Nitesh Sehwani
A Milankovitch cycle is related to the Earth’s orbit around the Sun. There are three
parts of the cycle: eccentricity, axial tilt, and precession. According to the
Milankovitch Theory, these three cycles combine to determine the amount of solar
heat that’s incident on the Earth’s surface and subsequently influence climatic
patterns.
Eccentricity
The path of the Earth’s orbit around the sun is not a perfect circle, but an ellipse. This
elliptical shape changes from less elliptical (nearly a perfect circle) to more elliptical
and back; and is due to the gravitational fields of neighbouring planets (particularly
the large ones – Jupiter and Saturn). The measure of an ellipse's deviation from being
a circle is called its eccentricity. Thus, the larger the eccentricity, the greater is its
deviation from a circle. Thus, in terms of eccentricity, the Earth’s orbit undergoes a
change from less eccentric to more eccentric and back. One complete cycle for this
kind of variation lasts for about 100,000 years!!
Credit: "Earth obliquity range" by NASA, Mysid (Wikimedia Commons)
Axial Tilt
We know the earth is spinning around its own axis, which is the reason why we have
night and day. However, this axis is not upright. Rather, it tilts at angles between 22.1degrees and 24.5 degrees and back. A complete cycle for the axial tilt lasts for about
41,000 years. Greater tilts mean that the hemispheres closer to the Sun, i.e., during
summer, will experience a larger amount of heat than when the tilt is less. In other
words, regions in the extreme upper and lower hemispheres will experience the
hottest summers and the coldest winters during a maximum tilt.