220 ASTRONOMYANDTHEBIBLE
Forexample, ifweviewalltheeclipses ina period
ofeighteenornineteenyears, wefindthatafterthis
time,theeclipsesrepeatthemselvesforanothersimilar
period. Henceifweobservealltheeclipsesinaperiod
as indicated,thenwecanpredictquitenearlyallthe
futureeclipsesforalongtimetocome,fortheeclipses
will apparently repeat themselves after the stated
periodoftime. This periodof repeatingeclipses is
6,585%days. Thisnumberofdaysafteroneeclipse,
anothersimilaroneoccurs. Thisperiodis calledthe
saros. Theexactlength ofa saros is6,585 days, 7
hours,and 42 minutes.
- Thesun also follows the moon's example, and
repeatsits eclipses. Since thesolarecHpticis larger
thanthelunar, asolar eclipsehas fromsixty-fiveto
seventyreturns,occupyingsometwelvehundredyears,
sothatthesun'smarkingonthedialoftheclockofthe
skiesis aperiodoftime overone thousandyearsin
length. Thereisnosuchlargedivisionasthisonthe
dialofmen'sclocks. - Thereisanotherdivisionoftimemarkedbythe
clockoftheskies. Itisindicatedbythenutationor
nodding of the earth's axis. Twenty-five thousand
yearsarerequired foronewobbleofthepoleofthe
earth;andduringthistime,themoonwillhavewob-
bled fourteenhundred times. Twenty-five thousand
yearsforone rotationofthepole! Thelargecycle
iscalledtheprecessionoftheaxisoftheearth;and
thenoddingbackandforthiscalledthenutation. - Themajorplanetsgiveussomeinterestingperi-
odsoftime. Theirrevolutionaroundthesunrequires