PDF Slides - UMBC
PDF Slides - UMBC
PDF Slides - UMBC
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… and this is a biggie …<br />
3) Precession of the Earth’s spin axis [text Sect.2.2]<br />
Since Earth’s shape is an oblate spheroid<br />
and it’s spin axis is tilted to the ecliptic<br />
(and also at ~5 O to the orbital plane of the moon)<br />
there are gravitational torques on the Earth<br />
due to the Sun & Moon (& the other planets)<br />
…eg. Sun trying to pull equatorial bulge into plane of the ecliptic<br />
… result is the direction of the spin axis moves<br />
around on a circular path every ~26,000 years<br />
“precession” (~50”/yr clockwise)<br />
Ian M. George PHYS 304 (2011 Fall) Meeting 04
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