1. Observation of Sirius: The Egyptians noticed that the heliacal rising of Sirius, the brightest star in the night sky, coincided with the annual flooding of the Nile River. This observation provided a reliable marker for the start of the agricultural year.
2. Solar Year and Sirius Cycle: The Egyptians realized that the time between two successive heliacal risings of Sirius was approximately 365 days. This led to the concept of a solar year, which formed the basis of the Egyptian calendar.
3. 12-Month Calendar: The Egyptian year was divided into 12 months, each consisting of 30 days. The months were named after various festivals, deities, and natural events.
4. Five Epagomenal Days: The Egyptians recognized that the solar year was slightly longer than 365 days. To account for this, they added five extra days, known as the Epagomenal Days, at the end of the 12-month period. These days were dedicated to honoring specific deities and religious ceremonies.
5. Coordination with the Solar Year: The Egyptian calendar was a civil calendar that was aligned with the solar year. This meant that the first day of the year always coincided with the heliacal rising of Sirius.
6. Leap Year: Over time, the Egyptians noticed that the actual solar year was slightly shorter than 365.25 days. To maintain alignment with the solar cycle, they introduced a leap year every four years by adding an extra day to the Epagomenal Days.
7. Adoption and Influence: The Egyptian calendar was widely adopted in ancient Egypt and influenced the development of calendars in other civilizations, including the Roman calendar, which eventually became the Gregorian calendar we use today.
The Egyptian calendar demonstrates the remarkable scientific and astronomical knowledge of the ancient Egyptians and their ability to create accurate timekeeping systems based on celestial observations.