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Sothic Cycle: Difference between revisions
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It is an important aspect of Egyptology, particularly with regard to reconstructions of the Egyptian calendar and its history. Astronomical records of this displacement may have been responsible for the later establishment of the more accurate Julian and Alexandrian calendars. <ref>[https://en.wikipedia.org/wiki/Sothic_cycle Sothic Cycle]</ref> | It is an important aspect of Egyptology, particularly with regard to reconstructions of the Egyptian calendar and its history. Astronomical records of this displacement may have been responsible for the later establishment of the more accurate Julian and Alexandrian calendars. <ref>[https://en.wikipedia.org/wiki/Sothic_cycle Sothic Cycle]</ref> | ||
==Mechanics== | |||
[[File:CanisMajorCC.jpg|thumb|Sirius as the brightest star in the constellation Canis Major as observed from the Earth (lines added for clarity).]] | |||
The ancient Egyptian civil year, its holidays, and religious records reflect its apparent establishment at a point when the return of the bright star Sirius to the night sky was considered to herald the annual flooding of the Nile. However, because the civil calendar was exactly 365 days long and did not incorporate leap years until 22 BCE, its months "wandered" backwards through the solar year at the rate of about one day in every four years. This almost exactly corresponded to its displacement against the Sothic year as well. (The Sothic year is about a minute longer than a Julian year.) The sidereal year of 365.25636 days is only valid for stars on the ecliptic (the apparent path of the Sun across the sky), whereas Sirius's displacement ~40° below the ecliptic, its proper motion, and the wobbling of the celestial equator cause the period between its heliacal risings to be almost exactly 365.25 days long instead. This steady loss of one relative day every four years over the course of the 365-day calendar meant that the "wandering" day would return to its original place relative to the solar and Sothic year after precisely 1461 Egyptian civil years or 1460 Julian years. | |||