Friday, September 18, 2009

Aurora Australis

We saw some faint auroras last night around 0100 high in the northern sky. They were visible as light white bands that dimmed and brightened as they shifted against the backdrop of stars.

Auroras are the result of interaction between gas particles of the earth' s upper atmosphere and solar wind (a constant stream of plasma traveling out from the sun at 250mile/sec). They occur 50-150 miles above the surface. Atmospheric atoms such as oxygen are excited by the solar winds and emit light of characteristic colors. Oxygen emits red and green light, nitrogen emits light blue-purple light, and neon emits a rare orange light. Astronomers are able to deduct the chemical composition of fawaray galaxies by measuring the electromagnetic frequency (ie color) of the light that reaches us from their direction.

Imagine poking a copper wire into the top of an orange, then bending the wire down and around and sticking its other end into the bottom of the orange. Your result would be a good model of the Earth's magnetic field. The geometry of this field means that solar wind speeds are greatest and excite atmospheric particles the most near the poles, especially during the equinoxes when the earth is straight on its axis. While most auroras are observed at high latitudes, in 1859 an aurora occured over the skies of Boston that was bright enough to read a book by. Such a powerful magnetic storm today would produce trillions of watts of electricity and disrupt telecommunications, air traffic control, power grids, and GPS systems.

Additionally, some of the outer planets, such as Jupiter and Saturn, have very strong magnetic fields that produce spectacular auroras in alien skies.

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