It took centuries, but we now know the size of the Universe [View all]
It took centuries, but we now know the size of the Universe
The sheer scale of the cosmos is hard to imagine, and even harder to put an accurate figure on. But thanks to some ingenious physics we now have a good idea of just how big it is
By Chris Baraniuk
13 June 2016
"Let us go rambling about the Universe." This is the invitation that American astronomer Harlow Shapley gave to an audience in Washington DC in 1920. He was taking part in the so-called Great Debate with fellow scientist Heber Curtis on the scale of the Universe.
Shapley believed that our Milky Way galaxy was 300,000 light years across. That is actually three times too big according to the latest thinking, but his measurements were pretty good for the time. In particular, he calculated broadly correct proportional distances within the Milky Way – the position of our Sun relative to the centre of the galaxy, for instance.
In the early 20th Century, though, 300,000 light years seemed to many of Shapley's contemporaries an almost absurdly large figure. And the idea that other Milky Way-like spiral galaxies – which could be seen with telescopes – were equally large was outlandish.
Indeed, Shapley himself believed the Milky Way must be exceptional. "Even if the spirals are stellar, they are not comparable in size with our stellar system," he told his listeners
More:
http://www.bbc.com/earth/story/20160610-it-took-centuries-but-we-now-know-the-size-of-the-universe
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