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Why Spring Gets About 30 Seconds Shorter Every Year

Spring is here, and you might want to make the most of it — because the season actually gets shorter every year due to astronomical quirks.
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/ Source: Live Science

Spring is here, 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. ET on Friday. At that exact moment — the Northern Hemisphere's vernal equinox — Earth's axis reaches 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).

On the calendar, the tick-tock of the seasons seems constant — moving from an equinox in March to a solstice in June, an equinox in September to a solstice in December, and then repeating. But astronomically speaking, spring has been losing time in the Northern Hemisphere for thousands of years. 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.

As the years go on, spring will continue lose time to summer, and winter will lose time to autumn. Summer in the Northern Hemisphere will be two days longer than spring and almost five days longer than winter in the year 3000, Gerstman said. [6 Signs Spring Has Sprung]

Earth's seasons are caused by the tilt of the Earth on its axis, not by how close the planet is to the sun. The tilt of 23.5 degrees from the straight up-and-down position means that for six months of the year, Earth's Northern Hemisphere leans slightly toward the sun, whereas during the other six months, the Southern Hemisphere leans toward the sun.

Image: Spring and summer view of Earth
Two satellite images from Eumetsat's Meteosat 9 satellite illustrate the difference between spring and summer: The picture on the left is from the March 20 equinox of 2011, when the tilt of Earth's axis lines up such that both the Northern and the Southern Hemisphere get equal exposure to the sun's rays. The picture on the left was taken during the time of that year's June 21 solstice, when the northern tip of Earth's axis was pointing at the sun.Eumetsat via NASA

The main reason spring is getting shorter is that 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 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. Thus, spring will end, and summer will begin, just a little bit earlier in the year. [50 Interesting Facts About The Earth]

Precession is a cyclical phenomenon: 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.

— Laura Geggel

This is a condensed version of a report from LiveScience. Read the full report. Follow Laura Geggel on Twitter. Follow LiveScience on Twitter, Facebook and Google+.