Earth tide lunar and the solar tidal maxima and minima (bulges and depressions) add together for the greatest tidal range at particular latitudes. At first- and third-quarter phases of the moon, lunar and solar tides are perpendicular, and the tidal range is at a minimum. The semi-diurnal tides go through one full cycle (a high and low tide) about once every 12 hours and one full cycle of maximum height (a spring and neap tide) about once every 14 days. The development of a systematic theory of Earth tides was started by George H. Darwin in 1879, and was then furthered by
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.