万物简史 第29期:走进太阳系(7)

　　And how far is that exactly? It's almost beyondimagining. Space, you see, is just enormous—justenormous. Let's imagine, for purposes of edificationand entertainment, that we are about to go on ajourney by rocketship. We won't go terribly far—justto the edge of our own solar system—but we need toget a fix on how big a place space is and what asmall part of it we occupy.

　　这到底有多远?几乎难以想像。你看，空间大得不得了--简直大得不得了。出于了解和娱乐的目的，我们来想像一下，我们就要乘火箭飞行器进行旅行。我们不会走得太远--只到我们自己太阳系的边缘--不过，我们先要明白：空间是个多么大的地方，我们占据的是个多么小的部分。

　　Now the bad news, I'm afraid, is that we won't be home for supper. Even at the speed of light,it would take seven hours to get to Pluto. But of course we can't travel at anything like thatspeed. We'll have to go at the speed of a spaceship, and these are rather more lumbering. Thebest speeds yet achieved by any human object are those of the Voyager 1 and 2 spacecraft,which are now flying away from us at about thirty-five thousand miles an hour.

　　哎呀，恐怕是坏消息，我们回不了家吃晚饭了。即使以光的速度(每秒30万公里)前进，也要花7个小时才能到达冥王星。而且，我们当然无法以这种速度进行旅行。我们不得不以宇宙飞船的速度前进。这个速度就很慢了。任何人造物体所能达到的最高速度是"旅行者1号"和"旅行者2号"宇宙飞船的速度，它们现在正以每小时5.6万公里的速度飞离我们。

　　The reason the Voyager craft were launched when they were (in August and September 1977)was that Jupiter, Saturn, Uranus, and Neptune were aligned in a way that happens only onceevery 175 years. This enabled the two Voyagers to use a "gravity assist" technique in whichthe craft were successively flung from one gassy giant to the next in a kind of cosmic versionof "crack the whip." Even so, it took them nine years to reach Uranus and a dozen to cross theorbit of Pluto.

　　当时(1977年8月和9月)之所以发射"旅行者"号飞船，是因为木星、土星、天王星和海王星排成了一条直线，这种现象每隔175年才发生一次。这就使得两艘"旅行者"号飞船能够利用"引力帮助"技术，以一种宇宙甩鞭的形式，被从一颗气态巨星连续甩到下一颗气态巨星。即使这样，它们也要花9年时间才能到达天王星，要花12年时间才能越过冥王星的轨道。

　　The good news is that if we wait until January 2006 (which is when NASA's New Horizonsspacecraft is tentatively scheduled to depart for Pluto) we can take advantage of favorableJovian positioning, plus some advances in technology, and get there in only a decade or so—though getting home again will take rather longer, I'm afraid. At all events, it's going to be along trip.

　　好的消息是，要是我们等到2006年1月(这是美国国家航空和航天局暂定向冥王星发射"新地平线"号宇宙飞船的时间)，我们就可以利用有利的木星定位法，加上一些先进的技术，只用10年左右的时间便能抵达那里--虽然再次回到家里恐怕要花上相当长的时间。