Mizar and Alcor

This month look for the stars, Mizar and Alcor. Mizar is the star that forms the bend in the handle of the Big Dipper. Look carefully at this star and you’ll probably notice that it has a fainter companion star very close to it. The name of the companion star is Alcor and it is located at an angle directed away from the direction handle bend. Use a pair of binoculars if you’re not certain that you can see the fainter Alcor. To me, the distance between the two stars is close to the angle that 1/8th of an inch spans when viewed at arm’s distance. It may be hard to believe, but that gives Mizar and Alcor an angular separation close to ½ the diameter of the moon. When you look at Mizar with even slight optical aid, get ready for another surprise; Mizar is a double star. In 1650, Mizar was the first double star that astronomers discovered.

Mizar is over twice as massive as our sun and Alcor is over 50% heavier than our sun.             The pair is located between 78 and 81 light years from the earth (the distance is uncertain). Therefore, if you were born between 1935 and 1932, Mizar and Alcor are your birthday stars this year. The actual distance between Mizar and Alcor may be anywhere between ¼ to over three light years. Therefore, it’s possible that these two stars are not actually in orbit around each other. However, if they are in orbit around each other, then their orbital period may be in the hundreds of thousands of years.       

What we call The Big Dipper is not a true constellation; it is a part of the constellation of Ursa Major or the Big Bear. The constellation of the Big Bear passes high over the north during May evenings. This means that during April evenings, the Dipper is upside down and pouring its contents on the Earth below.