Spring technically starts with the vernal equinox, defined as the moment when the sun crosses the celestial equator and day and night are of equal length. That happened while most of us were sleeping, at 1:14 a.m. Eastern time today, March 20. Factor in the time change and spring actually started on Monday, March 19, for the Mountain and Pacific time zones.
This year’s vernal equinox is the earliest one since 1896, Scientific American reports. As the sun now moves north of the equator (at equinox, the sun hovered above the Indian Ocean, southeast of Sri Lanka), the technical early start to spring comes from the inexactness of our calendar and the Earth’s slightly shifting orbit in relation to the sun.
Since our calendar was designed to chop up the seasons in four orderly sections, the changing position of the Earth in relation to its orbit around the sun (which gets even more convoluted when you factor in gravitational pulls from other planets) can slightly alter the length of each season. All that tugging pulls the equinox to and fro, but leaves it hovering around March 20. It isn’t even uncalled for to have spring kick off on March 21, but that hasn’t happened for 30 years.
Of course, all this talk of spring starting a tad early is purely astronomical. What most of us really care about is having the sun shine brighter, and more often. The warm weather doesn’t hurt, either.
MORE: A Map of the Equator