Sothic Cycle - Chronological Interpretation

Chronological Interpretation

Three specific observations of the heliacal rise of Sirius are extremely important for Egyptian chronology. The first is the aforementioned ivory tablet from the reign of Djer which supposedly indicates the beginning of a Sothic cycle, the rising of Sothis on the same day as the new year. If this does indicate the beginning of a Sothic cycle, it must date to about 2773 BC (July 17). However, this date is too late for Djer's reign, so many scholars believe that it indicates a correlation between the rising of Sothis and the lunar calendar, instead of the solar calendar, which would render the tablet essentially devoid of chronological value.

The second observation is clearly a reference to a heliacal rising, and is believed to date to the seventh year of Senusret III. This observation was almost certainly made at Itj-Tawy, the Twelfth Dynasty capital, which would date the Twelfth Dynasty from 1963 to 1786 BC. The Ramses (Turin) Papyrus Canon says 213 years (1991-1778 BC), Richard Parker reduces it to 206 years (1991-1785 BC), based on July 17 of 1872 BC as the Sothic date (120th year of 12th dynasty, a drift of 30 leap days). Prior to Parker's investigation of lunar dates the 12th dynasty was placed as 213 years of 2007-1794 BC perceiving the date as July 21 of 1888 BC as the 120th year, and then as 2003-1790 BC perceiving the date as July 20 of 1884 BC as the 120th year.

The third observation was in the reign of Amenhotep I, and, assuming it was made in Thebes, dates his reign between 1525 and 1504 BC. If made in Memphis, Heliopolis, or some other Delta site instead, as a minority of scholars still argue, the entire chronology of the Eighteenth dynasty needs to be expanded by some 20 years.