Atmospheric Optical Illusions 87 
Coast lines often appear very much distorted because of 
this kind of refraction. In the Straits of Messina an other- 
wise ordinary coast line is distorted into huge towers, magni- 
fied palaces, and marvelous castle-like structures of the most 
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COAST MIRAGE 
fantastic shapes and sizes. Italian fishermen call this mirage 
the Fata Morgana. Such mirages and the looming and sink- 
ing of objects above and below the horizon are frequently ob- 
served at sea. 
APPARENT CHANGE OF POSITION 
The apparent positions of the sun, moon, and stars are also 
affected by atmospheric refraction as every navigator knows. 
A star is not precisely in the location in which it seems to be: 
its actual position is somewhat lower in the sky than it ap- 
pears to the beholder. Because of refraction the sun and 
moon become visible about three minutes before they actu- 
ally rise, and they still remain visible for the same period 
after they have, in reality, already set. 
REFRACTION VARIATIONS 
Refraction is not always a constant amount—it changes 
continually with the condition of the air. As the air masses 
move about and flow across one another there are slight 
changes in refraction every few tenths of a second. These 
little changes are the cause of the twinkling of the stars. 
