Transcript
MARCUS DU SAUTOY
No matter how busy life gets, looking up at the night sky always fills me with wonder. And I’m not alone. Humans have been gazing at stars for as long as they’ve walked the Earth. It makes you think about our place in the universe, and it’s inspired many people throughout history to write down their observations to figure out more about our humble planet, and how we fit into the picture – the really big picture.
Early humans enhanced their own lives by gazing at the night sky. They worked out calendars which allowed them to improve their farming, and they could plan practical things, such as the best nights for moonlight if they had a long journey to make.
Around 280BC, Aristarchus of Samos proposed that the Earth moves around the Sun – a notion that was not accepted by his contemporaries. He made the first estimates of the distance to the Sun, and the relative sizes of the Sun and the Moon. Just a few decades later, Eratosthenes of Cyrene makes the first pretty accurate measurements of the size of the Earth, by comparing the lengths of shadows cast at different latitudes.
Around 400 years later, Claudius Ptolemy consolidated the prevailing picture of the universe with the Earth at the centre, and the Sun and planets rotating around it every 24 hours. He also estimated the distance of the Sun as 1210 times the radius of the Earth. This geocentric view remained unchallenged for 1400 years, although Muslim scholars from the 10th to the 14th century criticised the work, al-Haytham correctly pointing out that Ptolemy’s hypothesis regarding the arrangement and motion of the planets was contradictory between two of his own publications.
Many centuries later, Nicolaus Copernicus published his own model of the universe, showing the Sun at the centre, with the Earth and other planets moving around it, and with the stars lying on the outskirts. In 1785, William Herschel published the first map of the Milky Way galaxy, based on counting stars in all directions, and speculated that some of the faint cloud-like formations may be other galaxies beyond our own. In 1838, Friedrich Bessel measured the parallax of 61 Cygni, the first direct measurment of the distance to a star, showing it to lie about 10 light years away. That’s about 95 trillion kilometres.
Having spent most of history thinking that the Earth is the centre of the universe – only to find out that it isn’t – in 1918, Harlow Shapley told us that our Sun isn’t even in the centre of our Milky Way galaxy, but thousands of light years towards the edge. And just a few later, controvery over the scale of the universe was resolved as astronomers, led by Edwin Hubble, came to accept that objects such as the Andromeda galaxy are indeed not part of the Milky Way, but far outside it, and separate galaxies in their own right.
A few decades later, George Abell published the first part of a survey of clusters of galaxies, demonstrating the existence of superclusters as the largest structures in the universe. In 1964, while Arno Penzias and Robert Wilson were trying to trace the source of noise interfering with a radio antenna, they accidentally discovered it was not just static hiss, but the sounds of the universe being born. It was the cosmic microwave background radiation (CMBR), lending support to the Big Bang theory. The CMBR marks the edge of the observable universe. And in 2016, a team using the Hubble Space Telescope discovered the most distant known object, a galaxy called GN-z11, which is now around 32 billion light years away, and seen about 400 million years after the Big Bang.
And that’s only the story so far! With our ability to observe the universe improving all the time, who knows what we will discover over the next few years? But the universe still holds many great secrets. So, will there be things that we simply cannot know?