Equinoxes and Equiluxes

Most folks are aware there are equinoxes, that is the time of the year when day and night are nearly equal in length.  However most of us are in error to some degree.  An equinox is a point in time when the tilt of the earth on its axis is neither away from nor toward the sun.  It happens twice a year, not exactly, but close to March 20/21 (Vernal Equinox) and September 22/23 (Autumnal Equinox).  These are not entire days, but only an exact point in time.  This morning, September 23, 2011, the Autumnal Equinox was at 5:04 EDT.

However the days when day and night are closest to being equal, when sunrise and sunset are closest to being twelve hours apart, are called Equiluxes.  Thus an Equiluxe is an entire day as opposed to the instant of the Equinox.  This depends upon where you happen to be.  At 35 degrees (South and North Carolina border) and at 40 degrees North (bottom of Pennsylvania) Latitude the Equiluxe will be Monday, September 26^th when sunrise and sunset will both be at 5:51 EDT.  At 45 degrees North Latitude, along the northern border of New York State, Sunday September 25^th the day is twelve hours and two minutes long, while Monday, September 26 is eleven hours fifty-eight minutes long.  Take your pick.