C a s e E x a m p l e
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
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.
"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...
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
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
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
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).
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: http://www.opticsexpress.org/viewmedia.cfm?id=63418&seq=0).
(*) 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.