June 1, 2009
The following is a explanation of spring and neap tides in relation to lunar and solar cycles.
Since antiquity, people have noticed that oceans exhibit a much greater tidal range around the time of the full Moon and new Moon. This is when the Moon and Sun are either together in the sky or are on opposite sides of the heavens. Higher tides occur during these Moon phases because the Sun also exerts a gravitational pull on our oceans, although it is only 46 percent as strong as the Moon's.
When the gravitational effects of the Sun and the Moon combine, we get spring tides, which have nothing to do with the season of spring. The term refers to the action of the seas springing out and then springing back. These are times of high high tides and low low tides.
A week later, during either of the two quarter Moon phases, when the Sun and Moon are at right angles to each other and their tidal influences partially cancel each other out, neap tides occur, and the tidal range is minimal. In fact, because the oceans take a bit of time to catch up to the geometry of the Moon, spring and neap tides usually occur about a day after the respective lunar cycles.
Now morn has come,
And with the morn the punctual tide again.
–Susan Coolidge, American writer (1835-1905)