Starts With A Bang!

See those last two stars on the big dipper; the two farthest from the handle? They point the way to the North Star! Seriously, next time you see the big dipper in the sky, make an imaginary line with those two stars and follow it, follow it until you get to the next bright star:

The bright star that you get to is Polaris, also known as the North Star. There’s another constellation that starts with Polaris, which you can see if the sky is dark enough, called the little dipper; here’s what that looks like on a clear night:

Regardless of what shapes you see when you look up at these bright stars, they all appear to twinkle very brilliantly; flickering brighter and dimmer like candle flames. We know why they twinkle; it’s because of the fact that we have an atmosphere! As warm and cool air pockets move through the sky, they pass in between us and the stars we view, causing tiny fluctuations in the path that the light travels to reach our eyes. These tiny fluctuations appear as twinkling to us; you can tell a star from a planet by the simple fact that planets (much like the Moon) don’t twinkle. This is because the planets are so much closer to us, so the light from them doesn’t appear to come from a single point; instead, it comes from a small disk, but that disk is large enough that the little atmospheric fluctuations we have don’t affect the light we see enough to cause twinkling. And we know this is the cause, because when we look at stars through the Hubble Space Telescope, or when astronauts in space or on the Moon have looked at stars, there was no twinkling at all!

But the North Star is special. Not only because it’s so close to being directly over the North Pole of the Earth (which it is):

But because this is a star which has variations and fluctuations in its brightness all on its own. It’s a special type of star, known as a Cepheid Variable Star, which has intrinsic fluctuations. The really weird thing about the North Star is that they were measuring these variations very accurately, and they were disappearing; fading away. I’ll show you the graph, and you can see pretty easily that the fluctuations look to be dying away over the course of the last few decades:

And we thought that maybe this is what happens to all Cepheids; eventually these fluctuations calm down and the star reaches equilibrium, and it stops pulsing altogether. The North Star was the only Cepheid to do this; you can see that the variations had dropped from 10% to 2%, and these variations made a complete cycle every 4 days. So they made some detailed observations recently to see whether the variations had turned off completely. Here’s what they found:

The variations are ramping back up! We’ve never seen a star do either of these things before, either lose their variations or gain them back, and now a star that anyone can find without a telescope has been confirmed to be doing both. Keep your eye on the North Star, because it’s doing something that nobody has ever seen before!