Milankovitch Cycles

Eccentricity - the shape of the Earth's orbit

The Earth's eccentricity varies from circular to elliptical over 100,000-year cycles.  The Earth's closest approach to the sun is known as the perihelion, while the furthest distance from the sun is known as the aphelion.  The Earth receives less solar radiation in at the aphelion in the elliptical orbit.  The larger the eccentricity, the greater the difference in the solar radiation that reaches the Earth at the perihelion vs the aphelion.

Obliquity…