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: Refraction.
    From: John Brenneise
    Date: 2004 Jul 9, 11:14 -0700
    I'll buy most of what you said in your previous post.  In it you state:
        "In normal air, the index is 1.0003, so if the air is 5% denser, the index would be about 1.000315".
    Implicit in this statement is the assumption that the relationship between the increase in density and the increase in the index of refraction is linear.  Can you give me a reference about this?
    I believe that a correllation is there, but if the functional form is linear, then is the constant of proportionality exactly 1.0? If it is non-linear, then what is the functional form?
    ----- Original Message -----
    From: Frank Reed
    Sent: Friday, July 09, 2004 1:57 AM
    Subject: Re: Refraction.

    I wrote earlier:
    "So the net refraction (standard plus the weather front) is 4" of arc TOWARDS the zenith on one side of the zenith and 2" of arc AWAY from the zenith on the other side.
    Make sense?"

    Did that resolve the matter for everyone, or no? John B, does that make sense for you? You asked for a specific example (but that post more or less coincided in time with the above example so you may have missed the details). The conclusion is YES, the net refraction CAN place a star's apparent position lower in the sky than its true position, but rarely and not by much.

    By the way, I don't think temperature inversions (plane parallel) make any overall difference (that is, they can't make the net refraction opposite in sign from the standard refraction); if the atmospheric density is plane-parallel, the net refraction always puts the apparent stars above the "true" stars.

    Frank R
    [ ] Mystic, Connecticut
    [X] Chicago, Illinois
    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