Page 26 - BBC History The Story of Science & Technology - 2017 UK

Ideas & Inventions / Objects

2 JOHANNES
KEPLER’S MODEL
OF THE UNIVERSE

The harmonious musical
cosmos imagined by the
astronomer famous for
showing that planets move
in ellipses
In 1600, an impoverished astrologer and
former university teacher called Johannes
Kepler (1571–1630) found refuge in the
imperial court at Prague. While his three
laws describing how the planets move still
lie at the heart of Newtonian astronomy,
Kepler himself believed in a magnetic
musical universe structured to mirror God’s
perfect geometrical forms.
In Kepler’s harmonious vision, which he
illustrated by drawing an imaginary cosmic
model, God had spaced out the planetary
spheres so that symmetrical shapes could
be nested between them. The outermost
orbit of Saturn is separated from its
neighbour – Jupiter – by a cube. Moving
inwards, a pyramid lies between Jupiter
and Mars. Similarly, other solids frame the
paths of Earth, Venus and Mercury around
the Sun.
Kepler decided that the Sun must affect
the motion of the planets, and he started
by tackling the astrological God of War,
Mars. This planet’s orbit clearly deviated
from circular perfection, and after many
tortuous calculations and blind alleys,
Kepler showed that the orbit of Mars is
Tycho Brahe surveys the heavens in his mural quadrant, as depicted
in the frontispiece to Astronomiae Instauratiae Mechanica (1598) an ellipse.
Yet what might now seem like a great
scientific leap forward was ignored for
1 TYCHO BRAHE’S MURAL QUADRANT decades. It was only in 1631, after Kepler
had died, that his elliptical model was
The brass quarter-arc that helped an unorthodox vindicated, when Mercury passed in front
Danish astronomer compile the world’s most of the Sun exactly as he had predicted.
accurate set of star data

Tycho Brahe (1546–1601) was no wall and used to measure the precise
ordinary 16th-century astronomer. position of a star as it passes by the
Following an unfortunate duel he wore small sight on the top left. Behind the
an artificial nose, and he supposedly virtual Tycho’s outstretched arm lie
died from a burst bladder at a feast. illustrations of his observatory’s three
More importantly, Tycho rejected floors: the roof top for making
conventional academic career routes, night-time observations, the library
eventually acquiring royal funding for with its immense celestial globe, and
a massive observatory on the island the basement devoted to carrying out
of Hven, which is now a Danish experiments. An observer is just
heritage site on Swedish territory. visible on the right, calling out to his
He was particularly proud of his giant assistants who coordinate their
quadrant, the brass quarter-arc measurements of a moving star’s time
astronomical device around two and position.
metres in height that can be seen in Tycho compiled the world’s most
the frontispiece illustration above. accurate and comprehensive set of GETTY
Most of this picture is itself of a star data. And, although Tycho
picture – Tycho and his snoozing dog believed the Sun revolves about us, Kepler’s imaginary cosmic
belong to a mural painted within the Galileo used his observations to model shown in Mysterium
quadrant device, which is fixed to the confirm that the Earth indeed moves. Cosmographicum (1596)

26 The Story of Science & Technology