The Eureka! Moment by Rupert Lee

Author:Rupert Lee [Lee, Rupert]
Language: eng
Format: epub
Tags: History, General, Science, Social Science, Anthropology, Cultural & Social
ISBN: 9781136714696
Google: 0h4fDAAAQBAJ
Publisher: Routledge
Published: 2016-05-06T16:15:00+00:00

GALAXIES

‘Island universes’

‘Long, long ago, in a galaxy far, far away …’ Today, every film-goer knows that the Milky Way, with its billions of stars, is only one of the countless number of galaxies that make up the universe. But as recently as the 1920s, this was news. Astronomers had catalogued many ‘nebulae’—hazy patches of dim light that appeared in their telescopes, but they had no idea how far away they were, or even what they were. Best known of all was the Great Nebula of Andromeda, which is (just) visible to the naked eye (see Plate 6). By the start of the twentieth century, there were telescopes powerful enough to show that it was a clump of stars. But how far away was it? Was it a collection of dim stars, quite close to us, or of brighter stars, much further away?

The answer was provided in 1924 by a young American named Edwin Hubble. Born in 1889, Hubble had originally trained to be a lawyer. He studied first at Chicago University and then at Oxford University, where he acquired the style and manners of an upper-class Englishman. However, astronomy was his first love, and he decided to make it his profession soon after he returned to America in 1913. In 1920 he joined the Mount Wilson Observatory outside Los Angeles, which had just acquired a new telescope with a 250-centimetre aperture—then the biggest in the world.

Hubble was soon taking photographs of the Andromeda Nebula. In the winter of 1923 he saw something that excited him: a star in the Nebula whose brightness was changing from day to day. It was clearly a kind of star known as a ‘cepheid’, and that meant he could work out how far away it was. Cepheids are old, slightly unstable stars whose brightness fluctuates with clockwork regularity, and you can tell how bright a cepheid is by how fast it fluctuates. Big bright cepheids fluctuate more slowly than smaller, dimmer ones. So you can work out how far away a cepheid is, by comparing its apparent brightness as it appears in your telescope with its true brightness as you calculate it from its rate of fluctuation.

Hubble plotted the brightness of his cepheid from day to day, did the usual calculations, and came up with a figure: it was over a million light-years away. (A light-year is the distance light travels in a year, going at a speed of 300,000 kilometres every second). This made it easily the furthest object whose distance had ever been measured at that time. The Andromeda Nebula (and therefore, presumably, other similar nebulae that astronomers knew about) was far outside the Milky Way. The universe was clearly very much bigger than anyone had previously imagined.

Most scientific discoveries are first published in specialist scientific journals. Hubble’s discovery did get published this way eventually, in 1925, in the Astrophysical Journal But its first announcement was in the New York Times on November 23, 1924—not the first place one would normally look for cutting-edge science.

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