ESS200A
Prof.
Jin-Yi Yu
Earth’s Orbit and Its Variations
qFirst, Earth spins around on its
axis once every day č The Tilt.
qSecond, Earth revolves around the Sun once a year č The shape
of the Orbit.
qBoth the tilt and the shape of
the orbit have changed over time and produce three types of orbital
variations:
(1) obliquity variations
(2) eccentricity variations
(3) precession of the spin axis.
(from The Earth System)