You can’t go sailing on a cruise ship these days, but hey you can always fly one!
A New Zealand woman was driving along the stunning coastline of Mt. Maunganui in the country’s North Island in late April when she looked out over the deep blue waters of the South Pacific and saw a cruise ship flying – or at least that was what she thought she saw.
The New Zealand Herald reports that Monika Schaffner was travelling through Mt Maunganui on April 21 when she saw the UFO-like object.
“I filmed this optical phenomenon that made a ship look like it was floating in the air,” she told the Herald.
“It was like seeing something unreal. I thought my eyes were playing a trick on me … I had to ask my partner if he sees the same as me. So I asked him to pull over so I could take a photo.”
What Monika Schaffner really saw, of course, was an optical illusion known as a Fata Morgana, a mirage that is often seen over the ocean, in a narrow band right above the horizon.
Was it a cruise ship flying?
Wired magazine explains the phenomenon in detail in a fascinating 2015 article which also traces its historical appearances and the legends spawned by the mirage such as that of the Flying Dutchman.
When the sun heats up the atmosphere above the ocean, it creates a gradient of temperatures: Near the surface, the atmosphere remains relatively cool because water chills the lower layers of air, but the layer above is warmer.
When light hits the 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.
So how does refraction make cruise ships fly you may ask?
The answer is it doesn’t. The effect is caused by how your brain interprets the image it sees.
“When light hits your eyes, your brain assumes it arrived there in a straight path between you and the object reflecting the light,” Wired explains. “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. “
Cruise Ship Flying
Anyone who has ever gone snorkeling or diving will be familiar with how when you look down into the water from above, objects under the surface will appear to you not where they really are.
Wired continues to explain: “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. 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.”