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February 20, 2003
A: FROM MENTOR JOAN LUSK IN
RI
The refractive effect depends on the difference in air temperature
at
the road surface and above, not the absolute temperature.
So even in
winter the sun can warm the surface and the air nearby, relative
to
air some little distance above.
http://www.suite101.com/article.cfm/science_sky
/78177/article.cfm/science_sky/78177
You can get a similar but inverse effect over cold water -
there the
surface air is colder than air above. Instead of light from
the sky
appearing on the surface (an "inferior mirage"),
a sailboat on the
surface can appear to be in the sky (a "superior mirage")
and houses
on shore can look several stories high.
http://www.suite101.com/article.cfm/13646/92077.
I used to see the
effect on the shore a lot when I was sailing, but I don't
recall ever
seeing the illusion of an upside-down sailboat in the sky!
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