为什么会有四年一次的闰日?
<p><span word="At">At</span> <span word="some">some</span> <span word="point">point</span> <span word="in">in</span> <span word="elementary">elementary</span> <span word="school">school</span>, <span word="your">your</span> <span word="science">science</span> <span word="teacher">teacher</span> <span word="probably">probably</span> <span word="explained">explained</span> <span word="to">to</span> <span word="you">you</span> <span word="that">that</span> <span word="there">there</span> <span word="are">are</span> 365 <span word="days">days</span> <span word="in">in</span> <span word="a">a</span> <span word="year">year</span> <span word="because">because</span> <span word="that">that</span>'<span word="s">s</span> <span word="how">how</span> <span word="long">long</span> <span word="it">it</span> <span word="takes">takes</span> <span word="for">for</span> <span word="Earth">Earth</span> <span word="to">to</span> <span word="complete">complete</span> <span word="one">one</span> <span word="full">full</span> <span word="rotation">rotation</span> <span word="around">around</span> <span word="the">the</span> <span word="sun">sun</span>. <span word="What">What</span> <span word="they">they</span> <span word="might">might</span> <span word="not">not</span> <span word="have">have</span> <span word="specified">specified</span>, <span word="however">however</span>, <span word="is">is</span> <span word="that">that</span> <span word="it">it</span>'<span word="s">s</span> <span word="not">not</span> <span word="exactly">exactly</span> 365 <span word="days">days</span>—<span word="it">it</span>'<span word="s">s</span> <span word="actually">actually</span> <span word="closer">closer</span> <span word="to">to</span> 365.2421 <span word="days">days</span>.</p><p>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。</p><p><span word="So">So</span>, <span word="if">if</span> <span word="we">we</span> <span word="want">want</span> <span word="our">our</span> <span word="calendar">calendar</span> <span word="year">year</span> <span word="to">to</span> <span word="begin">begin</span> <span word="right">right</span> <span word="when">when</span> <span word="Earth">Earth</span> <span word="begins">begins</span> <span word="a">a</span> <span word="new">new</span> <span word="rotation">rotation</span> <span word="around">around</span> <span word="the">the</span> <span word="sun">sun</span>, <span word="we">we</span> <span word="have">have</span> <span word="to">to</span> <span word="account">account</span> <span word="for">for</span> (<span word="roughly">roughly</span>) <span word="an">an</span> <span word="extra">extra</span> <span word="quarter">quarter</span> <span word="of">of</span> <span word="a">a</span> <span word="day">day</span> <span word="each">each</span> <span word="year">year</span>, <span word="or">or</span> <span word="one">one</span> <span word="day">day</span> <span word="every">every</span> <span word="four">four</span> <span word="years">years</span>. <span word="History">History</span>.<span word="com">com</span> <span word="reports">reports</span> <span word="that">that</span> <span word="the">the</span> <span word="Egyptians">Egyptians</span> <span word="had">had</span> <span word="already">already</span> <span word="been">been</span> <span word="doing">doing</span> <span word="this">this</span> <span word="for">for</span> <span word="a">a</span> <span word="while">while</span> <span word="before">before</span> <span word="Europe">Europe</span> <span word="finally">finally</span> <span word="caught">caught</span> <span word="on">on</span> <span word="in">in</span> 46 <span word="BC">BC</span>, <span word="when">when</span> <span word="Roman">Roman</span> <span word="dictator">dictator</span> <span word="Julius">Julius</span> <span word="Caesar">Caesar</span> <span word="and">and</span> <span word="astronomer">astronomer</span> <span word="Sosigenes">Sosigenes</span> <span word="put">put</span> <span word="their">their</span> <span word="heads">heads</span> <span word="together">together</span> <span word="to">to</span> <span word="come">come</span> <span word="up">up</span> <span word="with">with</span> <span word="what">what</span> <span word="we">we</span> <span word="now">now</span> <span word="call">call</span> <span word="the">the</span> <span word="Julian">Julian</span> <span word="calendar">calendar</span>, <span word="which">which</span> <span word="includes">includes</span> 12 <span word="months">months</span>, 365 <span word="days">days</span>, <span word="and">and</span> <span word="an">an</span> <span word="additional">additional</span> "<span word="leap">leap</span> <span word="day">day</span>" <span word="every">every</span> <span word="four">four</span> <span word="years">years</span> <span word="on">on</span> <span word="February">February</span> 29.</p><p>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）。</p>
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