astronomy Astronomy is a natural science that studies celestial objects and the phenomena that occur in the cosmos. It uses mathematics, physics, and chemistry in order to explain their origin and their overall evolution. Objects of interest includ ...

, an octaeteris (, plural: octaeterides) is the period of eight

solar year A tropical year or solar year (or tropical period) is the time that the Sun takes to return to the same position in the sky – as viewed from the Earth or another celestial body of the Solar System – thus completing a full cycle of astronom ...

s after which the moon phase occurs on the same day of the year plus one or two days. This period is also in a very good synchronicity with five

Venus Venus is the second planet from the Sun. It is often called Earth's "twin" or "sister" planet for having almost the same size and mass, and the closest orbit to Earth's. While both are rocky planets, Venus has an atmosphere much thicker ...

ian visibility cycles (the Venusian synodic period) and thirteen Venusian revolutions around the Sun (Venusian sidereal period). This means, that if

is visible beside the

Moon The Moon is Earth's only natural satellite. It Orbit of the Moon, orbits around Earth at Lunar distance, an average distance of (; about 30 times Earth diameter, Earth's diameter). The Moon rotation, rotates, with a rotation period (lunar ...

, after eight years the two will be again close together near the same date of the

calendar A calendar is a system of organizing days. This is done by giving names to periods of time, typically days, weeks, months and years. A calendar date, date is the designation of a single and specific day within such a system. A calendar is ...

. : The octaeteris, also known as ''oktaeteris'', was noted by Cleostratus in

ancient Greece Ancient Greece () was a northeastern Mediterranean civilization, existing from the Greek Dark Ages of the 12th–9th centuries BC to the end of classical antiquity (), that comprised a loose collection of culturally and linguistically r ...

as a day cycle. The octaeteris is the calendar used for the

Olympic games The modern Olympic Games (Olympics; ) are the world's preeminent international Olympic sports, sporting events. They feature summer and winter sports competitions in which thousands of athletes from around the world participate in a Multi-s ...

; if one

Olympiad An olympiad (, ''Olympiás'') is a period of four years, particularly those associated with the Ancient Olympic Games, ancient and Olympic Games, modern Olympic Games. Although the ancient Olympics were established during Archaic Greece, Greece ...

was 50 months long, the next would be 49 lunar months long. This octaeteris calendar is used for the Olympic dial of the

Antikythera mechanism The Antikythera mechanism ( , ) is an Ancient Greece, Ancient Greek hand-powered orrery (model of the Solar System). It is the oldest known example of an Analog computer, analogue computer. It could be used to predict astronomy, astronomical ...

, to determine the time of the Olympic games and other Greek festivities. The 8 year short lunisolar cycle was probably known to many ancient cultures. The mathematical proportions of the octaeteris cycles were The Three Kings panel also contains more accurate ratios, ratios related to other planets, and apparent astronomical symbolism.

References

* {{Greek astronomy Ancient Greek astronomy Calendars Time in astronomy

See also

References