Astronomical Arrival Of Spring

Happy Vernal Equinox.   

The astronomical arrival of spring is a consequence of the earth’s tilt on its axis as it orbits around the sun.  Equinox from the Latin aequus (equal) and nox (night) means the the earth’s two hemispheres are receiving the sun’s rays equally.  On this date the sun rises exactly due east and set exactly due west with sunlight striking both hemispheres of the earth equally.   Night and day are approximately equal in length. 

As you observe the movement of the sun across the sky each day you will note that it is shifting toward the north.  Birds and butterflies begin their northward migration as a response to this change in daylight following the path of the sun.

 

Stonehenge View West

 

It would be premature to pack-away your winter outerwear, return the snow shovels to the shed or plant a garden.  Nevertheless, this is a harbinger of the arrival of astronomical spring for those of us in the northern hemisphere.  

 

The official start time will be today, March 20 at about 4.01 AM CST.  Where I live at mid-northern latitude today the amount of daylight added to each day peaks at three minutes.

 

Astronomers base season cycles upon the position of the earth in relation to the sun.  The beginning of Astronomical Spring or the Vernal Equinox marks the time when the sun passes directly above the equator.  Meteorological spring is based-upon annual temperature cycles.  Your weatherman will tell you that meteorological spring begins March 1 and goes thru the end of May.

 

No matter how you slice it the days will grow longer, the temperatures warmer and mud season is in full swing.