Daylight Hours And Calendar Year
The calendar of the Assyrians was based on the phases of the Moon. They knew that the time between full moons was 12.5 days, so their calendar year had 354 days. 3 years after this was established, they added another month in from time to time so they could keep seasons even.
The Assyrian calendar was also used by the Arabs, until Mohammed banned adding another month.
The Roman calendar had 31 or 29 days for each month, because they believed that even numbers were bad luck. The only exception was February, which had 28 days. Every second year, they added in another month called Mercedonius which was 22 or 23 days, so they could keep up with the solar system.
The Julian Calendar was named after Julius Caesar. Each month had 30 or 31 days and every fourth year was a leap year, which added on an extra day. Caesar had February shortened, so that he could add long months in named after him and Emperor Augustus which were called July and August. Caesar also made January the first month of the year.
In 1545, Pope Gregory XIII was authorised to design a new calendar. The new rule for leap years was that if the year was not divisible by four, it was not to be a leap year. This is the calendar used today.