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: 18 june 2013 lunar distance
    From: Frank Reed
    Date: 2013 Jul 1, 15:05 -0700

    Dave, you wrote:
    "true xld= in deg +106 deg 34' 28.466124" "

    Seeing as it's summer movie season, and the fish are biting, I shall paraphrase the original summer blockbuster about biting fish: "You're gonna need a bigger vernier...!"

    Note that differences smaller than 1 or 2" in lunars are meaningless since the Moon is so lumpy. Unless you build a model that accounts for the flat parts and the high parts and then correctly calculates the librations which rotate those points onto the limb in the appropriate direction to the other body, then you're calculating purely academic numbers. To put some of these numbers in perspective, the distance to the Moon just happens to be a bit more than 200,000 nautical miles on average. the conversion between angles as ratios to seconds of arc also happens to be just over 200,000 (it's 3438*60). So that means that a 1 second of arc difference in a measured angle at the Moon's distance corresponds to a change in the location of the Moon's center or equivalently a change in the the altitude of mountains of other features on the Moon's limb of just about one nautical mile. And for fun, that last digit in the angle that you've quoted, a millionth of a second of arc, is equivalent to a shift of 2 millimeters in the height of the Moon's limb. A grain of moondust! :)

    -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