Question: why are days 12 hours long

Kate Salmon answered on 12 Mar 2014:

Hi @blueorange. This is a really good question and I didn’t know the answer to it until I looked it up… this is what I found:

apparently the ancient Egyptians invented the way of telling time that we use today where they split the day into 24 hours. They split this into 10 hours for daytime plus an extra hour for twilight and dawn which gave 12 hours for daytime. They counted the day time hours using shadow clocks (similar to sundials). The remaining 12 hours were used for nighttime- but how can you tell the time at night without the sun?

Well, the Egyptians had an answer for that too! They used the stars. The Egyptians had 36 groups of stars called ‘decans’ which would ‘rise’ (just like the sun) but at night. The Egyptians chose groups of stars that would rise 40 minutes one after the other so during the night, they would be able to look at which stars were in the sky and immediately know the time!

You may have noticed that in summertime, the daylight becomes longer and in the wintertime it becomes shorter. This meant that the Egyptian’s time changed depending on the season so during the summer, the hours would become longer and the nighttime hours would become shorter but there always remained 12 in both daytime and nighttime!