Landesamt für Denkmalpflege und Archäologie Sachsen-Anhalt
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Leap years

Ordering time

The rhythms of the sky continue through the millennia: then as now, in the time of the Sky Disc the sun fixed the times of day and year, the moon set the month and the week. A new month is marked by the appearance of the New Moon, a very narrow crescent. The lunar year is 11 days shorter than the solar year, so the two were brought into harmony by adding an extra 'intercalary' month in certain years.

A leap year rule like this is known from a Babylonian cuneiform text, the Mul Apin (7th/6th century BC). The general sense of it is: if the New Moon of the Spring Month, with which the year begins, appears next to the Seven Stars, i.e. the Pleiades, then it is an ordinary year; but if the moon first appears beside the Pleiades only on the third day of this month, when the moon has waxed to a thicker crescent, then it is a leap year and an intercalary month should be added to the calendar.

This is precisely the information which is encrypted on the Sky Disc. The thickness of the crescent moon on the Sky Disc corresponds to the age of the moon in the leap year rule.