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: Latitude by two stars observed simultaneously
    From: David Pike
    Date: 2017 Dec 28, 11:49 -0800

    After posting my answer to the cave puzzle, I realised that I hadn’t allowed for dip and refraction.  I amended he spreadsheet accordingly, and it took me 6nm further towards the cave, but I was still a long way from it.

    Having put the spreadsheet together, I thought I ought to try it locally with some reliable altitudes.  I planned to use Vega-Alpheratz-Vega, the Astrovan being on the west side of my house.  However, by 20.00 there was so much haze, light pollution, and Moon glow to the SW that Alpheratz kept disappearing, so with some reluctance, I observed the Moon instead.  To my surprise, the technique placed me at 53degrees 11minutes N only 0.8nm north of my actual position.  Having always considered the Moon my ‘bete noir’, I think I ought to use it more often.

    I encountered two problems.  Firstly, unlike the stars, the moon is constantly moving.  All I could do was take the Moon’s declination from the Air Almanac and calculate an instantaneous SHA by subtracting GHA Aries from GHA Moon and adding 360.  This required accurate Greenwich time, so it rather defeated the object of the exercise.

    The spreadsheet also showed the undesirability of using the cosine rule to solve a side, side, side spherical triangle, because above 54N the spreadsheet crashed.  Somehow the formula was managing to come up with cosA values greater than unity.  Fortunately I was at 53.10N.

    My resolutions for 2018 are, try this again with two stars, learn how to plot graphs in Excel, and re-familiarise myself with the half angle formula. DaveP



    File:
    Lat-From-two-alts-one.xls

       
    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