Today is the autumn equinox, which marks the astronomical start of fall in the Northern Hemisphere, and the beginning of spring in the Southern Hemisphere.  The fall equinox is one of just two days each year when the number of daytime and nighttime hours are nearly equal all over the world. On this day, most of the Earth experiences about 12 hours of daylight and 12 hours of darkness. "In the Northern hemisphere, the September equinox marks the start of a period bringing us later sunrises and...