The 24 Hour Day

The day is a natural unit of measurement with which to measure time. Our own sleep cycles follow the rotation of the earth and its impact upon sunlight: during daylight hours we are awake, in the dark of night we sleep. The day is the most fundamental element of our time keeping system, which we use to define weeks (7 days) months (28, 30 or 31 days) and the year (365 days).

The practice of following the days has always been with man, but it was not until about 3500 BCE in ancient Egypt that a system for breaking up the day into smaller units first developed. In order to keep better track of time, the Egyptians separated day and night each into 12 units, resulting in an ultimate 24 hour day.

The hours of the day were not even from one day to the next under this system, however. The length of daylight changes every day, growing longer with each passing day in the spring and summer then receding after the summer solstice. The Egyptians, however, were content with their system and their uneven hours.

It was in Mesopotamia about 3000 BCE that a standardized hour first developed. The ancient Sumerians, whose base number for their counting system was 12, followed a 24 hour day like the Egyptians. (Roughly 12 day hours and 12 night hours). However, they standardized the hours so that they would no longer exactly correspond to the Sun, but would remain consistent throughout the year.

It is from these origins that we receive our own 24 hour day, which is now used throughout the entire world.

Counting the Minutes and Seconds

As timekeeping developed, more and more accurate units were needed to measure time. Eventually two smaller units were developed: what are now called the minute and the second. A minute is defined as 1 60th of an hour, and a second as 1 60th of a minute. Why the number 60 was used is not completely certain, although it most likely has to do with the Babylonians use of 60 as the base number of their counting system.