Egyptians celebrate new Egyptian year on September 11

CAIRO – 12 September 2021: September 11 marks the beginning of the Egyptian year within the first calendar in human history.

This year is the 6263rd Egyptian year. This solar calendar was developed by the ancient Egyptians to divide the year into 13 months. It depends on the cycle of the sun, and is considered one of the first calendars known to mankind.

Some historians believe that the first authenticated and historically formulated calendars date back to the Bronze Age, based on the development of writing in the ancient Near East, while others consider the Sumerian calendar to be the oldest, followed by the Egyptian, Assyrian and Elamite calendars.

Many indicate that the ancient Egyptian calendar was the first accurate calendar known to man throughout history.

A greater number of calendar systems for the ancient Near East appear in the archaeological record of the Iron Age, based on the Assyrian and Babylonian calendars. This includes the calendar of the Persian Empire, which in turn gave rise to the Zoroastrian calendar, and the Hebrew calendar.

Calendars in ancient times were usually solar-lunar, depending on the insertion of intercalated months to align the solar and lunar years. This was mostly based on observation, but there may have been early attempts to algorithmically model the interpolation pattern, as evidenced in the 2nd century Colony's Fragmentary Almanac.

However, the Roman calendar contained very old remnants of the 10-month pre-Etruscan solar year. 

The Roman calendar was reformed by Julius Caesar in 45 BC. The Julian calendar was no longer based on observing the new moon, but simply followed an algorithm to enter a leap day every four years. This led to the separation of the calendar month from the lunar month.

In the 11th century in Persia, the reform of the calendar led by Khayyam was announced in 1079, when the length of the year was measured as 365.24219858156 days. Given that the length of the year changes in the sixth decimal place over a person's life, which is very accurate. 

For comparison, the length of a year at the end of the 19th century was 365.242196 days, and today is 365.242190 days.

The Gregorian calendar was introduced as an improvement of the Julian calendar in 1582, and is today in use throughout the world as the de facto calendar for secular purposes.