Autumn equinox 2017

In 2017 autumn will begin on Friday 22^nd of September at 8:02pm UTC. This season will last 89 days, and it will end on 21^st of December with the beginning of winter.
The beginning of seasons is conventionally established by particular positions of the Earth during its orbit around the Sun.
An equinox occurs when the plane of Earth’s Equator passes the center of the Sun. The two annual equinoxes are the only times when the subsolar point (the place on Earth’s surface where the center of the Sun is exactly overhead) is on the Equator, and, consequently, the Sun is at zenith over the Equator. The subsolar point crosses the equator, moving northward at the March equinox and southward at the September equinox.
When that occurs, the daytime and night are of approximately equal duration. The word equinox comes from this definition, derived from the Latin aequus (equal) and nox, noctis (night).