Time is usually divided into smaller parts to make it easier on various occasions to express and perceive the passage of time. For example. It is easier to say that the child is five years, than 438 000 hours old.

Some of the time units are based on celestial movements.

The year is the time in which the Earth goes around the sun once.
Month is a time in which the moon goes round the earth.
Day is the time where the earth rotates around itself.

In addition to these other entities has been developed, such as week and hour to make measuring time easier. Month has been split into four seven-day weeks and the days are divided into 24 hours.

Week is an old invention, but it has not always everywhere been 7 day long. In theBible, God created the world in seven days, but the idea is older.

One explanation is that the number seven came from the seven observed pieces of heaven. Names of days in certain languages ​​still point to celestial bodies.

Sunday is the day of the Sun
Saturday is Saturn’s day
Monday is the day of the Moon