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This year, 2024, is a leap year.
今年，2024年，是闰年。
February 29 is known as "leap day."
2月29日被称为“闰日”。
But what is behind this rare extra day on the calendar?
但日历上这罕见的额外一天背后蕴含着什么呢？
Everyone knows the Earth takes 365 days to travel around the sun.
每个人都知道地球绕太阳公转一周需要365天。
Well, that is not exactly correct.
这并不完全正确。
The Earth really takes 365 days, five hours, forty-eight minutes and forty-six seconds to complete its orbit around the sun.
地球绕太阳公转一周其实需要365天5小时48分46秒。
So, almost every four years an extra day occurs and it is represented on the calendar.
因此，几乎每四年就会多出一天，并在日历上表现出来。
The Jet Propulsion Laboratory at the California Institute of Technology says the extra day is used to be sure the months stay connected to yearly events such as equinoxes and solstices.
加州理工学院的喷气推进实验室表示，额外的一天是用来确保月份与每年的事件（比如春秋分和夏冬至）保持联系。
NASA says that over time, our seasons would fall out of order without the leap day.
美国航空航天局表示，随着时间的推移，如果没有闰日，我们的季节将会紊乱。
Each calendar year is about six hours longer than 365 days.
每个日历年大约比365天多6个小时。
However, a leap day is not added every four years.
然而，闰日并不是每四年增加一次。
That would lengthen the calendar by 44 minutes, say experts at the National Air and Space Museum in Washington, D.C.
华盛顿特区国家航空航天博物馆的专家表示，这将会使日历延长44分钟。
Over time, that would mean summer would arrive in November, said Younas Khan, a physics instructor at the University of Alabama, Birmingham.
阿拉巴马大学伯明翰分校的物理讲师尤纳斯·汗表示，随着时间的推移，这意味着夏天将会在11月到来。
So a leap day is added nearly every four years, but not in years including 1700, 1800 and 1900.
因此，几乎每四年会增加一个闰日，但1700年、1800年和1900年除外。
There was a leap day in 2000 because it was a year divisible by both 100 and 400.
2000年有闰日，因为这一年既可以被100也可以被400整除。
Over the next 500 years, there will be no leap day in 2100, 2200, 2300 and 2500.
在接下来的500年里，2100年、2200年、2300年和2500年都不会有闰日。
There will be leap days in 2028, 2032 and 2036.
2028年、2032年和2036年会有闰日。
Without a leap day, farmers might have trouble planting in the correct season, Khan said.
汗说，如果没有闰日，农民可能难以在正确的季节种植作物。
"Christmas would be in summer. There will be no snow. There will be no feeling of Christmas," he said.
他说：“圣诞节会在夏天。不会下雪。没有圣诞节的感觉”。
You might wonder who came up with the idea of leap day.
你可能想知道是谁想出了设置闰日的主意。
Experts say the calendar change developed over time.
专家表示，日历的变化是随着时间的推移而发生的。
Ancient civilizations planned their years based on either the moon or the sun.
古代文明根据月亮或太阳来规划他们的年份。
By the time Julius Caesar controlled the Roman Empire, things had gotten more complicated.
到尤利乌斯·恺撒统治罗马帝国时，情况变得更加复杂了。
People had written down the calendars but seasons were "drifting."
人们已经写下了日历，但季节在“漂移”。
For example, the weather in July was not always the same.
例如，7月的天气并不总是一样的。
So in that time, they added months to the calendar.
因此在那个时候，他们在日历上增加了月份。
But that did not really fix the problem.
但这并没有真正解决问题。
The Romans fixed the problem in the year 46 BCE.
罗马人在公元前46年解决了这个问题。
The year became 365-and-one-fourth days long.
这一年有365又1/4天长。
So an extra day was added every four years.
因此，每四年增加一天。
The Romans came close, but a year is actually 365 plus 0.242 days, says Nick Eakes, an astronomy professor at the University of North Carolina in Chapel Hill.
北卡罗来纳大学教堂山分校的天文学教授尼克·埃克斯表示，罗马人的计算方法与此相近，但一年实际上是365年加0.242天。
There have been multiple calendars used by western societies.
西方社会使用了多种日历。
The Athenian and the Julian calendars were used thousands of years ago.
雅典历法和儒略历在几千年前就被使用了。
The Athenian calendar, however, ran into problems when holidays were not falling in the correct seasons, said Thomas Palaima, a classics professor at the University of Texas at Austin.
然而，得克萨斯大学奥斯汀分校的古典学教授托马斯·帕莱马表示，当节假日不在正确的季节到来时，雅典历法就会出现问题。
Over time, the current calendar also changed because of holidays.
随着时间的推移，当前的日历也会因为节假日而改变。
The leader of the Roman Catholic Church, Gregory XIII, fixed the calendar again in the late 1500s.
罗马天主教会的领袖格列高利十三世在16世纪后期再次修改了历法。
He wanted to be sure the Christian holiday of Easter happened in early spring.
他想确定基督教的复活节是在初春。
So Gregory and his advisors did the difficult math to come up with something very close to the calendar we use today.
因此，格列高利和他的顾问们做了艰难的计算，得出了一个非常接近我们如今使用的日历。
"If the solar year was a perfect 365.25 then we wouldn't have to worry about the tricky math involved," said Eakes, the astronomy professor.
天文学教授埃克斯说：“如果太阳年是完美的365.25年，那么我们就不必担心棘手的数学问题了”。
After the calendar, the main concern for leap day centers on those born on that day, February 29.
在历法之后，人们主要关注的是那些出生在2月29日的人。
It only comes around once every four years (for the most part.)
2月29日每四年才出现一次（在大多数情况下）。
It is a conversation starter for many.
对许多人来说，这是一个引发讨论的问题。
It can be an administrative headache – some people must fill out official documents and say their birthday is either February 28 or March 1.
这可能是一个令人头疼的管理问题——有些人必须填写官方文件，声称自己的生日要么是2月28日，要么是3月1日。
Some computer systems have not yet been updated to include February 29 as a choice.
一些计算机系统尚未更新，无法将2月29日作为选项。
Only about 5 million of the 8 billion people worldwide were born on February 29.
在全球80亿人口中，只有大约500万人出生在2月29日。
Shelly Dean of Seattle, Washington is one of them.
华盛顿州西雅图市的谢利·迪恩就是其中之一。
Growing up, she said, she had normal birthday parties each year, but every fourth year, she had a special party.
她说，从小到大，她每年都会举办正常的生日派对，但每隔四年，她就会举办一次特别的派对。
She is now 23, but has not had too many "special" birthdays.
她现在23岁了，但还没有过太多“特别”的生日。
So this year, she is planning one.
因此，今年，她计划过一个特别的生日。
She missed celebrating with her family four years ago, because she was attending school in New York.
她错过了四年前与家人一起庆祝其生日的机会，因为她当时在纽约上学。
So on Thursday, she gets to celebrate her special day for the first time in eight years with her family.
因此，周四，她可以和家人一起庆祝她八年来的第一个特别的生日。
"It's a very big day," she said.
她说：“这是一个非常重要的日子”。
I'm Dan Friedell.
丹·弗里德尔为您播报。
译文为可可英语翻译，未经授权请勿转载！
