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    Re: Refraction and humidity
    From: Richard B. Langley
    Date: 2007 Mar 28, 10:40 -0300

    Very thorough discussion on refraction: "Understanding Astronomical
    Refraction" by Andrew T. Young in The Observatory, Vol. 126, No. 1191,
    April 2006, pp. 82-115.
    
    -- Richard Langley
    
    On Wed, 28 Mar 2007, Alexandre E Eremenko wrote:
    
    >
    >
    >Bill,
    >The most advanced text on astronomical refraction
    >I have is the chapter of Chauvenet where he explains
    >the work of Bessel, and attaches tables computed by Bessel's
    >formula with refraction in fractions of a SECOND.
    >Bessel's formula does not take into account color or
    >humidity. Chauvenet says that Bessel's tables give
    >satisfactory results, and he does not mean observations
    >with a sextant to a fraction of a minute, but
    >he means real astronomical observations with instruments
    >of high precision.
    >
    >That's why I assume that color and humidity can be safely neglected
    >in the type of observations we do, as well as temperature and
    >pressure in most cases.
    >
    >Alex
    >
    >On Tue, 27 Mar 2007, Bill wrote:
    >
    >>
    >>
    >> Alex
    >>
    >> Following up on Sunday's conversation on refraction for star-to-star angular
    >> separation, the almanac states mean refraction is calculated for a
    >> temperature of 10C, pressure of 1010 mb, humidity of 80% and wavelength of
    >> 0.50169um.
    >>
    >> That would indicate my recollection that humidity is a component of
    >> refraction is correct, and my belief that the color of a star/body may
    >> affect refraction.  I do not know if dust in the air will affect refraction
    >> like humidity.
    >>
    >> The important point in context is how much refraction will be affected,
    >> especially for lower bodies (20d to 30d).  I don't have a clue.  Perhaps the
    >> list can be of help.
    >>
    >> Bill
    >>
    >>
    >>
    >>
    >>
    >> >
    >
    >
    >>
    >
    
    
    ===============================================================================
     Richard B. Langley                            E-mail: lang---.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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