1. How do we track the flow of time?
Calendars
How do we track the flow of time?

2. Ancient Calendars
Many ancient civilizations created calendars based on the patterns they observed from the stars. By studying the movements of the sun, the moon, the planets and the stars, they could create very accurate calendars based on the predictable movements of these celestial bodies.
Many ancient civilizations developed such calendars:
Egypt, China, Greece, Mayan, Aztec

3. Mayan Calendar One of the most famous of the ancient calendars.
Much information about Mayan beliefs were displayed on the calendar, (Ex: belief that Earth is flat and has four endpoints, one for North, South, East and West).
Very accurate calendar. Had a system for charting a year with approximately 360 days, very close to our current system.
No tools used; the calendar was developed solely on their observations of the stars and patterns. Based mainly on the movements of the sun, the moon, and Venus.

4. The End of the World???
A very popular rumor held that the Mayan calendar predicted many significant dates in history. And since the calendar appeared to ‘end’ or cease to go any farther, passed December 21, 2012, that this must signal the ending of the world.
This turned out to be a misinterpretation of the reading of the calendar. This date simply signaled the end of one of the calendars cycles, called the long count, which was used to track long periods of time in order to record historical events. A new long count simply begins anew after the old one ended, and no such cataclysmic event is predicted. The next long count is calculated to end on October 13, 4772.

5. Julian Calendar
Developed by the Roman empire and implemented by Julius Ceaser in 46 B.C.
It very much resembles our modern calendar, splitting the year into 12 months with alternating 30 and 31 days, (except February), with a total of 365 days in a year.
It also accounts for leap years, predicting that a year actually lasts days, and so every four years a leap year occurs to account for this additional day, making it 366 days every fourth year.

6. Gregorian Calendar
Our modern calendar, the one still in use today by us and most of the world.
Implemented by Pope Gregory XIII in 1582
Very closely resembles the Julian calendar: 12 months, 365 days/year, 30/31 days per month except Feb.
The only difference is that the Gregorian calendar acknowledges that the Earth’s actual year is slightly less than days, (more like .24). Even some ancient cultures knew this to be true.
The Gregorian calendar accounts for this by modifying the rules for leap years to adjust how often they occur, to make sure the years stay correct with the revolution of the Earth around the sun. The Julian calendar simply has a leap year every four years, meaning it will gradually drift away from the correct time.