Aurora are an atmospheric phenomenona that occur when high energy particles in space, often emitted by a nearby star, enter a planet's atmosphere near the north and south magnetic poles.
In Earth's solar system, there are several planets with auroras. In Jupiter's atmosphere, brilliant aurora the size of Earth or larger have been photographed in ultraviolet by NASA's Hubble Telescope and Cassini Spacecraft. They are extremely high energy. Saturn also has aurora that can be seen in ultraviolet.
Earth has auroras at its magnetic poles, and these are viewable in the visible spectrum. Near the north pole, the event is named Aurora Borealis. At the south pole, it is named Aurora Australis. The Borealis, also called the northern lights, are often seen from regions in northern Scandinavia and northern Canada, but can be seen further south in places such as Ireland.
These aurora events display a variety of colors, including pink or red, green, yellow, purple and blue. Each color occurs when the high energy particles entering Earth's atmosphere collide with a particular element in the atmosphere, and during the collision emit light at a particular wavelength. Collisions with nitrogen typically emit blue and purple light, and collisions with oxygen emit red, yellow or green light. The wavelength of the light is highly dependent on the altitude at which the collision takes place.
The Borealis is best viewed from the late fall to early spring, when there is ample darkness and weather is generally calmer with less storms. The Australis can be seen from locations in New Zealand, Tasmania and sometimes Australia if the conditions are right.