Hi there! Have you ever wondered why a day is divided into 24 hours? Why not 25 or even 100? Let’s dive into this fascinating topic and find out!
The idea of a 24-hour day comes from the ancient Egyptians. They were inspired by the Sumerians, who lived even earlier. The Egyptians divided the day into three parts: a 10-hour daytime, 2 hours for twilight (the time just before sunrise and just after sunset), and a 12-hour night. They used sundials, which are tools that tell time by the position of the sun’s shadow, to measure the day. The earliest sundials were just a stick in the ground, and they date back to around 3000 BCE!
The Egyptians loved the number 10, but they also used the number 12 a lot. They noticed that there were about 12 lunar cycles (or full moons) in a year, which might be why they chose 12 hours for the night. They also picked 36 stars, called deacons, to represent the weeks in their calendar. These stars helped them divide the night sky into 12 equal parts, each marking a new hour.
Around 1500 BCE, the Egyptians made a more advanced sundial with a T-shaped bar, divided into 12 parts. However, the length of each hour changed throughout the year because the days are longer in summer and shorter in winter. Later, a Greek astronomer named Hipparchus came up with a better idea. He used the equinoxes (times when day and night are about equal) to divide the day into 12 hours of daylight and 12 hours of darkness, making the hours more consistent.
Now, you might be curious about why there are 60 minutes in an hour and 60 seconds in a minute. This comes from the ancient Babylonians, who used a base-60 system. They were likely inspired by the Greeks, including Hipparchus. This system is called the sexagesimal system, and it’s why we have 60 minutes in an hour!
Thanks for exploring this big question with me! If you have more questions, feel free to ask. See you next time!
Gather some materials like a stick and a paper plate to create your own sundial. Place the stick in the center of the plate and mark the shadow every hour. Observe how the shadow changes throughout the day and discuss why the ancient Egyptians used sundials to measure time.
On a clear night, go outside with a parent or guardian and observe the stars. Try to identify constellations and discuss how the Egyptians used stars to divide the night into 12 parts. Create a simple map of the night sky as you see it.
Write a short story about traveling back in time to ancient Egypt. Describe how you would explain our modern 24-hour day to an Egyptian child. Include details about sundials and the number 12 in your story.
Learn about the base-60 system by solving simple math problems using this system. Discuss why the Babylonians might have chosen this system and how it relates to our current way of telling time.
Research when the next equinox will occur and plan an experiment to measure the length of day and night. Record your observations and compare them to the ancient Greek method of dividing the day into equal parts.
Sure! Here’s a sanitized version of the transcript:
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Hi, I’m Craig. Much like the show “24,” this video takes place in real time over a period of less than three minutes, and this is a Mental Floss video. Today, I’m going to answer a big question from fans: Why are there 24 hours in a day? Why not 25 or 100? Let’s get started.
The ancient Egyptians usually get credit for the 24-hour day system, but they were likely inspired by the ancient Sumerians before them. The number 24 is related to the division of the day into three parts: a 10-hour day, two hours for twilight, and a 12-hour night. There is evidence that Egyptians used sundials, making them probably the first to efficiently measure the day, likely for agricultural reasons. The earliest sundials were simple, consisting of a stake in the ground to note the shadow, dating back to around 3000 BCE.
The Egyptians used 10 as a base number for many things, including the number of days in their weeks. There are 36.5 weeks in the Egyptian calendar, so they chose 36 stars, called deacons, to represent eight weeks. These stars were evenly distributed in the night sky, with 12 rising above the horizon at roughly equal intervals, each representing the start of a new hour. It’s possible that the number 12 was chosen because it corresponds with the number of lunar cycles in a year.
Around 1500 BCE, they created a sundial with a T-shaped bar in the middle, divided into twelve parts. However, the lengths of the hours varied throughout the year due to the changing lengths of the days. They also developed an annual calendar based on the movement of the stars around 2500 BCE.
Eventually, a Greek astronomer named Hipparchus proposed a clock more similar to what we use today. He measured out 12 hours of sunlight and 12 hours of darkness using the equinoxes, making both the hourly clock and the annual calendar a bit more rigid.
In case you’re wondering why there are 60 minutes in an hour and 60 seconds in a minute, the answer lies in the sexagesimal system, which is attributed to the ancient Babylonians. They used a base-60 system, which was likely inspired by the Greeks, including Hipparchus.
Thanks for watching this Mental Floss video, made with the help of all these contributors. If you have a big question of your own that you’d like answered, leave it below in the comments. See you next time!
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Let me know if you need any further modifications!
Day – The period of time when the Sun is above the horizon, providing light to the Earth. – During the day, ancient astronomers would study the movement of the Sun to understand time.
Hour – A unit of time equal to 60 minutes, used to divide the day into smaller parts. – The Egyptians were among the first to divide the day into 24 hours using sundials.
Night – The period of darkness between sunset and sunrise when the Sun is below the horizon. – At night, the stars become visible, allowing astronomers to map the sky.
Egyptians – An ancient civilization known for its advances in writing, architecture, and astronomy. – The Egyptians used the stars to predict the flooding of the Nile River.
Sundials – Devices that use the position of the Sun’s shadow to tell time. – Sundials were used by the Greeks and Egyptians to measure the hours of the day.
Stars – Massive, luminous spheres of plasma held together by gravity, visible in the night sky. – The Babylonians used the stars to create one of the first known calendars.
Lunar – Relating to the Moon. – The Greeks developed a lunar calendar based on the phases of the Moon.
Greeks – An ancient civilization known for its contributions to philosophy, science, and astronomy. – The Greeks studied the stars and planets, laying the foundation for modern astronomy.
Babylonians – An ancient civilization known for its advances in mathematics and astronomy. – The Babylonians were among the first to record the movements of the planets.
Equinoxes – Times of the year when day and night are of equal length, occurring in spring and autumn. – Ancient cultures used equinoxes to mark the changing of the seasons.
