Vernal Equinox, Explained

March 19 is the vernal equinox and the official start of springtime on the northern hemisphere this year.

So what is an equinox?

It all comes down to the tilt of the earth.  Earth’s axis is tilted by 23-point-five degrees.  without this tilt, there would be no seasons, as the amount of light received on any given point on earth would not change.

First, let’s define “celestial sphere”– that is the imaginary sphere on which objects in the night sky appear to reside when viewed from earth.

The sun’s apparent path in the sky is called the ecliptic. That path crosses the celestial equator each year at the equinox. The celestial equator is where the earth’s equator would be if you extended it out into the celestial sphere. During the equinox, the ecliptic and earth’s axis align perfectly, so that both hemispheres get an equal amount of sunlight.

In the southern hemisphere, today is the end of summer for them and the beginning of autumn.   Here on the northern hemisphere, we can finally say goodbye to winter– at least, technically, and hello to spring. Across the North Coast area, flowers are blooming and the days are getting longer.  Whether it’s overcast or not, March 19 at 8:06pm PDT, it is officially the first day of spring.