Information AboutSaros |
| CATEGORIES ABOUT SAROS CYCLE | |
| eclipses | |
| time in astronomy | |
| technical factors of astrology | |
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The Saros was discovered by Babylonian astronomers. It is very useful since the calculations involved are simple. The only problem is that the next eclipse of the same Saros cycle occurs about 8 hours later in the day. In the case of an eclipse of the Sun this means the region of visibility shifts west one third of the way around the world, and most places from which the first eclipse was visible do not see any of the second one. In the case of an eclipse of the Moon the next eclipse might still be visible from the same location as long as the Moon is above the horizon. Therefore a longer cycle of three Saroses (54 years and a month, almost 19756 full days), known as a Triple Saros or ''exeligmos'' ( ''Greek'' : "turn of the wheel"), has been used. After an exeligmos, an eclipse will again be visible at or near the original location. In astronomical terms the Saros is due to several lunar and solar cycles repeating after about the same period of time:
Therefore the circumstances of an eclipse are also very similar to an eclipse one Saros earlier, and an eclipse (which happens when a Conjunction or Opposition of the Sun and Moon occurs in one of the nodes, that is, crossing the plane of the orbit) occurs again one Saros later. So in principle one Saros after an eclipse, there will be another eclipse: however this does not repeat indefinitely because the match of the underlying periods (223 synodic = 242 draconic = 239 anomalistic months) is not perfect. In practice there is a long series of eclipses separated by one saros, that lasts many centuries but has a definite first and last eclipse. At any one time theoretically there could be at most 223 possible Saros series of solar eclipses running simultaneously, because there are only 223 New Moons in the time span of a Saros. Similar for lunar eclipses at Full Moons.
The Saros cycle was probably known to the Chaldeans (ancient Babylonian astronomers), and later to Hipparchus , Pliny ( Naturalis Historia II.10 {Link without Title} ) and Ptolemy (''Almagest'' IV.2), but not under this name. The Babylonian "Saros" appears to have been a name for a period of 3600 years. The name "Saros" was first given to the eclipse cycle by Edmund Halley in 1691 , who took it from the '' Suda '', a Byzantine lexicon of the 11th century. Halley's naming error was pointed out by Guillaume Le Gentil in 1756 , but the name stuck. EXTERNAL LINKS
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