The Astronomy Book

179

W

hile working for Bell

Telephone Laboratories in

1930s America, telephone

engineer Karl Jansky was given the

task of plotting the natural sources

of static that might interfere with

long-wave radio voice transmissions.

To conduct his investigations,

Jansky hand-built a directional radio

antenna that was 100 ft (30 m) wide

and 20 ft (6 m) high. The contraption

rotated on four tires salvaged from

an old Model T Ford. His colleagues

dubbed the device “Jansky’s merry-

go-round” because the young

engineer would systematically

rotate the antenna to pinpoint

sources of atmospheric radio waves.

Radio astronomy

Jansky matched most sources

of radio waves to approaching

thunderstorms, but there was

a persistent hiss that remained

unidentified. The intensity of this

static rose and fell once a day, and

initially Jansky thought he was

detecting radio from the sun.

However, the “brightest” spot of

radio waves moved through the sky

following the sidereal day (relative

to the stars), not the solar day, and

Jansky realized that the radio waves

were coming from the constellation

Sagittarius, at the heart of the Milky

Way: radio waves were “shining”

from space just like visible light.

The newspapers reported the

discovery of “extraterrestrial radio,”

and astronomers soon began to

copy Jansky’s device—in effect the

first radio telescope. This opened

up the possibility of viewing the

universe in a new way—not from its

light but from its radio emissions. ■

ATOMS, STARS, AND GALAXIES

THE RADIO

UNIVERSE

RADIO ASTRONOMY

IN CONTEXT

KEY ASTRONOMER
Karl Jansky (1905 –1950)

BEFORE
1887 German physicist
Heinrich Hertz demonstrates
the existence of radio waves.

1901 Italian inventor
Guglielmo Marconi sends a
radio signal across the Atlantic,
unknowingly bouncing the
waves off the ionosphere.

AFTER
1937 American amateur
astronomer Grote Reber makes
the first radio survey of the sky.

1965 James Peebles proposes
that universal background
microwave radio waves are the
last remnant of the Big Bang.

1967 Antony Hewish and
Jocelyn Bell Burnell detect a
repeating stellar radio signal,
the first pulsar.

1998 Sagittarius A* is shown
to be a supermassive black hole
at the center of the Milky Way.

Jansky is pictured here with his

hand-built antenna. He published a

paper on his work in 1933, but soon

after was reassigned by Bell Labs

and did no more astronomical work.

See also: Searching for the Big Bang 222–27 ■ Quasars and pulsars 236–39 ■

Reber (Directory) 338 ■ Ryle (Directory) 338−39