by: Kathy A. Miles and Charles F. Peters II
Most people can point out the asterism known as the Big Dipper. No, the dipper is not a true constellation, rather it is an asterism, a familiar group of stars located within a constellation. The Big Dip is actually part of the constellation Ursa Major, the Great Bear. It is a group of stars that at our latitude, and anywhere north of here, is visible all night, every night of the year. That makes it handy for things like telling time, and with some practice, you can gauge time to within 30 minutes by observing the Dipper.
The scale of the universe is so immense that it is difficult to imagine the relative distances between celestial objects. The Sun, the Moon, the planets, the stars, and the galaxies - they all seem like distant objects in the sky. It is easy to just think of them all as being very far away, without giving much thought to the great differences in their distances from Earth. In order to grasp the diversity in true distances in the universe it helps to mentally scale things down - to compare with objects and distances we can understand. How far away would these objects be if the Earth, which is actually about 8,000 miles in diameter, were the size of a grape, or about one half inch in diameter.