* Astronomy

A great hall in Eleusis, Telesterion ("Initiation Hall") was one of the primary centers of the Eleusinian Mysteries. Devoted to Demeter and Persephone, these initiation ceremonies were the most sacred and ancient of all the religious rites celebrated in Greece. 
The festival of Eleusinia was celebrated each year in Eleusis and Athens for nine days from the 15th to the 23rd of the month of Boedromion (in September or October of the Gregorian calendar); because the festival calendar had 12 lunar months, the celebrations were not strictly calibrated to a year of 365 days.
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