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The reason for leap year is of course to keep the solar year in time with the sidereal day- which is another way of saying that the time it takes for the earth to rotate on its axis (a day) does not divide evenly into the time it takes for the earth to revolve around the sun (a year). So we need an extra day every four years to make up the difference.
Julius Caesar made this Roman law in 46 B.C, (the year 709 in the Roman Calendar) on the advice of the Greek astronomer Sosigenes. This "Julian Calendar" was adopted by the Roman Empire and all its territories and remained in use for over 1500 years! Making every fourth year a leap year with 366 days is based on the assumption that the true year is exactly 365.25 days long.
In the original Roman calendar, March was the first month which you can tell from the names of the months September October November and December- Latin for 7 (Sept) 8 (Oct) 9 (Nov) and 10 (Dec). January was named after Janus the god of change, and February after the feast of Februalia which Romans celebrated in the spring as their "new year" but it was a feast that lasted a whole month. March was after Mars the God of War. The next three months had names that are very ancient and whose origin is not fully known- Aprilis, Maius, and Junius are believed to be related to Roman gods of fertility... Junius was the most popular month for marriages even 2000 years ago! July was called Julius named after Caesar himself. The old name was Quintilus- Latin for "fifth month."
The original Julian Calendar had all the months with either 30 or 31 days alternating. Februalia had either 29 or 30 days depending on whether it was a leap year. When Augustus ascended to emperor after Julius Caesar's death, he decided that he would also name a month after himself as his great uncle had done- thus Hexilius became Augustus, and since Julius had 31 days, Augustus decided HIS month should have 31 days also, and stole another day from February to make up the difference*.
This system seemed fine and dandy for several hundred years, even after the adoption of Christianity as the official religion of the Holy Roman Empire. The Catholic Church adopted the Julian calendar but adapted it to their religious feasts and holidays. The religious calendar called for a certain number of Sundays (Masses) to fall between Christmas (Dec 25) and Easter (The first Sunday after the first full moon after the Vernal Equinox). The date of Dec 25 for Christmas is also an invention of the Catholic Church- when they "Christianized" the Roman pagan feast of Saturnalia, which corresponds roughly with the winter solstice.
Well, this is the part that gets tricky...
The seasons are determined by certain astronomical events that have been observed and recorded for thousands of years as far back as civilization. These are the solstices and the equinoxes. The original Julian calendar had the New Year, March 1, roughly in synch with the Vernal Equinox as the official start of spring and the new year. On the equinox, the sun rises due east and sets due west from EVERY location on earth other than the poles, and the length of day and night are equal (hence the name EQUI-NOX). That is a measurable event that you can check by setting up stones that are aligned exactly east-west, like some of the pillars at Stonehenge, or some of the Roman temples. The full moon is also a clearly observable event. THUS you can set the date of Easter by each of these observations, and know when it will be each year. In a sense, the day of Easter brings the universe into harmony, by synchronizing the motions of the earth, moon, and sun in a single event.
But a funny thing happened. The formula for figuring out the date of Easter (The "Golden Rule") relative to the sun and the moon was set in the 4th Century AD (at the Council of Nicea). The religious calendar called for a certain number of masses to be held between Christmas and Easter. By the year 1500 approximately, the number of Sundays was no longer the same, because the date of the equinox had shifted by over a week from where it had been when the rules were set. The equinox was taking place on March12 instead of March 21 as it had during the early days of the church.
This was brought to the attention of Pope Gregory XIII by a priest/astronomer named Christopher Clavius (note the name... another famous astronomer named Christopher). By 1582 the accumulated error was estimated to have amounted to 10 days, thus the real length of the solar year was not EXACTLY 365.25 days as had been believed, but closer to 365.2425. So the way to fix this was to add another correction factor by DROPPING 3 leap years every 400 years. To bring the religious calendar back into synch with the solar events, Pope Gregory XIII decreed that the day following Oct. 4, 1582, should be called Oct. 15, thus dropping 10 days.
Here is yet another interesting fact about religion, politics, and the calendar. The decree by Pope Gregory took place AFTER the "Reformation" when the German church under Martin Luther broke with Rome, AFTER the "Great Schism" when the Eastern Orthodox church broke with Rome, and after Henry VIII* formed the Anglican Church because the Pope wouldn't let him legally divorce one of his six wives. The Western European churches did NOT adopt the Gregorian calendar for over a hundred years, and the Eastern Church never did! Russia was the last country to officially convert to the Gregorian system, but only after the Bolshevik Revolution in 1917! That is also why "Greek Easter" is usually one week later than Catholic Easter.
This entire discussion is also an entirely Western Euro-centric view, because the Middle East and Asian countries use calendars that are totally different than ours anyway! The Hebrew calendar is really the only calendar that takes into account the motions of the sun, earth, and moon completely.
So other than the fact that the year is measured by fixed astronomical events, the calendar that we use has very little to do with astronomy. Why is it the case that the vernal equinox always takes place around March 21? Is there something special about that date? No- it was just because that was the approximate date it was happening in 300+ A.D. relative to the Julian calendar, and the Catholic church wanted to "lock in" that date to make their religious calendar work.
This brings up several more topics which I have researched extensively in my free time over the years... such as:
Does it really matter if we think the next millenium begins in the year 2000 or 2001?
The year "1" was set in the fifth century after Roman Empire adopted Catholicism, based on the year they BELIEVED Jesus to be born. But it is believed today that they were off by several years. One way to determine the correct date is to use ASTRONOMY because the Bible mentions certain astronomical events. For example, the King Herod who was reigning at Christ's birth is believed to have died during a total lunar eclipse that was observable from Palestine, so if we know which eclipse this was, we can set a bound on when Jesus was really born.
We now have PC based software that can simulate when lunar eclipses happened indefinitely back into the past. This software can also be used to look at planetary conjunctions that occurred during that time to see if any of these might be candidates for the Star of Bethlehem. My best evidence points to June 2, 2 B.C.
If you want to know more.... email me at gcmastra@mcs.drexel.edu.
*"30 days has September...": It has been pointed out to me recently that Augustus did not 'steal' an extra day- Here is a link to a page that explains the reason for Hextilius being longer. Februalia was always the shortest month of the Roman Calendar. Only four months have 30 days, so there must occur two months in a row with 31- December and January also have 31 days each contiguously.
*Henry VIII:
Ken Collins points
out: Rather than to obtain a divorce, "Henry VIII's primary motive
was to stop a financial hemorrhage so that he could defend his country
against the Spanish Armada--the Pope, who was related to King Philip of
Spain, backed the Spanish. The Pope neglected to appoint English bishops
to fill vacant dioceses, which sent the diocesan income to Rome, depressing
the English economy and making it hard for Henry to raise money for defense.
Of course the English government was also obligated to pay the salaries
of all the monks, nuns, and priests, of which there were too many. The
first thing Henry did after breaking with Rome was to lay off all the clergy
who had no duties."
(Thanks also to Robert Ridgeway
of Dumbarton Scotland for pointing out another inaccuracy about Henry VIII
which I already corrected.)
What do you think? Share your thoughts with me (gcmastra@mcs.drexel.edu)
via email.
Thanks in advance for your positive feedback. The response to
this page continues to surprise me!
Chris Mastrangelo
Washington DC USA
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