Octaeteris

In astronomy, an octaeteris (plural: octaeterides) 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.

This period is also in a very good synchronicity with five Venusian visibility cycles (the Venusian synodic period) and thirteen Venusian revolutions around the sun (Venusian sidereal period). This means, that if Venus is visible beside the moon, after eight years the two will be again close together near the same date of the calendar.

Comparison of differing parts of the Octaeteris
Astronomical period	Number in an Octaeteris	Overall duration (Earth days)
Tropical year	8	2921.93754
Synodic lunar month	99	2923.528230
Sidereal lunar month	107	2923.417787
Venusian synodic period	5	2919.6
Venusian sidereal period	13	2921.07595

The Octaeteris, also known as Oktaeteris, was noted by Cleostratus in ancient Greece as a 2923.5 day cycle. The 8 year short lunisolar cycle was probably known to many ancient cultures. The mathematical proportions of the Octaeteris cycles were noted in Classic Vernal rock art in northeastern Utah by J. Q. Jacobs in 1990. The Three Kings panel also contains more accurate ratios, ratios related to other planets, and apparent astronomic symbolism.

References

Mathematical Astronomy Morsels, Jean Meeus, Willmann-Bell, Inc., 1997 (Chapter 9, p. 51, Table 9.A Some eclipse Periodicities)

Ancient Greek astronomy

Astronomers	Acoreus Aglaonice Agrippa Anaximander Andronicus Apollonius Aratus Aristarchus Aristyllus Attalus Autolycus Bion Callippus Cleomedes Cleostratus Conon Eratosthenes Euctemon Eudoxus Geminus Heraclides Hicetas Hipparchus Hippocrates of Chios Hypsicles Menelaus Meton Oenopides Philip of Opus Philolaus Posidonius Ptolemy Pytheas Seleucus Sosigenes of Alexandria Sosigenes the Peripatetic Strabo Thales Theodosius Theon of Alexandria Theon of Smyrna Timocharis

Works	Almagest (Ptolemy) On Sizes and Distances (Hipparchus) On the Sizes and Distances (Aristarchus) On the Heavens (Aristotle)

Instruments	Antikythera mechanism Armillary sphere Astrolabe Dioptra Equatorial ring Gnomon Mural instrument Triquetrum

Concepts	Callippic cycle Celestial spheres Circle of latitude Counter-Earth Deferent and epicycle Equant Geocentrism Heliocentrism Hipparchic cycle Metonic cycle Octaeteris Solstice Spherical Earth Sublunary sphere Zodiac

Influences	Babylonian astronomy Egyptian astronomy

Influenced	Medieval European science Indian astronomy Medieval Islamic astronomy

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Octaeteris

See also

References