LYCOS RETRIEVER 
Julian Calendar
built 353 days ago
The Julian Calendar is a way of reckoning the current date by a simple count of the number of days that have passed since some remote, arbitrary date. This number of days is called the Julian Day (or Julian Date), abbreviated as JD. The starting point, JD=0, is January 1, 4713 BC (or -4712 January 1, since there was no year '0'). Julian Dates are very useful because they make it easy to determine the number of days between two events by simply subtracting their Julian Day numbers. Such a calculation is difficult for the standard (Gregorian) calendar, because days are grouped into months, which can contain a variable number of days, and there is the added complication of Leap Years.
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The Julian Calendar is a solar calendar that was introduced in the Roman Empire, in the year now referred to (in the Common Calendar) as -44, during the reign of Julius Caesar, for whom it and its fifth month are named. The calendar was slightly reformed by emperor August, for whom the sixth month is named. After this reform, which was complete by the year now referred to as year 8 C.E., this calendar was used continuously in many regions of Europe until 1582 C.E., though there was variation (over both time and region) in such things as the used epoch, the used day count within each month, and which day was the first day of the year. The following description reflects the modern choices for these things.
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The change from the Julian Calendar to the Gregorian Calendar involved turning the simple 4-year rule for leap years into a more complex one in which century years should only be leap years if they were divisible by 400. For example, 1700, 1800 and 1900 are not leap years whereas 2000 is.
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By the 15th century the Julian calendar had drifted behind the solar calendar by about a week, so that the vernal equinox was falling around March 12 instead of around March 20. Pope Sixtus IV (who reigned from 1471 to 1484) decided that another reform was needed and called the German astronomer Regiomontanus to Rome to advise him. Regiomontanus arrived in 1475, but unfortunately he died shortly afterward, and the pope's plans for reform died with him.
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The Julian calendar map can be put to good use with both solar returns and secondaries. Here are some examples. The tropical solar return for 1860, set for Washington, has Uranus on the Descendant (orb 51'), not a bad symbol for the U.S. Civil War. The solar return for 1917, set for Moscow, has Pluto on the Descendant (orb 53'). As for day-for-a-year secondaries, with solar-arc Midheaven, a good example is that for the beginning of the Second World War, 1st September 1939. This progressed map (set for the radical place, Rome) has the Moon applying to an opposition with Saturn, and the opposition straddles the progressed horizon; in fact Saturn is on the Moon/Ascendant midpoint (orb 35') in the 90-degree dial.
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The average length of a year in the Julian Calendar is 365.25 days (one additional day being added every four years). This is significantly different from the "real" length of the solar year. However, there is uncertainty among astronomers as to what the length of the solar year really is (see Simon Cassidy's Error in Statement of Tropical Year). The main competing values seem to be the "mean tropical year" of 365.2422 days ("mean solar days") and the "vernal equinox year" of 365.2424 days. The difference of the length of the Julian calendar year from the length of the real solar year is ... 0.0078 days (11.23 minutes) in the former case and 0.0076 days (10.94 minutes) in the latter case.
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Julian Calendar