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July 31 The Caesar MonthsWe are moving from July to August. Both months are named for Roman emperors. How did this come about? Well, we need to go back to the Roman calendar before Julius Caesar. In those days, the calendar was alternating months of 29 and 31 days. As I said in an earlier post, a month started as a cycle of the Moon's phases, about 29.5 days. So, why wouldn't the calendar be alternating 29 and 30 day months? Well, simply, the Romans thought that 30 was an unlucky number. But, alternating 29 and 31 day months don't add up to the right number of days to keep track of the seasons, which repeat about every 365.24 days. So, the Romans would take the last month of the year, February (they started in March), and add some days in the middle of it. How many days do you add? Well, they had people who decided that. The problem was that they didn't use any good reason for their decisions. Sometimes they'd put too many days in, and often too few. So, by the time that Julius Caesar became emperor, the whole thing was so screwed up that they had to add nearly a couple hundred days into the middle of February to fix the calendar so that the first month of the year, March, would be in the spring. After this "year of confusion" Julius Caesar imposed new rules for the calendar. Undoubtedly, he got the idea from Egypt. In Egypt, they knew the length of the year to very high precision. So, to keep the calendar right, they'd run a 365 day year, with an extra day between the years every now and then as needed. Generally that was every four years. It wasn't exactly a rule to do that every four years, but it would work that way for almost a century before they needed to skip a year. Probably Caesar didn't know that, so his rules did not allow for that provision, a problem that would require a major revision to the calendar by Pope Gregory XIII, but that is a different story. Anyway, the new calendar that Julius Caesar implemented had alternating 31 and 30 day months, except for February, which had 29 days, with one extra day every four years. After the new calendar went into effect, the fifth month of the year, the fifth month of the year (remember, starting in March), was renamed from Quintilius (meaning fifth) to Iulius (from which we get July). Eventually, Augustus became Caesar. Well, to honor him, the sixth month, Sextilius, was renamed Augustus (in English, simply August). The seventh, eighth, nineth, and tenth month were left September, October, November, and December. However, there was a problem. August had one fewer days than July. So, a day was moved from February to August, leaving February with 28 days, with one extra every four years. But, that left July, August, and September as three months in a row of 31 days. So, a day was moved from September to October, and from November to December. That left a calendar that looks just like what we have today (with the eventual change of starting the month with January instead of March). This was the Julian Calendar. The only problem was that the new calendar had an average year of length of 365.25 days. The seasons actually repeat about every 365.24 days. So, after long enough, there was a day's error in the calendar. Over the centuries, this error accumulated, to that by the Sixteenth Century, it was over a week off. Due to the rules for computing Easter (the Sunday following the Full Moon following March 21, which was supposed to be the Vernal Equinox), that holiday was being celebrated a month off about 1/4 of the time. The Catholic Church decided that that was a very bad thing. So after decades of study, Pope Gregory XIII issued a papal bull decreeing a new calendar. The new calendar, to replace the old Julian Calendar, is called the Gregorian Calendar. This calendar has months the same as the Julian calendar months. But, the rules for leap year changed. Now, leap year is every four years, except centennial years (the last year of each century), unless those centenial years are evenly divisible by 400. So, the year 1900, the last year of the Nineteenth Century was not a leap year, even though 1896 and 1904 were leap years. It was one of the ones skipped. But, the year 2000, the last year of the Twentieth Century, was a leap year since it was evenly divisible by 400. This new calendar went into effect in 1582. But the problem with Easter would remain unless the calendar were shifted so that the Vernal Equinox came closer to March 21. So, in the year 1582, October was shortened by ten days. October 4 of that year was followed by October 15, not October 5. That shifted the calendar to make March 21 the Vernal Equinox. But, of course the Pope is Catholic. Sadly, some Protestant countries went to war with Catholic countries over the calendar. As bizarre as it may seem, some people actually believed that the Pope was trying to steal 10 days out of everyone's life so that he'd live forever. Yep. People fought and died over what the date should be. Some countries did not adopt the new calendar for centuries to come. Anyway, enjoy these Caesar months! -Astroprof Comments (3)
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