1. The History of the Gregorian Calendar ED STAPLES

2. Close up of My Watch

3. 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.

4. 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.

5. Check your salary!

6. Because there are 313 fortnights in 12 years

7. 1 st Roman Calendar: Romulus 753 BC

8. Changes by King Numa: 7 th Century BC Lunar Calendar

9. Beware the ides of March!

10. 1 st Attempt to align with seasons: Numa 2

11. Julius Caesar 46BC (Sosigenes) The Julian Calendar

12. Caesar’s adjustment to the vernal equinox

13. 432BC : The Metonic Cycle (Greece)

14. Golden numbers still used to determine date of Easter Sunday Golden numbers

15. Solar year re-calculated as 365.2219 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.

16. Go to the Equator – look East E W

17. Solstice – Sun in Capricorn

18. equinox

19. Solstice – Sun in Cancer

20. equinox

21. Solstice – Sun in Capricorn

22. Like a coil of rope Solstice EAST

23. The precise moment of the equinox East

24. 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

25. Canberra Sun rising South East North Lat 90 - Lat

26. Motion of the Sun over the year North South Lat

27. Looking East in Canberra

28. Looking South in Canberra South Canberra Latitude 35 degrees

29. The equatorial ring 90 - Lat

30. The equatorial ring 90 - Lat

31. The equatorial ring 90 - Lat

32. The equatorial ring 90 - Lat

33. The equatorial ring Equinox point Shadow falls 90 - Lat

34. The equatorial ring Post Equinox point Shadow falls 90 - Lat

35. 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 )

36. A Canberra Sundial (35 deg gnomon) Equinox line Summer Solstice Winter Solstice

37. Hence….  Actual Tropical Year 365.24219 days  Julian assumption365.25 days  Difference 0.00781 days  (Spotted by the Venerable Bede in AD 725

38. Do the Maths!  0.00781 X 24 X 60 = 11 minutes and 15 seconds

39. 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

40. 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.

41. Pope Gregory: 1582 (Lilio) The Gregorian calendar

42. The UK experience 1751

43. 10 minute break

44. Zeller 1883

45. Conway’s Doomsday

46. Corrections