Have you ever looked up at the Pleiades? Or seen pictures? The asterism is also called the Seven Sisters. So why do we only see six stars?

In Greek mythology, the seven sisters were daughters of Atlas, who was being punished by Zeus for, well, being a Titan, and Atlas had to hold up the sky. To protect the daughters from the evil machinations of Orion the hunter, Zeus transformed them into stars, but one ran away to be with a mortal. Hence, six stars.

There’s a similar story found in Australia among Aboriginal groups. Still young women, important in women’s ceremonies and stories, still being hunted by their version of the Orion constellation. There are variations in why the seventh sister is missing, but there is always an explanation.

How do two disparate cultures have such similar explanations for an astronomical story? It turns out that this story reappears in culture after culture, and astronomers and anthropologists alike wanted to understand why.

Modern humans descend from people who lived in Africa, and the story possibly migrated from there outward early on and changed with the retelling while keeping the major elements the same. That’s the anthropological explanation. The astronomical explanation is that 100,000 years ago when humanity was still in Africa, the stars Pleione and Atlas were actually separated to the naked eye, but everything moves, and now they look like one star.

The data for this explanation came from measurements done with the Gaia space telescope, and I personally think that it’s a fascinating story all around.

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