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NOAA Ocean Facts: Why do we have spring tides in the fall?


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graphic showing full moon's orbit around Earth, demonstrating spring and neap tides

A spring tide refers to the 'springing forth' of the tide during new and full moon.

During full or new moons--which occur when the Earth, sun, and moon are nearly in alignment--average tidal ranges are slightly larger. This occurs twice each month. The moon appears new (dark) when it is directly between the Earth and the sun. The moon appears full when the Earth is between the moon and the sun. In both cases, the gravitational pull of the sun is 'added' to the gravitational pull of the moon on Earth, causing the oceans to bulge a bit more than usual.

These are called 'spring tides,' a common historical term that has nothing to do with the season of spring. Rather, the term is derived from the concept of the tide "springing forth." Spring tides occur twice each lunar month all year long, without regard to the season.

Seven days after a spring tide, the sun and moon are at right angles to each other. When this happens, the bulge of the ocean caused by the sun partially cancels out the bulge of the ocean caused by the moon. This produces moderate tides known as 'neap tides,' which also occur twice a month.


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