Photo B. G. Hauge, Norway

They are beautiful curtains of light that are only visible from high latitudes. Novas are stars which explode and thus suddenly flare up (in most cases these explosions are so far away, and the light has taken so long to reach us, that they actually took place hundreds of years ago). One might just appear in the sky from one night to the next, but they are very rare – and even rarer still are those prominently visible to the naked eye.

Telltale signs: Typically the auroras appear either as a diffuse glow or as “curtains” that approximately extend in the east-west direction. They are usually observed at night, particularly in the Polar Regions, and mostly near the equinoxes; from September to October and from March to April. They extend over a very large altitude range (from 50 to 600 kilometres) and their forms are categorized under Homogeneous arcs, Rayed arcs, Active auroras, Rising vapour column and Coronas. Their colours are made up of blue, green, and red light. The highest part of the aurora curtain is red, the middle is greenish-white and the lower edge is pink.

Resources: Frequently Asked Questions about Aurora and Answers, Geophysical Institute (University of Alaska):
http://odin.gi.alaska.edu/FAQ/#color
Asahi Aurora classroom:
http://www.gi.alaska.edu/asahi/wheresee.htm