“The grass has riz…”
That’s the beginning of a bit of English doggerel I learned at my dad’s knee.
According to EarthSky.org, spring (which arrived last night at 12:30 a.m. Eastern time) came earlier this year than it has since 1896. The reason?
The March equinox can come on March 19, 20 or 21. And 2016 has the earliest March equinox since the year 1896. Is it a coincidence that 2012 also had the earliest spring since 1896? No. Recall that both 2012 and 2016 are leap years. But 2016’s spring comes even earlier than the spring of 2012.
In a nutshell, this earliest spring is happening because the tropical year, as measured between successive March equinoxes, doesn’t have an even number of days (365.242 days). Our calendar, on the other hand, has an even 365 days in a common year and 366 days in a leap year.
The centennial year 2000 was a leap year, which causes the March equinox to arrive roughly three-quarters of a day earlier in the 21st century (2001-2100) than at corresponding years in the 20th century (1901-2000).
However, the suppression of the leap year in the centennial year 2100 will push the March equinox times upward again (by roughly one-quarter day) in the 22nd century (2101-2200). Why is 2100 not a leap year, by the way? It’s because, in 1582, Pope Gregory XIII revised the Julian calendar and stated that leap days should not be added in years ending in “00” unless that year is also evenly divisible by 400. (For instance, 2000 is equally divisible by 400, whereas 2100 is NOT). Read more about leap years here.
So … four years from now, in 2020, the March equinox will be earlier yet – on March 20 at 3:50 UTC (March 19 at 10:50 p.m. CDT).
Four years after that, in 2024, it’ll come earlier again – on March 20, at 3:06 UTC (March 19 at 10:06 CDT).
The March equinox comes earlier and earlier every leap year all through the 21st century (2001 to 2100).
If you’re considering Universal Time, the first actual March 19 vernal equinox will come in the year 2044 (March 19 at 23:20 UTC).
The earliest March equinox of the 21st century will occur in the year 2096 (March 19 at 14:03 UTC).
Plus – assuming you’re using Universal Time – the equinox will be on March 20 (Universal Time) for the coming four decades.
“… I wonder where the birdies is…
— The birds are on the wing!
But that’s absurd!
I thought the wings was on the bird!”