Spring arrives on Friday, and you might want to make the most of it. The season of flowers and showers actually gets shorter every year by about 30 seconds to a minute, due to astronomical quirks, researchers say.
This year, spring officially starts at 6:45 p.m. EDT on March 20, according to the U.S. National Weather Service (NSW). At that exact moment, which is called the vernal equinox, the Earth's axis will reach a halfway mark, where it points neither toward the sun (as it does on the summer solstice) nor away from the sun (as it does on the winter solstice), said Gavin Schmidt, the director of the Goddard Institute for Space Studies in New York City.
But for thousands of years, spring has been losing time in the Northern Hemisphere. This year, summer is the longest season, with 93.65 days, followed by spring with 92.76 days, autumn with 89.84 days and winter with 88.99 days, said Larry Gerstman, an amateur astronomer in New York. (Gerstman got his values from "The Astronomical Tables for the Sun, Moon and Planets," second edition, written by Jean Meeus and published in 1995 by Willmann-Bell, Inc.)
As the years go on, spring will lose time to summer, and winter will lose time to autumn. In the year 3000, the seasonal lengths will have shifted in the Northern Hemisphere: summer will be 93.92 days, while spring will be 91.97 days, autumn 90.61 days and winter 88.74 days, Gerstman said. [6 Signs Spring Has Sprung]
But why is this happening?
The Earth's seasons are caused by the tilt of the Earth on its axis (not by how close the planet is to the sun). This tilt of 23.5-degrees from the straight-up-and-down position means that for six months of the year, the Earth's Northern Hemisphere is leaning slightly toward the sun, whereas during the other six months, the Southern Hemisphere leans toward the sun.
The main reason spring is getting shorter is that the Earth's axis itself moves, much like a wobbling top, in a type of motion called precession.
Spring ends at the summer solstice, and because of precession, the point along the Earth's orbit where the planet reaches the summer solstice shifts slightly. Next year, the planet will reach the point in its orbit of the solstice slightly earlier.
Spring will end, and summer will begin, just a little bit earlier in the year. [50 Interesting Facts About The Earth]
Over thousands of years, the shift in the time of the vernal equinox becomes more apparent. For instance, spring will be shortest in about the year 8680, measuring about 88.5 days, or about four days shorter than this year's spring, Gerstman said. (After that point, spring will lengthen again.)
Why spring is shorter than summer At the point of perihelion, the Earth is about 91.6 million miles (148 million kilometers) away from the sun. When the Earth is farthest from the sun - in early July, during aphelion - the distance is about 94.8 million miles (153 million km).