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The difference between high tide and low tide peaks when the moon is full and also when the moon is new. At both of these points in the lunar cycle, the tides are known as "spring" tides.

On average, is the difference between high tide and low tide greater at new moon or at full moon, or is it about the same at one as it is at the other?

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  • $\begingroup$ It really depends on where the moon is in its orbit - apogee or perigee. $\endgroup$
    – WarpPrime
    Dec 17, 2021 at 15:31

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According to NOAA's ocean service division:

The elliptical orbits of the moon around the Earth and the Earth around the sun have a substantial effect on the the Earth’s tides. Once a month, at perigee, when the moon is closest to the Earth, tide-generating forces are higher than usual, producing above average ranges in the tides. About two weeks later, at apogee, when the moon is farthest from the Earth, the lunar tide-raising force is smaller, and the tidal ranges are less than average. When the Earth is closest to the sun (perihelion), around January 2 of the calendar year, tidal ranges are enhanced. At aphelion, when the Earth is furthest from the sun, around July 2, tidal ranges are reduced (Sumich, J.L., 1996; Thurman, H.V., 1994).

See the two diagrams below for clarity.

forces from the sun and moon

Earth orbit and moon orbit vs tides

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    $\begingroup$ It's true that a perigean spring tide will have a slightly greater high-low difference than an average spring tide, both when the moon is full and when it is new, but this doesn't answer the question, which assumes that perigean and apogean effects are averaged out. The question only concerns the moon-phase cycle (which has a much larger effect on tides than the perigee and apogee cycle and in any case is not synchronised with it). $\endgroup$
    – ool
    Dec 17, 2021 at 16:35
  • $\begingroup$ potentially some helpful resources available at Why do some location on Earth have only one tidal maximum per day instead of two? $\endgroup$
    – uhoh
    Dec 18, 2021 at 5:27

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