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: Measure the Sun's diameter
    From: Andrés Ruiz
    Date: 2013 Jan 9, 00:32 -0800

    Frank, it is a pleasure to read posts like this, for its clarity and compendium.

    Frank says:
    "There are several ways to do this. First, you need to decide whether you will determine the sextant's index correction separately and measure the diameter always "on-arc", like any standard sextant observation, or instead use on-arc and off-arc observations to cancel out the I.C. Note that this is a special advantage of short angle sights, and this also can apply to short distance lunars (but only under special circumstances). It's convenient to cancel out the I.C., of course, but it's also easy to screw up the off-arc readings so the benefits may not be that great.

    The math of this is simple enough. You take one or more on-arc observations where you bring the Sun and its opposite limb together. Each of this will read somewhere around 32' plus or minus a bit depending on the date and the IC of the instrument. You average those. Call that sum A. If you have previously determined the IC, then the reduction is relatively simple: the diameter is A+IC. If you also take off-arc observations, you average those and call that sum B. In this case, the diameter is (A+B)/2 and, though we don't need it, the IC is then (A-B)/2."

    ... things are a bit more messy when one lecture is on the arc and the other off the arc.

    Linked some examples from an excellent book in spanish:
    Manual de Navegación. Martínez Jiménez, Enrique, 1978. ISBN: 84-400-5327-4

    regards,
    --
    Andrés Ruiz
    Navigational Algorithms
    http://sites.google.com/site/navigationalalgorithms/

    ----------------------------------------------------------------
    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
    ----------------------------------------------------------------

    File:

      

       
    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