Question

What is the difference between eccentricity, obliquity, and precession?

Answer 1

Eccentricity is a characteristic of Earth's orbit around the Sun. Obliquity is angle between Earth's spin axis and the normal to ecliptic. Precession is periodic perturbation to the spin axis..

Explanation:

The orbit of the Earth is an ellipse with the Sun at a focus. The eccentricity of this ellipse e = 0.0167, nearly.

Obliquity is the inclination `23.4^o` of the Earth's spin axis (polar axis) to normal to ecliptic (the orbital plane of the Earth).

This polar axis turns around its mean position completely once in a great Year period of about 25800 years. This motion is called the Earth's axial precession.