David Guichard, Age 9, of Menlo Park, Calif., for his     question:

What is the Meaning of a.m. and p.m.?

The face of a clock shows only 12 hours, but a calendar day is 24 hours long. The hands of a clock must move around twice to show one calendar day. The first round trip is the a.m. Part of the day and the second round trip is the p.m. Part of the day. The a.m. Trip runs from midnight to noon. The P.M. trip runs from noon to the next midnight.

The letter M stands for meridian, which Means noon. At this Moment, the sun reaches the highest point it will climb in the sky. The letter A stands for ante, which Means before. The a.m. Trip around the 12 hour clock records the ante meridian or morning hours. The P.M. trip records the post meridian or afternoon hours of the calendar day.