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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Eclipse cycle | 5/12 | https://en.wikipedia.org/wiki/Eclipse_cycle | reference | science, encyclopedia | 2026-05-05T11:12:34.827205+00:00 | kb-cron |
Metonic cycle or enneadecaeteris Nearly 6940 days, but as an eclipse cycle can be taken as 235 synodic months. This is just an hour and a half less than 19 years of 365+1⁄4 days. It is also 5 "octon" periods and close to 20 eclipse years, so it yields a short series of four or five eclipses on the same calendar date or on two calendar dates. It is equivalent to 110 "hollow months" of 29 days and 125 "full months" of 30 days. Twenty four Metonic cycles of 235 months makes an eclipse cycle of 456 years, equivalent to 17 inex periods minus two saros periods. Semanex Equal to a whole number of weeks plus a hundredth of a day, so consecutive eclipses of the cycle are usually on the same day of the week. Each eclipse in this period is a member of a preceding saros series, always occurring on alternating nodes. Thix This eclipse cycle, which seems to have been known in Maya astronomy, is about one day more than 36 260-day tzolk'ins (the basis of the Maya calendar). The name was suggested by Charles H. Smiley in 1973 from the fact that it is around thirty six tzolk'ins. Inex Very convenient in the classification of eclipse cycles. One inex after an eclipse, another eclipse takes place at the opposite latitude. Inex series, after a sputtering beginning, go on for many thousands of years giving eclipses every 29 years minus 20 days, or 21 days if the last year has 366 days. Eighteen inex cycles (see "Basic period") are equal to 520.9996 Julian years so an inex is 28+17/18 Julian years. The inex cycle is the cycle that produces the highest number of eclipses while it lasts. Inex series 30 first produced a solar eclipse in saros series -245 (in 9435 BC), has been producing eclipses every 29 years since saros series -197 (in 8045 BC), and will continue long past AD 15,000, by which time it will have produced 707 consecutive eclipses. The name was introduced by George van den Bergh in 1951. Exeligmos A triple saros, with the advantage that it has nearly an integer number of days, so the next eclipse will be visible at locations near the eclipse that occurred one exeligmos earlier, in contrast to the saros, in which the eclipse occurs about 8 hours later in the day or about 120° to the west of the eclipse that occurred one saros earlier. Ptolemy in the Almagest mentions it after discussing what we now call the saros, and says that it is called the exeligmos (ἐξελιγμός, meaning "unrolling"). Aubrey cycle Named for the supposed calculation of eclipses measured with Aubrey holes, located at Stonehenge. With 1385 fortnights, eclipses alternate between lunar and solar in 56 years minus 3.5 days. Unidos Very close to 65 years. Equals 67 lunar years and exceeds 65 Julian years by only 1.3 days (1.8 days over 65 average Gregorian years). Name suggested by Karl Palmen in that 2 saros are added over an inex. A period of three Unidos (195 years, a "Trihex") is quite close to both a whole number of anomalistic years and a whole number of anomalistic months, which means the interval between two eclipses is quite constant. Callippic cycle Originally defined as 4 Metonic cycles minus one day or precisely 76 years of 365+1⁄4 days. In the table, taken as 940 synodic months, equivalent to 441 hollow months and 499 full months. This cycle, though useful for example in the calculation of the date of Easter, can produce at most two solar eclipses (both partial) and at most two lunar eclipses (both penumbral). The Callipic cycle is 20 octons, and series of octons often produce only 21 eclipses, so only the first and the last of such a series are separated by a Callipic cycle. Most eclipses are not followed by another eclipse 940 lunations later, but rather 939 lunations later (two inex and a saros), which comes near an integer number of draconic months, producing similar eclipses. This is called a Short Callippic Period. Triad A triple inex, with the advantage that it has nearly an integer number of anomalistic months, which makes the circumstances between two eclipses one Triad apart very similar, but at the opposite latitude. Almost exactly 87 calendar years minus 2 months. The triad means that every third saros series will be similar (central eclipses mostly total or mostly annular for example). Solar saros 127, 130, 133, 136, 139, 142 and 145, for example, all produce mainly total eclipses when they are central, because the moon is close to perigee. In fact, at the solar eclipse of October 17, 1781, which was in saros series 130 and inex 50, was both very central and at perigee. But this repetition is not perfect. About 2460 years later, the above-mentioned series, 130, 133... (equivalent to 1 modulo 3) will give central solar eclipses that are annular, near apogee. About 820 years later (around AD 2610) central lunar eclipses, but not solar ones, will be near perigee every three saros series, and after 1640 years (around AD 3420) the solar saros series with index equivalent to 2 modulo 3 will give central eclipses near perigee. Quarter Palmen cycle Named after Karl Palmen in that a saros is subtracted from 4 inex. Each eclipse is followed by an eclipse 4 saros series later, always occurring at the same node. It equals 97 years 9 months or 1209 lunations. Mercury cycle Equals approximately 353 synodic periods of Mercury, so that eclipses synchronize with the timing of Mercury's position in its orbit during each period, equaling 112 years minus one week or 1385 lunations. Tritrix Equals 3 inex plus 3 saros, which is 140 years 11 months or 1743 lunations, always occurring on alternating nodes. The tritrix is very close to a whole number of anomalistic months ((1867.9970) and close to a whole number of anomalistic years, which means the interval between two eclipses is quite constant. Two tritrix minus a saros (3263 lunations) is even closer to a whole number of anomalistic months (3497.0018), being exactly thirteen seventeenths of the Cycle of Hipparchus (see below). de la Hire cycle A sextuple inex, adopted by Phillippe de la Hire in his Tabularum Astronomicarum in 1687. It equals 6 inex periods, which is 173 years and around 8 months, or 2148 lunations, equaling 179 lunar years, always occurring on the same node at nearly an integer number of anomalistic months, as it equals 2 triads. Trihex Equals 3 inex plus 6 saros, lasting 195 Julian years and 4 days or 2412 lunations, equaling 201 lunar years, always occurring at alternating nodes. Just two days over a whole number of anomalistic years and near a whole number of anomalistic months, which means the interval between two eclipses is quite constant. Lambert II cycle An eclipse cycle in which eclipses occur in similar circumstances, according to Johann Heinrich Lambert in 1765. (The "Lambert I cycle" is what we also call the inex.) Very close to a half-integer number of draconic months. It equals about 278 and a half years.