91Èȱ¬

Some of our Weather Watchers in Scotland were lucky enough to see the Aurora Borealis, or Northern Lights, last night (Tuesday 21 March). But what causes this array of colours dancing in the night sky?

It all starts at the sun. A sunspot or coronal hole allows a batch of charged particles to leave the sun and travel towards the UK on the solar wind. Most are deflected away by the Earth's magnetic field, but where the Earth's magnetic field is weakest - at the poles - these charged particles can enter the atmosphere. What follows can be a dazzling display - providing, of course, that you are in the right place at the right time!

The colours that you see are caused by the charged particles interacting with the gases in the atmosphere around the Earth, some 50 to 300 miles above us. Almost like a tickling stick, the charged particles excite and energise the oxygen and nitrogen gases present, but as these 'relax' back into their initial state they emit visible colours that appear to dance through the polar night sky.

If it's primarily green or yellow colours that you see, then it's largely the oxygen molecules in the atmosphere that are reacting to the charged particles. Fantastic magenta/purple colours result from nitrogen molecules letting out their "post tickle" sigh. A vision of red in the night-time sky is slightly rarer, but comes from the charged particles interacting with oxygen much higher in the atmosphere.

For us here in the UK, sightings of the Aurora Borealis are most common in northern Scotland - closer to the North Pole.

However, on rare occasions if the event is big enough, skies are clear, and you're away from light pollution, the aurora can be seen as far south as southern England. Happy sky-gazing!