What's behind the UK's big aurora displays?

Melanie Windridge looks at the influence of recent increases in solar activity

- Melanie Windridge

This aurora season has proved a good one so far, particularly for aurora watchers in the UK, with numerous newspaper reports of Northern Lights seen in the UK since September. This is likely due to an uptick in solar activity as part of the solar cycle, but before we go into that, let's think about what causes the aurora in general.

The aurora is an incredible light show caused by charged particles accelerated into our upper atmosphere. This acceleration process is driven by the Sun, so the changing power - or activity - of the Sun affects the aurora we see.

When we are young we often think of the Sun as a uniform yellow ball in the sky, but look closely at NASA pictures and you'll see that the Sun's surface is anything but uniform. The Sun is made of plasma, an electrically charged gas of mostly hydrogen and helium. The surface is a bit like a boiling pan of water, with hot material welling up and cooler material dropping down. This motion is stirred up because the Sun also rotates at different speeds at its poles and equator, making for turbulent flows. Magnetic fields are generated, and are twisted into loops emerging from the surface by this rotation.

Some of the Sun's plasma is also released into space - the Sun's atmosphere expanding out in all directions. This is called the solar wind, and it is this that drives the aurora on Earth. In addition to the ordinary outflow of particles, the Sun also throws off extra particles when twisted magnetic loops break and fling out solar matter.