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Both the gravitational field of the sun and the moon affects all fluids on earth; the sea and the atmosphere. The moon, being close, accounts for roughly 70 percent of the effect.
Since the moon orbits around the earth in 24 hours and 50 minutes, the tide follows that frequency but since the water moves harmonically to and fro, it occurs mostly twice per day, around the world. It is then called the semi-diurnal tide. The difference between two low waters it then, roughly 12 hours and 25 minutes. At low tide, the water starts rising again. The speed at which it does it is, actually, a sinusoid but seafarers use the rule of thumb: 1-2-3-3-2-1 to calculate the actual height of the tide in hours after the low tide. For example, two hours after the low water, the height will be 1+2 = 3/12 of the actual tidal difference.
Note that the tide is higher during the spring tide; at the new moon and the full moon, when the sun and moon are on the same or opposite sides. Also note that the actual tide may vary from place to place, due to local effects like the estuary of a river or very shallow waters.
Since the moon orbits around the earth in 24 hours and 50 minutes, the tide follows that frequency but since the water moves harmonically to and fro, it occurs mostly twice per day, around the world. It is then called the semi-diurnal tide. The difference between two low waters it then, roughly 12 hours and 25 minutes. At low tide, the water starts rising again. The speed at which it does it is, actually, a sinusoid but seafarers use the rule of thumb: 1-2-3-3-2-1 to calculate the actual height of the tide in hours after the low tide. For example, two hours after the low water, the height will be 1+2 = 3/12 of the actual tidal difference.
Note that the tide is higher during the spring tide; at the new moon and the full moon, when the sun and moon are on the same or opposite sides. Also note that the actual tide may vary from place to place, due to local effects like the estuary of a river or very shallow waters.