The Astronomy Book

213

See also: The properties of sunspots 129 ■ The Homestake experiment 252–53 ■

Exoplanets 288–95

I

n 1960, American physicist

Robert Leighton made

observations with a camera

that he had devised, which led to

the discovery that the sun is “ringing

like a bell,” as he put it. Working

with Robert Noyes and George

Simons, Leighton picked up

perturbations of the sun’s surface

using Doppler shift solar cameras.

These cameras detected tiny

shifts in the frequency of the sun’s

absorption spectra as its outer layer

moved toward or away from Earth.

Five-minute oscillations

The complex patterns of vibrations,

with an average period of five

minutes (known as “5-minute

oscillations”), were at first thought

to be a surface phenomenon. Then

in 1970, Roger Ulrich explained

them as trapped acoustic waves

bouncing within the sun from one

side to the other, causing the star’s

surface to wobble as it resonated.

Today, these waves allow

scientists to investigate the interior

of the sun, in much the same way

that acoustic earthquake waves

reveal the inner composition

and structure of Earth. Known as

helioseismology, this process is often

compared to trying to build a piano

by studying the sounds it makes

when it falls down a flight of stairs,

but it has produced a model of the

sun’s interior processes. The model

places tight constraints on the

amount of helium in the star’s core,

which has important consequences

for models of the early universe. ■

NEW WINDOWS ON THE UNIVERSE

THE SUN RINGS

LIKE A BELL

THE SUN’S VIBRATIONS

IN CONTEXT

KEY ASTRONOMER
Robert Leighton (1919 –1997)

BEFORE
1954 Canadian astronomer
Harry Hemley Plaskett observes
the sun’s oscillation effect.

AFTER
1970 American physicist
Roger Ulrich proposes that the
oscillations are from acoustic
waves in the solar interior.

1970s Helioseismology opens
up a new way of investigating
the interior of the sun.

1995 The solar observatory
satellite SOHO is launched.

1997 The SOHO team discover
“jet streams” of plasma in the
convective zone.

1990–2000s Hundreds of
thousands of the sun’s
vibrational modes are identified.

2009 The Kepler satellite
measures oscillations in
sunlike stars to describe
conditions on exoplanets.

With his very inquisitive

mind, every funny effect

that you’d see in nature

he’d try to explain.

Gerry Neugebauer

Physicist and colleague

of Robert Leighton