September(redirected from 31 September)
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in chronology, the conventional period of a lunation, i.e., passage of the moon through all its phases. It is usually computed at approximately 29 or 30 days. For the computation of the month and its harmony with the solar calendar and for the months in others than the
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the ninth month of the calendar year. It is 30 days long. In ancient Rome and Old Rus’, September initially was the seventh month of the year. It was the first month of the year in the Russian state from the 15th to the 18th century.