Changes

The '''Julian calendar''', named after [[Julius Caesar]], has twelve months in a year and a leap day every four years. Thus a Julian year is exactly 365.25 days. The astronomical year is slightly shorter, causing the Julian calendar to "drift" out of sync with the seasons by one day every 128 years. This defect is corrected in the [[Gregorian calendar]], a modified version of the Julian calendar created by Pope Gregory XIII in 1582. The Julian calendar was used in Britain and its colonies until 1752, when they switched to the Gregorian calendar. George Washington was born in colonial Virgina on February 11, 1731 by the Julian calendar, but on February 22, 1732 according to the Gregorian calendar. Russia used the Julian calendar until 1918.

The '''Julian calendar''', named after [[Julius Caesar]], has twelve months in a year and a leap day every four years. Thus a Julian year is exactly 365.25 days. The astronomical year is slightly shorter, causing the Julian calendar to "drift" out of sync with the seasons by one day every 128 years. This defect is corrected in the [[Gregorian calendar]], a modified version of the Julian calendar created by Pope Gregory XIII in 1582. The Julian calendar was used in Britain and its colonies until 1752, when they switched to the Gregorian calendar. George Washington was born in colonial Virgina on February 11, 1731 by the Julian calendar, but on February 22, 1732 according to the Gregorian calendar. Russia used the Julian calendar until 1918.

The calendar was designed by Sosigenes of Alexandria and instituted in Rome by Caesar as dictator in 46 BC. The previous Roman calendar featured the insertion of intercalary days by an official called the pontiff, who could use this authority for political purposes. By Caesar time, the calendar was dramatically out of sync with the seasons. Sosigenes designed the calendar so that the spring equinox would occur each year on March 25. His alignment is based on observations published by Hipparchus of Nicaea and taken around 135 BC. The Gregorian calendar is aligned so that the equinox falls on March 21.

The calendar was designed by Sosigenes of Alexandria and instituted in Rome by Caesar as dictator in 46 BC. The previous Roman calendar featured the insertion of intercalary days by an official called the pontiff, who could abuse this authority for political purposes. By Caesar's time, the calendar was dramatically out of sync with the seasons. Sosigenes designed the calendar so that the spring equinox would occur each year on March 25. The precise date is based on observations of the equinox published by Hipparchus of Nicaea and taken around 135 BC. The Gregorian calendar is aligned so that the equinox falls on March 21.

==Months==

==Months==

=== Alignment ===

=== Alignment ===

Sosigenes aligned the calendar so that the spring equinox would fall on March 25 according to observations recorded by Hipparchus. Hipparchus was the standard astronomy reference work of the time. The observations he used are thought to have been made around 135 BC in Alexandria. At this time, the equinox occurred when the Sun entered the constellation Aries, or "first point of Aries." This alignment is still used in astrology. Although Hipparchus's work has been lost, it is quoted by Ptolemy in ''Almagest''. The Julian calendar drifts by one day every 138 years. In 8 BC, Augustus removed one day from the month February and added it to August, putting the calendar an additional day out of alignment. At the time of the Council of Nicene in 335, the equinox occurred on March 21.<ref>(335+135)/138 gives us 3.4 days of calendar drift, plus one day for Augustus's reform.</ref> The Gregorian calendar reestablished the alignment at the time of Nicene.

Sosigenes aligned the calendar so that the spring equinox would fall on March 25. He used observations of the equinox found in a work by Hipparchus, a standard astronomy reference work of this time. The observations are thought to have been made around 135 BC in Alexandria.

 

In the time of Hipparchus, the equinox occurred when the Sun entered the constellation Aries, or "first point of Aries." The star signs in astrology are also based on the observations of Hipparchus. In modern times, the Sun rises in Pisces on the day of the equinox due to [[precession of equinoxes]]. Although Hipparchus's work has been lost, it is quoted by Ptolemy in ''Almagest''. The Julian calendar drifts by one day every 138 years. In 8 BC, Augustus removed one day from the month February and added it to August, putting the calendar an additional day out of alignment. At the time of the Council of Nicene in 335, the equinox occurred on March 21.<ref>(335+135)/138 gives us 3.4 days of calendar drift, plus one day for Augustus's reform.</ref> The Gregorian calendar reestablished the alignment at the time of Nicene.

== Later history ==

== Later history ==