Good news for lovers of spring. Normally, the season begins on March 20th or 21st, but from the Central Time Zone west to the International Date Line, it starts later today, March 19th. Here in Duluth, Minn., we welcome the equinox this evening at 11:30 p.m. CDT (9:30 p.m. PDT, 12:30 a.m. EDT March 20). If March 19th sounds odd, your intuition is correct. We haven’t had a spring this early in 120 years!
It all goes back to the time it takes Earth to go around the sun — 365.242 days or very close to 365 1/4 days. Most years, a year is 365 days long, but every fourth year those quarter days add up to one extra day, which we tack onto February (Feb. 29) during a leap year. So far so good. Roman dictator Julius Caesar introduced leap years over 2,000 years ago using the 365.25 days as the length of a year. But notice that this is a tad longer — 11.52 minutes to be exact — than the correct length.
His system, called the Julian Calendar, was much better than what came before but ended up with too many leap days, causing the timing of the solstices and equinoxes to gradually drift out of sync with their fixed dates.
Pope Gregory XIII tidied up the system in 1582 by reducing the number of leap years, decreeing that years ending in”00″ wouldn’t be leap years unless they were also divisible by 400. So 2000 became our most recent special leap year because it divided neatly by 400, but 1700, 1800, 1900 were not even though they fell within the normal 4-year cycle. Our next “00” leap year will happen in 2400.
Normally, all those little fractions (11.52 minutes) of a day make leap days reset themselves so that the times of the solstices and equinoxes happen on the usual dates in a 400 year cycle. But because of the 2000 leap year, the dates of the solstices and equinoxes, instead of gradually returning to their normal dates — March 20-21, June 21-22, September 22-23, December 21-22 — have been getting earlier and earlier.
Spring now arrives, for at least part of the globe, on the 19th (or 20th), but later this century, there will be a March 19th start to the season for the whole globe. So will spring one day begin in February? Thank goodness no. The system will begin to reset itself starting at the turn of the next when spring will start migrating to March 21st. Gregory’s system, while not perfect, is quite serviceable, as it keeps our calendars correct to within about a day every 4,000 years.
Delightful leap year explanation after you make it through the painful ad
One other factor that causes spring to arrive earlier this year and indeed in every leap year is that extra day in February. The additional day advances the time of the equinox by about 6 hours earlier. Coupled with the approximately one-hour-per-year slippage since the 2000 leap year, those hours add up. Take a look at the table of solstices and equinoxes at the Timeanddate website, and you’ll see what I mean. You can also watch start-of-season date shift by selecting past and future 50-year periods in the Showing box in the upper right corner of the table.
Let’s take a look into the crystal ball at spring starts every four year for the next 24 years (every one will be a leap year):
* March 19, 2020 at 10:50 p.m. CDT
* March 19, 2024 at 10:06 p.m.
* March 19, 2028 at 9:17 p.m.
* March 19, 2032 at 8:22 p.m.
* March 19, 2036 at 8:03 p.m.
* March 19, 2040 at 7:11 p.m.
The spring or vernal equinox marks a wonderful moment in Earth’s yearly orbit, when the sun shines broadside to the globe (directly over the equator) and day and night are nearly identical in length across the globe. The sun shines from much higher up in the sky compared to winter, days are longer and the solar rays more direct and intense. If you are visited by a late snowstorm that dumps 10 inches of fresh snow, don’t worry about shoveling it away. The sun will do that for you soon enough.
Happy are those who happen to find themselves at the North Pole today. After six months of darkness and twilight, the sun rose for the first time there this week and will remain in the sky — never setting — until the first day of fall.
Now that we know spring starts early this year, we can use those extra minutes to better appreciate all the little changes we see in daylight length, animal activity, birdsong and the shifting stars.
* Special note: I’ve been working on a book about the many things you can see and enjoy in the night sky using only your eyes. Titled Night Sky with the Naked Eye and published by Macmillan, it’s now available for pre-order at Amazon and Barnes and Noble. Publication date is September 20th. If my blog isn’t updated every day, that usually means I’m still at work on the project. I appreciate your patience and hope you’ll enjoy the book.