The fall equinox marks the occasion when the Earth and the Sun are aligned such that the sun is observed to be passing directly above the Earth's equator. When one hemisphere is experiencing its fall equinox, the other hemisphere is experiencing its spring or vernal equinox. eSky: Autumnal Equinox On September 22, 2008, the northern hemisphere will experience the fall equinox at 15:44 UTC.

The equinox occurs because the Earth is tilted in relation to the Sun. Contrary to popular belief, the tilt of the earth does not change during the year. When the Earth rotates around the sun, the part of the Earth that is tilted towards the sun changes, even though the tilt of the Earth is fixed. As the Earth changes in position to the sun, the sun rises and sets across different parts of the sky. eSky: Autumnal Equinox Religious Tolerance: When and why the equinox happens