The History of the Gregorian Calendar ED STAPLES
Close up of My Watch
Lunar or Solar? The story of the calendar is essentially centred around the three natural cycles of the daily sun rise, the lunar cycle, and the tropical year.
The 7 day week The seven day week has no natural markers. It is an intellectual creation and does not fit well with the lunar or solar calendar.
Check your salary!
Because there are 313 fortnights in 12 years
1 st Roman Calendar: Romulus 753 BC
Changes by King Numa: 7 th Century BC Lunar Calendar
Beware the ides of March!
1 st Attempt to align with seasons: Numa 2
Julius Caesar 46BC (Sosigenes) The Julian Calendar
Caesar’s adjustment to the vernal equinox
432BC : The Metonic Cycle (Greece)
Golden numbers still used to determine date of Easter Sunday Golden numbers
Solar year re-calculated as years The time between two successive vernal equinoxes can be estimated accurately by using a device first used by Ptolemy of Alexandria (2 nd Century AD) called an equatorial ring.
Go to the Equator – look East E W
Solstice – Sun in Capricorn
equinox
Solstice – Sun in Cancer
equinox
Solstice – Sun in Capricorn
Like a coil of rope Solstice EAST
The precise moment of the equinox East
Walking south to Canberra Lat:35S If we walk south back to Canberra from the equator, the rising vertical star lines will appear to lean away from us (lean toward the north) This is because we are on a spherical earth
Canberra Sun rising South East North Lat 90 - Lat
Motion of the Sun over the year North South Lat
Looking East in Canberra
Looking South in Canberra South Canberra Latitude 35 degrees
The equatorial ring 90 - Lat
The equatorial ring 90 - Lat
The equatorial ring 90 - Lat
The equatorial ring 90 - Lat
The equatorial ring Equinox point Shadow falls 90 - Lat
The equatorial ring Post Equinox point Shadow falls 90 - Lat
Equinox by Sundial? The, shadow is shortest in Summer and longest in winter, so at some stage in its “vertical” journey, the shadow tip will touch the equinox line. (twice a year )
A Canberra Sundial (35 deg gnomon) Equinox line Summer Solstice Winter Solstice
Hence…. Actual Tropical Year days Julian assumption days Difference days (Spotted by the Venerable Bede in AD 725
Do the Maths! X 24 X 60 = 11 minutes and 15 seconds
How the small difference accrues 11 minutes 15 seconds each year 45 minutes over 4 years 1 day over 128 years 4,500 minutes or 75 hours or 3 days 3 hours over 400 years
Luigi Lilio’s solution Drop 3 leap years every 400 years If a centurial year is not divisible by 400, drop the leap year! So 1800,1900,2100,2200,2300,2500,… NOT leap years even though they are divisible by 4.
Pope Gregory: 1582 (Lilio) The Gregorian calendar
The UK experience 1751
10 minute break
Zeller 1883
Conway’s Doomsday
Corrections