Orbital Parameters, Obliquity

THE EARTH'S ORBIT and orientation around the Sun affects how solar energy is received. Obliquity is the degree of the Earth's tilt as it completes its daily rotation and yearly revolution around the Sun. It is the angle an imaginary rotational axis would make with the plane of the Earth's orbit. The axial tilt, which varies over time from 21.5 to 24.5 degrees and back again, is the reason for the seasons. A complete tilt cycle takes 41,000 years to complete. In concert with the eccentricity of the orbital path around the Sun and the precession effect, obliquity is a factor of climate change affecting Earths average surface temperature over the long term.

Chinese astronomers in the 11th century determined Earths obliquity of the ecliptic. They ...