Lunar standstill

A lunar standstill or lunistice is when the Moon reaches its furthest north or furthest south point during the course of a month (specifically a tropical month of about 27.3 days). The declination (a celestial coordinate measured as the angle from the celestial equator, analogous to latitude) at lunar standstill varies in a cycle 18.6 years long between 18.134° (north or south) and 28.725° (north or south), due to lunar precession. These extremes are called the minor and major lunar standstills.

The last minor lunar standstill was in October 2015, and the next one will be in 2034. The last major lunar standstill was in 2006, and the next one will be in 2024.

At this time the northern lunistice occurs when the Moon is seen in the direction of Taurus, northern Orion, Gemini, or sometimes the southernmost part of Auriga (as at the time of a major lunistice). The southern lunistice occurs when the Moon is in Sagittarius or Ophiuchus. Due to precession of the Earth's axis, the northernmost and southernmost locations of the Moon in the sky move westward, and in about 13,000 years the northern lunistice will occur in Sagittarius and Ophiuchus and the southern lunistice in the area of Gemini.

During a minor lunar standstill, tidal forces are slightly increased in some places, leading to increased amplitude of tides and tidal flooding.^[1]

At a major lunar standstill, the Moon's range of declination, and consequently its range of azimuth at moonrise and moonset, reaches a maximum. As a result, viewed from the middle latitudes, the Moon's altitude at upper culmination (the daily moment when the object appears to contact the observer's meridian) changes in two weeks from its maximum possible value to its minimum possible value above the horizon, due north or due south (depending on the observer's hemisphere). Similarly, its azimuth at moonrise changes from northeast to southeast and at moonset from northwest to southwest.

The times of lunar standstills appear to have had special significance for the Bronze Age societies who built the megalithic monuments in Britain and Ireland. It also has significance for some neopagan religions. Evidence also exists that alignments to the moonrise or moonset on the days of lunar standstills can be found in ancient sites of other ancient cultures, such as at Chaco Canyon in New Mexico, Chimney Rock in Colorado and Hopewell Sites in Ohio.