our logo


fairly stable data

Received: 01Jan1958

Yin And Yang Forces

As I understand it, there are a number of forces which combine to create tides. The table below summaries the most important forces and their relative amplitude.

VariableSymbolPeriod (solar hr)AmplitudeDescription
Semidiurnal tides
(two tides per day)
M212.42100Main lunar semidiurnal constituent
S212.0046.6Main solar semidiurnal constituent
S212.6619.1Lunar constituent due to monthly variation in the moon's distance
S211.9712.7Solar-lunar constituent due to changes in declination of Sun and Moon throughout their orbital cycle
Diurnal tides
(one tide per day)
K123.9358.4Solar-lunar constituent
O125.8241.5Main lunar diurnal constituent
P124.0719.3Main solar diurnal constituent
Long-period tidesM1327.8617.2Moon's fortnightly constituent

Hasn't Changed Much Lately

I got this stuff from Groliers; they got it from a book printed in 1958. I'll bet all these constituents and others whose amplitude is less than 12.7, are predictable for as far in the future as you want. - JR


Most scientist who study such things have concluded that us humans would not exist without the after-effects of the collision that formed the moon.