送交者: HunHunSheng 于 2005-1-12, 16:39:33:

First I have to say I read this story too when I
was very small. My book is one volume of
"one hundreds of thousand why?".

But my question is: how did ancient Greeks
managed to ensure the simultanity of two actions
at two distant places?

"这个古希腊情结，在我还在上小学时从《我们爱科学》上读到古希
腊一位科学家如何巧妙而准确地测定了地球周长起，便已种下了。这位
天才人物是亚历山大图书馆馆长埃拉托色尼。他从书中获悉在埃及南方
的色耶尼城市有一口枯井，每年只在夏至这一天的中午，阳光会直射井
底。但是他知道在同一时间，在他所在的亚历山大城太阳并不直射，而
会立竿见影。他测出了这个影子的角度，再根据两个城市的距离，计算
出的地球周长与今天测定的赤道长度非常接近。这种“视差位移”测量
法，直到现在还在天文学上使用。"

• 找杆子和影子间的最小角，或者找最短的影子。 - whiteshark (38 bytes) 2005-1-13, 00:22:02
  • 古希腊有指南针么？ - HunHunSheng (0 bytes) 2005-1-13, 00:29:20
  • 搞错了，角度都一样。还是找最短的影子 - whiteshark (0 bytes) 2005-1-13, 00:24:21
• It is so impressive, if they are trying to measure the perimeter of the earth - 008 (212 bytes) 2005-1-12, 21:50:48
• 二阶效应。 - peanut (0 bytes) 2005-1-12, 19:23:31
• 同时不是关键,同经才是. - outsider (296 bytes) 2005-1-12, 18:07:47
  • Hunhun has pointed this out - 008 (406 bytes) 2005-1-12, 21:58:02
  • 同经目的是为了保证两地中午是同时 - HunHunSheng (163 bytes) 2005-1-12, 19:28:58
    • 同经是为了保证两地"直线"距离等于两地所在纬线间的距离. - fagus (100 bytes) 2005-1-13, 04:50:59
    • If the two points are not - outsider (180 bytes) 2005-1-12, 22:56:35
      • Good idea - whiteshark (0 bytes) 2005-1-13, 00:06:20
  • 埃及国家的形状狭长，ref: Eratosthenes, Syene, and Alexandria - xj (5095 bytes) 2005-1-12, 18:29:30
• warren has the best answers below - Enlighten (0 bytes) 2005-1-12, 17:40:00
  • 可想而知古希腊的科技多发达了。昏昏这样物理高才生 - xj (172 bytes) 2005-1-12, 17:49:02
    • which part is bad? - 008 (157 bytes) 2005-1-12, 22:02:39
• 只有两个点应该算不出结果啊,应该要3个点才行啊. - wangle (128 bytes) 2005-1-12, 17:16:30
  • This is the worst answer we have got - HunHunSheng (0 bytes) 2005-1-12, 17:17:33
    • 他是先假设地球是圆的,再假设太阳是无穷远的. - wangle (46 bytes) 2005-1-12, 17:25:38
      • 古希腊人很早就认识到地是圆的 - warren (25 bytes) 2005-1-12, 17:30:54
        • 为啥没人用3点呢?既然能想到2点,3点是个自然的延伸. - wangle (123 bytes) 2005-1-12, 18:08:16
      • The sun is not a point so that all sunlight are paralle to each other - HunHunSheng (0 bytes) 2005-1-12, 17:28:03
• 不需要同时测量 - warren (312 bytes) 2005-1-12, 17:10:14
  • 如果色耶尼城市偏离亚历山大城的正南方 - warren (137 bytes) 2005-1-12, 17:19:32
  • 色耶尼城市在亚历山大城的正南方 ensure the two cities's noon are simultaneous - HunHunSheng (45 bytes) 2005-1-12, 17:15:26
    • Your emphasis on "simultaneous" is wrong - Enlighten (117 bytes) 2005-1-12, 17:25:40
      • The story quoted by FZZ emphasizes "同一时间" - HunHunSheng (101 bytes) 2005-1-12, 17:31:48
        • Fang's "同一时间" means “夏至这一天的中午” - wasguru (39 bytes) 2005-1-12, 17:37:01
          • 就是绝对时间 - HunHunSheng (0 bytes) 2005-1-12, 19:24:17
            • as long as the longitudinal distance - chouqilozi (65 bytes) 2005-1-12, 19:33:04
              • This is right if longitudinal means Zi-Wu distance - HunHunSheng (0 bytes) 2005-1-12, 20:58:44
• it is noon at both places, so not simoutaniusly. - chouqilozi (0 bytes) 2005-1-12, 17:08:49
  • It is SIMULTANOUES if they are located at the same longitude - HunHunSheng (40 bytes) 2005-1-12, 17:16:37
• It seems no one can answer this question of mine - HunHunSheng (0 bytes) 2005-1-12, 17:02:42
• 你理解错了。他知道这个影子在不同城市间的差别 - xj (113 bytes) 2005-1-12, 16:47:46
  • This works only when they are located at the same longitude - HunHunSheng (71 bytes) 2005-1-12, 16:52:23
    • doesn't matter - wasguru (121 bytes) 2005-1-12, 17:08:27
      • I don't think so. It must be Simultaneously in terms of absolute time - HunHunSheng (296 bytes) 2005-1-12, 17:12:57
        • 混混脑子糊涂了,你的同时也是可以算的,不过就不需要夏至这个概念了. - wangle (43 bytes) 2005-1-12, 17:22:11
          • That is my original question: how to you make sure 同时测定 - HunHunSheng (157 bytes) 2005-1-12, 17:26:33
            • 测量最短距离,就保证它是夏至中午,当然还要测出两地连线和这时影子的角度. - wangle (0 bytes) 2005-1-12, 17:32:21
              • Noon at one city might be ahead of or lag behind the noon at the other city - HunHunSheng (0 bytes) 2005-1-12, 17:34:21
                • It is still possilbe to get simultaneity if you really want it - wasguru (105 bytes) 2005-1-12, 21:29:41

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