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And another good book explaining atmospheric phenomema is Rainbows, Halos, and
Glories by Robert Greenler, emeritus professor of physics at the University of
Wisconsin - Madison. Chapter 7 is entitled "Atmospheric Refraction: Mirages,
Twinkling Stars, and the Green Flash." Various types of mirages are discussed
including the fata morgana (after the Italian for Morgana, the fairy --
Morgana was supposedly the half-sister of King Arthur who showed her power
by the use of mirages). The term was initially used to descibe the complex
mirages seen across the Strait of Messina.

Also discussed in the chapter is the presentation made by Rev. Samuel Vince
to the Royal Society in August 1797 on unusal atmospheric refraction.

Another good reference for mirages is Chapter 6, "Highway Mirages" in Craig
Bohren's What Light Through Yonder Window Breaks?, subtitled More Experiments
in Atmospheric Physics. Bohren is an emeritus professor in the Department
of Meteorology at Penn State University. This book is a sequel to his Clouds
in a Glass of Beer. Both books are both educational and entertaining. By the
way, in "Highway Mirages," Bohren discusses other kinds of mirage
besides the ones commonly seen along highways on a hot summer's day.

And, by the way, refractive index depends on the number density (number of
atoms/molecules per unit volume) not the mass density of the medium through
which light travels.

-- Richard Langley
   Professor of Geodesy and Precision Navigation

On Fri, 16 Jul 2004, Dan Allen wrote:

>M.G.J. Minnaert wrote a book entitled "Light and Color in the Outdoors"
>(originally in Dutch in 1937, revised until 1974) which was translated into
>English in 1992 and published by Springer-Verlag.  There are chapters about
>light reflections, light refractions, the curvature of light rays in the
>atmosphere, the Purkinje effect, seeing underwater, illusions, fogbows,
>rainbows, halos, coronas, Parry's arc, Haidinger's brush, distribution of light
>over the sky, crepuscular rays, the zodiacal light, luminescence of the sea, and
>an appendix on measuring angles out of Doors.  It has many fine illustrations,
>some equations, and tackles many optical phenomena as scientifically as
>possible.
>
>Highly recommended reading appropriate for such questions!  To wit, there is an
>photo of a "superior mirage above cold water: a tanker below the horizon appears
>upside down in the mirage" above the horizon.  Fascinating...
>
>Dan
>
>-----Original Message-----
>From: Navigation Mailing List
>[mailto:NAVIGATION-L@LISTSERV.WEBKAHUNA.COM]On Behalf Of Fred Hebard
>Sent: Sunday, July 11, 2004 9:07 PM
>To: NAVIGATION-L@LISTSERV.WEBKAHUNA.COM
>Subject: Re: Refraction. was: Bubble Horizon Altitude Corrections
>
>OK ladies & gentlemen.  We have the case of a mirage, where the image
>rises above the desert floor.  Are there any counter examples of an
>image sinking below the horizon?
>
>Fred
>>
>


===============================================================================
 Richard B. Langley                            E-mail: lang@unb.ca
 Geodetic Research Laboratory                  Web: http://www.unb.ca/GGE/
 Dept. of Geodesy and Geomatics Engineering    Phone:    +1 506 453-5142
 University of New Brunswick                   Fax:      +1 506 453-4943
 Fredericton, N.B., Canada  E3B 5A3
     Fredericton?  Where's that?  See: http://www.city.fredericton.nb.ca/
===============================================================================

   

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