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Thread: Will a saros "come back?

  1. #1
    Join Date
    May 2004
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    Will a saros "come back?

    A Saros series doesn't last indefinitely because the three lunar months are not perfectly commensurate with one another. In particular, the Moon's node shifts eastward by about 0.5 with each cycle.
    https://eclipse.gsfc.nasa.gov/SEsaro...0one%20another.
    So after 720 cycles or ~13,000 years will eclipses of a particular series start again?
    SHARKS (crossed out) MONGEESE (sic) WITH FRICKIN' LASER BEAMS ATTACHED TO THEIR HEADS

  2. #2
    Join Date
    Jul 2005
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    Well, no, because the nodal shift per Saros is not exactly 0.5 degrees, so 720 cycles doesn't bring the lunar node back to exactly the same position. You'll potentially get better and better repetitions by finding more exact common multiples of the three lunar periods, but then you'll start to reach such large durations that these periods will be varying significantly--so any sort of common-multiple periodicity you find will start to drift within centuries.

    Grant Hutchison

  3. #3
    Join Date
    Dec 2006
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    Each Saros eclipse family has a start and end date. Eclipses in each family occur first near one pole with partial eclipses. The subsequent locations then move across the equator, becoming steadily tighter, and end at the other pole with ever more partial eclipses, as tabulated for example at https://en.wikipedia.org/wiki/Solar_Saros_138#Events

    The difference between all eclipse families means it makes no sense to suggest a Saros family could repeat.

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