The "arctic" or "superior" mirage occurs when an image of an object appears above the actual object. This is due to the downward refraction (bending) of light waves as they go through the cold, dense air that is close to the ground.

Mirages can take looming, towering, or inverted forms, depending on the density structure of the air, and sometimes, that can be downright deceiving.

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.