|
 The
Shape of Earth's Orbit
The most important orbital change studied
by Milankovich is the change in the shape
of the Earth's orbit from nearly circular
to slightly elongate and back again. The
time it takes to go through a complete
cycle from circular to elongate and back
to circular is about 100,000 years.
Please note that the
change in orbital shape shown in the animation is much, much, much
larger than the actual change in the Earth's orbit. If the animation
showed the actual change in shape, you would not be able to detect
it with your eye. The effect has been greatly exaggerated so that
you can easily see it.
During
the portion of the shape change cycle
when the orbit is nearly circular, the
Earth-Sun distance is nearly the same
for all parts of the orbit, making the
Earth's average temperature the same all
year round. As the orbit becomes more
elongate, the Earth orbits slightly farther
from the Sun at aphelion
and slightly closer at perihelion,
making the average temperature slightly
lower at aphelion and slightly higher
six months later at perihelion. Also,
since the Earth moves more slowly near
aphelion, when the orbit is elongated,
the time during which the temperatures
are lower lasts slightly longer.
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