How to spot Mercury, Venus, Mars, Jupiter and Saturn etc and the annual Perseid meteor shower. Tonight, notice the 2 outer stars in the bowl of the Big Dipper – Dubhe and Merak. They always point to Polaris, the North Star. To find the Dipper at this time of year, look toward the NW in the evening. Once you’ve found it – after locating Polaris – look more carefully at the second star from the end of the Big Dipper’s handle. If your sky is dark enough, and your eyesight is good, you’ll see that this star, Mizar, has a nearby companion, called Alcor.
Arabian stargazers referred to Mizar and Alcor as the “horse and rider.” These stars are a good test of the night’s viewing conditions: if you can’t see Alcor, there might be thin clouds up there.
These two stars are what’s called “naked-eye double star,” appearing double from our earthly vantage point. But do they orbit each other? Astronomers aren’t sure. The distances to these stars (as to most stars) aren’t precisely known. If Mizar and Alcor make up a true binary star, it’s a very wide one. If they do lie at the same distance from Earth, their separation is 0.27 light-years … that’s in contrast to 8 light-minutes for Earth’s distance from our sun … or several light-hours for the distance to our sun of the most distant worlds in our solar system. Still, it’s possible that Mizar and Alcor could be this far apart and still be orbiting one another, with a very long orbital period of three-quarters of a million years.
For more summertime skywatching tips, visit https://nightsky.jpl.nasa.gov/index.cfm
http://earthsky.org/tonight/dipper-to-polaris-plus-mizar-and-alcor
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