Tides are the gradual daily rise and fall of the ocean over a large area caused mainly by the gravitational pull of the Moon. In most coastal areas, there are two high tides and two low tides every day. It takes about 6 hours for the ocean to go from high tide to low tide.

The difference in height between high and low waters over about half a day varies in a two-week cycle. About twice a month, around new moon and full moon when the sun, moon and Earth are lined up in a row, the tidal force due to the sun reinforces the tidal force caused by the moon. The tide is then at its maximum: this is called the spring tide.

When the moon is at first quarter or third quarter, the sun and moon for a 90° with respect to the Earth, and the solar tidal force partially cancels the lunar tidal force. At these points in the lunar cycle, the tide is at its minimum: this is called the neap tide.

There is a one week (approximately) interval between spring tides and neap tides.