Since antiquity, people have noticed that the greatest difference between high and low tide is around New Moon and Full Moon. These tides are known as spring tides. When the tidal range is smallest, they are called neap tides. Learn more.
The Moon’s phase plays a role in the tides. During each phase, the Sun and Moon are in different places in the sky.
During the Full Moon and New Moon phases, the Sun and Moon are aligned. They combine gravitational forces to pull the ocean’s water in the same direction and high tides occur.
Many folks do not realize that the Sun also exerts a gravitational pull on our oceans, although it is only 46 percent as strong as the Moon’s.
Spring Tides
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.
If a spring tide coincides with either the March equinox or the September equinox, it is called an equinoctial spring tide. At this time, expect largest tidal range of the year because, at the equinoxes, the Moon and Sun are aligned with the equator.
Neap 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 the smallest.
The term neaps comes from Anglo-Saxon, meaning without the power.
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.
Neaps always occur about 7 days after spring tides.
Now morn has come,
And with the morn the punctual tide again.
–Susan Coolidge, American writer (1835-1905)
The Supermoon Effect
When the Full Moon or New Moon reaches its closest point to Earth, it’s called perigee. This is also referred to as a Supermoon and leads to even larger variation between high and low tides, known as perigean spring tides. The difference from a normal spring tide is around 5 cm or 2 inches.
The opposite happens when the Full or New Moon is around its farthest from Earth, apogee.The apogean spring tides are around 5 cm (2 inches) smaller than regular spring tides.
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