The Aurora Australis or Southern Lights

The Aurora Australis or Southern Lights are mesmerizing, dynamic displays of light that appear in the Antarctic skies in winter.  It is also possible to see the Southern Lights from Tasmania, Australia. These four postcards from Australia Post show the Southern Lights seen from various locations in Tasmania.

Southern Lights from Browns River, Kingston Beach, Tasmania

What is the Aurora Australis?

Aurora is the collective name given to the photons (light) emitted by atoms, molecules and ions that have been excited by energetic charged particles (principally electrons) travelling along magnetic field lines into the Earth’s upper atmosphere. Aurora results from the interaction of the solar wind with the Earth’s magnetic field.

Southern Lights from Goats Bluff, South Arm Peninsula, Tasmania

The amazing colour displays and formations are produced by the solar wind — a stream of electrons and protons coming from the sun — as it collides with gases in the upper atmosphere. These collisions produce electrical discharges which energise atoms of oxygen and nitrogen causing the release of various colours of light. Earth’s magnetic field channels these discharges toward the poles. Variations in sunspot activity or the occurrence of so-called ‘coronal holes’ can often considerably enhance the auroral discharge adding to the intensity and duration of the displays.

Southern Lights from Dru Point, Margate, Tasmania

What are the Colours of the Aurora?

Auroral displays appear in many colours with pale green and pink the most common. However, different shades of red, yellow, green, blue, and violet have all been observed. The brightest auroral colour is generally a green light emitted by excited oxygen atoms. A red diffuse glow results from another oxygen atom transition. A purple colour results from a transition in a Nitrogen molecular ion. The mixture of the major green, red and purple emissions may combine to give aurora a general ‘whitish’ appearance. The colour variations are a product of the altitude of the storm and the density and composition of the ions at that altitude. The folding effect results from the electric field induced on either side of the auroral curtain by the electrons.

Southern Lights from Coles Bay, Tasmania

Source: Antarctic Connections