http://sunearth.gsfc.nasa.gov/eclipse/SEsaros/SEsaros.html is the most informative and well maintained home
website attached to http://sunearth.gsfc.nasa.gov/eclipse/ and dealing with lunar and solar
eclipses and their periodic
cycles. It is maintained by the famous astronomer Fred Espenak who closely works in association with NASA. In fact, he is the most authoritative person to provide any kind of information on eclipse related matter.
Solar /lunar eclipses are governed by periodic cycles known as the
saros cycles and this home website deals fully with this information. In this great website, astronomer Fred says that the periodicity and recurrence of eclipses is governed by the saros
Cycle, a period of approximately 6,585.3 days (18 years 11 days 8 hours).
He clearly says that one must understand that two different eclipses , occurring in a year at two different dates , should not necessarily belong to the same Saros cycle. These period cycles are numbered differently like Saros cycle 134, Saros cycle 135 and so on. One must also understand that any two or more solar /lunar eclipses occurring at different dates but belonging to the same Saros cycle , are bound to have some similarities.
Fred says that the saros period arises from a natural harmony between three of the
Moon's orbital periods which are as follows.Synodic Month (new moon to new moon) 29.53059 days = 29d 12h 44mDraconic Month (
node to node) 27.21222 days = 27d 05h 06mAnomalistic Month (perigee to perigee) 27.55455 days = 27d 13h 19m
From the above, we understand that One saros is equal to 223 synodic months or 242 draconic months or 239 anomalistic months. He further stresses that any two eclipses separated by one saros cycle share very similar geometries. It must be remembered that they occur at the same node with the Moon at nearly the same distance from Earth and at the same time of year. Because the saros period is not equal to a whole number of days, its biggest drawback is that subsequent eclipses are visible from different parts of the globe. It certainly is a great website for those trying to know something about the eclipses.
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