Geography - The Moon and Tides
Tides are defined as slight oscillations of sea level that occur approximately twice a day and attain exaggerated proportion in marginal seas, straits and estuaries. The major cause of the tides is the gravitational pull of the moon and the sun. Though both the sun and the moon exert gravitational force on the earth to produce tides, the moon, by nature of its closeness to the earth has a greater control over the timing of the tidal rises and falls.
Perigean and Apogean Tides