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
    Name or NavList Code:
    Email:
       
    Reply
    Re: Examples of cocked hat far from equilateral
    From: Bob Goethe
    Date: 2019 Feb 4, 10:31 -0800

    Bill,

    If you can find a good, real-world example, then great.  But it takes little more time to reverse engineer a set of sights than it would to reduce them from an actual set of sextant observations.  Assuming I was doing this and wanted my fix to be related to my house, I would do this:

    1.  Look at my phone and come up with my GPS position.  Use this as my dead reckoning position on my sight reduction worksheet.

    2.  Select a time that I am going to suppose is my time of observation.  Use the Nautical Almanac and Pub. 249 to come up with an assumed position and azimuth of celestial object.

    3.  Decide where you WANT your "fix" to be.  It can be as near or far from your dead reckoning position as you wish.  Draw a line of position at right angles to your LOP.

    4.  Measure what the intercept is for this LOP. 

    5. From this, you know what your Ho (height observed) would have to be to come up with the intercept you determined in step 4.

    6.  Work backwards to come up with a main correction for refraction.  Give yourself - if desired - some sort of index error and dip, and out of this you come up with what your actual observed sextant altitude would be if you were working from an actual sight.

    Do this with 3 LOPs and you can make your cocked hat as close or far from equilateral as you wish.

    I have done this before with students, where I picked a DR that was NOT near my house, but out somewhere on the ocean.  I picked a date for my supposed sights where I could emphasize d or v corrections, if that was on my lesson plan to teach.  I have used this approach to teach star/planet sights, or maybe instances where the sun and moon were in the sky together.  I use Stellarium or www.heavens-above.com to select dates and times where objects that I want are all properly visible.

    Bob

       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    Get a NavList ID Code

    Name:
    (please, no nicknames or handles)
    Email:
    Do you want to receive all group messages by email?
    Yes No

    A NavList ID Code guarantees your identity in NavList posts and allows faster posting of messages.

    Retrieve a NavList ID Code

    Enter the email address associated with your NavList messages. Your NavList code will be emailed to you immediately.
    Email:

    Email Settings

    NavList ID 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