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Nancy DiTucci, age 12, of Somerville, Massachusetts, for her question:

What is the diameter of Polaris?

We see Polaris across some 680 light years and from this distance you might suppose it to be no bigger and brighter than our own sun. Actually it is a binary system of a large and small star and we see them as one. The dominant one is classified as a "F" type star, somewhat similar to Procyon. The diameters of stars in this class average about 2 1/2 times wider than the sun, which is some 860,000 miles through the middle. Hence the diameter of Polaris must be somewhat greater than two million miles.

The "F" type stars are not only larger than the sun, but also hotter and brighter, though their gases are less dense. Polaris is about 1,000 degrees hotter than the sun and in brilliance it equals 3,000 sun type stars. However, its lighter gases make it less massive and our much smaller sun weighs almost as much as big, bright Polaris.

 

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