Professor Sharon Kay Evanshine

History Web Site

Timeline of interesting calendar facts

Length of the tropical year, defined as the average interval between vernal equinoxes. This calendar year was the objective of the Gregorian calendar reform, which finalized the calendar as we use it today.				365 days, 5 hours, 49 minutes (365.2424 Universal days)
Lengthening of the vernal equinox year over the last two millennia				About 10 seconds (0.0001 universal days per year)
Variation of this length in the next few millennia				less than 5 seconds
Lunar month in 2000 C.E.				29 days, 12 hours, 44 minutes, 2.9 seconds
The earliest known date				4236 B.C.E., the founding of the Egyptian calendar
Ancient Egyptian calendar year				365
Date Emperor Huangdi invented the Chinese calendar (legend)				2637 B.C.E.
Early Chinese year				354 days (lunar year) with days added at intervals to keep the Chinese lunar calendar aligned with the seasons
Early Greek year				354 days, with days added
Jewish Year				354 days, with days added
Early Roman year				304 days, amended in 700 C.E. to 355 days
The year according to Julius Caesar (The Julian calendar)				365 1/4 days
Date Caesar changed Roman year to Julian calendar				January 1, 45 B.C.E
Time the old Roman calendar was misaligned with the solar year as designated by Caesar				80 days
Total length of 45 B.C.E., known as the "Year of Confusion," after adding 80 days				445 days
Date Sanhedrin president Hillel II codified the Jewish calendar				ca. C.E. 359
The year as amended by Pope Gregory XIII (Gregorian calendar year)				365 days, 5 hours, 49 minutes, 12 seconds
Date Pope Gregory reformed the calendar				1582
Length of time the Julian calendar overestimates our calendar year per year, as determined by Pope Gregory				10 minutes 48 seconds
Days Pope Gregory removed to correct the calendar's drift				10 days
Dates Gregory eliminated by Papal bull to realign his calendar with the solar year				October 5-14, 1582
Dates most Catholic countries accepted the Gregorian calendar				1582-1584
Date Protestant Germany accepted the Gregorian calendar				partial acceptance in 1700, full acceptance in 1775
Date Great Britain (and the American colonies) accepted the Gregorian calendar				1752
Date Benjamin Franklin first proposed Daylight Saving Time				1784
Days eliminated by the British Parliament to realign the old calendar (Julian) with the Gregorian calendar				11 days
Dates Parliament eliminated				September 3-13, 1752
Date Japan accepted the Gregorian calendar				1873
Date Russia accepted the Gregorian calendar				1917 (and again in 1940)
Date China accepted the Gregorian calendar				1949
Date the Eastern Orthodox Church last voted to reject the Gregorian calendar and retain the Julian calendar				1971
Length of time the Gregorian calendar is off from the average vernal equinox year				about 12 seconds per year
Length of time the Gregorian calendar has become misaligned with the vernal equinox over the 414 years since Gregory's reform in 1582			1 hour and 20 minutes
When the Gregorian calendar will become twelve calendar hours ahead of the astronomer's mean tropical year			4th or 5th millennium C.E.
When the Gregorian calendar will become twelve calendar hours ahead of the mean vernal-equinox year			beyond the 7th millennium C.E.
Date Atomic Time replaced Earth Time as the world's official scientific time standard			1972
Current official definition of the second			time it takes for 9,192,631,770 oscillations of the Cesium atom at zero magnetic field
The mean vernal equinox year expressed in oscillations of atomic cesium at the year 2000			290,091,329,207,984,000