Lake Tekapo──南极光 Aurora Australis

Church of Good Shepherd

南极光每年出现在 Lake Tekapo 只有数次，多是在冬天。英语多称北极光称為 Northern Lights，南极光為 Southern Lights；但亦有一個转门的名词來称极光── Aurora。北极光叫 Aurora Borealis，南极光叫 Aurora Australis。Aurora 是罗马黎明女神的名字，而 Borealis 是來自希腊，北风之神 Boreas 的名字，意思是北极的；Australis 來自拉丁词语，南边的意思。
极光会在夏天出现吗？会的，出现机率比冬天更多。但夏天日长夜短，极光又只会在两极附近出现，两极的日照時间在夏天特別长，就算出现也因天空仍亮而看不到，所以多在冬天看到。

Aurora Australis

This is the name of the southern lights often seen at the lower latitudes of New Zealand on a clear dark night। The phenomenon begins at the sun where a particularly large coronal outburst creates a strong stream of charged particles known as the solar wind। The solar wind interacts with the Earth's magnetic field lines at the altitude called the magnetopause and the charged positive and negative charges are then associated with the Earth's magnetic field, creating a large charged electric field concentrated at the poles। In the southern hemisphere the field lines are streaming out of the Southpole which is like a north pole of a magnet। Current flows between these electrical polarities, through the ionosphere, across the polar region and back। The streams of electrons which are the negatively charged particles are flowing - spiraling, along the magnetic field lines and intercepting the oxygen and nitrogen atoms in the upper atmosphere। These excite the oxygen and nitrogen atoms causing them to fluoresce, just as they do in a conventional neon fluorescent light tube. The only difference is the excited oxygen atoms emit a greenish white light, and the nitrogen molecules which are excited by more energetic electrons are made to emit the red to pinkish colours. Ionised nitrogen gives off a blue violet light. The light emission or fluorescence from atoms is caused when electromagnetic energy strikes an atom raising the electron orbital level to a set, higher energy level, which may then collapse back again emitting a photon of light of a particular wavelength. This determines its colour.(Written by Peter Cattell 31 May 2005)