lec08 - Lecture 8 Precession and Tides Lecture 8 Purdue...

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Lecture 8 Precession and Tides Lecture 8 Purdue University, Astronomy 364 1
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Real Earth The Earth has the shape of an oblate spheroid, due to its rotation. – The equatorial radius and polar radius differ by about 0.3%. The deviation from spherical shape, coupled with the inclination of the rotation axis with respect to the ecliptic, leads to a net torque associated with gravitational pulls of the Sun and the Moon. – Cause of precession Lecture 8 Purdue University, Astronomy 364 2
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Moon’s Influence Lecture 8 Purdue University, Astronomy 364 3 F Moon = G M Moon m r 2 ˆ r F Moon ( r ) F Moon ( r 0 ) + ( r r 0 ) dF Moon dr r = r 0 ⇒ Δ F Moon = F Moon ( r ) F Moon ( r 0 ) ( r r 0 ) 2 GM Moon m r 0 3 Δ F Moon ( r A ) = 2 GM Moon mR E r 0 3 Δ F Moon ( r B ) = 2 GM Moon mR E r 0 3
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Tides • Because the Earth rotates faster than the Moon going around the Earth, the bulges do not lie along the Earth- Moon line but are ahead. • The offset causes a torque
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lec08 - Lecture 8 Precession and Tides Lecture 8 Purdue...

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