Welcome to the NavList Message Boards.

NavList:

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

Compose Your Message

Message:αβγ
Message:abc
Add Images & Files
    or...
       
    Reply
    Re: Refraction
    From: Kent Nordstr�m
    Date: 2008 Jul 4, 16:37 +0200

    Frank asked: Aha. Very nice! So that does appear to explain it. Kent, did
    you believe
    > that your refraction number was for 0 deg C or 10 deg C?
    
    Firstly I can confirm that the refraction formula given with the factor
    60,35 was for the frequency approx. 5500 Angstroem (same as 520 lamda
    nanometer).
    The formula is absed on Po=1013,25x10exp2 Pa and 273,15 degr. K, which
    should be 0 degr. C.
    Kent N
    
    ----- Original Message -----
    From: 
    To: 
    Sent: Friday, July 04, 2008 10:57 AM
    Subject: [NavList 5668] Re: Refraction
    
    
    >
    > Dave Walden, you wrote:
    > "They are functions of pressure, temperature and wavelength.  Two sets of
    > conditions can be calculated for easy comparisons.  Those included are for
    > the Nautical Almanac conditions and a more conventional set to conditions:
    > 760mb, 0 deg C, lamda .54 microns.   The K =60.4 sec, should look
    > familiar.
    > The Naut Alm STP yields 58.2, also familiar."
    >
    > Aha. Very nice! So that does appear to explain it. Kent, did you believe
    > that your refraction number was for 0 deg C or 10 deg C?
    >
    > And you wrote:
    > "The formulas can be found in Spherical Astronomy by Green.  This is the
    > "successor" to Smart's work.  Green was coauthor with Smart on later
    > editions and finally wrote his own.  (To my way of thinking, it's
    > better.)"
    >
    > Damn. Another book to buy. :-) What's the full title of Green's book?
    >
    > And:
    > "Also attached is a plot of errors of Bennett and simpler formulas
    > (minutes
    > refrac vs degrees alt).  There is indeed, nothing magic about Bennett.  It
    > get 34 min at 0 deg in case you've forgotten, but the added complication
    > to
    > do so only makes things worse at higher altitudes."
    >
    > A simple way to keep the best of Bennett (it is indeed more convenient
    > than
    > typing in the whole table) is to retain it for altitudes below 15 degrees
    > (or some other cut-off) and use some simple function of tan(z.d.) for
    > higher
    > altitudes.
    >
    > Anyone have any thoughts about the best color of light to use for the
    > refraction formulae/tables? At very low altitudes, the star images really
    > are smeared out substantially. What's the standard for astronomy? Is it
    > appropriate for sextant users?
    >
    > -FER
    >
    >
    >
    > >
    
    
    
    --~--~---------~--~----~------------~-------~--~----~
    Navigation List archive: www.fer3.com/arc
    To post, email NavList@fer3.com
    To unsubscribe, email NavList-unsubscribe@fer3.com
    -~----------~----~----~----~------~----~------~--~---
    
    

       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    Join NavList

    Name:
    (please, no nicknames or handles)
    Email:
    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:

    Email Settings

    Posting Code:

    Custom Index

    Subject:
    Author:
    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