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: Death to the Intercept Method!
    From: Sean C
    Date: 2016 Nov 5, 03:16 -0700


    You had mentioned this method before without going into too much detail. That piqued my curiosity, but I had forgotten to ask about the specifics. Before you elaborated, I decided to try and work it out for myself. It looks as though I pretty much got it right, although I used the equation: cos-1((sin(h) - sin(Dec)sin(Lat))/(cos(Dec)cos(Lat))) = LHA.

    This is an interesting alternative to the intercept method. Although, personally, I'm not sure if I find it any more or less convenient. After all, it's not exactly difficult to construct a scaled plotting sheet from scratch, and it is certainly quicker than hand ruling a sheet of graph paper if you don't have any handy. Also, the need to calculate a longitude for each of two assumed latitudes doesn't seem to offer much of an advantage over the altitude and azimuth calculations of the intercept method. Then (and I realize I'm reaching here), there's the possibility that, for whatever reason, the use of a calculator is suddenly inaccessible. I could get by in a pinch with nothing but the N.A., a sextant and a watch (and, of course, some plotting tools). On the other hand, if I planned to use this method I guess I might think to bring along some time sight tables, too. :) The only benefit obvious to me is that, when using Sumner lines and graph paper, one doesn't need a protractor/pre-printed compass rose or a ruler/scale of any sort. I suppose I'll have to try some more examples to see how I really feel about it. Thanks for pointing out this additional option.

    One question, though: Since computational power is cheap these days, why not go 'all out' and use the formula for calculating a fix found right in the N.A.? With a calculator like the TI-30X IIS, it's easy to do, and with a programmable calculator it would be even easier. If it weren't for logging the altitudes/times of observations and the ship's position, one could almost do away with using any paper altogether.


    Sean C.

    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