What is the Aurora Australis?
The Southern Lights (also known as the Aurora Australis) are a natural display of light in the night sky, typically seen over Antarctica and high southern latitudes in the winter. Its northern counterpart is called the Northern Lights or Aurora Borealis.
The name “Aurora” is given to a light phenomenon caused by energetically charged particles (primarily electrons) that travel along the Earth’s magnetic field lines.
Auroras are caused by solar winds – a stream of plasma particles (electrons and protons) emanating from the sun – and their collision with gas molecules in the Earth’s upper atmosphere. The interaction results in the ionizing of oxygen and nitrogen molecules, which in turn release a bright array of lights (photons). Being charged, these ionized particles are pulled towards the Earth’s magnetic poles.
Auroras result in brilliant color displays, at times for hours on end. The phenomenon occurs in the upper atmosphere of both the poles and is occasionally visible from mid-latitudes as an intense glow on the poleward horizon.
Best time to Observe the Aurora Australis
The best time to observe auroras is on a clear, cold night, during a period that coincides with intense sun spot activity. At the southern pole the Aurora Australis is usually visible during the months of March to September. Being in an airplane helps.
The Colors of the Aurora Australis
Green and purple are the most common colors, which result from excited oxygen and nitrogen atoms respectively. However, multiple shades of yellow, blue, violet and red are also seen. The variation in color is a function of the altitude of the phenomenon and the density and composition of the ions at that particular altitude.
The Altitude of an Aurora
An aural band with a clearly discernible lower border implies an altitude of about 60 – 70 miles. However, the bands may extend above the lower band for hundreds of miles. A pinkish edge to the lower band is indicative of an altitude of 50 – 60 miles. On the other hand, a diffuse red aurora generally occurs at around 150 miles from the surface of the earth.