Jesuit priests aren't especially known for their heavy drug use, but it we're to believe the account of Father Domenico Giardina, he was tripping pretty hard. Looking out over the sea from Messina, Sicily, Giardina saw “a city all floating in the air, and so measureless and so splendid, so adorned with magnificent buildings, all of which was found on a base of a luminous crystal.” The metropolis suddenly transformed into a garden, and next a forest. And then in a flash it all descended into chaos. Huge armies sprang forth, as did the towns they had laid waste to, before the whole mess disappeared.

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Father Giardina, you see, was high on life. (Though scholars believe he actually borrowed his "sighting" from another observer.)1 The “great and marvelous theater” he claimed to have witnessed was the mysterious fata morgana, an incredibly complex mirage that has historically both fascinated and scared the hell out of sailors and landlubbers alike. Whether it be the work of necromancers or fairies or a god, few phenomena have captivated humankind quite so thoroughly as fata morgana.

It was Jesuits like Father Giardina, argues Marina Warner in her brilliant book Phantasmagoria, who made the first “careful” observations of fata morgana, that is, not freaking out about them and instead beginning to apply a dash of science to the matter. The good Father claimed, writes Warner, that the minerals and salts in the region “rise up in hot weather in vapours from the sea to form clouds, which then condense in the cooler upper air to become a mobile specchio, a moving, polyhedrical mirror.” It was wrong, but it actually wasn’t that far off.

Light being refracted downward as it passes from air into a denser material, plexiglass. (Some light is also reflected upward) Zátonyi Sándor/Wikimedia Commons

At work here is some basic physics. When the sun heats up the atmosphere above the ocean, it creates a gradient of temperatures: Near the surface, it’s still relatively cool because the water is chilling that air, but sitting above that is a layer of warmer air. Now, light doesn't always travel in a straight line. When it hits a boundary between two layers of the atmosphere that are different temperatures (and therefore different densities), it bends and travels through the new layer at a different angle. This is known as refraction. The change in the light's angle of travel depends on the difference in density between the two layers.

How does bending light create a mirage? The rest of the effect is caused by how your brain works. When light hits your eyes, your brain assumes it arrived there in a straight path between you and the object reflecting the light. So if light is bent on its way toward you, your brain will think the object is where it would be if the light's path was straight. This is why when you are looking down on a surface of water, objects under the surface will appear to be in a different spot than they actually are—just ask a spear fisherman...if you happen to know a spear fisherman. The human brain doesn't automatically account for the refraction. (Interestingly, the brains of some birds like ospreys do correct for the effect so that when they dive headlong into the water after a fish, they are right on target.)

In the case of a fata morgana mirage, light reflecting from a distant object such as a ship is bent downward as it passes through the colder, denser air near the surface of the ocean (or sometimes cold land, particularly ice). But your brain places the object where it would be if the light came to you in a straight path—higher than it actually is. This bending effect can even work with the curvature of the Earth if conditions are just right, which is why some fata morgana images can actually be refracted cities and ships from beyond the horizon.

A superior mirage or fata morgana, left, and an inferior mirage, what you'd see on a hot day on asphalt, right. Ludovica Lorenzelli, DensityDesign Research Lab/Wikimedia

The opposite situation is what produces mirages like an oasis of water in the desert. In this case, a hot layer of air just above the surface bends light rays up toward your eyes, causing your brain to perceive things as much lower than they actually are. The desert oasis is actually the sky. This kind of mirage is known as inferior, while the fata morgana, which places objects higher than they actually are, is superior.

But before the Scientific Revolution and all its wonderful advances in physics, mirages were firmly in the realm of mysticism. Indeed, fata morgana takes its name from Morgan le Fay, the treacherous fairy, enchantress, and half-sister of King Arthur.

Morgan le Fay: fairy, enchantress, sandal enthusiast. John Roddam Spencer-Stanhope (1880), via Fine Art Photographic/Getty Images

According to Warner, the Normans brought stories of Morgan’s magic to Italy, particularly her penchant for luring sailors to an undersea palace with visions of castles in the air—fata morgana is particularly prevalent in southern Italy's Strait of Messina, where Father Giardina experienced his own vision. Another Italian version of the legend has Morgan falling in love with a regular fella, granting him immortality, and keeping him in captivity, then putting on shows in the sky when he gets bored with the whole never dying thing.

And long before Arthurian legend, it could have been that sightings of these phenomena gave rise to any number of the “whoa something is appearing in the sky” scenes in antiquity, Warner argues. The Second Book of Maccabees, for example, tells of sky-people coming to the aid of the Jews in their skirmishes with the Romans: “When the battle became fierce, there appeared to the enemy from heaven five resplendent men on horses with golden bridles, and they were leading the Jews.” The ghostly warriors fired arrows and thunderbolts at the rascally Romans, “so that, confused and blinded, they were thrown into disorder and cut to pieces.”

Fata morgana’s most famous offspring, though, is the legend of the Flying Dutchman, a ghost ship said to sail aimlessly around the high seas. The tale was first popularized in a story called “Vanderdecken’s Message Home” from 1821, which told of a boat from Amsterdam that haunts the Cape of Good Hope, trying to hand off letters from its dead crew to the vessels of the living (uh, no thanks, the sailors would say, you can deliver your own damn mail). Warner connects this to fata morgana showing a ship from beyond the horizon: The mirage vessel could suddenly disappear with no explanation, and there you have your legend.

The tale of the Flying Dutchman ghost ship likely came from sailors seeing ships caught up in fata morgana. Oh, also, probably the rum and poor diet and sleep deprivation. Wikimedia

In the decades following “Vanderdecken’s Message Home,” few other than the most superstitious (or most intoxicated) of sailors actually feared the Flying Dutchman, but real fata morganas made their way into the blossoming mass media of America. In 1871, the Sentinel of Santa Cruz, California reported a fata morgana that made a steamer appear “four or five stories high,” while other schooners played about beautifully in the mirage. Some 20 years later in Buffalo, New York, 20,000 people gathered to witness a fata morgana on Lake Ontario. Though Toronto was over 50 miles away, “its church spires could be counted with the greatest ease” through the mirage, reported Scientific American.

Gone was the mythologizing of fata morganas, yet the wonderment remained. And that right there is the beauty of science: The ghost ships full of angry dead dudes waving letters may be passé, but we get to keep 100 percent of the awe and zero percent of the scurvy. And I’d say that’s pretty good progress.

Reference:

Warner, M. (2008) Phantasmagoria: Spirit Visions, Metaphors, and Media Into the Twenty-First Century. Oxford University Press

1Update: 3:30 pm ET 07/14/16: This story has been updated to reflect the fact that scholars believe Father Domenico Giardina recycled the account of another witness of fata morgana, as opposed to witnessing the phenomenon himself.