File:Lunistices in 2006.png
Lunistices_in_2006.png (605 × 340像素,文件大小:28 KB,MIME类型:image/png)
摘要
描述Lunistices in 2006.png |
English: Absolute value of declination for lunistices in 2006, a year of a major lunistice. At the bottom are shown the times of phases and ecliipses. The declination of the lunistices follows a 18.6-year cycle, but with a small 173-day perturbation. The graph shows that in the short term, this perturbation causes much greater changes in declination than the slow change due to moving around the 18.6-year cycle. These perturbations peak when the sun is lined up with the moon's nodes, which is also near the times when eclipses occur. So there are always eclipses, lunar and solar, near the time of the major lunistices, when the moon reaches its furthest north or south point of the 18.6-year cycle, as well as near minor lunistices, when the declinations are closest to zero. These major and minor lunistices occur when the moon's node is near an equinox direction (right ascension 0° or 180°). This means that when the sun lines up with the nodes it is also near an equinox direction, and therefore the major and minor lunistices occur near the moments of the vernal or autumnal equinoxes. If the moment of the sun lining up with the nodes is more than two or three weeks away from an equinox, then the major or minor lunistice will occur around a later or earlier equinox.
Within two weeks before or after the moment of the sun lining up with the nodes there will be both a lunar and a solar eclipse (two weeks apart). About one week after the solar eclipse, in the spring, or three weeks before it, the moon will arrive at right ascension 90° and one of these will be the northern lunistice. In the autumn, this will be about one week before or three weeks after the solar eclipse. In any case, this will happen within about half a month of the sun lining up with the nodes, which as said will be within a couple of weeks of the equinox. The same goes for the southern lunistice.
In 2006, the moment when the node crossed zero right ascension was in June, but the furthest north lunistices were in early April and in mid-September, near the equinoxes, as seen in the graph. Likewise, the furthest south lunistices were in late March and late September.
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来源 | 自己的作品 |
作者 | Eric Kvaalen |
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当前 | 2024年3月9日 (六) 19:37 | ![]() | 605 × 340(28 KB) | Eric Kvaalen | Added more periodic terms. |
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