Ancient Egyptian calendar
This calendar was created based on the observation of groups of stars called 'decans'. Every ten days a different decan appeared on the horizon. The ancient Egyptians worked out that there were 36 decans in a year.
Five days were added on at the end of the year for the birthdays of five important gods and goddesses. This meant that there were 365 days in a year. This calendar was then written down and used for keeping track of the days during the year.