Page 63 - BBC History The Story of Science & Technology - 2017 UK

OF ASTRONOMY

of space has developed over the past 5,000 years

A Chinese star chart of
the sky seen from the 2 Mirror of the Earth 3 Ordering
northern hemisphere, Chinese astronomers were the first to make
c700 AD the heavens
accurate records of the sky. They regarded the
heavens as a mirror of the Earth, with the stars The Greek philosopher Pythagoras
representing different regions of China. So an was among the first to question
exploding star in a star pattern would indicate a the widely held view that the world
rebellion in a corresponding province. was flat when, in the sixth century
We have Chinese astronomers to thank for BC, he taught that the Earth must be
the earliest known records of Halley’s Comet a sphere, because of the shape of its
– in 240 BC – and an account of a supernova, shadow on the Moon during a lunar
from AD 1054, whose remains today form a eclipse. Over 200 years later
tangled mass of gas called the Crab Nebula. Aristarchus suggested the Earth
moves round the Sun – yet his idea
didn’t take off. Instead, it was left to
Ptolemy (pictured below) to leave the
Ancient Greeks’ most lasting imprint
4 The Earth moves Galileo saw that Jupiter was on astronomy when (around AD 150)
he concluded that the planets
Our perception of mankind’s importance
in the universe changed forever in 1543, accompanied by four moons moved in small circles carried by
larger circles, centred on the
when Polish canon Nicolaus Copernicus (overturning the argument that the Earth Earth. His theory
published a book arguing that the Earth couldn’t be in motion as it would leave was unchallenged
did not sit at its centre. Instead, the Moon behind) and observed the for 1,400 years.
it was merely a planet orbiting the Sun. changing phases of Venus, which showed
Copernicus had come to this conclusion this planet must be orbiting the Sun.
over 30 years earlier, but he largely kept it The church banned Galileo’s books
to himself. His case was proven in 1610, but, from then on, no one seriously
when Galileo Galilei – in Padua, Italy – doubted that the Earth had been
turned his telescope to the skies. dethroned from the centre of the universe.

7 Powerhouse of the stars Payne (pictured left) worked out the relative Digital artwork
of what the Big
Bang may have
“On the subject of stars… we shall never be
able by any means to study their chemical proportions of the elements, and proved looked like
composition.” So wrote the French positivist that most of the universe is made of
philosopher Auguste Comte in 1835. But hydrogen. It led to an understanding that
only two decades later, German chemists the powerhouse of the stars was basically
Gustav Kirchhoff and Robert Bunsen proved a hydrogen bomb running in slow motion.
him wrong. They identified elements in the And astrophysicist Fred Hoyle squared the
Sun by comparing the dark lines in its circle by showing how elements are built up
spectrum of colours with laboratory spectra in stars. So the gold in your wedding ring
of elements, such as hydrogen and iron. is nothing less than the product of an
8 The Big Bang
In the 1920s, British astronomer Cecilia exploding star.

In the 1920s, American astronomer
Edwin Hubble, along with former
Black and brilliant mule-driver Milton Humason, found
that galaxies are racing apart from
9 British army scientist Stanley Hey was the mass of the Sun. And they have
perplexed in February 1942. He was found giant black holes. These each other. The universe is
expanding, suggested Belgian priest
investigating what seemed to be an cosmic monsters weigh as much as Georges Lemaitre, because it was
outburst of German radar jamming – a billion suns, and their gravity is so born in an exploding “primeval atom”
but it moved around the sky during the powerful that light can’t escape. As – what we now call the Big Bang.
day. Hey realised that the emission the gas from the stars swirls round the This was proved in 1965, when
came from the Sun, and instigated black hole, it shines as brilliantly as American scientists Arno Penzias
the science of radio astronomy. hundreds of galaxies in an and Robert Wilson discovered a faint
Since then, radio astronomers have incandescent flickering maelstrom background of radio waves – the
discovered pulsars – dense balls of that astronomers call a quasar afterglow of the Big Bang.
matter only the size of a city, but with (illustrated on the left).

The Story of Science & Technology 63