The invention of the 24-hour clock dates back to the early Egyption culture. There was also another timekeeping system that was used in different parts of the world, but they became obsolete as soon as this system was introduced.
Egyptions were the first people that used the 24 hours time period system. Their system evolved around the time and it took certain constellations to pass through the sky, and eventually, a 360-day year came in.
ALG181541 Canonical clock with the heads of four prophets completed 1443 (fresco) by Uccello, Paolo (1397-1475)
Duomo, Florence, Italy
Italian, out of copyright
In those early civilizations, the method of keeping time made use of what are called temporal hours. Temporal hours reflect the different amount of daylight present different seasons of the year.
The day and night both had equal hours to account for the actual length of the time. The system was sufficient for measuring the change in the seasons and event that took place over a long span of time. One of the major drawbacks of this system was that it was only limited to measuring of celestial events that occurred every day.
The idea of equinoctial hours was developed by an ancient astronomer Hipparchus sometimes between 147 and 127 BCE. The hours were equal in length regardless of the season. The length of the hours, which is 60 minute, was determined during the equinox when the periods of day and night are equal in length. This system was used by laypersons for a long period of time for their everyday tasks. However, the advent of the equinoctial hours was critical to the advancement of astronomy elsewhere in the world.
12 hours timekeeping is the common way of keeping time in several countries. This way of keeping the time is also referred to as Military Time. A clock that counts the time from 0-12 twice keeps 12 hour time. It first counts the time 0-12 starting from midnight and then from 0-12 again after the noon has passed. The 24-hour clock is also used in some parts of the world to reduce the chances of confusion, resulting from having two cycles of time one at the day time and second at midnight. The United States of America, Great Britain and Canada all use the 12 hours time system for keeping the time.
The main reason for using the Military Time is generally a situation where a mistake in time may lead to a catastrophic situation or where there is an about the observation about where the sun is. And in such times it becomes quite critical for the people to keep accurate time.
For example, Polar explorers and scientists usually use the 24 hours clock because the Sun's presence in the sky is either reduced or prolonged than the usual. The night that lasts for all the day can extremely be disorienting, and the same is for the daylight situation. And that is why 24 hours time is best in such situations for the scientists. Its further usage is in the common hospitals because a small mistake as to when performing an operation or when medicine is to be given to a patient could really be lethal, so it is used as a precaution.
The 24 hours clock is also used by the military because of a large number of problems that may be caused by the confusion of the time. People in the military often tend to communicate across time zones, coordinating sensitive activities and performing highly time-sensitive tasks and activities.