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: My lunar distance tables
    From: Frank Reed
    Date: 2014 May 27, 21:05 -0700

    Francis, you wrote:
    "1) I've been interested in your "short clearance method" using vertical circle "collapse". Looking at your correspondence with the sadly late George Huxtable in 2010, I wonder if you or anyone got round to doing the "quick look up table" as a check test to see if in bounds?"

    I created some diagrams for this purpose, but there's an easier way. I'll see if I can make a quick lookup for it this week.

    And you added:
    "I think your idea is totally brilliant"

    Thanks. If only I had a time machine, I would show it to Nathaniel Bowditch and Jose de Mendoza y Rios, too.

    You wondered:
    "if it can be used reasonably often.(is it only viable near the tropics?"

    It's certainly more likely to be useful in and near the tropics, but I am always amazed by the specific cases that I find where it would indeed have worked. Half the cases of actual lunars I've found in logbooks could have been cleared with no trig whatsoever using this 'vertical circle' equivalent solution. All those poor logarithms died for nothing!

    You also wrote:
    "2)I'm also, totally irrationally, given the multiple quartz watches aboard, interested in " no clock longitude using lunars." (mostly sun/ moon "fix" using GMT from the lunar.) I've been trying to guess the approx , no clock GMT from the lunar Sd, using my home made 3 hourly predicted LDs printed out from your excellent site.(ie a pre 1912 almanac really). Am I correct in thinking that the maximum error of an non cleared LDsd is about 60'? or have I got it completely wrong? (I guess that would still be a huge incorrect longitude?)"

    Yes, that's right. But you know, you can actually do a fairly good job roughly estimating the correction without any tables: you can do HP*cos(alt_moon) in your head to within some reasonable error (within 10% ?), and you can estimate the "corner cosine" at the Moon to within maybe 10% so the net error in the correction would be +/- 15% most of the time just by eyeball estimation.

    I'll think more about your question regarding traverse table solutions to clearing lunars. That strikes me as a 'stunt solution' --fun that it can be done that way, but who would need to? Who would benefit?

    -FER

    ----------------------------------------------------------------
    NavList message boards and member settings: www.fer3.com/NavList
    Members may optionally receive posts by email.
    To cancel email delivery, send a message to NoMail[at]fer3.com
    ----------------------------------------------------------------

       
    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