Celestial bodies – the sun, moon, planets, and stars – have provided us a reference for measuring the passage of time throughout human existence. Ancient civilizations like: China, India, Babylon, and Greece relied upon the apparent motion of these bodies through the sky to record and determine seasons, months, and years. We know little about the details of timekeeping in prehistoric eras. However, records and artifacts usually uncover that in every culture, people were preoccupied with measuring and recording the passage of time. Stonehenge, built over 4000 years ago in England has no written records, but its alignments show its purposes apparently included the determination of seasonal or celestial events, such as lunar eclipses, solstices and so on. As time has passed so has the evolution of the calendar, a device created to track our time and seasons from the earliest recordings in Babylonia to the Gregorian calendar the history of this transformation is and interesting journey.
The earliest know calendar to keep track of the cycles of the celestial bodies was an Egyptian calendar that was based on the moon’s cycles and is thought to have been created in 4236 B.C.E. Many cultures and societies have embraced the idea of tracking time and seasons as they pass for a myriad of reasons, Seafarers needed to navigate their vessels, and farmers had to know when to plant their crops. (Chaisson / McMillan p.30) The Chinese are credited with having invented the second oldest method of time keeping; Emperor Huangdi implemented the Chinese legend in 2637 B.C.E.
Babylonia (where modern day Iraq can be found) is attributed with having some of the earliest surviving records of astronomical observations. It is believed, Babylonian astronomical knowledge spread far and wide to the East, to Persia, and to the Mediterranean. (Richards p. 38) However, the knowledge that was disbursed was not treasured by all that received it, in the Mediterranean the Greeks improved upon the theories of the Babylonians. The Greeks theories were recorded; however, when Rome over-took most of Europe the records fell into the hands of the Christian church. When Constantine was Emperor of Rome he declared Christianity to be the official religion of the empire; thus, giving the church officials the power to decide the validity of the recordings. Given that the Greeks theories were of a secular nature and they did not fit into Christian dogma, the documents were destroyed or sold during the Christian Middle Ages. Luckily, our neighbors to the East, the Arabs, found the documents to be of great interest and kept old Greek astrological records. In the Renisannce period of Christianity the church officials decided to re-examine the ancient records, and actually found some validity in some of the scientific data. Amazingly enough the Christian church decided to implement data from ancient pagan cultures to help create the most widely used calendar to date, the Gregorian calendar.
Ancient Greek astronomers made some amazing mathematical and philosophical discovers about our universe. From the Hellenistic Greek observations in approximately 300 B.C.E., to the invention of the first telescope in the seventeenth century, to the launching of todays space probes, one thing is evident: astrological observations are imperative to creating a calendar.
Currently, the concept of a year is based on the earth’s motion around the sun. The time from one fixed point, such as a solstice or equinox, to the next is called a tropical year; its length is currently 365.242. Our concept of a month is based on the moon’s motion around the earth, although this connection has been broken in the calendar commonly used now, the Gregorian calendar. The time for the moon to complete a full cycle of phases is called a synodic month, and its length is currently 29.53 days. Note that these numbers are averages. The actual length of a particular year may vary by several minutes due to the influence of the gravitational force from other planets. Similarly, the time between two new moons may vary by several hours due to a number of factors, including changes in the gravitational force from the sun, and the moon’s orbital inclination. It is unfortunate that the length of the tropical year is not a