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: GHA of the Moon
    From: Roger W. Sinnott
    Date: 2020 Oct 2, 00:49 +0000
    James,

    The Moon's orbit around the Earth is severely perturbed by the Sun (mainly).  For $5, willbell.com sells a booklet called "Low-precision Formulae for Planetary Positions" by Van Flandern and Pulkkinen.

    To calculate the Moon's GHA to 1-arcminute accuracy involves these steps:

    (1) Evaluate 7 preliminary arguments, each from a short polynomial in time.
    (2) Use them in a 55-term trig formula for the Moon's ecliptic longitude.
    (3) Use them again in a 38-term formula for the Moon's ecliptic latitude.
    (4) Transform the Moon's ecliptic long and lat to right ascension (RA).  
    (5) Obtain the Greenwich sidereal time (GST) from a short formula.
    (6) Combine the RA and GST to get the GHA.

    For greater accuracy than 1 arcminute, you'll need MANY more trig terms in steps 2 and 3 above.  Those can be found in other books besides Van Flandern and Pulkkinen.

    Roger S.

       
    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