More than half of the stars that we see in the sky are actually double stars - that is, two stars, or suns, in each other's gravitational field, rotating around each other. If we lived on a planet in such a solar system we would see two suns in the sky! They might both be in the sky at the same time, or, they might alternate so there would never be any night. What a strange world this would be.The most famous double star system, because it was the first one discovered, is made up of the stars Mizar and Alcor in the Big Dipper. It is the second to the last star in the handle of the Big Dipper (at the bend of the handle). Some claim they can actually see both stars with the naked eye on very clear nights away from city lights. It is clearly visible with binoculars. In ancient times it was a mark of excellent vision to be able to see both stars.
Modern astronomers discovered these two stars were not a double star system at all; they were too far apart and were not rotating around each other. They were only line-of-site doubles - stars that appear close to each other only because of the angle from which we on Earth see them.
However, much to astronomers' surprise, when they first looked at Mizar/Alcore with a high powered spectroscopic telescope, they discovered that each of the two stars is itself an actual double star system.
So, Mizar/Alcor, which most people see as one star. . . and some see as two stars. . . is actually four stars - two pairs of double stars.
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Send suggestions, astronomy tips, corrections or comments to Pete Harris
via e-mail at odyssey@ccnet.com. Pete is also the creator of the website
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