Today’s 24-hour system most likely originated from the astronomical observations of the Egyptians more than 4,000 years ago.

The relationship between humans and time was formed a long time ago and understanding the origin of many units of time measurement is a big challenge for experts. Some units originate from astronomical phenomena that are quite easy to explain and can be observed independently in many different cultures around the world. For example, measuring the length of a day or year can use the relative motion of the Sun relative to the Earth, while measuring months relies on the lunar phase.

However, some units of time have no obvious connection to any astronomical phenomenon, such as weeks and hours, according to Associate Professor of Astrophysics Robert Cockcroft and Professor of Interdisciplinary Sciences Sarah Symons at McMaster University. One of the oldest types of writing, Egyptian hieroglyphs, provides information about the origin of the hours. It originated in North Africa and the Middle East, was absorbed in Europe, then spread throughout the world, IFL Science reported on July 8.

Time in ancient Egypt

The Pyramid Texts, written before 2400 BC, were the first written records of ancient Egypt. In the text there is the word wnwt (approximately pronounced “wenut”), and the hieroglyph associated with this word is a star. Based on that, experts deduced that wnwt is related to night.

wnwt today is translated as “hour” and to learn about this term it is necessary to first go to the city of Asyut around 2000 BC. There, the inside of the rectangular wooden coffin lid was sometimes decorated with an astronomical panel.

The table contains columns representing 10-day periods in a year. The ancient Egyptian calendar has 12 months, each month has 3 weeks and each week has 10 days, and at the end of each year is a series of 5 days of festivals. In each column, the names of 12 stars are listed, forming 12 rows. The entire table shows changes in the sky over a year, similar to a modern star map.

These 12 stars were the earliest systematic division of a night into 12 time periods, each corresponding to a star. But during this period, the word wnwt does not appear with coffin tablets. By around 1210 BC, during the New Kingdom of Egypt (16th – 11th centuries BC), the relationship between the number of goods and the word wnwt was clarified. For example, in the Osireion temple at Abydos there is an astronomical table on the sarcophagus, in which 12 rows are labeled with the word wnwt.

During the New Kingdom of Egypt, there were 12 wnwt nights and 12 wnwt days, both meant to measure time. Thus, “wnwt” has almost the same meaning as modern “hour”, except for two points.

First, even though there are 12 hours of day and 12 hours of night, they are still shown separately instead of being combined into one 24-hour day. Daytime is measured based on the shadows cast by the Sun, while nighttime is mainly based on the stars. This can only be done when the Sun and stars are within view, so there are two times near sunrise and sunset that do not contain any hours.

Second, wnwt differed from today’s time in length. The length of the wnwt changes during the year, with night hours near the winter solstice being longer, and daytime hours near the summer solstice also being longer.

Stars measure time

To answer the question of where the numbers 12 or 24 come from, it is necessary to find out why the Egyptians chose 12 stars for each 10-day period. This choice is also the true origin of the hour.

The ancient Egyptians used Sirius (or Sirius, the brightest star in the night sky) as a model and chose other stars based on their similarity in behavior to Sirius. The key to selection seems to be that they disappear 70 days a year, like Sirius, although they are not as bright. Every 10 days, a Sirius-like star disappears and another star reappears.

Depending on the time of year, every night 10 – 14 such stars become visible (visible). If the 10-day periods of the year were recorded, experts obtained a table very similar to the astronomical table in the coffin.

It is therefore more likely that the choice of 12 as the number of hours of the night (which eventually resulted in a total of 24 hours a day) was related to the choice of a 10-day week. Thus, today’s human hours originate from the convergence of decisions more than 4,000 years ago.

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