Spring backwards? Why next spring will come earlier than it has in nearly 130 years

Spring is coming to Canada and officially begins March 20 at 5:24 p.m. ET/ 2:24 p.m. PT.

Known as the spring equinox, the day marks the end of winter, and brings hope for warmer weather.

The spring equinox occurs when the sun crosses the equator line going north, resulting in longer and warmer days for those living in the Northern Hemisphere.

On the first day of spring, the sun will be shining equally on both halves of the Earth, Space.com explains.

But next year, spring will come a whole calendar day early, with the first day falling on March 19, for the first time since the 1800s.

WHAT HAPPENS TO EARTH DURING THE SPRING EQUINOX?

The orientation of the Earth's elliptical (meaning oval-shaped) orbit is shifting, as it "slowly" rotates on its axis, the U.S. Astronomical Applications department website reads.

During winter in Canada, Earth is tilted on its axis diagonally, with the sun's rays hitting the Southern Hemisphere more directly, causing summer, the NASA website says. The opposite tilt occurs in the Northern Hemisphere's summer, bringing warm weather to countries north of the equator.

During spring and fall, the sun is shining equally on both the northern and southern hemispheres.

The Earth takes 365.25 days to orbit the sun, which is rounded down to 365 days -- the length of one year.

WHY IS SPRING A DAY EARLIER IN 2024?

The extra quarter of a day is not counted each year, but instead added up, so that every four years, February gains an extra day to make up those hours.

"Say that July is a warm, summer month where you live. If we never had leap years, all those missing hours would add up into days, weeks and even months," the NASA website says. "Eventually, in a few hundred years, July would actually take place in the cold winter months!"

Next year is one of these leap years, and the existence of Feb. 29 shifts the whole calendar, causing the spring equinox to occur on March 19 instead of March 20.

• Here's why some leap years are skipped

Leap years are also the reason the spring equinox used to occur on March 21, versus March 20, in the previous century.

The periodic shifting of the calendar due to leap years is the reason the official start of seasons shifts over a couple of days.

The first day of spring is often March 20 or 21, but next year won't be the first time it's fallen on the 19th. It is, however, the first time it's been on that day in over a century.

The most recent March 19 first day of spring was in 1896. Spring will also start on March 19 in 2028, according to time-keeping website TimeandDate.com.