🕐 时区：地球的“时间拼图”🕐 Time Zones: Earth's Jigsaw of Time
上一片在空间里造出新陆地，这一片给时间切片：🌍 蓝色星球向导同时视频打给北京、伦敦、纽约三位朋友，北京在吃午饭，伦敦刚吃早饭，纽约还在半夜打呼——同一时刻，三种时间。Last leaf built new land in space. This leaf slices up time itself: 🌍 Blue Planet Guide video-calls friends in Beijing, London and New York at the very same moment — Beijing is having lunch, London is having breakfast, and New York is snoring at midnight. One moment, three times.
第 1 步：太阳只照亮一半地球Step 1: The sun only lights half the planet
为什么同一时刻各地时间不一样？先看这通跨洋视频。Why does the same moment mean different times everywhere? Watch this cross-ocean video call.
地球是个圆球，太阳一次只能照亮一半：朝太阳的是白天，背过去的是黑夜。地球还不停自转，一天转一圈，所以每个地方都会轮流经过白天和黑夜。北京中午十二点吃午饭时，转到背面的纽约还是前一天深夜——时差就是这么来的。Earth is a ball and the sun can only light one half at a time: the side facing the sun gets day, the side turned away gets night. And Earth keeps spinning — one full turn a day — so every place takes turns in daylight and darkness. When Beijing sits down to lunch at noon, New York, spun around to the back, is still in the middle of last night. That is where time differences come from.
那全世界怎么统一“差几个小时”，总不能每个城市各说各的吧？So how does the world agree on “how many hours apart” — surely not every city for itself?
第 2 步：十五度，切一个时区Step 2: Fifteen degrees per time zone
办法像切橙子：地球一圈 360 度，一天 24 小时，360 ÷ 24 = 15，所以每 15 度切一个时区，相邻两区正好差 1 小时。从穿过英国的零度经线（本初子午线）开始往东数、往西数：北京在东八区，纽约在西五区。记住口诀“东加西减”：算东边的时间就加，算西边就减。The fix works like slicing an orange: Earth spans 360 degrees and one day holds 24 hours, so 360 ÷ 24 = 15 — one zone every 15 degrees, each neighbour exactly 1 hour apart. Count east and west from the zero line through Britain (the Prime Meridian): Beijing sits in the UTC+8 zone, New York in UTC−5. Remember “add east, subtract west”: add hours for places to the east, subtract for places to the west.
坐飞机跨时区旅行，时间会乱成什么样？还有“今天和昨天”的边界吗？What happens when you fly across zones — and is there really a border between “today” and “yesterday”?
第 3 步：航班时间与换日线Step 3: Flight boards and the Date Line
先记一条铁律：航班表上写的起降时间全是当地时间，上飞机前先换算。往东飞把钟拨回去，往西飞把钟拨快，一不小心就“今天出发、昨天到达”。太平洋中间还画了一条国际日期变更线：自西向东越过它，日子退一天；反方向则加一天。它就是“今天与昨天”的分界线。One golden rule first: every time on a flight board is local time — convert before you board. Fly east and turn the clock back, fly west and turn it forward; it is perfectly normal to “depart today and arrive yesterday”. Down the middle of the Pacific runs the International Date Line: cross it eastbound and step one day back, westbound and add one day. It is the border between “today” and “yesterday”.
🎮 你来当接线员（30 秒）🎮 Your turn: work the switchboard (30 seconds)
先拖滑块，看三座城市的钟怎么跟着北京转；再接下面 4 通电话，算出对方的时间和日子。First drag the slider and watch the three cities' clocks follow Beijing; then take 4 calls and work out each caller's time and day.
一句话记住它：时区是地球的“时间拼图”——自转造成昼夜，15 度一切，东加西减，减过头日子退一天。Remember it in one line: time zones are Earth's jigsaw of time — spin makes day and night, slice every 15 degrees, add east and subtract west, and step the day back when you subtract past midnight.
时差从自转来：太阳一次只照亮一半，北京中午时纽约还是前一天深夜Jet lag starts with spin: the sun lights only half at once, so Beijing's noon is still last night in New York算法是东加西减：360 ÷ 24 = 15 度一区，北京东八区、纽约西五区The math is add-east-subtract-west: 360 ÷ 24 = 15 degrees per zone, Beijing UTC+8, New York UTC−5旅行看当地时间：航班表全是当地时间，越过日期变更线日子加减一天Travel on local time: flight boards always show local time, and crossing the Date Line adds or removes a day
内容参考 OpenStax 等公开教材，多来源核对 · AI 生成、人工审核 · 发现错误欢迎指正，帮这片叶子长得更好。Based on OpenStax and other open textbooks, cross-checked across sources · AI-generated, human-reviewed · Spotted a mistake? Tell us — help this leaf grow.
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