Who decided how long a day is

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The duodecimal system, which has a base of 12, was popular probably because it takes 12 lunar cycles to make one trip around the sun. Despite the fact that they're only actually equal on seasonal equinoxes, days and nights each got assigned 12 hours.

The Ancient Babylonians take credit for the hour being made up of 60 minutes. For reasons that remain unclear, they used a base 60 system of counting. They also divided the circle into parts, which the Ancient Greeks built upon when they tried to divide the Earth into lines of longitude and latitude. Ptolemy divided these into smaller parts which he called the "first minute", and those got split into 60 parts which he called the "second minute".

Second minute became the second we know and use today. It wasn't until the 16th century that minutes and seconds were widely used, when more accurate mechanical clocks were able to keep up the first-ever clock with a seconds hand dates back to Germany, ca.

It was not practical for the general public to consider minutes until the first mechanical clocks that displayed minutes appeared near the end of the 16th century. Even today, many clocks and wristwatches have a resolution of only one minute and do not display seconds. Thanks to the ancient civilizations that defined and preserved the divisions of time, modern society still conceives of a day of 24 hours, an hour of 60 minutes and a minute of 60 seconds. 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.