The Astronomy Book

42

T

he Dane Tycho Brahe was

the last great astronomer

of the pre-telescope era.

Realizing the importance of trying

to record more accurate positions,

Tycho built some high-precision

instruments for measuring angles.

He accumulated an abundance of

observations, far superior to those

available to Copernicus.

Magnifying the image

The realm of heavenly bodies still

seemed remote and inaccessible

to astronomers at the time of

Tycho’s death in 1601. However,

the invention of the telescope

around 1608 suddenly brought

the distant universe into much

closer proximity.

Telescopes have two important

advantages over eyes on their own:

they have greater light-gathering

power, and they can resolve finer

detail. The bigger the main lens

or mirror, the better the telescope

on both counts. Starting in 1610,

when Galileo made his first

telescopic observations of the

planets, the moon’s rugged surface,

and the star clouds of the Milky

Way, the telescope became the

primary tool of astronomy, opening

up unimagined vistas.

Planetary dynamics

After Tycho Brahe died, the records

of his observations passed to his

assistant Johannes Kepler, who

was convinced by Copernicus’s

arguments that the planets orbit

the sun. Armed with Tycho’s data,

Kepler applied his mathematical

ability and intuition to discover

that planetary orbits are elliptical,

not circular. By 1619, he had

formulated his three laws of

planetary motion describing the

geometry of how planets move.

Kepler had solved the problem

of how planets move, but there

remained the problem of why

they move as they do. The

ancient Greeks had imagined

INTRODUCTION

1576

1600

1619

1639

1608

1610

Johannes Kepler describes

the elliptical orbits of

planets with his three laws

of planetary motion.

Italian friar Giordano Bruno is

burned at the stake as a heretic

after expressing a view that the

sun and Earth are not central

or special in the universe.

Dutch eyeglass-maker

Hans Lippershey

applies for a patent for

a telescope with

three-times

magnification.

Using a telescope with

33-times magnification,

Galileo Galilei

discovers four moons

orbiting Jupiter.

Tycho Brahe builds
a large observatory
on the island of
Hveen, from where he
makes observations
for 20 years.

English astronomer

Jeremiah Horrocks

observes the transit

of Venus across the

face of the sun.

If I have seen further it

is by standing on the

shoulders of giants.

Isaac Newton