Astronomy Cast: The Big Dipper

So when you’re looking at the Big Dipper, you have the bowl, and then moving away from the bowl, you have the three stars that make up the handle, and the middle star of those three if you have really keen eyesight, you’ll see there’s a little buddy hanging out next to the really bright star, and that little buddy is Alcor, and this was an eye test to get into the elite military for a while, so while it’s hard to track down exactly where the constellation came from, I find it fascinating that this may have been one of the very first eye tests around. Now when you say double star, that’s just two stars that appear close together. These aren’t stars that are orbiting one another or anything like that, but it does qualify as a widely-spaced double star. Now, the thing is these stars, if you keep looking at them better, they then split themselves apart again, making this a quadruple system because each of them are independently binary systems.  So, while they are both double systems, you can’t actually split both of them. It’s one of those unfortunate things where Alcor – it really… it’s a spectroscopic binary, so if you look at it with a big telescope attached to a spectrograph, watch it over time, you see the lines dancing apart from the two different stars, but with your standard backyard system, you’re not going to split it into two different stars. Mizar, on the other hand, all you really need is clear skies and a really good eyepiece on even a small backyard telescope, so I’d say pull out your handy dandy friendly 70 mm refractor and a 4 mm eyepiece, if your sky supports it, and you should be able to split those.  So that is one of the brightest stars, but we’re used to thinking of constellations as politely being: alpha’s the brightest, beta’s the next, gamma’s the next, but with this particular constellation, they actually labeled things right to left and sort of didn’t worry about what was the brightest or not, so if you want to keep track of which is which, you start at the upper right-hand star and go around in a clockwise direction and you get alpha, beta, gamma, delta as you go around. So yeah there’s a bunch of stars, they’re not individually as spectacular as the stars in Orion. In Orion you have Betelgeuse and Rigel and it’s a party, but in The Big Dipper, Ursa Major, really it’s about the objects that are clustered around the constellation itself . Many of the most famous Messier objects — ones that you all recognize looking at pictures from Hubble — are all located in this one constellation.