Southern Skies

"Day after day the hours of darkness dwindled, and the sun instead of rising in the east, rose almost in the south and swept in a great circle about the horizon, sinking at last in almost the same spot from which it was to emerge but a few minutes later." Charles Laseron, South With Mawson

Antarctic skies are extremely clear. With little free moisture and no dust there is almost no haze, but southern skies do feature a number of unique visual phenomena: auroras, parhelion, sun dogs or mock suns, sun pillars and mirages. Parhelion, sun dogs or mock suns are halos that form around the sun or moon in the shape of circles, arcs or spots. They appear to the observer when light is scattered, diffracted, reflected or refracted off ice crystals that occur in clouds or are just suspended in the air. Sun pillars, vertical shafts of glowing rays, are also a result of ice crystals in the sky at sunset.

Possibly the most spectacular of the visual phenomena in the southern skies are the auroras. The sighting of auroras is naturally restricted to those times when the sky is dark, so most summer visitors to the continent miss seeing the shimmering curtains of multicolored light. The aurora australis or "southern dawn" (the Southern Hemisphere's version of the northern aurora borealis ) is a form of electrical disturbance 50 to 595 miles (80 to 950 km) up in the stratosphere. Auroral displays appear as beautiful colored arcs, bands and even waving-curtain effects of light in the night sky. These can shimmer and pulse in displays that last for minutes or hours.

Auroras in the southern hemisphere are concentrated in an oval shape about 30 ° north of the magnetic axis of the earth, the South Magnetic Pole. They are extremely difficult to photograph because they are very faint and can move rapidly and change color. Incidentally, the Magnetic Pole is constantly moving and is currently off the coast of Dumont d Urville -- some 1400 miles from the geographical South Pole!

The final main visual phenomena in the Antarctic, mirages, are more commonly found in hot deserts but they also occur at the Poles. Here they are caused by low-slanting sunlight, passing through layers of cold air close to the surface, being refracted towards the observer. These are known as Superior Mirages which cause objects to seem to float in the shimmering air, and seem closer that they really are.