Thread: Spring Tides
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Old November 29th 05, 01:49 AM posted to uk.rec.sailing,uk.sci.astronomy,alt.astronomy
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Default Spring Tides

Wasn't it Ronald Raygun who wrote:
Sjouke Burry wrote:

Yokel wrote:
I cannot remember seeing a full explanation, but the main cause is most
likely to be the eccentricity of the moon's orbit. The moon's distance
from us varies significantly through the month and this would result in a
variation of the gravitational force which produces the tides.


There also is a suntide , and you have to add both,
that gives you all sorts of levels, because they are
not in sync(sun 1 day, moon 1/28th different).
Suntide is moontide, so the summ is mainly locked
to the moon.
I do not think that the shape of the moon orbit
has much influence.


The shape of the moon's orbit has an enormous influence because
it means there is a significant variation in the Earth/Moon
distance. The tidal force in inversely proportional to the
cube of the distance, and the contribution due to eccentricity
is nearly half as strong as the contribution from the sun.


So I'd therefore expect the strength of the spring tide force to be
seasonal. The strongest force occurring at spring tides which occur near
lunar perigee. That would be at new moon in February and full moon in
August. At February new moon, the Earth is closer to perihelion, so the
solar tide would be slightly enhanced, making that the biggest tidal
force of the year.

--
Mike Williams
Gentleman of Leisure