Time Cycle - Egyptians and Roman Calendar

egypt, inscription, hieroglyph

Egyptians of ancient ages came up with a calendar which had 12 by 30-day months and five additional days, making 365 days total. It was founded ~2300 B.C. and based on the star Sothis (Egyptian name for Sirius). Observation of this star allowed making a conclusion that it appears at the dawn over equal periods of time in the east. What was intriguing for Egyptians is that appearance of Sirius coincided with the flood of river Nile. Egyptians’ calendar was also respected and used in Middle Ages.

Egyptians noted right that the period between heliacal sets of the Sirius are unexplainably close to the real duration of the Sun’s year. And yet the calendar’s 6-hour deviation resulted in lack of synchronization with the seasonal periods in the Earth’s year, especially notable after a pair of centuries passed. The Egyptian priests swiftly acknowledged this mistreat and came up with an idea to recompense this deviation by adjusting the calendar to a secondary one, which was supposed to reflect the Sun’s cycle more precisely. However Egyptian seasonal celebrations were still arranged by the lunar calendar.

The ruler Julius Caesar, who was the leader of the Romans, was keen on science and he highly respected astronomical knowledge acquired by Egyptians. Particularly, he was under impression made by Sisogenes (astronomer from Alexandria, Egypt). Together with Sisogenes, Caesar developed a calendar based on Egyptian one, but solar cycles were taken into consideration, and so there appeared a concept of the “leap year” containing 1 day more on every 4th year for cancelling deviation from natural cycles.

On fifth century B.C., astronomer Meton from Greece introduced a cycle which is now named after him. It incorporated 6940 daytimes made of 235 Moon’s months and approaching around 19 Earth’s years. The sense behind a 19-year period is that the Sun and the Moon are aspected coincidentally, on the identical time piece (the Meton’s calendar deviation rate equals around 12 hr. per 109.5 yr.).

Introduced at around year 400 B.C. and developed by Callippus (Greece), there was a 76-yr. period having the same idea as Metonic cycle, just with 1 day contracted. Despite of not so great precision, these cycles were appreciated in sequential calculations which were common for astronomers in ancient Egypt and up to Julian calendar reform.

Intriguing fact is also that the Julian date notation starting point is set at the first year of a Metonic period, 19 yrs. of a whole 76-yr. Callipic period. This evidence points out that the creators of the Julian calendar were inspired by the concepts depicted in both Calliptic and Metonic cycles in terms of mathematical accuracy.