ASK TOM: How does the moon control ocean tides?

Dear Tom,

How does the moon control ocean tides when there is no gravitational pull in outer space?

– Mel Dormer, Aurora


Dear Mel,

The pull of gravity DOES exist in outer space. It spreads outward equally in all directions from all astronomical bodies like the Earth, sun and moon. The Earth’s gravitational pull keeps the moon in its orbit around the Earth; the sun’s gravitational pull keeps the Earth in its orbit around the sun. Similarly, the moon’s gravity tugs on the oceans of the Earth and is a contributor (along with the sun’s gravity) to the ocean tides. Gravity is the force of attraction that two bodies exert on each other. Broadly speaking, the strength of the attraction depends on the mass of the bodies (the greater the mass, the stronger the attractive force) and the distance between them (the smaller the distance, the greater the attraction).