Double Your Viewing

Test Your Eyes with Alcor and Mizar

The Big Dipper as seen from Kalalau Valley, Hawai'i. Courtesy User: gh5046; used under a Creative Commons ShareAlike License. on Wikipedia.

The Big Dipper is one of those constellations we all learn (in the Northern Hemisphere) pretty early on. It’s easy to spot, it’s a shape that most of us recognize — even if some of us in Europe and other regions call it a Plough. It’s a pattern that we use to teach people how to find other things in the sky, such as the star Arcturus or the North Star (Polaris).

Of course, the Big Dipper is part of a larger constellation called “Ursa Major” which is Latin for “Greater Bear”.  The Dipper forms the back and tail of the Bear, and there are tales across many of the world’s cultures about this Bear and its exploits.  Most of us don’t look for all the stars of the bear, preferring to concentrate on the Dipper itself.

If you look at the Big Dipper’s handle, there’s a double star you can spot with your  naked eye (provided you have a good dark viewing area).  If you live in a city, you can probably spot the double with binoculars or a small telescope.

Those two stars are called Alcor and Mizar and for many years, people would use the ability to spot these two without magnification as a test of their eyesight.  They lie about a light-year apart and they are moving together through space as part of a larger group of stars called the Ursa Major Moving Group.

As it turns out, when you look at Alcor and Mizar, you’re looking at a six-star system. Alcor itself is actually two stars called Alcor A and B, and Mizar is really a system of two binary stars (making four total stars for Mizar).   It’s worth checking out and the weather this time of year is great for kicking back and seeing if YOU can make out Alcor and Mizar with your naked eye. (You won’t find the other stars without some major magnification, but that’s okay.  The objective here is to see what you can find just by taking a gander at the bend in the Dipper’s handle. Check it out!


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