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 side...
Found on http://en.wikipedia.org/wiki/Octaeteris

octaëteris

(from the article `calendar`) The main use of cycles was to try to find some commensurable basis for lunar and solar calendars, and the best known of all the early attempts was ... ...arbitrary system of time reckoning even after the introduction of the Julian calendar throughout the Roman Empire. As late as 200, they used the ... ...
Found on http://www.britannica.com/eb/a-z/o/5
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