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At some point in elementary school, your science teacher probably explained to you that there are 365 days in a year because that's how long it takes for Earth to complete one full rotation around the sun. What they might not have specified, however, is that it's not exactly 365 days—it's actually closer to 365.2421 days. 上小学时，你们的科学老师很可能会向你们解释一年有365天，因为这是地球绕太阳公转一圈的时间。不过，他们可能没有详细说明，地球公转一圈并不是精确的365天，实际上说是365.2421天更准确一些。 So, if we want our calendar year to begin right when Earth begins a new rotation around the sun, we have to account for (roughly) an extra quarter of a day each year, or one day every four years. History.com reports that the Egyptians had already been doing this for a while before Europe finally caught on in 46 BC, when Roman dictator Julius Caesar and astronomer Sosigenes put their heads together to come up with what we now call the Julian calendar, which includes 12 months, 365 days, and an additional "leap day" every four years on February 29. 因此，如果我们希望年历的开端正好是地球开始新一轮公转的时候，我们就必须每年多算（大约）四分之一天，或每四年多算一天。历史网报道称，埃及人先采用了这种算法，后来到了公元前46年欧洲人才开始这么算。当时罗马独裁者尤利乌斯·恺撒（恺撒大帝）和天文学家索西琴尼商讨后制定了我们今天所谓的儒略历，儒略历共有12个月、365天，每四年加上一个闰日（2月29日）。 | 
