Recording the passing of time has always been of great interest to people even from ancient times. It was important to know how time was elapsing from day to night and from one season to another so that people could plan for their survival.

The earliest estimation of time was done with the use of natural light. Here, a month could be said to be the time between two new moons. A year, in some societies, could be estimated according to the time it took between two harvesting seasons or the sprouting of leaves on a certain tree. This is according to the web-based educational platform, History World.

The first calendar to be used was the lunar calendar. According to Reference a web-based knowledge platform, there were 12 pits with large rocks which were placed according to the time between the new and the full moon. By this approximation, a month was twenty-nine and a half days. Using a lunar calendar, a year is 354 days. Muslims use this type of calendar.

Egyptians were the first to create a calendar based on the sun. In other words, they created the solar calendar. According to the online education platform Astronomy Trek, the Egyptian solar calendar goes as far back as 4236 Before Common Era (BCE). Their estimation was that a year was 365.242199 days. They divided the year by allotting 30 days to each month and then adding five extra festive days.

Today’s calendar follows the mean solar day system. A year is estimated by how long it takes for the earth to make a complete orbit of the sun. According to enotes, an online study resource, it takes 365.25 days. To make up for the 0.25 days, every four years an extra day is added so that the year has 366 days. This is known as a leap year.

There are several other calendars that were used in different territories and religions in the past. For example, 1st century BC Romans used the Julian calendar which was introduced by Julius Caesar the emperor of Rome at the time. There was also the Maya calendar which estimated that a year was made up of 365 days and divided those days into 18 months consisting of 20 days each.

The months of the year obtained their names from planets, supernatural beings and rulers. For instance, according to Calendar Origin a history platform about calendars, January was named after Janus, the god of beginnings. February was named after Februa the feast of purification. December was the tenth month in the early Roman calendar.

Ancient Babylonians are credited with naming days of the week according to the seven planets that are visible to man; Moon, Mars, Mercury, Jupiter, Venus, Saturn and Sun for Monday to Sunday respectively.

When seven days were adopted as the time for each week, other cultures came up with their own names. For example, according to Wikipedia the online encyclopedia, Saturday was derived from Saturn, the ancient Roman god of fun and feasting.