Because Earth doesn’t orbit upright, but is instead tilted on its axis by 23 and a half degrees, the Northern and Southern Hemispheres trade places in receiving the sun’s light and warmth most directly, according to EarthSky. There are equinoxes twice a year – spring and fall – when the tilt of the Earth’s axis and Earth’s orbit around the sun combine in such a way that the axis is inclined neither away from nor toward the sun.
*The name "equinox" comes from the Latin aequus (equal) and nox (night).
*The day of an equinox is a good day for finding due east and due west from your yard or other favorite site for watching the sky, according to EarthSky. Just go outside around sunset or sunrise and notice the location of the sun on the horizon with respect to familiar landmarks. http://www.al.com/news/index.ssf/2014/09/autumnal_equinox_tonight_--_as.html