3. Ancient Timekeeping
All calendars began with people recording time by using natural cycles: days, lunar cycles (months), and solar cycles (years). Ancient peoples have attempted to organize these cycles into calendars to keep track of time and to be able to predict future events of importance to them, such as seasons (e.g. the annual Nile flood in ancient Egypt), eclipses etc. The main problem was that these natural cycles did not divide evenly.
A calendar is a system of organizing time. It is used for social, religious, commercial, or administrative purposes. Timekeeping is done by giving names to periods of time, typically days, weeks, months, and years. Periods in a calendar (such as years and months) are synchronized with the cycle of the sun or the moon (ancient astronomers also used planet Venus and/or star Sirius) .
The astronomical day had begun at noon ever since Ptolemy chose to begin the days in his astronomical periods at noon. He chose noon because the transit of the Sun across the observer’s meridian occurs at the same apparent time every day of the year, unlike sunrise or sunset, which vary by several hours. Midnight was not even considered because it could not be accurately determined using water clocks. Nevertheless, he double-dated most nighttime observations with both Egyptian days beginning at sunrise and Babylonian days beginning at sunset.
The Babylonians were the first to recognize that astronomical phenomena are periodic and apply mathematics to their predictions.
Early people could either try to stay in sync with the moon, perhaps making months alternating combinations of 29 and 30 days, with special rules to re-sync occasionally with a solar year by adding leap months (such as the Jewish or Chinese calendar) or abandon lunar cycles and concentrate on the solar year (such as the Ancient Egyptian calendar of 12 same-sized months).
Calendars in Ancient Egypt
The Ancient Egyptians are credited with the first calendar of 12 months, each consisting of 30 days, comprising a year. They added 5 days at the end of the year to synchronize somewhat with the solar year. By making all their months an even 30 days, they abandoned trying to sync with lunar cycles and concentrated instead on aligning with the solar year. The Egyptians recognized that this calendar didn’t quite align with a actual year. Since the traditional Egyptian calendar of 365 days fell about one-fourth of a day short of the natural year, the ancients assumed that the helical rising of Sirius would move through the Egyptian calendar in 365 x 4 = 1,460 Julian years (that is, one Sothic peniod).
The earliest Egyptian calendar was based on the moon’s cycles, but the lunar calendar failed to predict a critical event in their lives: the annual flooding of the Nile river. The Egyptians soon noticed that the first day the “Dog Star,” which we call Sirius, was visible right before sunrise was special. The Egyptians were probably the first to adopt a mainly solar calendar. This so-called ‘heliacal rising’ always preceded the flood by a few days.
They eventually had a system of 36 stars to mark out the year and in the end had three different calendars working concurrently for over 2000 years: a stellar calendar for agriculture, a solar year of 365 days (12 months x 30 + 5 extra) and a quasi-lunar calendar for festivals. The later Egyptian calendars developed sophisticated Zodiac systems. According to the famed Egyptologist J. H. Breasted, the earliest date known in the Egyptian calendar corresponds to 4,236 B.C.E. in terms of the Gregorian calendar.
Among their other accomplishments, the ancient Mayas invented a calendar of remarkable accuracy and complexity.
The Maya calendar was adopted by the other Mesoamerican nations, such as the Aztecs and the Toltec, which adopted the mechanics of the calendar unaltered but changed the names of the days of the week and the months. The Maya calendar uses three different dating systems in parallel, the Long Count, the Tzolkin (divine calendar), and the Haab (civil calendar). Of these, only the Haab has a direct relationship to the length of the year.
The length of the Tzolkin year was 260 days and the length of the Haab year was 365 days. The smallest number that can be divided evenly by 260 and 365 is 18,980, or 365×52; this was known as the Calendar Round. If a day is, for example, “4 Ahau 8 Cumku,” the next day falling on “4 Ahau 8 Cumku” would be 18,980 days or about 52 years later.
- Read the entire article about calendars:
- Aztec Calendar
One of the most astonishing inventions related to calendar is so called the Antikythera Mechanism.
In 1901 divers working off the isle of Antikythera found the remains of a clock-like mechanism 2,000 years old. The mechanism now appears to have been a device for calculating the motions of the sun, the moon and planets – an arithmetical counterpart of the much more familiar geometrical models of the solar system which were known to Plato and Archimedes and evolved into the orrery and the planetarium. The mechanism is like a great astronomical clock without an escapement, or like a modern analogue computer which uses mechanical parts to save tedious calculation.
- Antikythera Mechanism
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