Beverly Blakey, age 11, of Ottawa, Canada, or her question:
How does the moon make the tides?
A high tide washes up on the beaches as the moon passes overhead. Each month the moon swells from a new born sliver to a golden coin and then shrinks again to a sliver. Each month we get the highest high tides when the moon is new and when the moon is full. Certainly the moon seems to be related to the tides .. but this does not explain the whole picture,
In the Space Age we hear a lot about gravitation, the built in pulling force which hugs us to the face of the earth. The moon, the sun and the planets each have their quota of gravity and this mighty force reaches out into space, getting weaker as it goes.
The gravity of the mighty sun is strong enough to hold the distant planets in their orbits. The gravity of our small planet is strong enough to hc1d the moon captive. The earth’s gravity is six times greater than the gravity of the moon. But the moon's gravity is strong enough to pull up the heaving tides on our watery oceans.
The moon pulls up a high tide as it passes overhead and this seems reasonable. The bulging high tide leaves a trough of low water on both sides and this also seems reasonable. The high tide pulled up by the moon comes between two low tides. But meantime a second high tide heaves up on the opposite side of the earth from the first or direct high tide.
This is not easy to understand and even the scientists are not sure they can explain it. Some suggest that the moon may pull the solid earth slightly away from the ocean water on the far side. Some say that the opposite high tide may sway back from the troughs of low tides. Some say that perhaps the water Jogs back and forth in the ocean basins.
When you tip a pail of water the surface heaves up on one side and then dogs back to heave up on the other side. Maybe all these and other factors work together to form the direct and opposite high. tides.
The moon passes overhead each day because the earth rotates on its axis and the direct high tide is followed by a low tide, an opposite high tide and another low tide. The moon rises fifty minutes later each night and for this reason the parade of tides is fifty minutes later today than it was yesterday.
In twenty seven and one third days the moon orbits the earth. Sometimes it is between us and the sun and sometimes we are between the moon and the sun. At such times the sun adds a boost to the moon’s gravity and the high tides are higher. Then the moon’s orbit takes it around to where the moon and sun pull at the earth from different directions. Then we have the lowest high tides of the month.