Gary Rinard, age 10, of Huntsville, Ala., for his question:

HOW DO THEY DETERMINE THE DATE OF EASTER?

Easter, as we know, is a movable date which varies from year to year. This year Easter fell on March 30. Last year the date was April 14, and next year it will be April 18. These changes are related to bright moonlit nights. This is not so strange as it may sound. For in 325 A.D., when the system was started, pilgrims to holy places needed a full moon to travel to Easter services.

The spring festival of Easter may fall as early as March 22 or as late as April 25. It all depends on the date of the first full moon that comes on or after March 21. Easter is the first Sunday that comes after this particular full moon. The date changes from year to year because the phases of the moon do not match the calendar.