The Dawn of Time: A Tale of Egyptian Astronomy


Ancient Egyptians were famous for their knowledge in the field of astronomy. The Egyptians’ vision of what they saw in the skies took a mythological form that was closely bound to the definition of the religious structure. The Sun was identified as the ancient god who gave rise to creation and life.

Egyptian astronomers left to modern astronomy a fundamental legacy; two measurements that defined the evolution of astronomy and the everyday life of civilization. These were the yearly calendar as we know and use it today, and the division of day and night into 12 hours each.

In a world with no history, time was one of the first quantities measured. Measuring time originated in response to the needs of agriculture, the cycles of which were the basis for the transformation of human society. Therefore, the idea that the calendar was based on the annual solar cycle is doubtful; it is not clear whether the Egyptian calendar was of astronomical or agricultural origin.

A relationship was detected between earthly and celestial phenomena, leading to the division of time into repeated periods linked to the phases of the moon and river. The forthcoming occurrence of the flood was predicted by observing the rising of the star Sepdet (the Greek Sothis, known to us as Sirius). This was the link between the astronomical definition of the calendar and its purely agricultural origin. It connected the annual cycle to the religious cycles of death and resurrection, the daily cycle of the Sun from East to West, people’s lives and the annual flood cycle.

As Egypt adopted a decimal numerical system, the duration of the Egyptians’ ‘vague’ year was divided into weeks of 10 days, with a total of 36 weeks in the year. The length of the months, which in some ways linked to an archaic lunar calendar, was 30 days and they had three weeks each.

The months were gathered into three seasons, each comprising four months; all in all totalling 360 days, to which the Egyptians added five final days to complete the cycle of 365 days. However, the year was still missing a quarter of a day to complete the actual solar year; as time passed, a huge gap occurred.

The Egyptians’ ‘vague’ year of 365 days survived in astronomical practice until precise measurements prompted its correction and replaced it in common usage with the Julian year. In this sense, over the centuries, the Egyptians’ ‘vague’ year of exactly 365 days provided the link, via the Arabic astronomy, between the Greek and Ptolemaic astronomy and the development of the Copernican system at the height of the Renaissance.

The division of the day into 24 hours stemmed directly from the ancient Egyptian calendar structure. The Egyptians developed clocks that measured time independently of the path of the stars. The appearance of sundials and clepsydrae in a papyrus of the 19th dynasty is proof of the introduction of the concept of hours of equal duration.

Despite huge gaps, the documentation retrieved enables us to declare the Egyptians’ astronomical science one of the great fields in which they excelled.

*Adapted from the Galileo, Images of the Universe from Antiquity to the Telescope exhibition; edited by Paolo Galluzzi; original text by Alessandro Roccati and Edoardo Detoma. Some information was also provided by Dr. Fatehi Saleh; Director, Center for Documentation of Cultural & Natural History (CULTNAT). Rewritten and edited for the PSC newsletter by Maissa Azab and Ingy Hafez.

**The original article was published in the PSC Newsletter, 1st School Semester (2009/2010).

***Banner picture copyrights PSC.

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