When highly energetic charged particles from the Sun enter the Earth’s upper atmosphere, they collide with oxygen and nitrogen atoms. This stimulates the atoms into a temporary excited state, and on returning to their normal resting state, the atoms emit visible light. Oxygen emissions are green or brownish-red, whereas nitrogen emissions are blue or red.
As a result, a natural light display – an aurora – can be seen during the hours of darkness in the sky at high latitudes. During daylight hours, the aurora cannot be readily seen.
Normally, these spectacular light displays are restricted to Arctic and Antarctic regions, but during a geomagnetic storm, the auroral zone reaches lower latitudes.
In the southern hemisphere, auroral displays are referred to as the Aurora Australis, whereas in the northern hemisphere, it is called the Aurora Borealis.
The word ‘aurora’ is named after the Roman goddess of dawn Aurora.
Photo courtesy of Fraser Gunn