MOON AND TIDES

MOON AND TIDES Tides are defined as slight oscil­lations of sea level that occur approximately twice a day and attain exaggerated proportions 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 earth to produce tides, the moon, by nature of its closeness to the earth has a greater control over the timings of the" tidal rises and falls.

Lunar Tides As the moon travels in its orbit in the same direction as the earth's rotation, a period of 24 hours, 50 minutes elapses between two successive occasions when the moon is vertically above a point. The highest level the water reaches is called a high tide and the lowest level is called a low tide. High and low tides occur twice each during the period of 24 hours, 50 minutes, giving an interval of about 121h hours between successive high (or low) tides.

Under the influence of the moon, water at H2 is pulled towards the moon more than towards the earth and therefore water piles up at H2 forming a high tide. The earth is pulled towards the moon more than the water at Hl; therefore water lags behind and piles up at Hl forming a high tide. The moon's pull causes water to be drawn from Ll and L2; therefore there are low tides there.