Debra A. Dobbins, age 9, of St. Louis, Missouri, for her question:

Who first figured out eclipses ahead of time?

The earliest astronomers were the Magi who lived in ancient Chaldea, south of Babylon. They watched the stars parade over the sky, and also the sun and the moon. And they marked their paths on charts. Naturally they marked every eclipse, when and where it appeared. Through the ages they noticed that eclipses follow each other in a set pattern. So they learned when to expect the next one ahead of time.

The Magi discovered that this pattern has around 30 eclipses of the moon and 40 eclipses of the sun. It takes 18 years and 11 days to finish    and then it repeats again. Thousands of years ago, they named this pattern of eclipses the saros, meaning repetition. Modern astronomers know that each saros moves westward, one third of the way around the globe. After three saros cycles, the pattern of eclipses returns to almost the same part of the world. So we can figure ahead of time that each eclipse will repeat overhead in about 60 years    or three saros periods later.