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  • When I was a kid,

    在我小時候,

  • my understanding of the seasons

    我對季節的理解

  • was that December and January were cold

    就是十二月和一月份很冷

  • and covered with snow,

    白雪覆蓋大地;

  • April and May were bursting with flowers,

    四五月百花盛開;

  • July and August were hot and sunshiny,

    七八月炎熱、陽光普照;

  • and September and October were a kaleidoscope of colorful leaves.

    九月十月,則像是各種顏色的樹葉組成的萬花筒。

  • It was just the way the world worked,

    這就是世界運行的方式,

  • and it was magical.

    多麼神奇。

  • If you had told me back then

    如果你反過來告訴我

  • that one-third of Earth's population

    地球上有三分之一的人口

  • had never seen snow

    從沒看過雪、

  • or that July 4th was most definitely not a beach day,

    或是七月四號對多數人來說 不適合去海灘玩,

  • I would have thought you were crazy.

    我一定會覺得你瘋了。

  • But in reality, seasonal change with four distinct seasons

    但事實上,所謂的四季分明

  • only happens in two regions on the planet.

    只在這星球的兩個區域出現。

  • And, even in those two,

    就算在這兩者中

  • the seasons are reversed.

    季節也是顛倒的。

  • But why?

    為什麼呢?

  • A lot of people have heard of an astronomer

    許多人可能聽過一位天文學家,

  • called Johannes Kepler

    他叫刻卜勒 (Johannes Kepler),

  • and how he proved that planetary orbits are elliptical

    他證明行星軌道是橢圓的

  • and that the sun is not at the center of the orbit.

    而且太陽並不在這軌道的中心。

  • It was a big deal when he figured this out

    他這個想法

  • several hundred years ago.

    在數百年前很驚人。

  • His discovery solved a lot of mathematical problems

    這個發現解決許多數學上的問題,

  • that astronomers were having

    那些天文學家們

  • with planetary orbit measurements.

    在測量行星軌道時所面臨的問題。

  • While it's true that our orbit's not perfectly circular,

    由於地球的軌道不是個完美的圓形,

  • those pictures in our science books,

    所以那些科學書籍裡的圖片,

  • on TV, and in the movies

    或是電視上、電影片的,

  • give an exaggerated impression

    都給我們誇大的印象,

  • of how elongated our orbit is.

    告訴我們的軌道有多扁平。

  • In fact, Earth's orbit is very nearly a perfect circle.

    事實上,地球的軌道跟正圓相去不遠。

  • However, because Earth's orbit is technically an ellipse,

    然而,因為地球的軌道嚴格來說是個橢圓

  • even though it doesn't look like one,

    ──儘管它看起來不像──

  • and the sun isn't quite exactly at the center,

    同時太陽也不剛好就在中心,

  • it means that our distance from the sun

    這表示我們到太陽的距離

  • does change through the year.

    會在一整年中不斷變化。

  • Ah-ha!

    啊哈!

  • So, winter happens when the Earth is further away from the sun!

    所以冬天就是是地球離太陽最遠的時候!

  • Well, no, not so fast.

    噢不,別太早下定論。

  • The Earth is actually closer to the sun

    實際上地球在一月份的時候

  • in January than we are in July

    比七月份的時候更靠近太陽,

  • by 5 million kilometers.

    兩者相差 500 萬公里。

  • January is smack-dab in the middle

    一月恰恰

  • of the coldest season of the year

    恰恰就是一年之中最冷季節的中間,

  • for those of us up north.

    對我們北半球來說是如此。

  • Still not convinced?

    還是沒辦法說服你嗎?

  • How about this:

    想想看這個:

  • Summer and winter occur simultaneously

    夏季和冬季在這地表上

  • on the surface of our planet.

    會同時發生。

  • When it's winter in Connecticut,

    當康乃狄克是冬天時,

  • it's summer in New Zealand.

    紐西蘭是夏天。

  • So, if it's not the distance from the sun,

    所以,如果跟太陽的距離無關,

  • what else could it be?

    那還有什麼可能?

  • Well, we need to also need to know

    嗯,我們還需要知道

  • that the Earth doesn't sit straight up.

    地球並不是直立的。

  • It actually tilts.

    它有點傾斜。

  • And that axial tilt of the Earth

    而地軸傾斜

  • is one of the main reasons for the seasons.

    是造成四季的主要原因之一。

  • The Earth spins on an axis

    地球繞著地軸自轉,

  • that's tilted 23.5 degrees from vertical.

    而地軸和鉛直線偏差 23.5 度。

  • At the same time, the Earth revolves around the sun

    同時,地球也繞著太陽公轉,

  • with the axis always pointing in the same direction in space.

    而地軸總是指向宇宙中的同一個方向。

  • Together with the tilt,

    搭配上地軸傾斜,

  • the spinning and revolving causes the number

    自轉和公轉就造成了

  • of hours of daylight in a region to change

    一年之中各地區

  • as the year goes by,

    白日時數的變化。

  • with more hours in summer

    夏天白晝長、

  • and fewer in winter.

    冬天白晝短。

  • So, when the sun is shining on the Earth, it warms up.

    所以當陽光照耀著大地時,地球就開始升溫。

  • After the sun sets, it has time to cool down.

    太陽下山後,地球就開始降溫。

  • So, in the summer,

    因此,在夏天、

  • any location that's about 40 degrees north of the equator,

    大約北緯 40 度的地區,

  • like Hartford, Connecticut,

    像是康乃狄克州的哈特福,

  • will get 15 hours of daylight each day

    每天會有 15 小時的白晝、

  • and 9 hours of darkness.

    還有 9 小時的黑暗。

  • It warms up for longer than it cools.

    升溫的時間比降溫的時間長。

  • This happens day after day,

    日復一日,

  • so there is an overall warming effect.

    就造成整體氣溫上升。

  • Remember this fact for later!

    把這件事記住,等等會用到!

  • In the winter, the opposite happens.

    在各天,則是相反的機制。

  • There are many more hours of cooling time

    降溫的時數

  • than warming time,

    比起升溫的時數多了好幾小時,

  • and day after day, this results in a cooling effect.

    日復一日,就造成氣溫下降。

  • The interesting thing is, as you move north,

    有趣的是,當你愈往北移,

  • the number of daylight hours in summer increases.

    夏天的日照時數就愈長。

  • So, Juneau, Alaska would get about 19 hours of daylight

    所以阿拉斯加州的朱諾有將近 19 小時的白畫、

  • on the same summer day that Tallahassee, Florida gets about 14.

    而同一時間的夏日,佛羅里達州的塔拉赫西只有 14 小時的白晝。

  • In fact, in the summertime at the North Pole,

    事實上,在北極的夏天

  • the sun never sets.

    太陽是不會下山的。

  • OK, then, it's all about daylight hours, I've got it!

    好吧,就是日照時數的關係,我懂了!

  • Well, no, there's another important piece to this puzzle.

    嗯,不完全!這謎團裡還有另一個要素。

  • If daylight hours were the only thing

    如果日照時間

  • that determined average temperature,

    是影響平均氣溫的唯一因素,

  • wouldn't the North Pole be the hottest place

    那在北半球的夏天,

  • on Earth in northern summer

    北極不就應該是最熱的地方嗎?

  • because it receives 24 hours of daylight

    因為在夏至附近的月份,

  • in the months surrounding the summer solstice?

    北極都接收了 24 小時的日照。

  • But it's the North Pole.

    但那裡是北極。

  • There's still icebergs in the water

    海上還是有冰山、

  • and snow on the ground.

    陸上還是有雪。

  • So, what's going on?

    是怎麼回事呢?

  • The Earth is a sphere

    地球是個球體,

  • and so the amount of solar energy an area receives

    所以一塊區域所接收到的太陽能量

  • changes based on how high the sun is in the sky,

    會隨著太陽在天空中的高度而變化,

  • which, as you know, changes during the day

    如你所知,

  • between sunrise and sunset.

    這高度會在日出日落間變化。

  • But, the maximum height also changes during the year,

    但是,最大的高度同時也會在一年之中有變化,

  • with the greatest solar height during the summer months

    夏天的時候太陽較高

  • and highest of all at noon on the summer solstice,

    而在夏至正午的時候達到最高,

  • which is June 21st in the northern hemisphere

    也就是北半球的七月二十一號、

  • and December 21st in the southern hemisphere.

    南半球的十二月二十一號。

  • This is because as the Earth revolves,

    這是因為隨著地球的公轉

  • the northern hemisphere ends up tilted away

    北半球在冬天傾斜的方向

  • from the sun in the winter

    會較遠離太陽,

  • and toward the sun in summer,

    而在夏天會較靠近太陽,

  • which puts the sun more directly overhead

    這讓太陽有更長的時間、

  • for longer amounts of time.

    也更能容易直射下來。

  • Remember those increased summer time daylight hours?

    還記得夏天那較多的日照時數嗎?

  • And solar energy per square kilometer increases

    當太陽愈高掛天空的時候,地球上每平方公里

  • as the sun gets higher in the sky.

    所接收到的太陽能量就愈多。

  • So, when the sun's at an angle,

    所以當太陽沒直射時,

  • the amount of energy delivered

    每塊區域接收到的能量

  • to each square of the sunlit area is less.

    就愈少。

  • Therefore, even though the North Pole is getting 24 hours

    因此,儘管北極有 24 小時的白晝

  • of daylight to warm up,

    可以加熱升溫,

  • the sunlight it receives is very spread out

    但它接收到的陽光很分散,

  • and delivers less energy than a place further south,

    同時傳遞的能量也比南方的少,

  • where the sun is higher in the sky

    這是因為南方傾斜的方向較靠近太陽,

  • because it's more tilted toward the sun.

    所以太陽在天空中較高。

  • Besides, the North Pole has a lot to make up for.

    此外,北極寒冷還有其它原因。

  • It was cooling down without any sunlight at all

    它有 6 個月都不會接收到陽光,

  • for 6 months straight.

    因此降溫。

  • So, as the seasons change, wherever you are,

    所以當季節變化的時候,不論你身在何處,

  • you can now appreciate not just the beauty of each new season

    你現在不只可以欣賞每個新季節的美麗

  • but the astronomical complexity

    同時還有帶給你這些變化的

  • that brings them to you.

    宇宙的奧妙。

When I was a kid,

在我小時候,

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B1 中級 中文 TED-Ed 太陽 地球 北極 軌道 傾斜

【TED-Ed】四季變化的原因 (Reasons for the seasons - Rebecca Kaplan)

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    阿多賓 發佈於 2014 年 05 月 01 日
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