What are the Earth's "two shields"?

The Sun is about 150 million km away, but what happens on its surface can still reach us. Scientists call it space weather.

The Sun is always throwing gas and tiny particles out into space, a steady stream known as the solar wind. These particles come from the Sun's hot outer atmosphere, the corona, and they carry an electric charge. The solar wind can carry them towards the Earth at more than a million kilometres an hour.

We are protected by two shields. The Earth is surrounded by a magnetic field, an invisible area of magnetic force, and by a jacket of gases, the atmosphere. Together they turn aside most of the solar wind. The charged particles crash into the magnetic field and flow around it, squashing the side that faces the Sun and stretching the far side into a long tail.

Some particles get caught in the magnetic field, gain energy there, and then rush into the atmosphere near the North and South Poles. When they do, they make the sky glow with shifting colours: the auroras.

Space weather is not always so beautiful. During strong solar storms, the solar wind becomes much more powerful, and at its worst it can damage satellites and cause electrical blackouts on the Earth.