Why is a day 24 hours? Why is an hour 60 minutes?
The short answer
A day has 24 hours because the ancient Egyptians divided daytime and nighttime into 12 parts each, making 24 hours in total. There are 60 minutes in an hour because the Babylonians adopted a sexagesimal (base 60) system for their astronomical calculations, influencing the division of an hour into 60 minutes. This is why we have 24 hours in a day and 60 minutes in an hour.
The long answer
Why are there 24 hours in a day?
"Ancient-egyptian-sundial" by University of Basel is part of the public domain.
The ancient Egyptians are largely credited with why we have 24 hours in a day. As early as 1500 BCE, they used an advanced sundial to segment the duration between sunrise and sunset into 12 parts, creating 12 "hours" of daylight.
When night made sundials less useful, Egyptian astronomers turned to the stars to track the hours. Initially, they identified a set of 36 stars to divide the sky into equal parts. This system later became more streamlined, settling on 12 stars marking the passage of night. The combination of 12 hours of daylight and 12 hours of nighttime created the 24-hour day that we use today.
Why 12? This division possibly stemmed from the 12 lunar cycles in a year or even the 12 finger joints (excluding the thumbs) on our hands. Using your thumb, you can count up to 12, which may have influenced the way ancient cultures divided time and measurements.
Combining 12 hours for daylight and 12 for nighttime gave us the 24-hour day. But since the length of daytime hours varies with the seasons, fixed-length hours weren't embraced until mechanical clocks were invented in 14th-century Europe, standardizing the way we measure time throughout the year.
Why are there 60 minutes in an hour?
The ancient Babylonians' 4,000-year-old sexagesimal system (inherited from the Sumerians), which breaks things into 60s, is the reason our clocks (and maps) have the divisions they do today.
Although we're not exactly sure why 60 was chosen, it may be because 60 has convenient mathematical properties. It can be evenly divided by the first six counting numbers (1, 2, 3, 4, 5, 6), as well as by 10, 12, 15, 20 and 30. This versatility made it a useful base for dividing time and other measurements.
Greek astronomers built upon this by dividing circles and spheres into 360 degrees for geographical mapping. Each degree was then split into 60 "minutes", and each minute further into 60 "seconds". The word "minute" comes from Latin, meaning "first small part," while "second"means "second part." This method influenced not just our maps but also how we tell time today, which explains why an hour has 60 minutes and why we have 24-hour days.
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Sources
Andrews, K. (2011, November 15). Why are there 24 hours in a day?. ABC (Australian Broadcasting Corporation). https://www.abc.net.au/science/articles/2011/11/15/3364432.htm
Baker, K. (2022, September 27). Why 24 hours to the day and 60 minutes to an hour?. Fremont News-Messenger. https://www.thenews-messenger.com/story/news/local/2022/09/21/timing-is-everything-why-24-hours-to-day-and-60-minutes-to-hour/69503622007/
Garner, K. (2021, January 26). A history of time – the story behind our days, weeks, and months. St Neots Museum. https://www.stneotsmuseum.org.uk/articles/a-history-of-time-the-story-behind-our-days-weeks-and-months/
Lombardi, M. A. (2007, March 5). Why is a minute divided into 60 seconds, an hour into 60 minutes, yet there are only 24 hours in a day?. Scientific American. https://www.scientificamerican.com/article/experts-time-division-days-hours-minutes/
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