"'It's in winter you see the northern lights, isn't it?'"

Aurora australis
Public DomainAurora australis - Credit: Mozasaur (Paul Moss)
The northern lights, also known as the aurora borealis, are a naturally occurring light effect which may sometimes be seen in the night sky in the Northern Hemisphere. The phenomenon is caused by geomagnetic disturbance and occurs most frequently at latitudes close to the Arctic, although the northern lights may occasionally be seen in the skies over Britain. The northern lights may be seen most often between September and April, and the light effects created may be a variety of colours, including green, blue, red, purple or violet.

An equivalent light effect, known as the aurora australis, occurs in the Southern Hemisphere.