Stevie Raines, age 9, of Asheville, North Carolina, for his question:

How is the year measured?

As you know, our dizzy old world spins around like a top    while it circles a huge orbit around the sun. Each spin around gives us one calendar day and night. Each swing around the orbit gives us a year. The distance around the orbit is about 600 million miles and the earth whizzes around it at about 66,000 miles per hour. Astronomers check our progress by measuring where the sun happens to appear in the sky. This way they know when one yearly orbit is finished and the next one begins.

You might think that the apparent route of the sun over the sky is the same every day. But actually the path of the sun as seen from the earth is a little different every day of the year. This tells astronomers how far the earth travels around its orbit. They measure the path of the sun on the first day of spring. When this pattern is repeated again, they know that the earth has been all the way around its yearly orbit. The time it takes is about 365 days, 48 minutes and 46 seconds.