Solar Calendar

A solar calendar is a type of calendar that is meant to show the position of the earth on its revolution around our sun.
Egyptians are also responsible for the appearance of the solar calendar. To make it, they took the yearly sunrise recurrence of Sirius (the Dog Star) in the eastern sky as a fixed point. Interestingly enough, this period coincided with the yearly flooding of the Nile River. Ancient Egyptians developed a calendar that featured 365 days and 12 months (30 days in each month and additional 5 days at the end of the year).

Due to the fact that Egyptians didn't manage to account the additional fraction of a day, their calendar steadily went into showing the wrong data. However, Ptolemy III Euergetes of Egypt, decided to add one day to the 365 days every 4 years.