Mark Meyer, age 10, of Washington, Illinois, for his question:
How close are the stars of the Big Dipper?
As a rule, the see only the seven brightest stars of the Big Dipper, though there also are 14 other ones in the famous constellation. These shy ones form the head and parts of the bulky bear shape known as the Big Bear, alias Ursa Major. Our seven Big Dipper stars form his rump and his long curved tail. That tail qualifies the Big Bear as an imaginary superstar. Earthly bears have stubby little tails not worth mentioning.
Stars and other celestial objects seem to do their best to fool our eyes. We can't trust our eyes to measure the distances between them in degrees of sky distance. For example, the two pointer stars of the Bid Dipper are about five degrees apart, which is ten times as wide as the full moon.
Even in the sky, objects tend to shrink with distance. So me might guess that some stars in the Big Dipper are closer to us because they appear bigger and brighter. However, astronomers discredit this sort of guessrrork. Patiently they use complex methods to measure the true sizes and distances of separate stars. what appears to be a big bright star just might be a smallish neighbor. Or it might be a distant whopper.
Separate stars also move hither and thither at fantastic speeds. But space is so vast that we could observe only slight changes in 1,000 years. The Big Dipper stars prove to be enormous distances from us and from each other. The figures may vary in different books because astronomers constantly recheck and correct their measurements.
We must eye the Big Dipper stars one by one, so let's use the common Arabic names they have had for 1,000 years or more. The sparkler at the tip of the handle is Alkaid. The distance of this bright, white whopper has been estimated as 210 light years. Each light year equals about 27 million million earth miles.
Next in line, from our point of view is Mizar/Alcor a very famous binary star systen. Its distance from us is 30 light years which is a giant stride of 130 light years from Alkcaid. The third star in the candle is Alioth, tagged at a distance of 68 light years. The second pointer star, at the lip of the bowl, is big; bright Dubhe, also about 6:3 light years from the earth.
Merak is the first pointer, at the base of the bowl. In the other corner is Phecda. Dimmer Megrez joins the handle to the bowl. These stars also are different distances from the earth and from each other.
Five of the seven stars belong to a moving cluster, traveling in more or less the sane direction. Allcaid and Dubhe are going; in the opposite direction. By 100,000 A.D., these stars will have turned the Big nipper upside dorm. Long before that, light years will be added or subtracted to the distances of the seven stars. Some may be closer, others will be farther from us and each other.