why divide the day into 24 hours?not 10?or 38?

Answer 1

The Egyptians were responsible for the 24 hour day. The Eqyptians were fond of counting in base twelve (instead of base 10 which is commonly used today). This is thought to be because they counted finger joints instead of fingers. Each of your fingers has three joints, so if you count by pointing to finger joints with your thumb you can count to twelve on each hand. This might seem arbitrary, but is actually just a strange as counting in base ten simply because we have ten digits.

Another reason the Egyptians (and Indians) liked counting in base 12 is that 12 has a larger number of integer factors than 10. ie. 12/6=2, 12/4=3, 12/3=4, 12/2=6, while 10/5=2 and 10/2=5 are all there are for the number 10).

The Egyptians divided the clock into 12 hours of daytime and 12 hours of night-time (or alternatively 10 hours between sunrise and sunset, an hour for each twilight period and 12 hours of darkness). This is known because of various sundials from the period which have been found to be marked with hours. Interestingly this means that hours started out changing in length with the seasons (as the amount of daylight vs. darkness changes).

There is a more in-depth explanation for the division of night-time into 12 hours which is based on the number of "decan" stars which were seen to rise during summer nights in Ancient Egypt. A "decan" star was a star which rose just before sunrise at the beginning of a 10-day "decade" in Ancient Egypt. 36 "decan" stars marked the passage of a year for the Egyptians (or 36 10 day periods). During summer nights, 12 decan stars rose - one for each "hour".

However, hours did not have a fixed length until the Greeks decided they needed such a system for theoretical calculations. Hipparchus proposed dividing the day equally into 24 hours which came to be known as equinoctial hours (because they are based on 12 hours of daylight and 12 hours of darkness on the days of the Equinoxes). Ordinary people continued to use the seasonally varying hours for a long time. Only with the advent of mechanical clocks in Europe in the 14th Century, did the system we use today become common place.

There was not a decan star every modern hour. Remember that the length of darkness in the summer is actually less than 12 "modern" hours. The Egyptian "hours" marked by the rising of each of the 12 decan stars were shorter than what we call an hour now. As I said, hours did not have a fixed length until much later when people decided that would be useful! Initially 12 hours was always the length of night/day, but the hours themselves changed in length with the seasons, and a nighttime hour would have been different to a daytime hour! The "hours" in this era were only equal to our current hours on the equinoxes.

Answer 2

Because the hour is based on the 15 degree time zone. There are 24 time zones around the globe each representing 15 degrees. This adds up to 360 degrees. One earth rotation = 1 day = 360 degrees = 24 hours.

Answer 3

We divide the day into 24 hours because that's the amount of time it takes for the earth to spin on its own axis thus causing night and day within those 24 hrs.

Answer 4

A day is not 24 hours, it is actually 23 hours 56 minutes and 4 seconds.

Why people decided to divide the day into 24 units, I don't know.

Answer 5

It takes 24 hours for the rotation of the earth to take you through a full day.

Answer 6

It has to do with the rotation of the earth. It takes 24 hours.

Answer 7

Because it takes 24 hours for the Earth to spin on its axis.. Causing day and night.. I think

Answer 8

I'm not sure anyone knows with certainty when, where and why the number '24' was chosen. There are many theories, going back to Sumerians, Babylonians, and Egyptians. There's also disagreement as to whether the hour was defined before its subsections (minutes, seconds) or vice-versa.

Answer 9

You have already asked this different ways - 24 hrs is the nearest whole hour to the rotation of the earth.

You could split it into smaller bits based on 24 (i.e. 48 hrs) but this was considered accurate and workable.

Answer 10

that's the amount of time that the earth rotates on its axis, thus creating night and day. in simpler terms, half of the earth faces the sun 12 hours and faces the moon or darkness the rest of the 12.