Welcome to the NavList Message Boards.


A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Add Images & Files
    Re: Terrestrial refraction
    From: Richard B. Langley
    Date: 1999 Feb 05, 16:03 EST

    For a good discussion of astronomical refraction, including horizontal
    refraction, see Chapter 15 of Jean Meeus's Astronomical Algorithms.  He gives
    as one reference a paper by Bennett: "The Calculation of Astronomical
    Refraction in Marine Navigation" in the Journal of the (U.K.) Institute of
    Navigation, Vol. 35, 1982, pp. 255-259.
    -- Richard Langley
       Professor of Geodesy and Precision Navigation
    On Fri, 5 Feb 1999, Tom McHugh wrote:
    >R.H. van Gent wrote: (and others as well have stated substantially the
    >same thing regarding dip)
    >> The small angle between both horizons is known as the 'dip', and can be
    >> approximated by the following relation found in almost any astronomical
    >> or navigational handbook:
    >>   dip (minutes of arc) = 0.97 sqrt(h[ft])
    >> with 'h' denoting the height of the observer?s eye above sea level in
    >> feet.
    >I think, that for beginners on the list, to avoid confusion, it
    >would be well to state clearly that the above dip formula refers to
    >the sea level as being one's local horizon of reference. and relates to
    >vertical elevation of eyepoint above sea level. It must be pointed out
    >that this formula will not be correct if one is on a horizontal plane
    >at some considerable distance above sea level where the local horizon is
    >well above sea level. Put another way, someone living in Denver or
    >other high plateau regions would have to calculate dip based upon
    >height above the local horizontal plane, not referred to sea level.
    >I am of course, referring to that portion of dip which is related to
    >atmospheric refraction. Naturally, the eye level position above the
    >will be the same.
    >Even at "sea level" there would be differences in dip, as it has been
    >determined that there are areas of the ocean's surface which are below
    >mean sea level because of mass concentrations within the earth's crust
    >or mantle.
    >Tom McHugh
     Richard B. Langley                            E-mail: lang@XXX.XXX
     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/
    ?  TO UNSUBSCRIBE, send this message to majordomo@XXX.XXX:     ?
    ?      unsubscribe navigation                                         ?

    Browse Files

    Drop Files


    What is NavList?

    Join NavList

    (please, no nicknames or handles)
    Do you want to receive all group messages by email?
    Yes No

    You can also join by posting. Your first on-topic post automatically makes you a member.

    Posting Code

    Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.

    Email Settings

    Posting Code:

    Custom Index

    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site