Welcome to You Ask Andy

Bruce Fort, aged 14, of Wichita, Kansas for his question:

What is the smallest star?

Sirius, the Dog Star, has been studied for thousands of years. It is the most brilliant star ever seen from the earth. On a winter's night it sparkles for us like a diamond in the sky. North of the equator, Sirius is the nearest star in the night sky. The light from Sirius, traveling at 16,000 miles each second, reaches us in 8.9 years. The sun and Sirius are almost 53 trillion miles apart ‑ which is fairly close for star neighbors.

Long, long ago it was noticed that the Dog Star seemed to turn in an orbit. In 144, figures were worked out. Sirius seemed to be curling around an invisible companion. Then, in 162, a new 19 inch telescope was being tested at the University of Mississippi. The Dog Star's companion was seen for the first tire. Naturally it was named the Pup.

Lots of information has been gathered about the Pup since that time. Great Sirius is 27 times brighter than our sun. The Pup is only one tenth as bright as our sun. No wonder the bright Dog Star outshone it for so long: Because of its paleness, the Pup was thought to be a cool star. Then someone took its temperature.

Our sun has a surface temperature of about 6000 degrees Centigrade. The Pup has a surface temperature of 8000 degrees. So instead of being a red hot star, the Pup is a white hot star. But when it comes to size, the Pup is truly a midget among stars.

The diameter of our sun is some 866,500 miles. The diameter of Sirius is one and half million miles ‑ almost twice that of the sun. The little Pup has a diameter of only 2,000 miles. In size the Pup is about as big as a large planet. It has been compared in size with our planet Uranus. The sun has room enough to gobble up almost a million stars of the size of the Pup.

But , what it la eke in s i ze, the Pup makes up for in we fight. The little star weighs almost as much as our sun. A cubic foot of the Pup's material weighs as material weighs as much as 27,000 cubic feet of the sun's material. Suppose you could fill a quart milk bottle with material from the Pup. That bottle would weigh over fifty tons;

Stars have been graded according to size, weights and brilliance. The giants and supergiants are made of soft, woolly light gases. Our sun is an average star. The Pup is at the small end of the starry scale. It is called a white dwarf star. All white dwarf stars are small, hot and heavy. The Pup may not be the smallest white dwarf star in the sky. But it is one of the smallest. And it is the one we know most about. If there are any smaller stars, They are not too different from the white dwarf which tae call the Pup.

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