*What happens on the autumnal equinox Sunday?
The 23.5-degree tilt of the Earth's axis is responsible for the seasons, changing how directly sunlight hits parts of the planet.
Earth reaches the autumnal equinox at 4:44 p.m. Sunday, marking the start of fall in the Northern Hemisphere and spring in the Southern Hemisphere.
At the equinox, the Earth is spinning upright relative to the sun -- this only happens twice a year because the Earth's axis is tilted by 23.5 degrees. During our fall and winter, the axis is tilted away from the sun, while during spring and summer the North Pole is tilted toward the sun, giving us more direct sunlight and warmth. (The axis always points the same direction, as the above graphic explains; its orientation relative to the sun just changes as the planet revolves around the sun.)
*September 20, 2013|By Scott Dance, The Baltimore Sun
http://articles.baltimoresun.com/2013-09-20/news/bal-wx-what-happens-on-the-autumnal-equinox-sunday-20130919_1_equinox-shortest-day-summer-solstice
