Birthdays. Family celebrations. Work-related or academic requirements deadlines. Meeting schedules. Societal events. Business appointments. And etcetera. All these things existed because we knew about dates, days, months, and years with the use of calendars. It might be just a piece of paper or an app on your smartphones, but it helps make a lot of things work for us every day. Thanks to ancient people who have discovered the concept and the use of calendars.
Before today’s Gregorian calendar was adopted, ancient Egyptians had their calendaring system. Although the old Egyptian calendar’s exact origin is unknown, it is estimated to have started around 5,000 years ago. They first used a lunar calendar until they adopted a solar calendar.
Times of the Egyptian Calendar
1 week = 10 days
1 month = 3 weeks
1 season = 4 months
1 years = 3 seasons + 5 holy days
Season 1 – The first season was called Akhet which means a flood
Season 2 – The second season was called Proyet which means the emergence
Season 3 – The third season was called Shomu which means low water
Each month consists of a three ten-day-periods called decades or decans. All the months were individually named but commonly referred by the festival names they represent. The last two days of each decade considered holidays or rest days for Egyptians.
One month was 30 days on the Egyptian solar calendar since they did not account for all the days in the year. They added an intercalary month, which was five days long, occurred outside of the regular calendar year. The five intercalary days used to celebrate Egyptian gods’ birthdays, which is why they didn’t work on those days.
In ancient Egyptian astronomy, decans are a group of stars used to tell time at night. There were 30 groups, and the rising of each group signaled a new sidereal day. Each decan consisted of 10 days, which yielded a 360-day year.
Decans’ names were known but not their locations and relationship to modern constellations. A sidereal day is equal to one rotation of the earth relative to the stars. It’s around four minutes shorter than a solar day.
Ptolemy III issued the Canopus Decree, which provided for a sixth epagomenal day every fourth year to correct this discrepancy. However, there were disapproval and resistance from the priests and the population, in general, and was eventually abandoned until Augustus established the Coptic calendar in 25 BC.
There was no known exact origin of the ancient Egyptian calendar, but it is estimated to have started around 5,000 years ago. The ancient Egyptians used a lunar calendar solely for their religious festivals and rituals. The calendar was based on the 29 1/2-day lunar cycles and is more closely linked with agricultural processes and the movements of the stars until they adopted their solar calendar, which started the use of 365 days per year.
Based on Egyptians’ calculations, the solar year was closer to 365 1/4 days. However, they let the one-quarter day accumulate instead of having a single leap every four years to account for the fractional day. After 1,460 solar years or four periods of 365 years, 1,461 Egyptian years had passed. It means that as the years passed, the Egyptian months fell out of sync with the seasons so that the summer months eventually fell during winter. Only once every 1,460 years did their calendar year coincides precisely with the solar year.
Fast facts about Egyptian solar calendar
- The old Egyptian calendar was used in the Middle Ages because its days and months remained consistent. It facilitated their calculations.
- A day for the Egyptians started at sunrise, while many surrounding cultures began their day at sunset.
- Egyptians initially used sundials, hourglasses, and obelisks to tell time during the day and the stars to tell time at night. The introduction of water clocks enabled them to describe time more accurately.
- A civil lunar year, not tied to Sirius, was added every four years to account for the extra day needed to balance the solar calendar to the Egyptian calendar. It was known as the wandering year or annus vagus.
- July 19th was the Egyptian New Year. That was the date that Sirius reappeared on the eastern horizon after a 70-day absence, and the date the Nile began to flood.
- Some historians believe that Sirius was the star that the wise men followed en route to the birthplace of the baby Jesus.
- Why dates and years are different in different calendars?
- Who brought the idea of a leap year in our calendar, and why?