为什么闰年不是每四年一次
文章来源:未知 文章作者:enread 发布时间:2020-09-19 07:46 字体: [ ]  进入论坛
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2020 is a leap year, and as we all know leap years happen every four years, right? Wrong. That extra day in February is designed to keep the Earth in sync with the astrological or seasonal1 year. But, what you might not realise is that the maths isn't that simple and occasionally we have to wait eight years.
 
The method behind calculating when leap years occur might be a bit more complicated than you think. Way back in 1582 the calendar we now use was first implemented2. The Gregorian calendar was named after the pope at the time, Gregory X1V. The people who created it realised it wasn't perfect to just add an extra day every four years. 
 
Here's where the maths comes in. A day, of course, is measured by the amount of time it takes for the Earth to complete one full rotation3 on its axis4. A year is the number of days it takes the Earth to orbit the Sun, which most people assume is 365. However, the Earth actually takes just under 365 and a quarter days to complete one full revolution around the Sun.
 
So, every four years we get an extra day, which falls on the 29th February. However, as mentioned earlier, it is in fact just under a quarter of a day. So, by rounding it up, we put the calendar out of sync again – which means that after a while we have too many days.
 
That imbalance has to be readdressed, otherwise after 400 years you'd end up with three extra days. So back in 1582, they realised that every turn of a century should skip their extra day to subtract those three extra days. This is why the years 1700, 1800, and 1900 weren't leap years.
 
But wait, there's more. The year 2000, the millennium5, was a leap year. That's because over a period of four hundred years we only need to remove three days. So, every 400 years the turn of the century is a leap year. This means the next time you hear someone saying 'leap years happen every four years' you can tell them why they're wrong.


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1 seasonal LZ1xE     
adj.季节的,季节性的
参考例句:
  • The town relies on the seasonal tourist industry for jobs.这个城镇依靠季节性旅游业提供就业机会。
  • The hors d'oeuvre is seasonal vegetables.餐前小吃是应时蔬菜。
2 implemented a0211e5272f6fc75ac06e2d62558aff0     
v.实现( implement的过去式和过去分词 );执行;贯彻;使生效
参考例句:
  • This agreement, if not implemented, is a mere scrap of paper. 这个协定如不执行只不过是一纸空文。 来自《现代汉英综合大词典》
  • The economy is in danger of collapse unless far-reaching reforms are implemented. 如果不实施影响深远的改革,经济就面临崩溃的危险。 来自辞典例句
3 rotation LXmxE     
n.旋转;循环,轮流
参考例句:
  • Crop rotation helps prevent soil erosion.农作物轮作有助于防止水土流失。
  • The workers in this workshop do day and night shifts in weekly rotation.这个车间的工人上白班和上夜班每周轮换一次。
4 axis sdXyz     
n.轴,轴线,中心线;坐标轴,基准线
参考例句:
  • The earth's axis is the line between the North and South Poles.地轴是南北极之间的线。
  • The axis of a circle is its diameter.圆的轴线是其直径。
5 millennium x7DzO     
n.一千年,千禧年;太平盛世
参考例句:
  • The whole world was counting down to the new millennium.全世界都在倒计时迎接新千年的到来。
  • We waited as the clock ticked away the last few seconds of the old millennium.我们静候着时钟滴答走过千年的最后几秒钟。
TAG标签: calendar year leap
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