Phenomenon of the day is the Fata Morgana mirage, which I heard about this afternoon. Named after Arthurian antagonist Morgana Le Fay, whose home was a floating castle, the mirage creates the appearance of large structures floating in the air. This photo of a phantom city, floating above the ocean, was taken in China earlier this month:
It could be a hoax, but multiple sources have the same kind of image, and the illusion has recognisable characteristics.
Hot air on top of cold ocean water refracts light back downwards and around the Earth, resulting in the appearance of objects that are actually located over the horizon. This has apparently resulted in sailors witnessing actually distant ships floating in the sky towards them. The effect is rarely smooth and commonly results in objects becoming stretched both horizontally and vertically, resulting in what look like spires and towers, hence the Morgana Le Fay link.
The non-smooth refraction can also cause the image to repeat in places, and this can be seen in the above photo. The buildings aren’t really as tall as they seem – if you look closely you can see that there’s a repeating section in their middle.
It’s an example of a superior mirage – superior meaning that the false image is above the actual image – an effect which can be seen at sunrise/sunset, when the sun is visible for a couple of minutes when really below the horizon.
I heard about this from the rather excellent Skeptics’ Guide to the Universe podcast, which I only discovered yesterday.