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Concept
Lunar standstill
Résumé
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 draconic month of about 27.2 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 May 2034. The last major lunar standstill was in June 2006, and the next one will be in January 2025.
Presently the northern lunistice occurs when the moon is in 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.
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.
Source officielle
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