Today our days are made up of 24 hours, but it was not always like this. The civil day in ancient cultures was made up of 'watches'. The length of the watches varied with the season, and they were called seasonal or temporal hours. They were related to the length of the Sun's time above the horizon. This meant that they were longer in the summer and shorter in the winter. It was the Egyptians, thousands of years BC who divided the day into a solar day of 24 hours. In fact, it takes the earth, 24 hours 3 minutes and 56.55 seconds to take one turn on it's axis. Like the ancient Egyptians, we round this off to 24 hours. The extra time is added on as an extra day every 4 years on February 29, which we call a leap year.

Today the official day starts at midnight but in ancient times it started at sunrise and the Jewish religious day starts at sunset. In AD 321 the Christian Emperor Constantine made the 7-day week. He named the days after the Sun , the Moon and Roman gods. In English we use the Scandinavian names for these gods such as Thursday from Thor, the god of lightening. The word day also refers to the period of light as opposed to nighttime. This changes in different parts of the world depending on the time of year - in countries near the equator it is constantly around 12 hours and in polar regions there is 24 hours of day light in the summer.