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Calendars Roman Calendar Lunar based on 29.5 day lunar cycle of phases. Months equaled 29 or 30 days 12 lunar months = 354 days NOT 365.35 days A leap month was added every 4 years

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roman calendar
Roman Calendar
  • Lunar based on 29.5 day lunar cycle of phases.
  • Months equaled 29 or 30 days
  • 12 lunar months = 354 days NOT 365.35 days
  • A leap month was added every 4 years
  • Priests determine year to which a month was to be added. However, they abused the privilege whenever their friends were in office and would sneak in an extra leap month.
how do current political systems mess with time keeping
How do current political systems mess with time keeping?
  • Time zones (they do not all equal 1 hour of time.)
  • Daylight savings time (some states observe and some do not.)
  • Nixon declared daylight saving year round to conserve fuel in 1973 oil crises.
julian calendar
Julian Calendar
  • Things got out of hand because of the leap month and travelers did not always know what month or year is was in different places within the Roman Empire
  • In 44 BC Julius Caesar started a new calendar on January 1, 45 BC
julian calendar5
Julian Calendar
  • Lunar months abandoned in favor of a 12 month year with 365 days.
  • Months alternated having 31 & 30 days.
  • Every 4th year February was given an extra day, leap year.
  • 1st day of spring (Vernal Equinox) was declared to be March 25th.
  • Julius named July after himself and stole a day from February making it 29 days long.
  • Augustus named August after himself and stole another day from February.
  • Soooo, July and August have 31 days and February has only 28 days.
julian calendar the problem
Julian CalendarThe Problem!
  • 1 year = 365.25 days not 365 days
  • which was 11 min and 14 sec longer.
  • By 325 A.D. this slight difference added up to cause the 1st day of spring to be occurring on March 21st not the 25th.
  • By 1582 the 11 min 14 sec difference was causing a 10 day disparity and the 1st day of spring was occurring on March 11th!
tower of winds
Tower of Winds
  • Windowless chamber.
  • All four walls decorated in a large fresco showing winds of the Bible.
tower of winds8
Tower of Winds
  • One of the fresco’s depicts the shipwreck of St. Paul.
  • A hole in the south wind allows a beam of sunlight to shine onto a sundial on the floor.
  • A Jesuit astronomer Christopher Clavius showed Pope Gregory XIII that the calendar was running ten days behind the actual 1st day of spring.
  • This meant that sometime in the future Easter would be occurring at Christmas, and Christmas near the 1st day of fall in Sept.

gregorian calendar
Gregorian Calendar

In 1582 Pope Gregory XIII instituted the following changes.

  • Drop the 10 days and make Vernal equinox be on March 21st. So, Oct. 4, 1582 became Oct. 15, 1582. (He is the Pope and can do whatever he wants.)
  • Leap years remain the same except that three out of four century years will NOT be leap years ( they were in the Julian Calendar).
  • The average year became 365.2425 years, which in error by only 1 day in 3300 years.
gregorian calendar eastern orthodox version
Gregorian CalendarEastern Orthodox Version
  • In 1923 Churches of Constantinople made a slight modification to improve the Gregorian Calendar.
  • NEW LEAP YEAR RULE: Century years that when divided by 900 had a remainder in the 200’s or the 600’s will be leap years.
  • 2000 and 2400 are leap years and 2100, 2300, 2500, 2600, and 2700 are NOT leap years.
  • This Eastern Orthodox version has an error of only 1 day in 44,000 years.

Abell, G. O. (1982). Exploration of the Universe, 4th Ed.

Gingerich, O. (1992). The Great Copernicus Chase and Other Adventures in

Astronomical History.