Saturday, September 22, 2012

Autumnal Equinox

Today is the Autumnal (fall) Equinox.  Although most people hardly even notice it, the natural world is now speeding up the process of winter preparation.  The young of spring are now mature and for some learning their last lessons in survival.  The sun’s quickening demise is triggering the internal clocks for others to start heading southward.    Those that must stay are packing on the pounds in preparation for the lean months ahead.  Plants are reacting by sowing their seeds and green plants are decreasing chlorophyll production.  This will eventually lead to exposing the other colors that had been hidden by the green into the brilliant colors of fall.  For the farmers who still live by the seasons, it means the last harvest of the year.  
      Thanks to the earth’s 23.5° tilt, equinoxes occur twice a year – in March and September.  It is when day and night are nearly exactly the same length.  The word equinox is derived from Latin, meaning “equal night”.  However, to the casual observer, this doesn’t seem correct.   The day time seems longer than the 12 hours. There are two reasons for this.  First, sunrise and sunset times are calculated by the outer edge of the sun’s disk not the center.  So the disk is still in the sky after sunset occurs.  Second, the Earth’s atmosphere refracts light.  This gives the illusion that the sun is in the sky longer than it really is.  The Autumnal Equinox is the herald of winter.  If this depresses you, head to the southern hemisphere where today it is the Spring Equinox.  (Picture credit: Kimberly Achelis Hoggan)

No comments: