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: the answer...?
    From: Jim Manzari
    Date: 1998 Sep 28, 14:12 EDT

    Russell Sher wrote:
    > Hi - I think that the nav. list seems to be on the blink (or just quiet??)
    > So - what was the answer the the noon sight question ( two suggestions below
    > from Joe and myself...)
    Russell and Joe,
    I was wanting to see if more answers might come in.  Nothing...so it
    looks like the winner is Joe Shields.  The ship is moving on a nearly
    south to north line.  The relative motion -- ship + sun -- causes the
    sun to reach its highest altitude _before_ local apparent noon.  The
    clue to the question is the 16kts ship speed.  Had it been a slower
    vessel, say a yacht sailing at 5kts, this effect would be very
    difficult, indeed, to detect.
    Here's a bit of the conversation between the ship masters and a
    further twist on the subject of noon sights...comments welcome.
    ...I consider myself to be a reasonably experienced (celestial)
    navigator, but I am puzzled by the problem.  The only explanation that
    I can think of, is that you were on a heading directly opposite to the
    sun (I confess that I am not familiar with the geography of the area
    between Mauretania and the Schedlt) and thus the sun appeared to be
    decreasing in height but still approaching your meridian.
    And now, I have to add a bit of my own opinion regarding the noon sun
    shot.    Before I commence, put on your armour,   get your daggers
    ready for I am about to utter a bit of heresy.
    The noon sun shot is overrated.    It's beauty lies in the simplicity
    of the calculations required to obtain one's latitude, but that is
    where it ends.    One can easily take a few quick observations at
    "around" noon hour, reduce the sight as normal and plot the resultant
    east-west LOP on your chart to obtain your latitude.    This method is
    particularly useful at high latitudes where the trajectory of the sun's
    passage tends to be fairly flat and determining the exact moment at
    which the sun reaches its maximum height can be somewhat subjective.
     In the winter time here in Iqaluit, I have sat outside, freezing my
    tail off, for up to 45 minutes, waiting for the sun to reach its
    maximum height of 3 degrees above the horizon.
    Even in the mid-latitudes, I have seen people up on deck taking
    observation after observation, trying to determine the exact moment of
    meridian passage, and even after all of that, there is no guarantee of
    a satisfactory result; I have rarely seen two people obtain the same
    numbers.    I am not suggesting  that the noon sun shot should be
    discarded - I still like to perform the operation - but it is not the
    be all and end all.
    Ok, allow me to put on my bullet-proof suit....fire away folks!
    =-=  TO UNSUBSCRIBE, send this message to majordomo@XXX.XXX:     =-=
    =-=      unsubscribe navigation                                         =-=

    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