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Arctic Mirage
11/29/2002
Listen in RealAudio 
Weather has profoundly influenced human explorations over the ages. One atmospheric phenomenon
- the arctic mirage - may even have allowed early explorers to see the unseeable, what was
over the horizon. Hi, I'm Bryan Yeaton for The Weather Notebook.
The arctic mirage occurs when light is refracted in a downward arc by cold, dense surface air.
Under these conditions, images of objects located below the horizon - mountains or glaciers -
rise into view, overcoming visual restrictions imposed by Earth's curvature. While a
3,000-foot mountain normally disappears about 72 miles away, under arctic mirage conditions,
it may remain visible beyond 250 miles.
The arctic mirage possibly aided Eighth-Century Celtic mariners, voyaging into the open
Atlantic from the Faeroe Islands, in discovering Iceland. Under mirage conditions, Iceland's
Vatna Glacier, rising 6,600 feet, becomes visible from the Faeroe coast 240 miles
distant.
Upon his banishment, Viking Erik the Red sailed from Iceland northwestward directly toward an
unknown land rumored to lie beyond the horizon. By sailing this heading, however, his ships
faced contrary winds and currents, to arrive at a coastline protected by sea ice.
Had Erik initially sailed southwestward, following known favorable winds and currents, he
would have easily reached the accessible Greenland south coast. What, then, persuaded him to
select the northwest route? Under arctic mirage conditions, Greenland coastal mountains, 186
miles away, become visible from the cliffs of northeast Iceland.
Having settled Greenland, Viking mariners continued westward into North America's Arctic,
further encouraging exploration.
Subaru of America and The National Science Foundation contribute support for our show, which
is produced by the Mount Washington Observatory.
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