Being Wrong - Kathryn Schulz [24]
Needless to say, under normal circumstances, we don’t see mountains from 200 miles away and conclude that they are nearby. In fact, barring optimal conditions, we don’t see mountains from 200 miles away, period. But by bending light rays from beyond the horizon up toward us, superior mirages lift objects into our field of vision that are usually obscured by the curvature of the earth. Such mirages begin with a temperature inversion. Normally, air temperatures are warmest near the surface of the earth and start dropping as you go up. (Think about how much colder it is on top of a mountain than in the valley below.) But in a temperature inversion, this arrangement reverses. A cold layer of air close to the earth—say, directly above the polar land or sea—meets a higher, warmer layer of air created by atypical atmospheric conditions. This inverted situation dramatically increases the degree to which light can bend. In the Arctic or Antarctic, where surface air temperatures are extremely cold, light sometimes bends so much that the photons that eventually strike any available human retinas can be reflected from objects up to several hundred miles away. The result is, in essence, another kind of false fire—a trick of the light that leads unwary travelers astray.
The illusory Croker Mountains, as drawn by John Ross in his travel journal.
Ross was by no means the first or last seafarer to be fooled by an Arctic mirage. The Celts, who sailed from the Norwegian Sea’s Faroe Islands in the eighth century and made landfall on what is now Iceland, were probably tempted into their boats by mirages that made the distant land appear far closer than it was. Likewise, historians speculate that the Vikings ventured to North America (where they landed sometime around AD 1000) after spotting a superior mirage of the mountains of Baffin Island from the coast of Greenland. As these examples suggest, superior mirages are particularly likely to consist of mountains and other large land masses. But because such mirages can show us anything that actually exists, rather than the shimmering illusion of water that is the inferior mirage’s only trick, their subject matter is, in theory, almost unlimited. Accordingly, sailors have also reported seeing arctic mirages of relatively small objects, including icebergs, pack ice, and—most hauntingly—other ships.*
To get a sense of just how compelling such mirages can be, consider the comparatively recent experience of the Canadian captain Robert Bartlett. On July 17, 1939, while sailing between Greenland and Iceland, Bartlett suddenly spotted the coast of the latter country, looming so large that he could easily make out many familiar landmarks. Like John Ross, Bartlett estimated the apparent distance of the coast at twenty-five or thirty miles away. But he knew its actual distance was more than ten times that, since his ship was positioned roughly 350 miles from the Icelandic coast. That he could see land at all is astonishing—akin to seeing the Washington Monument from Ohio. And yet, 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 [glacier] showed up unbelievably near.”
Only 125 years’ worth of improvements in navigational tools and geographic knowledge prevented Bartlett from making virtually the same mistake as Ross. Thanks to those advances in technology, including information technology, Bartlett was able to override his own judgment. His resources may have been better,