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326946.  Tue Apr 29, 2008 6:03 am Reply with quote

Q: Where would you find a superior mirage?

F: The desert

A: The arctic

The arctic or superior mirage is quite the opposite phenomenon from the desert or inferior mirage, which is familiar to all highway travelers as an apparent pool of water lying on the roadway disappearing as it is approached. Under conditions favorable for viewing a desert mirage, the light rays from the sky are bent upward in a curve away from the surface by hot, light air near the ground and to the eye of the observer. The arctic mirage, on the other hand, occurs when the light rays are refracted downward by cold, dense air near the earth into an arc bending toward the observer.



In 1818, while seeking the Northwest Passage, British explorer John Ross sailed into Lancaster Sound but saw mountains blocking his way. He decided he could go no further and named the range the Crocker Mountains, after the First Secretary of the Admiralty.

This was unfortunate, because Lancaster Sound is indeed a route to the Northwest Passage. William Edward Parry sailed through those very "mountains" the following year.

The mountain range had been a mirage. Not only was an opportunity missed, but the Admiralty wasn't very happy with Ross - especially Crocker, who had imaginary mountains named after him! The Admiralty wouldn't give Johnny another ship, and he had to find private funding for his next expedition.

327207.  Tue Apr 29, 2008 10:43 am Reply with quote

Possible link to the question about how far away is the horizon? Arctic mirages allow you to see beyond the horizon by bending the light around. Bunter's link describes Captain Robert A. Bartlett's experience of heading towards Iceland and catching sight of the 4,715 ft high Snaefells Jökull glacier.

Bartlett wrote: "If I hadn't been sure of my position and had been bound for Reykjavik, I would have expected to arrive within a few hours. The contours of the land and the snow-covered summit of the Snaefells Jökull showed up unbelievably near." The apparent distance of those landmarks was judged to be 40 to 50 km (25 or 30 miles) distant; however, from ship's actual recorded position, they were located 536 to 560 km (335 to 350 miles) away! Without the influence of the arctic mirage, the Snaefells Jökull should not have been visible beyond 150 km (94 miles).

327493.  Tue Apr 29, 2008 5:28 pm Reply with quote

Yes, good idea.


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