What are the main difference between the Julian calendar and the Gregorian calendar? and when and why did the Julian calendar come about?
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Julian calendar
Stolen from wikipedia
The Julian calendar began in 45 BC (709 AUC) as a reform of the Roman calendar by Julius Caesar. It was chosen after consultation with the astronomer Sosigenes of Alexandria and was probably designed to approximate the tropical year (known at least since Hipparchus).
The Julian calendar has a regular year of 365 days divided into 12 months with a leap day added to February every four years. The Julian year is, therefore, on average 365.25 days long. The motivation for most calendars is to fix the number of days between return of the cycle of seasons (from Spring equinox to the next Spring equinox, for example), so that the calendar could be used as an aid to planting and other season-related activities. The cycle of seasons (tropical year) had been known since ancient times to be about 365 and 1/4 days long.
The more modern Gregorian calendar eventually superseded the Julian calendar: the reason is that a tropical year (or solar year) is actually about 11 minutes shorter than 365.25 days. These extra 11 minutes per year in the Julian calendar caused it to gain about three days every four centuries, when compared to the observed equinox times and the seasons.
In the Gregorian calendar system, first proposed in the 16th century, this problem was dealt with by dropping some calendar days, in order to realign the calendar and the equinox times. Subsequently, the Gregorian calendar drops three leap year days across every four centuries
The Julian calendar began in 45 BC (709 AUC) as a reform of the Roman calendar by Julius Caesar. It was chosen after consultation with the astronomer Sosigenes of Alexandria and was probably designed to approximate the tropical year (known at least since Hipparchus).
The Julian calendar has a regular year of 365 days divided into 12 months with a leap day added to February every four years. The Julian year is, therefore, on average 365.25 days long. The motivation for most calendars is to fix the number of days between return of the cycle of seasons (from Spring equinox to the next Spring equinox, for example), so that the calendar could be used as an aid to planting and other season-related activities. The cycle of seasons (tropical year) had been known since ancient times to be about 365 and 1/4 days long.
The more modern Gregorian calendar eventually superseded the Julian calendar: the reason is that a tropical year (or solar year) is actually about 11 minutes shorter than 365.25 days. These extra 11 minutes per year in the Julian calendar caused it to gain about three days every four centuries, when compared to the observed equinox times and the seasons.
In the Gregorian calendar system, first proposed in the 16th century, this problem was dealt with by dropping some calendar days, in order to realign the calendar and the equinox times. Subsequently, the Gregorian calendar drops three leap year days across every four centuries