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: Examples of cocked hat far from equilateral
    From: David Pike
    Date: 2019 Feb 5, 11:37 -0800

    Bill

    What a pity you didn’t post this a day earlier.  We had the Sun all day yesterday, and I was greatly tempted to get a sextant out.  The Astrovan is still full of rubbish dumped there so we could sleep ten indoors over Christmas.  However, I’ve since found that a suitably chocked bubble sextant will sit nicely on a south facing bedroom window ledge.  Also, I can open the window to avoid observing through double glazing and kneel with my front against a radiator, lovely! 

    Even if you avoided the sin of using LOPs closer than thirty degrees, just observing a single body, e.g. the Sun over up to six hours might still lead to trouble, because all your observations would be on one side i.e. within 90 degrees of azimuth of each other.  Therefore, a significant systematic error, e.g. 3 minutes of arc of unrealised instrument error, not uncommon in a 70 year old non-professionally calibrated bubble sextant or when using a mirror artificial horizon, might well place the symmedian point of the triangle you’ve observed outside the triangle caused by random errors alone, see below.

    Had you considered using a sandwich fix from three suitably placed stars?  Last night would have been ideal here.  We had gin clear skies until 23.00.  You could observe A,B,C,B,A over ten minutes using a single mid-time for the calculation.  Using a different bubble sextant from three different windows would save time setting up between observations, but deciding whether this would be beneficial or detrimental to the error distribution might tax even the brain power of a Professor of Errors from Cambridge University.  One glutton for punishment actually designed a form for recording a three star sandwich fix, and the RAF chose to reproduce it, see below.  I never met anybody who used it. Most people were content with two star sandwich fixing. DaveP

    File:


    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