Ancient Greek astronomical device with calendar dials
National Archeological Museum, Athens, GreeceMaterial: Bronze
Date range: Original from approximately 150-100 BC
Origin: Ancient Greece
The Antikythera mechanism is an ancient Greek device that calculated astronomical positions and eclipses. The front view shows dials tracking the zodiac and Egyptian calendar with pointers indicating planetary positions.
The back view displays the Metonic calendar dial organizing 235 lunar months into 19 years. Additional dials show the Callippic cycle, Saros eclipse prediction cycle, and the Olympiad dial marking Greek games.
This mechanism represents one of the most sophisticated scientific instruments from ancient times. It demonstrates advanced knowledge of astronomy and mechanical engineering in the Hellenistic period.
Museum label reference:
BACK VIEW
THE METONIC CALENDAR Describes the 235 months of a 19-year cycle, with month names from Corinth or one of its colonies.
THE CALLIPPIC DIAL A predictive supplement for the 76-year Callippic period (4 times 19 Metonic periods).
THE OLYMPIAD DIAL Each of the four sectors contains the local sources of the games, separated by vertical lines. Important Panhellenic games are listed, including Olympia, Nemea, Isthmia, and Delphi.
THE ZODIAC SCALE A scale with Greek letters for the signs of the zodiac. Key letters link to the observations on the Parapegma.
THE SAROS DIAL A predictive dial for the Saros period, which includes 223 lunar months and is used to predict eclipses.
THE EXELIGMOS DIAL A dial for the Exeligmos period, a more accurate eclipse prediction cycle of 669 lunar months (3 Saros periods).
FRONT VIEW
THE EGYPTIAN CALENDAR A fixed solar calendar with 365 days, used in ancient Egypt.
THE ZODIAC SCALE A scale with Greek letters for the signs of the zodiac.
THE MOON DISPLAY Possibly the most sophisticated part of the mechanism, showing the Moon’s phase and position.
THE SUN POINTER The motion of the Sun across the zodiac is displayed with a pointer.
THE PLANETS In addition to the Sun and Moon, the mechanism may have included pointers for the five known planets: Mercury, Venus, Mars, Jupiter, and Saturn.
The Metonic Cycle:
The cycle of the Moon from one new Moon to the next is called the lunar month. The problem for calendars is that a year is not a whole number of lunar months. The Metonic Cycle (named after the Athenian astronomer) addresses this problem by using the close identity of 235 lunar months with 19 years and 6,940 days. Meton proposed a calendar based on this cycle, starting at the summer solstice in 432 BC. Even today, the variable date of Easter, which depends on the phases of the Moon, is calculated using the Metonic Cycle.
The Callippic Cycle:
About a century later, the Ionian astronomer Callippos improved the accuracy of the cycle by equating four Metonic periods (4 times 19, equal to 76) with 27,759 days (4 times 6,940 minus one day).
Saros and Exeligmos Cycles:
The Babylonians observed that every 223 lunar months (6,585 and 1/3 of a day, approximately 18 years), lunar eclipses repeat with similar characteristics – a cycle called the Saros Cycle. The Saros period is not a whole number of days, and this means that the repeat eclipse is shifted by about 8 hours in time. The ancient astronomers identified a triple Saros cycle of 669 lunar months, which is a whole number of days. They called this cycle the "Exeligmos Cycle".
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