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: Sunset Intercepts
    From: Gary LaPook
    Date: 2012 Aug 4, 05:09 -0700
    I did three of these while crossing the Atlantic, see:
    http://fer3.com/arc/m2.aspx/Longitude-Sunrise-example-LaPook-feb-2010-g11795

    gl

    --- On Fri, 8/3/12, Antoine Couëtte <antoine.m.couette@club-internet.fr> wrote:

    From: Antoine Couëtte <antoine.m.couette@club-internet.fr>
    Subject: [NavList] Re: Sunset Intercepts
    To: NavList@fer3.com
    Date: Friday, August 3, 2012, 11:03 PM

    Yes, Greg, thanks for your last note.

    Given the importance of the Refraction Correction for h=0°, any small change in either Temperature and/or pressure might yield a significant modification in the computed intercept value.

    For example, if I now enter your values with 72°F and 1016 mb, which are not "immensely" far from standard values (50 °F and 1013.25 mb) and the effects of which also partially cancel each out (if I am right), the intercept already jumps from +0.5 NM to a new value of +1.8 NM.

    But we all know, don't we, that Refractions at low altitudes are subject to strong and unpredictable variations. Therefore our Intercepts published with 0'1 figures cannot be taken at face value for such low heights.

    Best Regards and Thanks

    Kermit

    *****************************************************************************

    Kermit,

    Refraction values seem to vary with NAs, apps, and on-line computers when using hs 0* as an entry.

    Naval Observatory NA -33.8'
    Tamaya NC-77 -34.8'
    Palm Pilot -34.4'
    Umland (on-line) -34.0'
    Wise (on-line) -33.8'

    The NA standard- temp 10*C press. 1013 mb (29.93 in.). Any deviation from standard changes values noticeably.

    Greg Rudzinski


    [NavList] Re: Sunset Intercepts
    From: Antoine Couëtte
    Date: 3 Aug 2012 08:46
    Thanks Greg.

    Under standard conditions, I find I/Az = +0.5 NM T /291°8

    The intercept difference (you found +1.1 T) seems mostly due to refraction, then.

    I am aware that the Nautical US and French Refraction tables differ by 0.5' or 0'6 for Altitude 0°, and that above 5° they differ by less than 0'1.

    Thanks again, Greg, and

    Have a Great Day

    Kermit
    --

    ----------------------------------------------------------------
    NavList message boards and member settings: www.fer3.com/NavList
    Members may optionally receive posts by email.
    To cancel email delivery, send a message to NoMail[at]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