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Re: Nutation

At 6:39 PM -0400 9/22/03, David Bowman wrote:
Also besides this 41 kyr +/-2 deg nutation there is supposedly a
much shorter term nutation of about 9.18 arcsec in amplitude and has
an 18.6 yr period. I don't know anything about what causes it,
though.

18.6 year period sounds suspiciously like the amount of time that it
takes for the Jewish calendar to realign with the Gregorian calendar
(or vice versa of course.)

18.6 years cycle is also known to the ancients as the 'saros'.

ah here is a nasa url:
http://sunearth.gsfc.nasa.gov/eclipse/SEsaros/SEsaros.html excerpt:

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). It was known to the Chaldeans as a period when lunar eclipses
seem to repeat themselves, but the cycle is applicable to solar
eclipses as well.

The saros arises from a natural harmony between three of the Moon's
orbital periods:
Synodic Month (new moon to new moon) 29.53059 days = 29d 12h 44m
Draconic Month (node to node) 27.21222 days = 27d 05h 06m
Anomalistic Month (perigee to perigee) 27.55455 days = 27d 13h 19m
One saros is equal to 223 synodic months. However, 242 draconic
months and 239 anomalistic months are also equal to this same period
(to within a couple hours)!


Yes, lets take the word 'astrology' back to its original meaning. -cvb-
--
Chuck Britton Education is what is left when
britton@ncssm.edu you have forgotten everything
North Carolina School of Science & Math you learned in school.
(919) 416-2762 Albert Einstein, 1936