Why Are There 60 Seconds in a Minute? The Ancient Origins of Time Units
The 60-second minute, the 24-hour day, and the 7-day week all trace their roots to ancient civilisations — Sumerians, Babylonians, and Egyptians — whose choices about counting time still govern every clock on Earth. Here is why.
Every time you glance at a clock, you are using a measurement system invented over 4,000 years ago. The 60-second minute, the 60-minute hour, and the 24-hour day are not the result of any scientific optimisation — they are the accumulated decisions of ancient astronomers and mathematicians who chose their numbers for reasons that made perfect sense at the time. Understanding where these units came from explains why our timekeeping looks so different from the decimal metric system.
The Babylonians and the Number 60
The Babylonians of ancient Mesopotamia (modern Iraq) used a base-60 number system — called sexagesimal — around 2000 BCE. They chose 60 because it is divisible by an unusually large number of factors: 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, and 30. This makes it extraordinarily easy to work with fractions without remainders. Dividing 60 into thirds gives 20. Into quarters gives 15. Into sixths gives 10. In an era before decimal fractions or calculators, this was enormously practical.
The Babylonians divided the circle into 360 degrees (6 × 60) — which is why we still use 360° today — and applied the same logic to time. Their division of the hour into 60 minutes, and the minute into 60 seconds, was inherited by Greek astronomers and eventually became universal.
Where Do the Words Minute and Second Come From?
The Latin phrase for the first small division of the hour was 'pars minuta prima' — the first small part. This was shortened to 'minuta', which became 'minute'. The second division was 'pars minuta secunda' — the second small part — giving us 'second'. So a second is literally 'the second small division' of an hour. When mechanical clocks became precise enough to display seconds in the 17th century, the name had already been in use by astronomers for over a millennium.
The 24-Hour Day: Ancient Egypt
The division of the day into 24 hours comes from ancient Egypt, around 2000 BCE. Egyptian astronomers observed 36 star groups (decans) that rose sequentially throughout the year. During a night, 12 of these decans would rise in sequence — giving a natural division of night into 12 parts. By symmetry, the day was also divided into 12 parts. Day plus night = 24.
These were not equal hours by our standards: Egyptian hours varied in length with the seasons, because the night is shorter in summer and longer in winter. Fixed-length 'equinoctial hours' — hours of equal duration throughout the year — were introduced by Greek astronomers and later adopted by the Romans.
The 7-Day Week: Planets and Religion
The seven-day week has a more complex origin. The ancient Near East recognised seven celestial bodies visible to the naked eye: the Sun, the Moon, Mars, Mercury, Jupiter, Venus, and Saturn. Babylonian astrology assigned each hour of the day to one of these bodies in a rotating sequence. The body assigned to the first hour of each day gave that day its name.
This system spread through the Hellenistic world and was reinforced by the Jewish and later Christian traditions of a seven-day creation cycle. The Romans adopted seven-day weeks around the 1st century CE. The names of the days still reflect the original planetary associations in many languages: Saturday = Saturn's day, Sunday = Sun's day, Monday = Moon's day. In English, Tuesday through Friday were replaced by Norse gods (Tiw, Woden, Thor, Frigg) during the Anglo-Saxon period.
The Second: Now Defined by Atoms
For most of history, the second was defined as 1/86,400 of a mean solar day (24 hours × 60 minutes × 60 seconds = 86,400 seconds per day). But the Earth's rotation is not perfectly constant — it slows down over geological time and has irregular small variations. This made the second based on Earth rotation insufficiently precise for modern science.
In 1967, the second was redefined using atomic physics. One second is now defined as the duration of exactly 9,192,631,770 oscillations of the radiation corresponding to the transition between two energy levels of the caesium-133 atom. Atomic clocks based on this definition are accurate to about one second in 300 million years — far more precise than any astronomical observation.
Did the French Try to Decimalise Time?
Yes. During the French Revolution, the same reformers who created the metric system also attempted to create decimal time: a 10-hour day, each hour divided into 100 minutes, each minute into 100 seconds. Decimal time clocks were manufactured and the system was briefly official in France from 1793 to 1805.
It failed completely. People refused to use it. Coordination with other countries was impossible. And unlike length and weight, time is deeply embedded in religious practice, agriculture, and daily rhythm. The French eventually abandoned decimal time and kept the ancient Babylonian system that everyone already knew.
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