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Flat Earth
Wed Mar 31, 2004
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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