University Lowbrow Astronomers

Ancient Time Keepers

by Lorna Simmons
Printed in Reflections:  June, 1999.

Do you often wish you could throttle the folks who invented time and time keeping devices?  These contraptions cut into your leisure time by making it almost impossible to enjoy “a nice relaxing day”!  Well, here are some of the sparse historical facts, and now you can know whom to blame for your lack of leisure - The ancient astronomers!  Your very own astronomical kin.

Early on, humans started keeping time in one way or another for a variety of reasons.  They must have noticed the regularity of the rising and setting of the sun and needed to have accurate measurements of such events.  Notches which were carved on the discovered artifacts of early humans have been interpreted as being tally marks or counters, as a means of keeping track of the seasons and times of the year, and, importantly, as records of the lunar cycle.  Early humans were keeping records early on.  A marked bone which was probably used as a record of months and lunar phases and which was from approximately 9000 to 8001 BC or as late as 6500 BC was found in Ishango, which is now Zaire.  Primitive hunter-gatherers had already detected patterns in the apparent motions of the stars and possibly even in the real motions of the planets through the night sky.  These same traditions appeared later in Egypt and in Central America and are thought to have been associated with specific apparent motions of Sirius and Venus.

Of first importance to early people, and upon which all people could agree, with any degree of accuracy, was the measurement of time using fairly large amounts of time.  Large amounts of time are easily measured because the “clockwork” is supplied by the universe, itself, as seen in the daily and annual motion of Earth and the Moon.  Even so, the more careful measurements of time were not easy to come by.  One revolution of Earth constitutes a day and a “moon” is from one new moon to the next; but yearly measurements were not very simple to measure.  In addition, a day is not very easy to measure accurately.  It took some time before humans learned to measure the day from one noon (when the Sun is at its highest point in the sky) to the next.

A good length for the year was first established by the ancient Egyptians, probably because the Nile floods annually about the same time.  This flooding generally occurs when Sirius rises at approximately the same time as the sun (helical rising).  A year is approximately 365 days, 5 hours, 48 minutes and 46 seconds, approximately one quarter of a day longer than 365 days.  Between 5000 to 4001 BC, the Egyptian calendar appeared, being the first known calendar to be based on 365 days (indicating 12 months of 30 days and 5 days of festival, beginning with the day that Sirius, the Dog Star, rises in line with the Sun in the morning, which coincides with the annual flood of the Nile).  From astronomical evidence only, it was possibly instituted as early as 4241 BC or perhaps about 1500 years later.  Because the Egyptian calendar is known to have accurately matched the seasons with dates in 139 AD and gradually went into and out of alignment with the seasons with a period of about 1455 years, astronomers have deduced that the year of 365 days began about 4228 BC or 2773 BC.

Hellenic astronomers added the missing 1/4 day to the Egyptian calendar by adding an extra (leap) day every four years, but most people ignored it.  The calendar with a leap day was finally adopted by the Romans under Gaius Julius Caesar in 4 BC.  Since then, the calendar has had one major modification, when Pope Gregory, in 1582, on the advice of astronomers, dropped the leap day in years that end in two zeros.

Later, sometime between 2600 and 2501 BC, the Chinese used a vertical pole to project the shadow of the sun for the purpose of estimating time.  Sometime, between 2200 and 2101 BC, the Sumerians began to use a 360-day year, 12-month solar calendar along with a 354-day lunar calendar.  This calendar included an extra month every eight years in order to keep it in step with the seasons.  From 1500 to 1451 BC, the gnomon, which is the L-shaped indicator on a sundial, was regularly used by the Egyptians.  Thutmose III erected the “Needle of Cleopatra” in Heliopolis.  Its shadow was used to calculate the time, the seasons, and the solstices.

The earliest history of humanity has no known dates.  After writing began to be used, people started dating events, but these were usually in relation to other events that we can no longer date.  The long histories of the Egyptian and the Chinese dynasties, however, provided fairly good year dates for those cultures back to 3000 BC.

The Mayans recorded specific day dates that go back in time tens of thousands of years.  Since many of the events dated in this system occurred before the most optimistic early date for humans in North America, it is assumed that these very early dates are for mythical events that were invented much later.  Very early Chinese dates also are thought to have been late inventions.

A strong candidate for the first real date in history, that is, the first specific day on which an event can be pinpointed as having occurred, is May 28, 585 BC.  The event was a battle between the Medes and the Lydians that was suddenly called off when an eclipse of the Sun frightened both armies.  This eclipse, supposed to have been forecast correctly by Thales (although at best he would have had the year right, not the date), could only have been the one observable in the Middle East on May 28, 585.  No other solar eclipse would have been visible in that region for many years on either side of 585.

A similar candidate for the first date, September 6, 775 BC, comes from Chinese astronomical records.  It is the earliest date that records an astronomical event that we can say occurred at a particular time.  However, it is not connected with any other event such as the war of the Medes and Lydians.

Dates were not rigorously kept during the Greek and Hellenistic period, although Chinese dates at this time were more certain.  To make matters complicated for us, most dates were given in “Olympiads” which could only be localized to within a four-year period.  Approximate dates for the lives of many of the well-known scientists and philosophers in that era have been worked out by historians from bits and pieces of evidence.  For instance, if you read in some sources that Thales was born in 624 BC and died in 546 BC you can assume that such dates are indefinite as to source.  Instead, historians have been clever and, when only one date in a person’s life is known, the historians assumed that the person must have been around 40 when the event occurred.  For instance, historians know the year that Thales is said to have predicted an eclipse, which astronomical calculations put at 585 BC.  Therefore, it is assumed that Thales may have been born around 623 BC.  Because there is a tradition that Thales lived to be about 70, historians think he may have died in 546 BC.  Therefore, because of the uncertainty of the dates during this period, consider all dates as occurring within the decade surrounding that date, or even, possibly, in an adjacent decade.  Sometimes it had to be assumed that events listed only in the first decade of a century should be considered as having occurred at some date during that century.  Often, the century is uncertain, as well.  An early astronomer, Kiddinu, who was born in Babylon between 340 and 331 BC, devised an early version of the precession of the equinoxes which was somewhat inaccurate.  The precession of the equinoxes refers to the apparent change over a period of 26,700 years in the position of the fixed stars which is caused by Earth’s wobbling in its orbit.  Later, from 160 to 141 BC, Hipparchus of Nicea (in Turkey), who was born around 190 BC, listed the fixed stars and more accurately discovered the precession of the equinoxes.

Andronikos of Kyrrhestes, from 50 to 41 BC, built in Athens the Tower of Winds, which was a water clock combined with solar clocks positioned in the eight principal directions.  It is the most accurate device that the Greeks had devised by then for keeping time.  In 132 Zhang Heng in China combines a water clock with an armillary to produce a device, somewhat like the modern planetarium, to keep track of where stars are expected to be in the sky. 

Often misguided writers will believe that there was some coordination between the early peoples and that they corresponded with each other to produce these devices.  Wrong!  While at rare instances there might have been some correspondence between the members of various civilizations (particularly as one civilization conquered another more scientifically or technically advanced civilization), most of this invention was begun with the single fact of the night sky to lead them.  All of these astronomers were able to devise means of keeping time, first generally, but becoming more and more specific as their methods improved, simply because of the improvement of astronomical techniques.

Let us hear a cheer for the ancient astronomers!  Where would we have been without them?  Next time you visit Peach Mountain (or any dark site); observe a moment of silence, contemplating their brilliance in achievement over the millennia.  Your excellent observing powers of today began with their humble first efforts.


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