How do the moon’s phases influence the tide on Earth?
In: Physics
Most of the tides are due to the moon, but about a third of the tides are due to the sun. At full moon and new moon the tides from both the sun and the moon are working together and so they’re more extreme. These are called “spring” tides (no relation to the season of the same name). When the tides from the sun and the moon are not working together, as at first and last quarter, the tides are less extreme. These are called “neap” tides.
The phases of the moon are linked to the way the sun and moon are aligned in the sky. If the sun and moon are in the opposite parts of the sky then we see the side of the moon that’s fully lit by the sun: full moon. If the sun and the moon are close together in the sky then we see the side of the moon that’s unlit by the sun: new moon. In both of these two cases, the sun, earth and moon are roughly in a line and the tidal forces add.
Very roughly, there’s a high tide on the part of the earth that’s nearest the moon as well as on the part of the earth that’s farthest from the moon. That’s why most places have two tides on most days, and why the sun and moon are working together when they’re on opposite sides of the sky.
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