The Ancient Egyptian calendar(s) evolved over quite a lengthy period and changed as it became either inconvenient or unsuitable.

It was based on the Lunar cycle and was, as was the case in other near eastern civilisations, devised to coincide with it. So, there were 12 lunar months in a year. At this point, the Egyptians subdivided the year into three seasons of four months each:

	The Inundation
	Winter - the season of ‘emergence’ of the fields from water
	Summer

The great feast of the rising of Sothis, which was called "the opening of the year" (wpt rnpt), gave its name to the 4th month of the 3rd season i.e. the last month of the year. This was quite different from the other month festivals (e.g. first quarter day, full moon day) because the rising of Sothis was a stellar event.

Sothis (or Sopdet), was the goddess who was a representation of the ‘dog star’ Sirius, the brightest star in the sky. The Egyptians must have noticed that the Nile began to rise afresh at about the same time that the heliacal rising of Sirius was observed. (The heliacal rising of a star is when, after a prolonged absence of the star in the night sky, the star is again observed shortly before sunrise.)

The placing of the rising of Sothis in the last month of the year was to be a problem. The lunar year of 12 months has an average of 354 days …. about 11 days short of a natural year. So, if the rising of Sothis took place in the last 11 days of the month wpt rnpt, then in the following year, the rising of Sothis would be out of its month. To correct this and retain the rising of Sothis within its month an intercalary (extra) month was introduced. This ‘Great Year’ of 384 days was used every 3, or occasionally every 2 years, in much the same way as we have a leap year every 4 years.

This system suited other near eastern people well enough, but not so the Egyptians. It may have seemed too complicated, or just plain awkward. Whatever the reason was, the Egyptians deemed it necessary to create the ‘Civil Year’. This probably arose from the calculation of the averaged lunar year by counting the number of days between successive heliacal risings of Sothis. This would only have taken a few years for them to have arrived at the result of 365 days in a year.

The new ‘Civil Year’ consisted of 3 seasons, each of four months. All the months were of 30 days, thus necessitating 5 intercalary days to complete the year. These extra days were known as ‘the days upon the year’.

This ‘Civil Year’ served for economic and administrative purposes with the old ‘Great Year’ running along side for religious purposes.

In time, the Egyptians realised that the ‘Civil Year’ was slipping at a rate of a quarter of a day per year. This could easily have been corrected by having 6 intercalary days instead of 5, once every 4 years. However, the solution the Ancient Egyptians adopted was rather bizarre. They instituted a third year, a civil lunar year which was not tied to the rising of Sothis. So, from about 2,500 b.c. Egypt had three calendars running concurrently, one civil and two lunar.

© Vern Beaumont 1999