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Currently, Earth’s perihelion occurs near the northern hemisphere’s winter and the southern hemisphere’s
summer. Thus, the southern hemisphere in summer gets a little more solar energy than the northern hemisphere gets in its summer and the reverse happens in Winter. Northern hemisphere winters get a little more
solar energy than southern hemisphere winters. Note that the points of solstice are determined by the
direction of the tilt, and perihelion and aphelion are determined by eccentricity. The solstices do not have
to occur near perihelion and aphelion.
Now, consider precession. Precession determines the placement of seasons in relation to Earth’s orbit. Figure
6 shows the seasons as quarter sections of Earth’s orbit:
Figure 6: Earth’s seasons shown as a 4-color ring (not to scale)
ICY SCIENCE | QTR 1 2014