homework encyclopedia

16 Space

The planet we live on is the third closest planet to the Sun.

It takes one year to orbit the Sun, and one day to spin

around on its. AXIS. From space, Earth looks

mainly blue because that is the colour of its

oceans, which cover more than 70 per cent

of its surface.

WHAT MAKES EARTH DIFFERENT FROM

ALL THE OTHER PLANETS?

Earth is the only planet that provides the

right conditions for life. Temperatures are

not too hot and not too cold, there is

liquid water, and there is oxygen in the

atmosphere. With warmth, water, and

oxygen, Earth is home for millions of

different living species, from tiny

bacteria to giant blue whales.

IS THE AXIS TILTED?

Earth’s axis is not at right angles to its orbit – it tilts over

at an angle of 23.5 degrees. This tilted axis causes our

seasons. As Earth travels on its year-long orbit of the

Sun, its North Pole leans first towards the Sun, then, six

months later, leans away from it. This makes northern

parts of our planet warmer, then cooler, giving us

summer and winter. As the North Pole leans one way, the

South Pole leans in the opposite direction, so the north

and south of the planet have opposite seasons.

WHAT IS THE EARTH MADE OF?

Earth is one of four rocky planets in the Solar System.

Underneath an atmosphere, which contains mainly

oxygen and nitrogen gases, there is a hard rock crust.

Beneath the crust is a layer of heavier rock called the

mantle. At the Earth’s centre is a huge mass of iron,

which is molten (liquid) on the outside but solid

inside. This is called the core.

As Earth travels in slow orbit around the Sun, it also spins around

an imaginary line called its axis. This straight line passes through

the North and South Poles, and turning around it gives us

our day and night – one half of Earth faces the Sun

while the other side is dark.

FIND OUT MORE. Life on Earth 70 –71 • Planet Earth 36–

EARTH’S WOBBLING AXIS 3

As Earth spins on its axis and orbits the Sun, it

also wobbles very, very slowly. In our lifetimes,

the axis will always seem to point in the same

direction in space, but over 26,000 years, it

creeps around an imaginary circle. At present,

the axis points almost at the star Polaris in the

north, so Polaris is called the Pole Star.

AXIS

EARTH

Earth

Earth’s axis slowly

traces an imaginary

circle in space

EARTH DATA

Axis stays tilted

at 23.5° as

Earth wobbles

23.5°

Diameter (width) at Equator 12,756 km (7,926 miles)

Average distance from Sun 149.6 million km (93 million miles)

Time to orbit Sun 365.25 days

Time to spin around own axis 23.93 hours

Mass 6,000 million million million tonnes

(5,900 million million million tons)

Surface temperature –70°C to +55°C (–94°F to +131°F)

Number of moons 1 (the Moon)

Earth