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: My lunar distance tables
    From: Frank Reed
    Date: 2014 May 27, 21:14 -0700

    Francis, you wrote:
    "There are rare occasions when the moon /sun altitudes are such that the LDsd is the same as the LDo.(no clearance required) Is there any way of telling this from eyeballing the sky? Or predicting from the almanac?"

    I'm not quite sure what you're asking here, but I have a guess. There are cases where the observed limb-to-limb lunar --the actual angle taken off the sextant-- nearly equals the cleared lunar after all the work is done. Is that what you're talking about? This happens because the pre-clearing step adds the sum of the semi-diameters which is close to half a degree. And the effect of the Moon's parallax, which is the primary component of the clearing, can easily be around half a degree subtracted from the distance. There's no special significance to these cases. The Moon's parallax along the lunar arc is HP*cos(alt_moon)*cos(alpha) where alpha is the angle between the lunar arc at the Moon and the vertical at the Moon, and since HP is nearly a degree, if the product of those two cosine factors is about equal to one-half, then the clearing correction will be about the same as the sum of the semi-diameters.

    -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?

    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