Summer Ends, Fall Begins: Autumnal Equinox

Almanac.com; Ashley Wells, Dhr. Seven, Crystal Quintero, Wisdom Quarterly

These are the dates and times for the four seasons (Eastern Time).

Seasons of 2016
SPRING EQUINOX	March 20, 12:30 AM EDT
SUMMER SOLSTICE	June 20, 6:34 PM EDT
FALL EQUINOX	Sept. 22, 10:21 AM EDT
WINTER SOLSTICE	Dec. 21, 5:44 AM EST

 
Why Do the Seasons Change?

On the assumption of a spherical and revolving planet, rather than a flat stationary one, this is a plausible explanation for seasonal change and sunlight duration patterns (NASA).

The four seasons are determined by shifting sunlight (not heat) -- which is determined by how our planet orbits the Sun and the tilt of its axis.

• On the vernal equinox, day and night are each approximately 12 hours long (with the actual time of equal day and night, in the Northern Hemisphere, occurring a few days before the vernal equinox). The Sun crosses the celestial equator going northward; it rises exactly due east and sets exactly due west. See First Day of Spring.
  
• On the summer solstice, we enjoy the most daylight of the calendar year. The Sun reaches its most northern point in the sky at local noon. After this date, the days start getting “shorter,” that is, the length of daylight starts to decrease. See First Day of Summer.
  
• On the autumnal equinox, day and night are each about 12 hours long (with the actual time of equal day and night, in the Northern Hemisphere, occurring a few days after the autumnal equinox). The Sun crosses the celestial equator going southward; it rises exactly due east and sets exactly due west. See First Day of Fall page. More

First Day of Fall?

Autumnal Equinox (TimeAndDate.com) In the Northern Hemisphere, the fall equinox marks the first day of fall (autumn) in what are called astronomical seasons. There's also another, more common definition of when the seasons start, namely, meteorological definitions, which are based on average temperatures rather that astronomical events.