爱德文·哈勃Edwin Hubble

爱德文·哈勃是一个改变了我们宇宙观的人。1929年，他证明了星系正以与距离成正比的速度远离我们。解释很简单，但却是革命性的：宇宙在膨胀。

哈勃于1889年出生于密苏里州。1898年，他的全家搬到芝加哥，在那里上高中时，他是一个有前途但并不出众的学生。他更引人注目的是他的运动才能，打破了伊利诺伊州跳高纪录。在大学里，他也是一名出色的运动员，为芝加哥大学篮球队效力。他获得了前往牛津大学的罗德奖学金，在那里学习法律。直到回到美国一段时间后，他才决定自己的未来在于天文学。

20世纪20年代初，哈勃在确定星系究竟是什么方面发挥了关键作用。人们已知一些旋涡星云（夜空中模糊的光云）包含单个恒星，但对于这些究竟是我们自己星系——横跨天空的“银河”——内相对较小的恒星集合，还是可能是独立的星系，即“岛宇宙”，与我们自己的星系一样大但远得多，当时并没有共识。1924年，哈勃测量了仙女座星云的距离，那是一片微弱的光斑，视直径与月亮大致相同，并表明它的距离大约是最近恒星距离的十万倍。它必定是一个独立的星系，大小与我们自己的银河系相当，但远得多。

哈勃当时只能测量到少数几个星系的距离，但他意识到，作为一个粗略的指南，他可以把星系的视亮度作为其距离的指示。由于星系光线的多普勒位移，测量星系向我们靠近或远离的速度相对容易。正如赛车远离我们时声音会变低，星系的光也会变得更红。虽然我们的耳朵能听到赛车引擎音调的变化，但我们的眼睛无法察觉光线的微小红移，然而借助灵敏的光谱仪，哈勃能够确定来自遥远星系的光的红移。

到1929年，哈勃可获得的观测数据还很粗略，但无论是受灵感直觉的指引还是出于难以置信的好运，他正确地推断出数据点之间呈直线拟合，表明红移与距离成正比。此后，大为改进的数据表明这一结论是可靠的。随着宇宙膨胀，星系正在远离我们，也彼此远离。在亚伯拉罕·阿德里安·艾伯特阿尔伯特·爱因斯坦于1915年提出的引力理论——广义相对论中，不可避免的结论是，所有星系以及整个宇宙都起源于数十亿年前的一次大爆炸。于是，现代宇宙论科学诞生了。

哈勃用当时世界上最好的望远镜——位于南加利福尼亚威尔逊山上的100英寸望远镜——做出了他的伟大发现。如今，他的名字由我们拥有的最好的望远镜承载，这望远镜不在地球上，而是一个环绕我们星球的卫星天文台。哈勃空间望远镜正在继续哈勃本人开创的绘制宇宙地图的工作，并产生出前所未见的遥远星系的最非凡图像，其中许多可通过万维网获取。

Edwin Hubble was a man who changed our view of the Universe. In 1929 he showed that galaxies are moving away from us with a speed proportional to their distance. The explanation is simple, but revolutionary: the Universe is expanding.

Hubble was born in Missouri in 1889. His family moved to Chicago in 1898, where at High School he was a promising, though not exceptional, pupil. He was more remarkable for his athletic ability, breaking the Illinois State high jump record. At university too he was an accomplished sportsman playing for the University of Chicago basketball team. He won a Rhodes scholarship to Oxford where he studied law. It was only some time after he returned to the US that he decided his future lay in astronomy.

In the early 1920s Hubble played a key role in establishing just what galaxies are. It was known that some spiral nebulae (fuzzy clouds of light on the night sky) contained individual stars, but there was no consensus as to whether these were relatively small collections of stars within our own galaxy, the 'Milky Way' that stretches right across the sky, or whether these could be separate galaxies, or 'island universes', as big as our own galaxy but much further away. In 1924 Hubble measured the distance to the Andromeda nebula, a faint patch of light with about the same apparent diameter as the moon, and showed it was about a hundred thousand times as far away as the nearest stars. It had to be a separate galaxy, comparable in size our own Milky Way but much further away.

Hubble was able to measure the distances to only a handful of other galaxies, but he realised that as a rough guide he could take their apparent brightness as an indication of their distance. The speed with which a galaxy was moving toward or away from us was relatively easy to measure due to the Doppler shift of their light. Just as a sound of a racing car becomes lower as it speeds away from us, so the light from a galaxy becomes redder. Though our ears can hear the change of pitch of the racing car engine our eyes cannot detect the tiny red-shift of the light, but with a sensitive spectrograph Hubble could determine the redshift of light from distant galaxies.

The observational data available to Hubble by 1929 was sketchy, but whether guided by inspired instinct or outrageous good fortune, he correctly divined a straight line fit between the data points showing the redshift was proportional to the distance. Since then much improved data has shown the conclusion to be a sound one. Galaxies are receding from us, and one another, as the Universe expands. Within General Relativity, the theory of gravity proposed by Albert Einstein in 1915, the inescapable conclusion was that all the galaxies, and the whole Universe, had originated in a Big Bang, thousands of millions of years in the past. And so the modern science of cosmology was born.

Hubble made his great discoveries on the best telescope in the world at that time - the 100-inch telescope on Mount Wilson in southern California. Today his name carried by the best telescope we have, not on Earth, but a satellite observatory orbiting our planet. The Hubble Space Telescope is continuing the work begun by Hubble himself to map our Universe, and producing the most remarkable images of distant galaxies ever seen, many of which are available via the World Wide Web.