
   The two 'musts' are the books of Tape and Greenler:

                                        
       "Atmospheric Halos" 
        by Walter Tape 
        Antarctic Research Series, Vol. 64, 
        American Geophysical Union, 
        Washington, 1994
        ISBN 0-87590-834-9
             0066-4634

                                                       
       "Rainbows, Halos, Glories" 
        by Robert Greenler
        Elton-Wolf Publishing, Milwaukee, WI, 2000
        ISBN 0-89716-926-3

           Now back in print and obtainable from:
           BlueSky Associates
           Cat. No. RBK119                                                                              


   An fascinating introduction to atmospheric halos and 
   the optics of many other outdoor phenomena:

       "Color and Light in Nature" 
        by David K. Lynch & William Livingston 
        Cambridge University Press, June 2001
        ISBN 0-521-775043 

    A classic of observation and description of light, 
    color and halo phenomena:

       "Light and Color in the Outdoors" 
        by M.G.J. Minnaert 
        Springer-Verlag, New York, 1993 
        ISBN 0-387-94413-3

