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: Frank Reed CT
    Date: 2005 Aug 16, 14:09 EDT

    Marcel, you wrote:
    "Index with "dry part"  only =1.000277  -> Refraction = 30.27 minutes
    Index with "dry part"  and "wet part" =1.000293  -> Refraction = 32.17"
    
    I don't think  the effect of humidity is this large. Going from one end of
    the humidity scale  to the other (20% to 85%) changes the refractivity by only
    about 0.2% so that  the change in refraction even at the horizon is less than
    0.1 minutes of arc. By  comparison, a 1 degree Celsius change in temperature
    yields 0.3% change in the  refraction. Accurate knowledge of the exact
    temperature is far more important  than the humidity.
    
    And:
    "At this point it really would be interesting  to know to what values Bennett
    fitted the approxiation  formula."
    
    That's easy. They're the values in the tables in the front of  the Nautical
    Almanac --which have been the same for decades (apart from an  absurdly trivial
    and pointless modification in 2004).
    
    -FER
    42.0N  87.7W, or 41.4N 72.1W.
    www.HistoricalAtlas.com/lunars
    
    
    

       
    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