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The Pleiades - the Seven Sisters - shown in star catalogs six thousand years ago. Visible from northern and southern hemispheres, probably every culture that ever watched the sky had a name for it. But what is this group of stars? And are there actually seven of them?

Pleiades - the Seven Sisters

I've come across a beautiful picture that includes northern lights and the night sky including the Pleiades - Seven Sisters.

If you click on Astronomy Picture of the Day, you can probably spot the Pleiades. Jupiter is the brightest object in the picture and the Pleiades are above and to the right of it. Maybe you'll recognize some constellations, too. But if you're not sure, run your mouse over the photo for some labels.

There's been a big problem for astronomers about the distance to the Pleiades, and it's been resolved recently. For a long time the best distance for the cluster was 430 light years. Since it's a nearby and bright cluster, astronomers studied it as part of their models for how stars evolve..

But then the Hipparcos satellite was launched in 1989. Its job was to make the most accurate measurements ever of thousands of stars. It said the Pleiades were 390 light years away. Uh oh! That really wasn't going to work for astronomers. So to settle the matter, recently, a global network of radio telescopes was used to measure the parallax of the Pleiades. (The parallax is what astronomers use to calculate the distance of nearby stars.) The answer: 443 light years, accurate to 1%.

That's close enough to the old value to avoid tearing up the theory and starting again.

No one knows what the problem with Hipparcos was.

Look at this. It's a beautiful painting of the Pleiades, inspired by mythology and images from the Hubble Space Telescope.

So artistic.

The Pleiades is the brightest open cluster of stars we can see with the unaided eye in the northern sky. A nebula - a cloud of gas and dust - is passing through the cluster and the dust is affected by the Pleiades stars. You can see how the dust around the blue reflection nebula is filamentary and stratified. And by the way, if you look in the lower left of the image, you should be able to spot Comet C/2015 ER61 (PanSTARRS).

Image Credit & Copyright: Juan Carlos Casado (TWAN, Earth & Stars), Miquel Serra-Ricart & Daniel Padron, FECYT