The Earth travels around the Sun once a year.
地球绕着太阳转一圈，就是一年。
But one trip takes 365 days and a quarter.
可这一圈，要走365天还多四分之一。
A quarter of a day is hard to put on a calendar.
四分之一天，日历上可没法记呀。
So we save the quarters for four years.
于是我们把零头，攒够四年。
Then we add one day to February.
再在2月里，多加一天。
That day is February 29, a leap day.
这一天就是2月29日，闰日。
Leap babies wait four years for a real birthday.
闰宝宝们，要等四年才过一次真生日。
