Under the Microscope: The Spring Equinox

This time of year, as the last snow melts from yards and mountainsides, I always find myself getting excited for the spring equinox, which happens to be this Thursday, the 20th.  Although picnics and gardening may be weeks or even months off yet, the spring, or vernal, equinox marks the point in the year that daylight hours will start to become longer than nighttime hours.  No matter how many snowstorms happen between now and June, I take comfort in knowing the days are finally becoming longer than the cold winter nights had been.

Technically, the equinoxes occur when Earth’s orbit and axis tilt cause the Sun to pass directly over the equator, shining its light equally on the northern and southern hemispheres.  This has the effect of giving most places on Earth roughly 12 hours of daylight and 12 hours of night, which is where the term “equinox” comes from:  in Latin, “equi” means equal and “nox” means night, making it literally “equal night.”

The Equinoxes only happen twice per year, around March 20^th and September 22^nd, and mark the generally accepted beginnings of spring and autumn, respectively.  It’s easy to forget though that just as our northern hemisphere is slowly blooming into spring, the southern hemisphere will be celebrating the autumn harvest.  Another interesting fact:  the sun rises precisely from the east and sets precisely in the west on equinoxes.  

As the days lengthen the average temperature rises and nature is quick to take note.  Trees begin budding and grass shoots and wildflowers begin poking through the last of the slush.  Before too long insects are hatching, the birds are returning and larger wildlife are migrating out of their wintering grounds.  The number of daylight hours keeps on increasing until the summer solstice, the longest day of the year, which is on June 21^st this year.  The days then gradually get shorter through the autumnal equinox, up to the winter solstice on December 21, 2014. 

In Missoula, there is still a chill in the air and ice on the Clark Fork River’s banks.  But thanks to the passing of the equinox, summer’s warmth really can’t be too far off.