A long and hot summer has officially come to an end.    At a precise moment each September, usually on the 22nd or 23rd, the sun is directly above the equator, marking the autumnal equinox. This year, on Sept. 23, the center of the sun will be directly over the equator at 2:50 a.m. EDT, according to EarthSky.com. In the Northern Hemisphere, the sun will get lower in the sky and days will become shorter until the winter solstice on Dec. 21. Read more at the link in our bio.