In the developed world our lives are driven every day by calendars and clocks: What time is my flight, what day should we meet, how late can you work? In the world of scheduling and time-scaled planning, start dates, end dates, and durations is the order of the day. As far as we know we are the only creatures on earth who have a concept of passing time. But how many of us have stopped to consider where time and dates come from? Who invented the calendar? Is time really relative? Time does not seem especially relative on the critical path of a networked schedule!
A retrospective look at the humanity’s quest to understand dates and times may offer the reader a new perspective on the planning process and a broader understanding of the actual underpinnings of that thing we call a time-scaled plan.
“The calendar is intolerable to all wisdom, the horror of all astronomy, and a laughing-stock from a mathematician’s point of view” – Roger Bacon, 1267
Why was a Roman Catholic Monk raging against calendars in the mid 13th century? One might imagine an orderly, synchronized system of straight forward, almost mechanical precision, lurking just below the methodical appearance of calendars and clocks. However, as Holden Caulfield famously declared of his roommate, Stradlater, in Salinger’s “Catcher in the Rye”: time is a secret slob. Oh sure it looks all put together on the surface, but just peel back the top layer and one will find a messy contrivance worthy of Rube Goldberg!
Take for instance the formula below, used to calculate the day of Easter in the non-Orthodox, Christian church
a = year%19
b = year/100
c = year%100
d = b/4
e = b%4
r = (b + 8) / 25
g = (b – f + 1) / 3
h = (19 *a + b – d – a + 15)%30
i = c/4
k = c%4
1 = (32 + 2 * e + 2 * i – h – k)%7
m = (a + 11 * h + 22 * 1)/451
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Easter month = (h + 1 – 7 * m + 114/31 [3 = March, 4 = April]
p = (h + 1 – 7 * m + 114) % 31
Easter date = p + 1 (date in Easter month)
/ = division neglecting the remainder
% = division keeping only the remainder
* = multiply
One would typically imagine these types of mathematical machinations would have little to do with the orderly world of dates and times. But in fact at the time of Roger Bacon the calendar was an unstable mass if workarounds and shims. Today with all we know of the solar system, we still make adjustments to time, because of the gradual slowing of the rotation of the earth.
The Ancients
Creation of calendars
The Moon, the Stars, and Sun
27,000 years ago humankind was recording the passage of time through the phases of the moon. Archeologists note the 13 marks in this depiction of a moon shaped horn held skyward as a depiction of the phases of the moon. Archeologists have also discovered a moon phase calendar etched into an eagle bone from 11,000 BC. Around 3,000 BC Egyptians used a stick on the banks of the Nile (called a Nilometer) to measure the passage of time. As the waters of the Nile rose the stick would record the highpoint and thus the farmers could schedule their work towards the floods and next year’s crops. Later, observation of the stars, most specifically the Dog Star Sirius, enhanced the accuracy of the Egyptian calendar.
Around 1,000 BC Mesoamerican peoples developed complex pictorial representation of a, given its time in history, highly precise solar year. The development of calendars seems to be a global phenomenon throughout history regardless of race, religion, or geography. The Mayan calendar was so accurate that when Spaniards arrived the calendar they brought was less accurate than the Mayan calendar. Maya were able to calculate the cycle of Venus and would wage wars at the beginning of the cycle.
In the next entry we will explore the introduction of the Julian calendar and the amazing circumstance of the Gregorian correction.