The Astronomy Book

214

THE DATA CAN

BEST BE EXPLAINED

AS X-RAYS FROM

SOURCES OUTSIDE

THE SOLAR SYSTEM

COSMIC RADIATION

X

-rays are a form of high-

energy, electromagnetic

radiation released by

extremely hot objects. In the early

20th century, astronomers realized

that space should be flooded with

X-rays from the sun. Moreover, the

sun’s X-ray spectrum would reveal

a lot about the processes at work

within the star. However, X-ray

astronomy was not possible until

the advent of rockets and satellites.

Despite their energy, X-rays are

easily absorbed, which is why they

are so good at imaging the body.

Water vapor in Earth’s atmosphere

effectively blocks X-rays from

reaching the surface—a good

thing for life, because high-energy

IN CONTEXT

KEY ASTRONOMER

Riccardo Giacconi (1931–)

BEFORE

1895 German physicist

Wilhelm Röntgen discovers

high-energy radiation, which

he names “X-rays.”

1949 Solar X-rays are first

detected by sounding rockets.

AFTER

1964 Cygnus X-1, the first

confirmed black hole binary

system, is discovered.

1966 X-rays are detected

from galaxy cluster M87,

in the Virgo cluster.

1970 Uhuru, the first dedicated

X-ray mission, is launched.

1979 X-rays from Jupiter

are detected by the

Einstein Observatory.

1999 The Chandra X-ray

Observatory is launched.