1 of 3 Astronomical Tables in the Temple of Dandera, Egypt Photo: GETTY IMAGES Astronomical Tables in the Temple of Dandera, Egypt Photo: GETTY IMAGES
Humanity’s relationship to the measurement of time began long before the appearance of the first written word. It is therefore a challenge today to investigate the origin of many units of time.
However, some units of time derived from astronomical phenomena are fairly easy to explain and have likely been independently observed by many different cultures around the world.
For example, the measurement of the length of a day or year is based on the apparent movements of the sun relative to the earth, while the measurement of months is derived from the phases of the moon.
However, there are some time measurements that are not clearly related to astronomical phenomena. Two examples are week and time.
One of the oldest written traditions, Egyptian hieroglyphic texts, offer us a new perspective on the origin of the Hour. It is believed to have originated in the region that includes North Africa and the Middle East and was adopted in Europe before spreading around the world in modern times.
The Pyramid Texts, written before 2400 B.C. BC are the earliest writings of ancient Egypt. These include the word wnwt (pronounced “wenut”) and an associated star hieroglyph. It follows that wnwt refers to the night.
To understand why the word wnwt is translated as “hour”, one has to go back in time to the city of Asyut in 2000 BC. travel. C. There, the inside of rectangular wooden coffin lids was sometimes decorated with an astronomical tablet.
2 of 3 Nut, the goddess of the night, wraps her body and arms around astronomical symbols on the ceiling of the Temple of Dandera, Egypt Photo: GETTY IMAGES Nut, the goddess of the night, wraps her body and arms around astronomical symbols on the ceiling of the Temple of Dandera, Egypt Photo: GETTY IMAGES
This tablet contained columns representing 10day periods of the year. The Egyptian civil calendar had 12 months, each with three 10day “weeks” followed by five feast days.
Each column lists 12 star names forming 12 rows. The entire panel represents the changes in the starry sky over the course of a year, similar to a modern astronomical chart.
These 12 stars are the first systematic division of the night into 12 time periods, each ruled by a star. However, the word wnwt is never associated with these astronomical coffin tables.
Not until 1210 BC. B.C., in the New Kingdom the period of ancient Egypt between the 16th and 11th centuries B.C. BC the connection between the number of lines and the word wnwt became clear.
A temple, the Osireion, at Abydos contains a wealth of astronomical information, including instructions for making a sundial and a text describing the movements of the stars. It also features a coffinlike starboard with all 12 lines clearly labeled with the word wnwt.
In the New Kingdom there were 12 nocturnal cycles and 12 diurnal cycles, both of which were clear units of measurement of time. The idea of the hour is almost in its modern form if it weren’t for two things.
First, although there were 12 hours in the day and 12 hours in the night, they were always expressed separately, never together as a 24hour day.
Daytime was measured by the shadows cast by the sun, while nighttime hours were measured primarily by the stars. This was only possible while the sun or stars were visible, and there were two periods around sunrise and sunset that did not contain hours.
Second, the New Kingdom period and our modern period differ in length.
Sundials and water clocks show very clearly that the length of the wnwt varied throughout the year with long night hours around the winter solstice and long daylight hours around the summer solstice.
To answer the question of where the number 12 or 24 came from, we need to find out why 12 stars were chosen within 10 days.
Undoubtedly this choice is the true origin of the hour. Was 12 just a practical number? Perhaps, but the origin of the astronomical coffin tablets suggests another possibility.
3 of 3 The Temple of Osireion at Abydos, Egypt provided a range of astronomical information Photo: GETTY IMAGES The Temple of Osireion at Abydos, Egypt provided a range of astronomical information Photo: GETTY IMAGES
The ancient Egyptians chose the bright star Sirius as their model and chose other stars for their behavioral similarity to Sirius.
The key point seems to be that the stars they used as a reference to keep time disappeared 70 days a year, just like Sirius, although the other stars weren’t as bright.
According to the Osireion star text, a Siriuslike star disappears every ten days and another reappears throughout the year.
Depending on the time of year, between 10 and 14 of these stars are visible each night. Charting them at 10day intervals throughout the year produces a chart similar to the coffin star chart.
Around the year 2000 B.C. BC the representation became (as we understand it) schematic rather than accurate and a 12line table appeared, giving rise to the tablets on coffins that we can see in museums in Egypt and elsewhere.
It is therefore possible that the choice of 12 as the number of hours in the night and finally 24 as the total hours from noon to the following noon is related to the choice of a 10day week.
And so modernity has its origins in a confluence of decisions that took place more than 4,000 years ago.
*Robert Cockcroft is Associate Professor of Physics and Astronomy; and Sarah Symons is Professor of Interdisciplinary Science, both at McMaster University in Canada.