In order to understand the phenomenon called a 'perigean spring
tide,' you first have to know that the gravitational pull of the
moon and the sun cause tides. Tides are actually long-period
waves that roll around the planet as the ocean is 'pulled' back
and forth as the moon and the sun interact with the Earth in
their monthly and yearly orbits. The next thing you need to know
is that the moon follows an elliptical path around the Earth in
its monthly orbit, and the Earth follows an elliptical path in
its yearly orbit around the sun. This means that, at times, the
moon and the sun are closer to Earth. At other times, they are
farther away. What happens when the moon and the sun are close
to the Earth? You guessed it: the gravitational pull they exert
is stronger, resulting in slightly higher tides. While both the
moon and the sun influence tides, the moon plays a much larger
role because it is so close to the Earth. Its gravitational pull
is about twice as strong as that of the sun. Now consider these
two cas