The rumors are true. It’s the earliest spring of your life. Spring, marked by the vernal equinox, will begin on March 19, 2020 in all US time zones. Spring is earlier than it has been in 124 years (since 1896). It’ll even get earlier in a few years. And there’s an amazing story behind this.
The Quirks of Our Calendar
If you went to school in the 60’s, say, you remember how spring reliably began every March 21. So what’s going on?
This earlier-than-usual spring has everything to do with time, which is something we humans do perfectly. Atomic clocks divide each second into 9,192,631,770 parts, and the super-accurate time is then transmitted to anyone with an “atomic wall clock” or GPS or even a smart phone.
The calendar is nearly as perfect. Even before this record-breaking equinox and earliest-ever-spring, this year offered us a February 29—the rarest birthday—with consequences that affect everyone.
Want to be the only one in your state who truly understands what’s going on? It’s easy if you first rewind to the year 2000. That February, for the first time in four centuries, there was a February 29 on a century year.
Well, review how our calendar works. Years divisible by four are leap years, like this one, 2020. But if a year is divisible by 100, it SKIPS a leap year, so in 1700, 1800, and 1900 there was no February 29.
Hang in there, we’re about to get to the punchline.
Our calendar system further decrees that while most century years skip February 29, if the year is divisible by 400, it will be a leap year anyway. So 2000 was a leap year. The consequences of that little move are what’s affecting us now. You’ve waited twenty years for this moment even if you weren’t aware of it.
So Why Is Spring Early This Year?
You see, equinox and solstices happen earlier and earlier as each century wears on.
That date resonated because each summer and winter also began on the 21st of the month. As every century wears on, the date slips earlier to the 20th and possibly even to the 19th of March, but this slippage gets halted and rectified by the omission of a leap day during the next century year, like in 1700, 1800 and 1900. That creates a sudden “jump” of one day, with the first day of summer, spring, and winter pushed to the 21st again, and all seems right with the world.
Anyway, because 2000 had a leap day instead of omitting it, thanks to that once-every-four-century-tweak, ensuing equinoxes were prevented from returning to the 21st, and solstices and equinoxes instead continued to creep earlier. The equinox slipped from the 21st to the 20th, where it’s been for many years now, and it’s still creeping earlier. Now, finally, it’s reached the point where the equinox happens on the 19th for US time zones. Later this century, it’ll even start happening on the 19th in the Greenwich time observed in the UK.
And listen to this, every four years from now on—on every coming leap year like 2024, 2028, 2032, and so on—there will be a brand new “record earliest” start to spring. You heard it here first.
What Causes These Shifting Dates?
The headaches are caused by the number of days in a year not being even. A year lasts 365 days, 5 hours, 48 minutes, and 46 seconds. Call it 365.2422 days. If only the year were 11 minutes longer, or 365.25000 days, we could simply add one day every fourth year and take care of the fraction forever.
But because Earth spins a hair less than 365 1/4 times per year, we must sometimes omit that once‑every‑four‑year additional day. Back when they didn’t do that, seasons kept moving around. In the previous Julian calendar (where all century years were leap years) the annual 11‑minute error accumulated to where equinoxes were March 10. The Easter Bunny was hopping around in the snow.
Pope Gregory stepped in to fix the calendar. It wasn’t hard. Skip three leap years every four centuries and you’re accurate to one day in about 3300 years. We’ll even deal with THAT little glitch by skipping February 29 in the year 4000. So what’s the simplest way to hold leap years every fourth year, but skip three of them every four centuries? His solution: banish leap years if they’re century years like 1900, but do have it if the century year can be divided by 400 like in 2000. Voila!
The present calendar takes care of everything. So hopefully you celebrated this leap-year on February 29, and will celebrate again on March 19. If you want to be precise, the equinox occurs at 11:50 PM, or ten minutes to midnight, EDT. And if you’re an old timer who misses having it on the 21st, don’t worry about a thing. That will again happen starting in 2103, after the skip of the leap year in 2100 resets the system.