will disperse like seeds across the galaxy, much like our Sun and its siblings did five billion years ago.
Some incredibly inventive storytellers gave us the beginning of a great story. Science has stepped in to give the myth a fitting finale.