How is 60 seconds a minute

Around -2,, the year is divided into three four-month seasons, and each month consists of three ten-day weeks, which will then be transformed into seven-day weeks, presumably to allow workers to rest more often on the last day of the week, and also for religious reasons. In relation to this month calendar of 30 days, Babylonians and Greeks divided the circle into degrees 12 times At the same time, around -2,, the Egyptians cut the day into 12 hours of daylight and 12 hours of night, probably because the year was already divided into 12 months.

This means that an hour of summer day lasted longer than an hour of winter day, conversely for the night. So, minutes and seconds also had a random duration. So we weren't yet on our traditional second cutting that give one minute, and 60 minutes an hour! Because this base 60 was used by Babylonian astronomers for their calculations, who had noticed that 60 is divisible by 2, 3, 4, 5 and 6, which is handy for making quarters, thirds Let's go back to this circle divided into degrees 12 times When the first clocks were designed, a clock dial being a circle, it is only natural that this ancient division was used in 12 to show the hours.

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. That's why we now divide circles into parts, or degrees: 60 goes into six times. Advances in the science of timekeeping, however, have changed how these units are defined. Seconds were once derived by dividing astronomical events into smaller parts, with the International System of Units SI at one time defining the second as a fraction of the mean solar day and later relating it to the tropical year.

This changed in , when the second was redefined as the duration of 9,,, energy transitions of the cesium atom. Interestingly, in order to keep atomic time in agreement with astronomical time, leap seconds occasionally must be added to UTC. Thus, not all minutes contain 60 seconds. A few rare minutes, occurring at a rate of about eight per decade, actually contain Already a subscriber?

Sign in. Thanks for reading Scientific American. Create your free account or Sign in to continue. See Subscription Options. Go Paperless with Digital. References Time's Pendulum. 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.