Why do hours have 60 minutes

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Jo Ellen Barnett. Plenum Press, A History of Mathematics. Florian Cajori. MacMillan and Co. History of the Hour. Gerhard Dohrn-van Rossum. University of Chicago Press, Get smart. Sign up for our email newsletter. Sign Up. Support science journalism. Knowledge awaits. See Subscription Options Already a subscriber? Create Account See Subscription Options.

Continue reading with a Scientific American subscription. Ten is easy to count—you have 10 fingers and 10 toes—but 10 can only be divided by two and five. To tell time at night, the Egyptians looked to the stars. Like the Sun, the stars move across the sky as time passes.

By choosing a handful of stars to follow, the Egyptians could tell what time of night it was by looking up to check where they were in the sky. They chose 12 stars to track to help them measure the time when it was completely dark outside. Another ancient people called the Babylonians liked to use the number Lots of civilizations borrowed from this number system, including the ancient Egyptians.

The first civilizations divided the day into smaller parts, however, using different number systems, namely binary base 12 and hexadecimal base Because of the documented evidence of the use of Egyptian sundries, most historians believe early civilizations divided a day into smaller parts. The first sundial was simply a pile attached to the ground, indicating the time by the length and direction of the shadow of the stake printed on the ground. As early as BC, the Egyptians developed a more advanced sundial, consisting of a T-shaped bar placed on the ground.

This tool is adapted to divide the time interval between sunrise and sunset into 12 parts. This tool reflects the use of the binary system by the Egyptians. The number 12 is said to be equal to the number of moon cycles in a year or the number of knuckles per hand excluding the thumb. This sundial forms what we call today. Although the number of hours in each day is equal, the length of each hour will vary according to the season of the year every hour in the summer is much longer than every hour in the winter.

Without artificial light, people in this period considered the light and dark periods as opposites rather than as part of the same day. Without the help of a sundial, the division of the time period from dusk to dawn becomes very complicated. In an era when sundial clocks were first used, Egyptian astronomers also observed for the first time a set of 36 stars dividing the sky into equal parts.

The period of darkness completely covered is marked by 12 of these stars. Again, the night time is divided into 12 parts signs of using binary. During the New Kingdom of Egypt to BC , this measurement system was simplified to use a set of 24 stars, 12 of which marked the passing of the curtain.

The water meter clepsydra is also used to record night time, and is probably the most accurate device of the ancient world. Such a clock specimen was found at the Ammon temple in Karnak, dating back to BC, marking the division of the night into 12 parts in different months.