Why does week have 7 days?

Answer 1

This is actually a very complicated question. Many historians say the 7 day week s come from the ancient Babylonians over 3000 years ago.
However, others believe we have 7 day week because in the first pages of The Bible it is written
that God created the world in six days and rested on the seventh.

There is also an explanation that has to do with the geometry and mysticism of the number 7.
If you wrap a string or a band around 7 circular objects, you have a perfect hexagon with the 7th round object in the middle. This hexagon is the only stable configuration of wrapping more than 3 circular objects.

One more belief is that the number 7 has to do with the Sun, the Moon, Mars, Mercury, Jupiter, Venus, and Saturn. These were what they used to believe were the 7 planets.

So the answer is not known for sure and there are many more beliefs and stories.
Furthermore, many other cultures have had many different number of days in the week throughout history.