Calendar and timekeeping facts
extracted from David Ewing Duncan: The Calendar
London: Fourth Estate, 1996 (pp. v-viii, 18, 277-278)
General
year measurements | Length variations in natural
years | Ancient calendar years |
Varying
duration of different calendar years | Gregorian
calendar correction dates |
Year
2000 equivalents according to various calendars | When’s
Easter? |
|
Length of the (tropical) year in 2000 AD |
365
days, 5:48:45 (365.2422 days)
|
|
Time
that the year has slowed since AD 1
|
10
seconds
|
|
Average decrease in the year due to a gradual slowing of the earth's rotation |
½
second per century
|
|
Lunar Month |
29
days, 12:44:2.9 (29.5306 days)
|
|
Length of year in Atomic Time (replaced Earth Time as official world standard in 1972) |
290,091,200,500,000,000 |
Length
variations in natural years
|
Type of year |
Mean Time Interval (year 2000) in days |
| Lunar |
354.3672
|
| Sidereal |
365.2564
|
| Tropical |
365.242199
|
| Between vernal equinoxes |
365.24237
|
| Between summer solistices |
365.24162
|
| Between autumnal equinoxes |
365.24201
|
| Between winter solistices |
365.24274
|
|
Type
of year
|
Duration
|
|
Ancient Egyptian year |
365 days |
| Early Chinese year | 354 days (lunar year) + days added at intervals to keep the lunar calendar aligned with seasons |
| Early Greek year | 354 days, with days added |
| Jewish year | 354 days, with days added |
| Early Roman year | 304 days, amended in 700 BC to 355 days |
Varying
duration of different calendar years
| Type of year |
Date
|
Duration
|
Error
|
| Hipparchus' year |
130
BC
|
365d 5hr 55m | +0:06:14 |
| Julian calendar year |
45
BC
|
365d 6hrs | +0:11:14 |
| Ptolemy's year |
139
AD
|
365d 5:55:13 | +0:06:27 |
| Aryabhata's year |
499
AD
|
365d 8:36:30 | +2:47:44 |
| al Battani's year |
882
AD
|
365d 5:48:24 | -0:00:22 |
| Omar Khayyámm's year |
1100
AD
|
365d 5:49:12 | +0:00:26 |
| Alfonsine Tables year |
1252
AD
|
365d 5:49:16 | +0:00:31 |
| Copernicus' year |
1543
AD
|
365d 5:49:29 | +0:00:43 |
| Gregorian
calendar (Pope Gregory XIII) |
1582
AD
|
365d 5:48:20 | -0:00:26 |
Gregorian
calendar correction dates
|
Date
|
Correction
|
| 45 BC | 'Year of Confusion' (445 days). 80 days added to realign old Roman calendar with the solar year (Julian calendar). |
| 1582 | 10 days (5-14 October) eliminated by Pope Gregory's papal bull to realign his calendar with the solar year. |
| 1584 | Most Catholic countries have accepted the Gregorian calendar |
| 1752 | British and American colonies accept Gregorian calendar. British Parliament eliminates 11 days (3-13 September) to realign. |
| 1775 | All Protestant Germany has accepted Gregorian calendar. |
| 1873 | Japan accepts Gregorian calendar. |
| 1917 | Russia accepts Gregorian calendar. |
| 1971 | Most recent Eastern Orthodox Church decision to reject the Gregorian calendar and retain the Julian calendar. |
| 2002 | Gregorian calendar 2 hours behind solar year |
| 4909 | Gregorian calendar 1 day behind solar year |
Year
2000 equivalents according to various calendars
|
Calendar
type
|
Year 2000= |
|
First
Egyptian
|
6236
|
|
Jewish
|
5760
|
|
Current
Maya great cycle
|
5119
|
|
Ab
urbe condita
|
2753
|
|
Ancient
Babylonian
|
2749
|
|
Buddhist
|
2544
|
|
From
Christ's birth in 4 BC
|
1997
|
|
Coptic
|
1716
|
|
Moslem
|
1420
|
|
Persian
|
1378
|
|
French
revolutionary
|
208
|
|
Chinese
|
Dragon
|