Leap Day CalendarFirst taxes, then Leap Seconds, now this. A Leap Day. We got an extra second tacked onto our clocks at the end of 2015. And an extra day was added February 29, 2016. We never did get the calendar year just right. We’ve been at it for 5,000 years, and the year is still 26 seconds too long anyway. Welcome to the planet Earth. This story involves a cast of thousands, is long, confusing, fraught with danger and dissidence, a “thoroughly messy subject,” said astronomer LeRoy Doggett (whose job it was to figure these things out), but here goes…

Leap Day

The year, or the motion of the Earth around the Sun, is measured from Equinox to Equinox. (A particular place in the sky, against which we wait for the Sun to appear). Doing this, we find that the year is 365.2422 days long. The last Leap Day was on February 29, 2019 and the next Leap Day is February 29, 2020.

The Year of Confusion

Back around 46 B.C., Julius Caesar didn’t know all this to such precision. But he did know he was living by a calendar that was 3 months out of sync with the seasons. His Greek astronomer, Sosigenes, knew that the year was about a quarter of a day too long. So he made some very clever suggestions that seemed like nifty ideas to Caesar. At that time, in Rome as well as in much older kingdoms, the fellow on the throne regularly inserted or deleted days from the calendar whenever his astronomers recommended it.

So, in 46 B.C., Caesar ordered an extra 67 days packed into the calendar. That’s an extra day for the end of every fourth February. (the last month of the year in those days) This is what we now call “The Julian Calendar Reform.” The year 46 B.C., without question, became known as “The Year of Confusion”, but things were at least back on track – for awhile, that is.

There was one small problem. Sosigenes did a little too much rounding off. The difference between .2422 of a day and one quarter of a day is .0078 of a day, or 11 minutes. Sosigenes and Caesar were long gone before anyone noticed it. By 1582 A.D., all these extra minutes had added up to a whopping 10 days. And so, the seasons were slipping backwards again – spring into winter, winter into fall, and so on.

Nine Days That Never Existed

Along came Pope Gregory the Thirteenth, who realized what was happening. “Drat!” he said*, and sent his astronomers back to the drawing board. He established a commission to figure it all out and here’s what they said to do.

“Order 10 days dropped from the calendar, and declare that henceforth the centennial years would be Leap Years only if divisible by 400.”

That would get the whole “leap day” thing back in gear, and it would be thousands of years before the seasons would slip out of joint again. (With a year that is still 26 seconds too long, we will accumulate 1 day every 3,000 years.) October 5 – 14 became the nine days that never existed in 1582. Well, the crowds went wild…

The Gregorian Calendar

The Gregorian Calendar, was also called the “New Style”. It was immediately (but probably grudgingly) adopted by France, Portugal, Spain and of course Italy. These were Catholic countries. The German Protestants, fond of neither Popes nor Papal Bulls, waited another 120 years or so to accept it. And it wasn’t until 1752 that England and her colonies finally knuckled under. By that time the calendar was 11 days out of step with the seasons.

September 2 to 13 were then lopped off the calendar, and with that, the general populace took to the streets. The cry became “Give us back our fortnight!” accompanied by riots, and lots of general misunderstanding. For example, that being robbed of 11 days, one would thus die early. Many communities adamantly clung to the Old Style (one still sees “O.S.” on many gravestones) until forced by a new generation to adopt the change.

Japan made the change in 1873. Not long after that Commodore Matthew Perry, in a memorable display of gunboat diplomacy, opened the gates of Japan to the West. China adopted the Gregorian Calendar in 1911. But it wasn’t until the Bolsheviks had come to power, and Pope Gregory had been dead over 300 years, that the Russians finally came around.

They did one more thing, too, and that was to further refine the rule to say that centennial years would be Leap Years only if, after dividing the date by 900, the remainder is either 200 or 600. The Soviet calendar therefore, is about 5 times as accurate as anyone elses.

Looking Back

Well, these were the sort of problems that Dr. Doggett, along with his colleagues at the Royal Greenwich Observatory, grappled with. This was all in order to determine the dates of the seasons published in our yearly Almanacs. Calendar reform is a troublesome and awkward subject. One which has generated hundreds of calls and letters to the Naval Observatory. It may explain why Dr. Doggett kept this sign up over his desk:

Christmas and New Year’s have been cancelled. Go directly to dyeing eggs. * Or something like that.


LeRoy Doggett was in charge of the Nautical Almanac Office at the U.S. Naval Observatory, passed on April 16, 1996 after a battle with cancer.

He was an expert in celestial mechanics, ancient and contemporary calendar systems, astronomical phenomena and history of astronomy as well as archaeoastronomy. For the last 20 years, he compiled and edited The Astronomical Almanac, the world standard authority for the precise determination of astronomical events and positions of celestial objects. He was also responsible for the Nautical Almanac and the Air Almanac.


LeRoy was born on 22 October 1941 in Waterloo, Iowa. He received a BS from the University of Michigan in 1964, an MS from Georgetown in 1970, and his PhD in engineering mechanics from North Carolina State University in 1981.


He worked as an astronomer in the Nautical Almanac Office since1965 and headed that office from 1991 until his passing. His dissertation in celestial mechanics was on the use of Chebyshev polynomials for the generation of a high precision ephemeris of Mars. The early, practical application of these polynomials by Doggett, with others, made those functions the choice for digital representation and transmission of astronomical data. The Almanac for Computers, introduced in 1976, the Floppy Almanac (1986), and the Multiyear Interactive Computer Almanac (1993), are among the important applications based on those compact polynomials.


Quoted Source: American Astronomical Society