Milankovitch Theory

Eccentricity

The Earth’s orbit is elliptical. Eccentricity is a measurement of how much the orbit differs from being a circular orbit. Sometimes it’s more like a circle with a lower eccentricity. Sometimes it’s longer and narrower with higher eccentricity. This change in eccentricity that occurs every 100 thousand years or so accounts for an increase in seasonal changes on Earth.

Axial Tilt

The Earth’s axis of rotation tilts in a range between 22.1° and 24.5° with respect to the Earth’s orbital plane. It takes the Earth roughly 41,000 years to go from 22.1° to 24.5° and back again. As the tilt increases, the solar radiation during the summers increases in both hemispheres. As the tilt increases, the solar radiation during the winters decreases in both hemispheres.

Precession

The Earth’s axis of rotation has a gyroscopic motion caused by the gravitational forces of the sun and moon. Precession is the term for the direction that the axis moves in relationship to fixed stars. It takes the Earth roughly 26,000 years to complete one cycle. Depending on where the Earth is in the cycle, one hemisphere will have a greater difference between seasons than the other hemisphere because it will be closer of farther from the sun when it is pointing toward it.