Randy Laird, age 10, of Richmond., Va., for his questions

What is a neap tide`'

Two high tides and two low tides are forever following each other around our globe. Most of this rise and fall of the ocean is caused by the pull of the moon's gravity. But the sun also helps, though its pull is not so strong because it is so much further away. Sometimes the moon and the sun pull together and sometimes they pull in opposite directions.

This happens because the moon orbits the earth. When the moon is new or full, the sun, moon and earth are in a straight line. The sun and moon pull at the earth together and we get very high tides. We call them spring tides. When we see the half moon, the moon is at one side or the other of its orbit. The sun and the moon are then pulling at the earth from opposite directions and some of the moon's pull is cancelled out. We then get low high tides, which are called neap tides. Each month we get two spring tides and two neap tides.