Debbie Riffee, age 12, of St. Albans, W. Va., for her question:

Do other planets have day and night?

A planet, of course, gives off no light of its own. It shines with the reflected glory of the sun, and its shiny side is bathed in daylight. It is a solid round globe, and so far as we know each planet spins around its axis, in some cases faster and in some cases slower than our world rotates on its axis. As it rotates, each planet turns to one side, then another side to face the sun.

The side facing the sun is in daylight, and as the planet rotates, this side turns to face the darkness of the night sky. The opposite side then rotates into the sunshine. The length of each day depends upon the time of each rotation. The Martian day equals 24 Earth hours, but on fast spinning Jupiter the day and night period is over in 10 hours.