Lunistice

The last major lunar standstill was in June 2006, and the next one will be in April 2025. Presently the northern lunistice occurs when the moon is in Taurus, northern Orion, Gemini, or sometimes the southernmost part of Auriga . 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 solistice 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. In a year of a major lunar standstill, solar eclipses occur in March at ascending node and in September at descending node, whereas lunar eclipses at descending node occur in March, lunar eclipses at ascending node occur in September. In a year of a minor lunar standstill the situation is reversed. 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. 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 Chimney Rock in Colorado and Hopewell Sites in Ohio. A major lunar standstill occurs when the Moon's declination reaches a maximum monthly limit, stopping at 28.725° north or south. An eclipse season near the March equinox has solar and lunar eclipses at an odd-numbered saros, while another eclipse season near the September equinox has solar and lunar eclipses at an even-numbered saros. A minor lunar standstill occurs when the Moon's declination reaches a minimum monthly limit, stopping at 18.134° north or south. An eclipse season near the March equinox has solar and lunar eclipses at an even-numbered saros, while another eclipse season near the September equinox has solar and lunar eclipses at an odd-numbered saros. The term lunar standstill was apparently first used by engineer Alexander Thom in his 1971 book Megalithic Lunar Observatories. The word tropic, as in Tropic of Capricorn, comes from ancient Greek meaning "to turn", referring to how ascending motion turns to descending motion at the solstice. As Earth rotates on its axis, the stars in the night sky appear to follow circular paths around the celestial poles. Since Earth's rotational axis is tilted by about 23.5° with respect to a line perpendicular to its orbital plane , the Sun's declination ranges from +23.5° at the June solstice to ?23.5° at the December solstice, as the Earth orbits the Sun once every tropical year. Therefore, in June, in the Northern Hemisphere, the midday Sun is higher in the sky, and daytime then is longer than in December. Consequently in under a month, the Moon's altitude at upper culmination can shift from higher in the sky to lower above the horizon, and back. Thus the Moon's declination varies cyclically with a period of about four weeks, but the amplitude of this oscillation varies over an 18.6 year cycle. A lunar standstill occurs at the points in this latter cycle when this amplitude reaches a minimum or a maximum. The Moon differs from most natural satellites around other planets in that it remains near the ecliptic instead of Earth's equatorial plane.