Shoushi Calendar

Shoushi Calendar appeared in the Yuan Dynasty (1279-1368) thanks to the efforts of Guo Shoujing and his co-workers.

Guo employed several methods of calculation, including interpolation, spherical trigonometry to solve four main problems in the previous calendars, such as the arrangement for the intercalary month, the prediction of solar and lunar eclipse.

The calendar had 365.2425 days in a year and 29.530593 days in a month, figures that were the same as those in the Gregorian Calendar published in 1582 by the Roman Pope Gregory XIII. But the calendar was 301 years earlier than the Gregorian Calendar.