Len Boesman, age 12, of Shreveport, Louisiana, for his question:

Where does the water go at low tide?

The heaving tides must be viewed on a global scale. This is a watery world, where oceans cover three Quarters of the surface. Two high and two low tides occur during a calendar day, but this parade of ups and downs chases around the globe. As this happens, the level of the world ocean is heaved up and lowered several feet. After the low tide recedes from your favorite beach, your local part of the ocean begins to rise with the next high tide.

This global parade of humps and troughs is, of course, governed by the moon and the rotating earth. As the moon passes overhead, its gravity heaves up a high tide in the ocean below it. This huge hump of water leaves a trough of low water on both sides. It also causes the ocean to heave up a matching high tide on the opposite side of the earth. The level of your local ocean merely lifts and sinks as the tidal parade sweeps around the globe.