To many Scots, "The Northern Lights of Old Aberdeen" is a popular traditional song by Mary Webb – the sort of thing your Uncle Jimmy might sing after too many wee drams at Hogmanay, writes Victoria Summerley.
However, the Northern Lights – or aurora borealis – are a regular feature of the night sky, from the autumn until spring, in the north of Scotland. This month, thanks to the solar flare eruption of 17 February, they have been particularly spectacular, and Royal Deeside, west of Aberdeen, has been as good a place as any to see them.
The Northern Lights are created by incoming solar particles colliding with gases in the Earth's atmosphere. Different gases produce different colours. At around 185 miles high, oxygen is the most common gas, and collisions there can create a rare red aurora.
The yellow-to-green light is produced by collisions with oxygen at lower altitudes (between 60 to 185 miles). At around 60 miles, nitrogen molecules produce a red light, which often seems to form the lower fringes on auroral "curtains", while lighter gases such as hydrogen and helium make blue and purple colours. Try explaining that to Uncle Jimmy when he's had a few.