obliquity definition astronomy
Obliquity of the ecliptic Obliquity of the ecliptic is the term used by astronomers for the inclination of Earth's equator with respect to the ecliptic, or of Earth's rotation axis to a perpendicular to the ecliptic. It is about 23.4Â° and is currently decreasing 0.013 degrees (47 arcseconds) per hundred years due to planetary perturbations.