什麼是國際換日線？
The International Date Line, set up in 1884, runs through the middle of the Pacific Ocean and roughly follows the line of 180 degrees longitude. It lies halfway around the world from the prime meridian, the line of 0 degrees longitude that passes through Greenwich in England.
The date line separates two calendar days. When you cross it, you become a kind of time traveler! Cross it heading west, and it's suddenly one day later. Cross back again, and you've "gone back in time".
Despite its name, the International Date Line has no official status under international law, and countries are free to choose which date they use. Although it generally runs from the North Pole to the South Pole, the line zigzags around national borders, such as those in eastern Russia and Alaska's Aleutian Islands. It also bends around several Pacific island nations, which is why places like Tonga and Samoa are among the first in the world to see each new day.
國際換日線設立於 1884 年，它穿過太平洋中部，大致沿著經度 180 度的經線分布。它和本初子午線（也就是穿過英國格林威治的 0 度經線）正好隔著半個地球。
換日線把兩個日曆日分隔開來。越過它的時候，你就成了某種意義上的「時空旅人」！往西越過換日線，日期會突然往後跳一天；再越回來，你就「回到過去」了。
雖然名字裡有「國際」兩個字，國際換日線其實並沒有國際法上的正式地位，各國可以自由選擇要用哪一個日期。這條線大致從北極延伸到南極，但它會繞開一些國家的邊界，彎彎曲曲地走，例如俄羅斯東部和阿拉斯加的阿留申群島一帶。它也繞過了幾個太平洋島國，所以東加、薩摩亞這樣的地方，是全世界最早迎接新的一天的地方之一。