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Where Does the 24 Hour Clock Format Come from?


Today, we use a type of clock that is referred to as an analog clock in order to tell time. It displays time in 12-hour increments, even though there are actually 24 hours in a day. To differentiate between the two 12-hour time periods, we include a suffix of either AM, which stands for before noon, or PM for after noon. 


Knowing all that, a couple of questions come to mind. Where did this time format come from? Why don’t we just use a 24-hour clock instead?


Who Came up with the 24-Hour Clock?


The format actually dates back to ancient times. The Mesopotamians and Egyptians used a similar system to record the current time of day. During the hours of sunlight they used devices called sundials to calculate the time, and at night they relied on something called a water clock. 


The science behind the theory has not been completely proven, but many researchers believe that the Egyptians were the first responsible for taking a whole day and dividing it into 24 equal parts; or two 12-hour increments. 


Their system actually divided the day into two 10-hour increments with an hour at the beginning of the day called the twilight hour, and another hour at the end. 


The Egyptians also used visible stars to tell time after the sun set. This system included a total of 36 different, easily-recognizable star groups which they called “decans”. They took note of the fact that these star groups would continuously rise 40 minutes after each other, and they used this information to create a clock. 


In many places, they recorded their night-based time system as a reference in time tables, along with information on how they worked. Some of these time tables were found etched on the inside of coffins – or sarcophagi. Scientists believe the Egyptians did this so their dead could still tell time. If the dead were not on time, they would miss the ferry transporting them to the afterlife.


All in all, many theorize that the Egyptians were responsible in some small manner for the time system we use today.


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