As if 2020 hasn’t already been the longest decade of our lives, we’re now told that spring is set to make its earliest arrival in 124 years. 

This shift has largely to do with our quirky calendar system, resulting from more than a century of leap years and the impact of those extra days over time, according to the Farmer’s Almanac. Every year, it takes Earth 365.25 days to revolve around the Sun, according to NASA. In order to compensate for that extra quarter of a day, our calendar system adds an extra day, February 29, every four years or so.

“To keep our yearly calendars consistent with our orbit around the Sun, every four years we add one day. That day is called a leap day, and the year it's added to is called a leap year,” writes the space agency.

There’s a quick trick to determining whether a year will be one that leaps. If the last year is divisible by 20, like this year’s 2020, then we will add the extra day. But if it is divisible by 100, it skips a leap year. Hold up, there’s more. Under our current calendar system, most century years, for example, 1700, will skip February 29 unless the year is divisible by 400, which was the case in 2000. That last rule is what has put us in this earlier-than-usual spring equinox.

Still with us? Good. Now to the astrophysics bit.

The axis of the Earth is tilted 23.4 degrees, which is what causes the cycle of our seasons. During part of the year, the Northern Hemisphere is tilted toward the Sun, positioning this part of the world closer to it and thus providing more heat (aka summer), while the Southern Hemisphere of our planet is tilted away. In six months, these seasons will again shift. But the spring and fall equinoxes mark two days a year when both hemispheres receive roughly the same amount of light from the Sun.  

“Most years, the Spring Equinox is on the 20th or 21st. For the first time since 1896, it will occur on the 19th in all of the US time zones,” tweeted a WBAL-TV meteorologist Tony Pann in Baltimore, Maryland.

The vernal equinox marks the moment the Sun crosses the equator from south to north, which occurs at 11:49 pm ET in the US and in the early hours of Friday, March 20, in the rest of the world. You can check Time and Date to see when your hometown will see its equinox.