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Visit a cosmic zoo

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Ken Tapping, May 06, 2009

In the sky this week...

> Saturn dominates the southern sky during the evening.

> Jupiter rises about 3 a.m., Venus and Mars about 5 a.m.

> The Moon will be Full on May 8.

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One night in the 1980's, I was in a car with an ionospheric physicist friend in the depths of the Algonquin Provincial Park in Ontario. Outside, among the trees we had laid a huge loop of cable, with the ends coming into the vehicle, where they were connected to a sensitive amplifier and tape recorder, all battery powered. We chose a location at least 50 km from the nearest power line, because our experiment was very vulnerable to the interference radiated by power lines. I'll always remember the silhouettes of the pine trees dark against an incredibly clear starry sky, and the incredible sounds coming out of the speaker. However, before getting to that it is better to start at the beginning during the First World War.

World War I was a war of high tech trench warfare. Vast systems of trenches with bunkers, communications and planning centres faced each other across a pulverized strip of ground known as No Man's Land. Because the fighting was highly static, the opposing sides had laid huge telephone networks for passing information and for planning. In addition, because it was obviously advantageous to know what the other side was up to, attempts were being made all the time to pick up their communications. One way was to lay a long wire along your trenches, connected to the most sensitive amplifiers available in order to pick up the signals radiated by the enemy's telephone lines. It is impossible to send a signal along a wire without some of it radiating off into space, so this form of electronic eavesdropping was a logical thing to do. It did work, at least some of the time. To the surprise of the operators, other things were being picked up too: swishing noises, crackling, chirps and long descending whistles. At first they thought they were hearing artillery shells on the way over. However, it soon became clear that what they were hearing was something else altogether. They had come up with a way to monitor goings-on the in Earth's magnetic field. These observations started a line of research that is now being applied not only to our Earth, but to other planets too.

Our Earth and some of the other planets are surrounded by magnetic fields. These are blown back by the solar wind to form long, teardrop shapes. The rubbing of the solar wind over the surface of the magnetic field makes waves, rather like the ones the wind makes blowing over water. Sometimes these waves get big enough to snap magnetic field lines, accelerating particles to high energies, and all the time high-energy particles are leaking in from the solar wind. In addition lightning strokes twang the magnetic field lines. The result is a menagerie of waves that sound like feeding time in a cosmic zoo. These waves follow the magnetic field lines downward towards the Earth's surface. Some of them passed through our looped cable, and we recorded them. We heard varying hisses, whistles, chirps and piping noises. We often play these recordings at talks, and get exclamations of "Aliens!" Of course these waves are natural phenomena, but when we consider they are born in apparently empty space hundreds of kilometres over our heads, through exotic physical processes, calling them alien might not be that far off.


Ken TappingKen Tapping is an astronomer at the National Research Council Herzberg Institute of Astrophysics (NRC-HIA), and is based at the Dominion Radio Astrophysical Observatory, Penticton, BC, V2A 6J9 Tel (250) 493-2277, Fax (250) 493-7767,
E-mail: ken.tapping@nrc-cnrc.gc.ca