Apogee Tide

An apogee tide is the reduced tide that occurs when the Moon is near apogee, its farthest point from Earth at about 405,500 km, where the lunar tide-generating force, which falls off as the inverse cube of distance, is at its monthly minimum. Because the force varies with the cube of distance, the apogee-to-perigee swing changes the lunar contribution by roughly 20 to 30 percent, so apogean tides have a smaller range than perigean tides. The effect is carried in harmonic analysis by the larger lunar elliptic constituent N2 (12.6583 h) beating against M2 over the 27.55-day anomalistic month. Apogean springs and neaps are correspondingly weaker than perigean ones.