《那些古怪又讓人憂心的問題》第104期:最長的落日(1)
LONGEST Sunset
Q. What is the longest possible sunset you can experience while driving, assuming we are obeying the speed limit and driving on paved roads?
Q．假設你遵守交通法規不超速駕駛，並且在鋪有路面的道路上行駛，那麼你能觀賞到的最長日落會持續多久？——Michael Berg
——邁克爾•伯格
A. TO ANSWER THIS, WE have to be sure what we mean by “sunset.”
A．要回答這個問題，首先我們要確定什麼叫“日落”。This is a sunset:
這算是一個日落：Sunset starts the instant the Sun touches the horizon, and ends when it disappears completely. If the Sun touches the horizon and then lifts back up, the sunset is disqualified.
日落在太陽開始沒入地平線的那一瞬間就算開始了，當太陽完全沒入地平線以下之後日落也就結束了。如果太陽碰了一下地平線又重新升了起來，那這就不能稱爲日落。For a sunset to count, the Sun has to set behind the idealized horizon, not just behind a nearby hill. This is not a sunset, even though it seems like one:
要算得上日落，太陽必須沒入理想地平線之下，而非只是躲在附近一座小山後面。以下這種情況雖然看起來像日落，但其實不是：The reason it can't count as a sunset is that if you could use arbitrary obstacles, you could cause a sunset at any time by hiding behind a rock.
至於原因很簡單：你不能隨便躲在某個看不見太陽的障礙物後面就說太陽落下去了，否則你只要藏在石頭背後就隨時能夠製造出一場日落。We also have to consider refraction. The Earth's atmosphere bends light, so when the Sun is at the horizon it appears about one Sun-width higher than it would otherwise. The standard practice seems to be to include the average effect of this in all calculations, which I've done here.
注意我們要考慮折射情況。地球的大氣層會使光線彎折，因而當太陽實際碰到地平線的時候，你會發現太陽實際比地平線高出一個身位。在所有常規的計算中這種情況的平均效應都已經被考慮在內，我這裏也是。At the equator in March and September, sunset is a hair over two minutes long. Closer to the poles, in places like London, it can take between 200 and 300 seconds. It's shortest in spring and fall (when the Sun is over the equator) and longest in the summer and winter.
如果你身處赤道，那麼3月和9月的日落略微比2分鐘多一點。在像倫敦這樣靠近極點的地方，日落可能長達200～300秒。日落的持續時間在春季和夏季最短（在這些時候太陽直射點在赤道上方），在至日和春分（秋分）的時候最長。If you stand still at the South Pole in early March, the Sun stays in the sky all day, making a full circle just above the horizon. Sometime around March 21, it touches the horizon for the only sunset of the year. This sunset takes 38–40 hours, which means it makes more than a full circuit around the horizon while setting.
如果你在早春3月在南極站定，太陽整天都高高掛在天上，在地平線上方繞一整個圈子。有時在3月21日前後太陽會落到地平線之下，這也是一年中唯一一次。這樣的日落會長達38～40小時，這也意味着在日落的過程中太陽轉了一整圈還不止。But Michael's question was very clever. He asked about the longest sunset you can experience on a paved road. There's a road to the research station at the South Pole, but it's not paved-it's made of packed snow. There are no paved roads anywhere near either pole.
但是邁克爾的問題問得很好。他問的是你在鋪有路面的道路上能看到的最長的日落有多久。有一條路通向南極的科研站，但它沒有鋪路面——它是由雪堆出來的。兩極附近都沒有任何一條鋪有路面的道路。The closest road to either pole that really qualifies as paved is probably the main road in Longyearbyen, on the island of Svalbard, Norway. (The end of the airport runway in Longyearbyen gets you slightly closer to the pole, although driving a car there might get you in trouble.)
能夠符合上述標準的離極點最近的道路估計是挪威斯瓦爾巴特羣島上朗伊爾城的主幹道。（如果你能開到朗伊爾城中的機場跑道末端，你可以離極點更近一點，不過這麼做你可能會惹上大麻煩。）Longyearbyen is actually closer to the North Pole than McMurdo Station in Antarctica is to the South Pole. There are a handful of military, research, and fishing stations farther north, but none of them have much in the way of roads; just airstrips, which are usually gravel and snow.
朗伊爾城離北極的距離比南極洲的麥克莫多站離南極的距離還近。還有一大把軍事基地、研究站和釣魚站離北極更近，不過它們都沒有鋪有路面的道路，有的只是用碎石或雪鋪成的飛機跑道。If you putter around downtown Longyearbyen,1 the longest sunset you could experience would be a few minutes short of an hour. It doesn't actually matter if you drive or not; the town is too small for your movement to make a difference.
如果你在朗伊爾城中心城區1閒逛，你能看到的最長的日落差幾分鐘滿一小時。至於你有沒有開車基本不會有什麼影響，因爲這個城市實在是太小了。
