Why do we have 24 hours in a day?

The decision to use equal length hours is usually
credited to the Greek astronomer Hipparchus. Before him, the measure of "an hour" was not something constant! Before Hipparchus, the period of
time between sunrise and sunset was simply divided by
twelve, so the length of an hour would depend on the
time of year as well as where you were on the planet.

Nobody knows for sure why we have 24 hours in a day. Here are a few

1.) The maths theory: 24 is just a nice number to work with!

It may be that the day was divided into 24 hours for
much the same reason as the old British pound was
divided into 240 pennies: it made division easier.

24 can be divided easily by 2,3,4,6,8 and 12. So
dividing a full day into three shifts is easy – eight
hours each. On board ship there are six watches – so
each is four hours long. If you want to buy someone’s
time for a quarter of a day (excluding the night),
that’s three hours of pay. Try doing that with a day
made up of ten hours!

2.) The Finger Counting Theory: There are exactly 24 segments on your fingers

A popular theory is that the
Sumerians counted in base twelve rather than in the
base ten we use today. This is said to have been done
using the fingers: 

If you look at the fingers of one hand – excluding the thumb – you will see that each finger contains
three segments. Three segments on each of four fingers
gives twelve. The thumb can then be used to point to a
particular segment and indicate a number.

So, twelve segments on each hand, one hand for day
and the other for night – and we have a possible origin
of the 24 hour day.

3.) Zodiac Theory: 12 zodiac signs for day, 12 for night

The more mystically inclined like to
think that the 24 hours figure comes from astrology and
other such fields. The zodiac contains twelve signs and
the number twelve has been considered important by many
civilisations. So it would be natural to assign twelve
hours to the night and twelve to the day.

4.) Babylonian/ Egyptian Invention
The Babylonians came up with 12 daylight hours.  They really loved the
number 12, and it’s the reason we have 12 zodiac signs and 12 months. 

Later, the Egyptians decided it might be nice to have 12 night-time hours, too, and 12+12=24, so we get a 24 hour day. 

This is also why we do it as two sets of 12 hours rather than as one 24
hour clock, though it was a later innovation to break the day at
midnight and noon rather than morning and evening.



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