C a s e E x a m p l e
A U F O d i v e s i n a n d o u t o f t h e O c e a n
The following story was published in the January/February 1965 issue of the British UFO journal Flying Saucer Review:
On January 10, 1958, Captain Chrysólogo Rocha of Curitiba, was sitting with his wife on the porch of a house at Guarujá, on the coast of the State of Sao Paulo, overlooking the South Atlantic. The Captain was trying to pick out a small island with his binoculars. When he managed to focus on the island, he was astonished to find that it was something quite different, and was growing! Eight other persons were hurriedly called to the porch to watch the phenomenon.
The "thing" consisted of two parts, both of a clear, grey colour. One part was in the sea, whilst the other seemed to be suspended above it. Without warning, both parts suddenly sank out of sight. Shortly afterwards a steamer came in sight, on a course that would have taken it very close to the object. About a quarter of an hour later, when the ship was out of sight, the object again rose slowly out of the sea. The excited onlookers now saw clearly that the two parts were joined by several narrow upright shafts, or tubes, which were quite bright and visible to the naked eye. Up and down these shafts, small objects, "like beads on a necklace" passed in "disorderly and simultaneous movement". Shortly afterwards the two parts of the object closed up again, and it disappeared below the waves.
Meanwhile, one of the witnesses, a Brazilian Army officer's wife, had telephoned the barracks (Forte das Andradas at Guarajá). The barracks in turn advised the local Air Force Base, and an aircraft was sent to investigate. Unfortunately it arrived too late to see anything.
- BOWEN, Charles, "A South American Trio - II-Unidentified floating object" in Flying Saucer Review, Vol. 11, No. 1, January/February 1965, pp. 20-21.
- BROOKESMITH, Peter (Editor), The UFO Casebook, Macdonald & Co Ltd, London,1989, p. 72
Let's take a closer look at the circumstances in which this sighting took place. Just prior to spotting the unknown object, Captain ROCHA was looking through his binoculars trying to focus on a small island in the distance. Convinced at first that he had found it, the captain soon realized that the object was not the island but "something quite different". The reasons why he changed his mind were threefold: (1) the object got bigger; (2) it consisted of two parts, one of them floating above the water and (3) there were narrow shafts visible with small objects moving up and down them. Plenty of reasons to conclude that the object was not an island. At least so it seems...
Actually, the description given here could equally well have appeared in a textbook dealing with mirages. There is in fact a rather common class of mirages known as the "inferior mirage" which offers a satisfactory explanation for the different phases described by Captain ROCHA.
Inferior mirages, like all mirages, are caused by abnormal atmospheric refraction. They occur over hot surfaces, especially highways, desert plains and large bodies of water that have received much sunlight during the day.
When the air near the surface - the South Atlantic in our case - is much warmer than the air above there is a strong temperature gradient, meaning that the atmosphere close to the water is composed of multiple layers, each with a different density and a different refractive index. Light rays travelling through such air layers will be bent upward from their normal horizontal path. Because of this, distant objects can appear displaced (a ray of light that enters your eye from the direction of the water in the distance, may actually have originated higher up in the sky). Density variations in air layers between an object and an observer may also act as an uneven magnifying glass, causing enlarged or distorted images. But the most typical feature of mirages is that they produce inverted images. In the case of an inferior mirage this inverted image will appear below the "normal"(*) upright image (in the case of a "superior mirage" the inverted image appears on top of the erect one.
Everyone is familiar with the highway or asphalt mirage whereby the impression is created that distant vehicles are being reflected by a puddle of water on the road. The "water" is actually an inverted image of the vehicle and a portion of the sky. The same effect can also occur when looking at a distant island. An inferior mirage can easily make an isolated island look like an airship that appears to hover above the water.
With this information, Captain ROCHA's description becomes much less strange. According to the captain the unidentified object consisted of two nearly identical but mirrored parts, "one in the Sea" (the upside-down image of the island), the other (the erect image of the island) "suspended above it".
Photos OP-IM-01 to OP-IM-07 of our mirage gallery are examples of inferior and superior mirages of small islands that appear to be floating above the horizon.
When the conditions that cause abnormal refraction disappear (a gust of wind can be enough) the image will return to its normal position behind or close to the horizon, making it seem as if it sinks into the sea (actually, it is the optical horizon that regains its normal position).
As for the second phase of Captain ROCHA's sighting, i.e. the phase during which the object reappeared with the two parts "joined by several narrow upright shafts", we suspect that this was the same island observed under slightly altered conditions.
Complex refractions through multiple layers with different densities often cause a secondary effect known as "towering". Towering occurs due to irregular refraction. Light rays curve upward, with the rays at the base of the object curving more than those on top, producing vertically elongated images in the mirage producing air layer. When towering occurs, the elongated images of contrast-rich objects (such as highly reflective structures and objects painted in striking colours), will give the impression of narrow shafts or pillars that connect the upright image with the inverted one. Moreover, details of the erect image (such as windows and fences) that "touch" the axis of reflection, will look twice as long because the images of those objects connect with those of the same details in the inverted image below. Photos OP-IM-09 and OP-IM-10 are examples of this.
As for the "beads on a necklace passing up and down these narrow shafts, in a disorderly and simultaneous movement", we believe that these were the refracted images of glints of sunlight reflecting off the waves close to the island. The up and down movements can be accounted for by either the movements of the waves themselves or by the fact that inferior images are not stable. Since hot air rises and cooler air (being more dense) descends, the layers will mix, giving rise to vertical turbulence. Because of these fluctuations in the air stream portions of the mirage will be in constant movement.
The witnesses saw an inferior mirage of an island in combination with a towering effect. The small objects may have been the refracted images of glints of sunlight reflecting off waves.
- MINNAERT, Dr. Marcel, De Natuurkunde van 't Vrije Veld, W.J. Thieme & Co, Zutphen, 1949, pp. 57-63 (published in English as Light and Colour in the Open Air, New York: Dover, 1954).
- FRASER, Alistair B. & MACH, William H., "Mirages" in Scientific American No. 231, January 1976, pp. 102-111
- FLOOR, C.: "Atmosferische straalkromming" in Natuur & Techniek Vol. 46, No. 7, July 1978, pp. 448-463.
- TRÄNKLE, Eberhard, "Simulation of inferior mirages observed at the Halligen Sea" in Optics Express Vol. 5, No. 4, August 1999, pp. 64-74 (this excellent paper can also be found at: www.opticsexpress.org).
(*) We put "normal" in quotation marks because the upper image is often designated as the object itself, whereas in reality both are only images, having elevations and magnifications that differ from that of the object seen under normal conditions.