Spring (Vernal) Equinox - 411
First lets understand what equinox is. Equinox, derived from Latin, meaning "equal night", it marks the moment the Sun crosses the celestial equator, the imaginary line in the sky above the Earth’s equator, from south to north.
The Earth spins around the Sun at an angle, which is why we have different seasons. The Earth's axis is always tilted at an angle of about 23.4° in relation to the ecliptic plane, the imaginary plane created by the Earth's path around the Sun. On any other day of the year, either the Southern Hemisphere or the Northern Hemisphere tilts a little towards the Sun. But on the equinox, the tilt of the Earth's axis is perpendicular to the Sun's rays.
During the Equinox day and night are of approximately equal duration around the world, though the Northern Hemisphere experience the opposite season than the Southern Hemisphere. In other words, while the Northern Hemisphere may Experience the Vernal/Spring Equinox, the Southern Hemisphere will be experiencing the Autumnal/Fall Equinox, therefore vice-versa. The day is approximately 12 hours in duration an so i the night. Marking the beginning of the Spring or Fall season, Vernal or Autumnal.
March Equinox in Boston, Massachusetts, USA is on Monday, March 20, 2017 at 6:29 am EDT.
Happy Spring, Northern Hemisphere. And Happy Fall, Southern Hemisphere.