With the last month as February, Romulus’s calendar now had 12 months but it did not account for the remaining 1/4th day. (Because it takes Earth not exactly 365 days but 365.25 days to complete one circle round the Sun.) Many years later when Julius Caesar ascended the throne of Rome the calendar formulated by Romulus was ahead by nearly 80 days when compared to the solar year. If this mistake was not taken care of immediately then it would only have become larger. Julius Caesar found it necessary to create a new calendar. He assigned the responsibility of this to the scientist named Sosigenes who lived in the city of Alexandria in Egypt. This scientist who had already counted the number of days the Earth took to complete one revolution around the Sun had to only just manage the number 365.25 properly. Just as before, he too divided the year into 12 months, but called January the first month. So, February became the second month and consequently December became the twelfth month. Sosigenes allotted 30 and 31 days alternatively to each month except February to which he allotted 29 days. He had brought the total to 365 and also did not forget to take into account the remaining 1/4th day. He decided to count 30 days in February after every 4 years. Therefore, after every 4 years, the four 1/4th days cumulatively became a whole day. He allotted 366 days to every 4th year. He was the first one to have the idea of leap year. Mankind has had to take up and accept this idea always.

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