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Space^17

In space, the closest object to Earth is the

Moon. It orbits Earth and appears to change

shape as it moves – the different shapes are

called. PHASES. The Moon has no light

of its own but shines by reflecting

sunlight. It is the only other world

that humans have set foot on.

WHAT IS THE MOON MADE OF?

The Moon is rocky. It has no atmosphere to protect it, so

anything heading towards the Moon will crash into its

surface, which is covered with craters from meteorites. The

Moon has a hard outer crust of granite-like rock. The typical

rock of the mare (plains) regions is similar to volcanic basalt on

Earth. The Moon’s core, or centre, may be partly molten (liquid).

HOW DOES THE MOON GO THROUGH ITS PHASES?

The phases begin when the Moon comes between the

Sun and the Earth. The bright side of the Moon is

facing away from us, and we see the dark near side.

We call this the New Moon. As the Moon moves along

its orbit, we see more and more of the near side lit up,

until we see it all lit up at Full Moon. Then we see

less and less of the Moon lit up, until it shrinks to a

crescent and then disappears at the next New Moon.

HOW DOES THE MOON AFFECT THE EARTH?

The Moon’s gravity pulls on Earth’s oceans and distorts them, causing

tides. The water on the side of Earth nearest the Moon experiences the

biggest pull, and bulges outwards. The water on the opposite side also

bulges, and the two bulges follow the Moon’s motion and the Earth’s rotation.

Our changing views of light on the Moon are

called phases. As on Earth, one half of the

Moon is lit up by the Sun while the other

half is dark. As the Moon orbits us, we see it

from different angles, with its light side

pointing towards us or away from us.

Diameter (width) at Equator 3,476 km (2,160 miles)

Average distance from Earth 384,400 km (238,900 miles)

Time to orbit Earth 27.3 days

Time to spin around own axis 27.3 days

Time to go through phases 29.5 days (1 month)

Mass 0.01 x Earth’s mass

Gravity 0.17 x Earth’s gravity

Average temperature -20°C (-4°F)

CHANGING SHAPES 1

When the Moon seems to grow in size from night to night, we say it is

waxing. When it seems to shrink, we say it is waning. A crescent Moon

is mostly dark, and a gibbous Moon is mostly light. As the Moon orbits

Earth, it spins on its own axis so the same half (the near side) always

faces Earth – we never see the far side of the Moon.

FIND OUT MORE. Coasts 59 • Forces 164 • Meteors 23 • Space Travel 30

NEAP TIDE

The pull of the Sun and Moon

affects the tides. The lowest

(neap) tides occur when the

Sun and the Moon pull at

right angles to each other

and their pulls partly cancel

each other out.

MOON

Moon

1 THE MOON FROM SPACE

This view of the Moon can be

seen only from space. The picture

was taken during the Apollo 16

Moon mission.

PHASES

EARTH’S OCEAN TIDES

MOON DATA

Crater, a pit

gouged out by

a meteorite

Mare, a flat

dusty plain

1 CRATERED SURFACE

Craters are found everywhere

on the Moon. Most of them

are billions of years old. Some

measure more than 250 km

(152 miles) across.

SPRING TIDE

When the Sun and Moon line

up in space, their gravities

combine and create the

highest (spring) tides.

Light from

the Sun

Phases as we

see them

New

Moon

Waning

gibbous

Waning

crescent

Last quarter

Line of sight

from Earth

Waxing

crescent

Waxing

gibbous

Full

Moon

First quarter

Moon’s

orbit

Earth

Moon

Earth

Earth Moon

Sun

Sun

Moon