日历的编排是每400年一个大循环周期，即今年的月、日、星期几和400年前的完全一样。现行天文历法根据天体运行规律，取每年365.2425天。这样，每400年共有365.2425×400＝146097天。如果以365天作为一年，每400年就少了0.2425×400＝97天。这97天要靠设置闰年（每年366）天来凑齐，所以，每400年要设置97个闰年。-Scheduling calendar every 400 years a large cycle that this year' s month, day, week, and 400 years ago, exactly the same. Existing under the celestial law of astronomical calendar, take a year 365.2425 days. So, for every 400 years a total of 365.2425 × 400 = 146097 天. As if 365 days a year, every 400 years to less 0.2425 × 400 = 97 天. This set 97 days depends on a leap year (366 per year) days to cobble together, so every 400 years a leap year to set up 97.