homework encyclopedia

10 Space

WHERE DOES SPACE BEGIN?

From Earth, space begins at the outer edge of our

planet’s atmosphere. There is no clear line between

the atmosphere and space – the atmosphere gradually

fades away until it merges into space about 500 km

(300 miles) above Earth. However, there are tiny

traces of atmosphere even farther out than this.

WHERE IS EARTH IN SPACE?

Earth is a tiny speck of matter in space. It is one of

the eight major planets which circle round the Sun.

In turn, the Sun is one of several hundred billion

stars, which together form a great star island in space

called the Milky Way Galaxy. There are billions of

galaxies in space. Together, all the galaxies and the

enormous voids between them make up the Universe.

HOW MUCH SPACE IS THERE?

Astronomers believe that space is infinite – it has no

edge or boundary. Earth’s nearest neighbour in space,

the Moon, is 384,400 km (238,900 miles) away on

average. The Sun is 150 million km (93 million miles)

away. Most other stars in the Milky Way are between

a million and a billion times more distant than the

Sun. Other galaxies are millions of times farther still.

WHAT IS A LIGHT YEAR?

A light year is a unit for measuring distances in space.

It is the distance that light travels in a year – about

9.5 million million km (5.9 million million miles).

Proxima Centauri is the nearest star to the Sun. It lies

about 4.2 light years away from Earth, which means

that its light takes 4.2 years to reach us.

WHAT CAN WE SEE WHEN WE LOOK INTO SPACE?

Without a telescope, we can see about 2,500 stars

on a really dark night. We often see the Moon, and

sometimes the planets Mercury, Venus, Mars, Jupiter,

and Saturn, as well as comets. The farthest thing we

can see just with our eyes is the Andromeda Galaxy.

150 CE Ptolemy claims

Earth at centre

of Universe

1543 Copernicus puts

Sun at centre

of Universe

1609 Galileo first to

use a telescope

to study space

1687 Newton

publishes the

laws of gravity

1781 Herschel

discovers the

planet Uranus

1846 Galle discovers

the planet

Neptune

1926 Goddard

launches first

liquid-fuelled

rocket

1930 Tombaugh

discovers Pluto

1957 First satellite,

Sputnik 1,

orbits Earth

1961 Yuri Gagarin

becomes first

man in space

1965 Mariner 4 sends

back pictures

of Mars

1969 Apollo 11 makes

the first manned

Moon landing

1981 First launch of

space shuttle

1990 Launch of

Hubble Space

Telescope

1998 International

Space Station

construction

begins

When you look up at the night sky,

the blackness you see is space.

It is the great void, or emptiness,

in which Earth, the Moon, the Sun,

and the stars travel. Space is totally

silent and most of it is incredibly

cold – around –270°C (–454°F).

It is also called outer space.

4 JOURNEY INTO SPACE

This powerful rocket launch

vehicle, Ariane, sends satellites

and other spacecraft into

space to explore the stars

and planets and view

Earth from space.

THE MILKY WAY 3

This pale band of light in the night

sky is the Milky Way. Its light

comes from hundreds of billions

of stars in our galaxy. Billions

more stars are hidden behind

giant, dark clouds of dust and gas.

SPACE

Space

SPACE TIMELINE

FIND OUT MORE. Galaxies 27 • Solar System 14 • Stars 24–25 • Universe 26

space