The Metonic cycle or Enneadecaeteris in astronomy and calendar studies is a particular approximate common multiple of the year (specifically, the seasonal i.e. tropical year) and the synodic month. 19 tropical years differ from 235 synodic months by about 2 hours. The Metonic cycle's error is one full day every 219 years, or 12.4 parts per million. Radio telescopes are among many different tools used by astronomers Astronomy (Greek: αστρονομία = άστρον + νόμος, astronomia = astron + nomos, literally, law of the stars) is the science of celestial objects (such as stars, planets, comets, and galaxies) and phenomena that originate outside the Earths atmosphere (such as auroras and cosmic background radiation). ... A calendar is a system for naming periods of time, typically days. ... In arithmetic and number theory the least common multiple or lowest common multiple (lcm) or smallest common multiple of two integers a and b is the smallest positive integer that is a multiple of both a and b. ... A year is the time between two recurrences of an event related to the orbit of the Earth around the Sun. ... A tropical year is the length of time that the Sun, as viewed from the Earth, takes to return to the same position along the ecliptic (its path among the stars on the celestial sphere). ... The month is a unit of time, used with calendars, which is approximately as long as some natural period related to the motion of the Moon. ... The hour (symbol: h) is a unit of time. ... Parts-per notation is a measure of concentration that is used where low levels of concentration are significant. ...

 19 tropical years = 6939.602 days 235 synodic months = 6939.688 days 

It is helpful to recognize that this is an approximation of reality. The period of the Moon's orbit around the Earth and the Earth's orbit around the Sun (ignoring also exact definition of the year) are independent and have no known physical resonance. Examples of a real harmonic lock would be Mercury, with its 3:2 spin-orbit resonance or other orbital resonance Note: This article contains special characters. ... In celestial mechanics, an orbital resonance occurs when two orbiting bodies exert a regular, periodic gravitational influence on each other. ...

The Greek astronomer Meton of Athens introduced the cycle c. 432 BC. The Chaldean astronomer Kidinnu (4th century BC) knew of it, but the Babylonians may have learned of it earlier. They measured the Moon's motion against the stars, so the 235:19 relation may originally have referred to sidereal years, instead of tropical years as it has been used in various calendars; however, ancient astronomers did not make a clear distinction between sidereal and tropical years before Hipparchus discovered precession of the equinoxes c. 130 BC. An astronomer or astrophysicist is a scientist whose area of research is astronomy or astrophysics. ... Meton of Athens was a Greek mathematician, astronomer, and engineer who lived in Athens in the 5th century BCE. He is best known for the 19-year Metonic cycle which he introduced into the lunisolar Attic calendar as a method of calculating dates. ... Centuries: 6th century BC - 5th century BC - 4th century BC Decades: 480s BC 470s BC 460s BC 450s BC 440s BC - 430s BC - 420s BC 410s BC 400s BC 390s BC 380s BC Years: 437 BC 436 BC 435 BC 434 BC 433 BC 432 BC 431 BC 430 BC... Chaldea, the Chaldees of the KJV Old Testament, was a Hellenistic designation for a part of Babylonia. ... Kidinnu (also Kidunnu) (circa 400 BC – possibly 14 August 330 BC) was a Chaldean astronomer and mathematician. ... (2nd millennium BC - 1st millennium BC - 1st millennium) The 4th century BC started on January 1, 400 BC and ended on December 31, 301 BC. // Overview Events Bust of Alexander the Great in the British Museum. ... The sidereal year is the time for the Sun to return to the same position in respect to the stars of the celestial sphere. ... A tropical year is the length of time that the Sun, as viewed from the Earth, takes to return to the same position along the ecliptic (its path among the stars on the celestial sphere). ... Hipparchus. ... Precession of the equinoxes refers to the precession of the Earths axis of rotation. ... Centuries: 3rd century BC - 2nd century BC - 1st century BC Decades: 180s BC 170s BC 160s BC 150s BC 140s BC - 130s BC - 120s BC 110s BC 100s BC 90s BC 80s BC Years: 135 BC 134 BC 133 BC 132 BC 131 BC - 130 BC - 129 BC 128 BC...

This cycle is used by the Hebrew calendar. It is also used in the computation of the date of Easter. The Hebrew calendar (Hebrew: ) or Jewish calendar is the annual calendar used in Judaism. ... Computus (Latin for computation) is the calculation of the date of Easter in the Christian calendar. ...

It is possible that Homer knew about the cycle some centuries before Meton. In the Odyssey, after Odysseus leaves Ithaca, he returns to secretly meet Penelope at the exact moment when one Metonic cycle has passed. ^{[1] [2] [3]} The Homère Caetani bust at the Louvre, a 2nd century Roman copy of a 2nd century BC Greek original. ... Odysseus and Nausicaä - by Charles Gleyre For other uses, see Odyssey (disambiguation). ... Odysseus and the Sirens. ... For other places named Ithaca, see Ithaca (disambiguation). ... Penelope represented as a statue in the Vatican, Rome Penélopê (Πηνελοπεια) is a character of the Odyssey, one of the two great epic poems (the other being the Iliad; both are attributed to Homer) of ancient Greek literature. ...

In a typical lunisolar calendar, most years are lunar years of 12 months, but some years have an extra month, known as an intercalary or embolismic month. There are 7 of these intercalary months in the 19 years of a Metonic cycle. Traditionally (in the ancient Attic and Babylonian calendars, as well as in the Hebrew calendar), the years: 3, 6, 8, 11, 14, 17, and 19, are the long (13-month) years of the Metonic cycle. A lunisolar calendar is a calendar whose date indicates both the moon phase and the time of the solar year. ... Intercalation is the insertioffn of an extra day, week or month into some calendar years to make the calendar follow the seasons. ... The Attic calendar is the calendar that was in use in ancient Attica, the ancestral territory of the Athenian polis. ... In the Babylonian calendar a year consisted of 12 lunar months, each beginning when a new crescent moon was first sighted low on the western horizon at sunset. ... The Hebrew calendar (Hebrew: ) or Jewish calendar is the annual calendar used in Judaism. ...

The Metonic cycle incorporates two less accurate subcycles, for which 8 years = 99 lunations to within 1.5 days, with an error of one day every 5 years (an Octaeteris), and 11 years = 136 lunations within 1.5 days, with an error of one day every 7.3 years. The Metonic cycle itself is a subcycle of the next more correct 334 years = 4131 lunations to within 41 minutes, with an error of one day every 11598 years. In astronomy, an octaeteris is the period of eight solar years after which the moon phase occurs on the same day of the year plus one or two days. ...

Meton approximated the cycle to a whole number (6940) of days, obtained by 125 long months of 30 days and 110 short months of 29 days. The Callippic cycle was a more accurate approximation, obtained by taking one day away from every fourth of Meton's cycles, so creating a 76-year cycle with a mean year of exactly 365.25 days. Meton of Athens was a mathematician, astronomer and engineer who lived in Athens in the 5th century BCE. He is best known for the 19-year Metonic Cycle which he introduced into the Athenian luni-solar calendar as a method of calculating dates. ... Eclipses may occur repeatedly, separated by some specific interval of time: this interval is called an eclipse cycle. ...

The 19-year cycle is also close (to somewhat more than half a day) to 255 draconic months, so it is also an eclipse cycle, which lasts only for about 4 or 5 recurrences of eclipses. The month is a unit of time, used with calendars, which is approximately as long as some natural period related to the motion of the Moon. ... Eclipses may occur repeatedly, separated by some specific interval of time: this interval is called an eclipse cycle. ...

References

1. ^ Gilbert Murray. The Rise of the Greek Epic. Oxford, (1907)
2. ^ Joseph Campbell. The Masks of God: Occidental Mythology, vol III (1964)
3. ^ J.F. del Giorgio. The Oldest Europeans. A.J. Place (2006)

Gilbert Murray (or George Gilbert Aime) (January 2, 1866 - 1957) was a British classical scholar and diplomat. ... This article or section does not cite its references or sources. ... To meet Wikipedias quality standards, this article or section may require cleanup. ...

See also

• Antikythera mechanism
• Baha'i calendar