Perigean spring tide Perigean spring tide A proxigean spring tide (also known as a perigean spring tide) is a tide that occurs three or four times per year when the Moon's perigee (its closest point to Earth during its 29.5-day elliptical orbit) coincides with a spring tide (when the Earth, Sun and Moon are nearly aligned every two weeks). This tide usually adds only a couple of inches to normal spring tides. The Moon's orbit around Earth is elliptical, which causes the Moon to be closer to Earth and farther away at different times. The Moon and the Sun are aligned every two
Full moon the first full moon of 2000. The true time of a full moon may differ from this approximation by up to about 14.5 hours as a result of the non-circularity of the moon's orbit. See New moon for an explanation of the formula and its parameters. The age and apparent size of the full moon vary in a cycle of just under 14 synodic months, which has been referred to as a full moon cycle. Full moons are traditionally associated with temporal insomnia (inability to sleep), insanity (hence the terms "lunacy" and "lunatic") and various "magical phenomena" such as lycanthropy.