The Earth’s magnetic field shields us from a lot of the ionising radiation that comes from space. The Moon may be the remains of a planet which collided with the Earth during the early years of the Earth’s existence.

Artificial satellites have many uses, including telecommunications and weather predicting, but can be disrupted by solar flares from the Sun.

Magnetic fields

Magnets have a north pole and a south pole. You can use plotting compasses to show the direction and shape of a magnetic field. In diagrams of magnetic field the arrows on the lines show the direction from the north to the south poles.

A magnetic field is also created if an electric current moves through a coil of wire.

The Moon is the Earth’s natural satellite. It may be the remains of a Mars-sized planet that collided with the early Earth as it was forming:

• The iron cores of the two planets merged.
• Less dense material was ejected by the collision.
• The less dense material merged to form the Moon.

Evidence for the collision

Here is some evidence for the collision theory:

• The Earth has an iron core but the Moon does not.
• Moon rocks are similar in composition to rocks found on Earth

Among other jobs, artificial satellites orbiting the Earth are used for:

• telecommunications (transmitting information between distant parts of the Earth)
• satellite navigation systems (‘satnav’)
• spying on other countries, and
• weather forecasts.

Communications satellites occupy a geostationary orbit. They are in orbit above the equator at just the right distance so that it takes them one day to complete an orbit. As a result, they always appear in the same position when seen from the ground. This is why satellite television dishes can be bolted into position and do not need to move.

Earth observation and monitoring satellites occupy polar orbits. The Earth spins beneath the satellite as it moves, so the satellite can scan the whole surface of the Earth.

The Sun is a source of ionising radiation. Clouds of charged particles can be ejected from the Sun at high speed. These solar flares produce strong magnetic fields. They can disrupt satellite communications and cause electricity blackouts on Earth.

Cosmic rays are fast-moving charged particles. They create gamma rays when they hit the Earth’s atmosphere. These have the potential to harm living organisms.

The Earth’s magnetic field deflects cosmic rays, causing them to spiral around the magnetic field close to the poles. They ionise atoms in the atmosphere, which recombine with electrons to give off light. This causes a dramatic display of coloured light in the sky near the poles, called the aurorae. You see the Northern Lights, or Aurora Borealis, in the night sky near the North Pole, and the Southern Lights, or Aurora Australis, in the night sky near the South Pole.