In the Solar System, the inclination of the orbit of a planet is defined as the angle between the plane of the orbit of the planet and the ecliptic — which is the plane containing Earth's orbital path. It could be measured with respect to another plane, such as the Jupiter's orbital plane.

The invariable plane, is the plane that represents the angular momentum of the solar system and is approximated to be the orbital plane of Jupiter. The inclination of the Earth's orbit has a 100,000 year cycle relative to the invariable plane.

The Earth is inclined to the invariable plane by about 1.57869(1.57869 degrees)

Notes

All planetary orbital planes wobble around the invariable plane, meaning that they rotate around its axis while their inclinations to it vary, both of which are caused by the gravitational perturbation of the other planets. That of Earth rotates with a quasi-period of 100,000 years and an inclination that varies from 0.1 to 3. If long-term calculations are performed relative to the present ecliptic, which is inclined to the invariable plane by about 1.57869, it appears to rotate with a period of 70,000 years and an inclination that varies between 0 and 4. Specifically, Earth's orbit (the ecliptic) is inclined to the invariable plane by 134'59"−18"T, where T is the number of centuries since 1900. Its J2000.0 value is 134'43.3". The inclination of the orbit of Jupiter to the invariable plane varies over the range of 14'–28'.