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Flat Earth
Wed Nov 30, 2005
Listen in RealAudio 
Through observing ships slowly sinking below the horizon as they sailed away, the ancient Greeks, even around 300 BCE, understood the Earth's surface was curved. However, ancient Celt and Viking legends widely described the world as either flat or saucer shaped, where beyond the edge lurked the dreaded abyss. Hi, I'm Bryan Yeaton for The Weather Notebook.
The source of these legends may have arisen from visual observations of the first mariners to sail the North Atlantic and Arctic Oceans. What they saw possibly derived from a common polar atmospheric phenomenon: the arctic mirage.
The arctic mirage is a found in northern latitudes when temperature layering bends light rays to alter the appearance of the earth's horizon and permit viewing of objects actually located below the true horizon.
These superior mirages are caused by cold air lying beneath warmer air: a temperature inversion. They are strongest in polar regions where the surface is covered by ice, snow or the cold, cold sea.
When temperature rises 6 Fahrenheit degrees per 100 feet of elevation, the Earth's horizon will appear flat. As the inversion becomes stronger, the apparent horizon continues to lift. And when the inversion strength reaches 10 degrees/100 feet, observers will have the illusion of being in a saucer - that is, the horizon appears turned upward.
The arctic mirage impact is most pronounced at sea. Viking legends described a land in the farthest north called Ultima Thule. There at the edge of the world, all ocean waters flowed back into the earth from the upturned landscape, regenerating the world's rivers through underground channels. The Celtic word "Thule" means "to raise."
Thanks to our contributing writer, meteorologist Keith Heidorn. Our show is underwritten by Subaru and the National Science Foundation. Thanks also to Davis Instruments, at www.davisnet.com.
Today's Links
The Superior Mirage: Seeing Beyond
http://www.islandnet.com/~see/weather/elements/supmrge.htm
The Arctic Mirage: Aid To Discovery
http://www.islandnet.com/~see/weather/history/artmirge.htm
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