Question: what is the difference between gregorian calendar and julian calendar

title: Julian calendar
text: The Julian calendar has two types of year : `` normal '' years of 365 days and `` leap '' years of 366 days . There is a simple cycle of three `` normal '' years followed by a leap year and this pattern repeats forever without exception . The Julian year is , therefore , on average 365.25 days long . Consequently the Julian year drifts over time with respect to the tropical ( solar ) year . Although Greek astronomers had known , at least since Hipparchus , a century before the Julian reform , that the tropical year was slightly shorter than 365.25 days , the calendar did not compensate for this difference . As a result , the calendar year gains about three days every four centuries compared to observed equinox times and the seasons . This discrepancy was corrected by the Gregorian reform of 1582 . The Gregorian calendar has the same months and month lengths as the Julian calendar , but , in the Gregorian calendar , year numbers evenly divisible by 100 are not leap years , except that those evenly divisible by 400 remain leap years . This means since 16 February Julian ( 1 March 1900 Gregorian ) and until 15 February Julian ( 28 February 2100 Gregorian ) Julian is 13 days behind Gregorian and the disparity will widen . 

Answer: answer: The Julian calendar has two types of year: "normal" years of 365 days and "leap" years of 366 days.  There is a simple cycle of three "normal" years followed by a leap year and this pattern repeats forever without exception. 
 The Julian year is, therefore, on average 365.25 days long.   As a result, the calendar year gains about three days every four centuries compared to observed equinox times and the seasons.   The Gregorian calendar has the same months and month lengths as the Julian calendar, but, in the Gregorian calendar, year numbers evenly divisible by 100 are not leap years, except that those evenly divisible by 400 remain leap years.  This means since 16 February Julian (1 March 1900 Gregorian) and until 15 February Julian (28 February 2100 Gregorian) Julian is 13 days behind Gregorian and the disparity will widen.