History of mathematics the Roman Kingdom and included 356 days plus a leap year every other year. In contrast, the lunar calendar of the Republican era contained 355 days, roughly ten-and-one-fourth days shorter than the solar year, a discrepancy that was solved by adding an extra month into the calendar after the 23rd of February. This calendar was supplanted by the Julian calendar, a solar calendar organized by Julius Caesar (100–44 BC) and devised by Sosigenes of Alexandria to include a leap day every four years in a 365-day cycle. This calendar, which contained an error of 11 minutes and 14 seconds, was
Solar Hijri calendar calendar of 365 days for three consecutive years plus an extra day in the next year, save for exceptions to the latter in three out of every four centenaries). The start of the year and its number of days remain fixed to one of the two equinoxes, the astronomically important days which have the same duration of the sun. It results in less variability of all celestial bodies comparing a specific calendar date from one year to others. Each of the twelve months corresponds with a zodiac sign. The first six months have 31 days, the next five have 30