Did you ever wonder why a week has seven days, or how the days got their names? The answers lie far back in history, in the times when people first developed calendars to keep track of the days as the year passed.
ancient calendars were very different from what we use today. The Chinese, for
example, developed a calendar with sixty-day months and ten-day weeks. The
Mayan Indians of Central America had thirteen-day weeks. But in ancient
Mesopotamia, the Babylonians used a seven-day week. Their calendar was based on
observations of the night sky, and they named each day for a different heavenly
body. The ancient Hebrews also chose the seven-day week. For them, it mirrored the
biblical story of creation, which says that the world was created in six days
and that the seventh day was a day of rest.
calendar of the Romans, who conquered much of the ancient world, originally had
months but no weeks. But the Romans eventually adopted the seven-day week, and
this custom gradually spread through their empire. The Romans named the days for
the sun, the moon, and the gods that they associated with the five planets that
can be seen with the naked eye.
Western calendar is based on the Roman one, the seven-day week is still with us.
There have been a few attempts to change it – during the French Revolution, for
example , French authorities tried to switch to a ten-day week. But the change
didn't take hold. And perhaps Because the seven-day week is so old, each day has
a tale of its own. (Grolier Book of Knowledge Encyclopedia)