The ancient Egyptians created one of the first calendars based on the sun, with 365 days in a year. It is the distant ancestor of the calendar we use today.
Three seasons
The Egyptian year was divided into three seasons of four months each, following the life of the Nile: Akhet, the flood; Peret, the growing season; and Shemu, the harvest. Each month had 30 days, divided into three weeks of ten days. That made 360 days, and five extra days were added at the end of the year, celebrated as the birthdays of the gods Osiris, Horus, Seth, Isis and Nephthys.
The star Sirius
The rise of the Nile was linked to the reappearance of the star Sirius, called Sopdet, in the dawn sky after a period of being invisible. Because the civil calendar had no leap year, it slowly drifted against the seasons, coming back into line about every 1,460 years.
From Egypt to us
Julius Caesar’s calendar reform of 46 BC, advised by the astronomer Sosigenes of Alexandria, was based on the Egyptian year with a leap day added every four years. The Coptic Church in Egypt still uses a calendar descended from the ancient one, with the same three seasons and 13 months. You can see a carved festival calendar at Kom Ombo and astronomical ceilings at Dendera and Esna.
