Welcome to the NavList Message Boards.


A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Add Images & Files
    Re: getting GHA from MICA
    From: Paul Hirose
    Date: 2014 Mar 19, 14:47 -0700

    Sean C wrote:
    > Question: Is calculating the sidereal time and then the apparent geocentric 
    equator of date position the only way to get the GHA of a body?
    I don't have the latest MICA version, but 2.0 has "Apparent Topocentric
    Equator of Date (LHA, Dec)" as one of the choices for position type. In
    theory, that will give you GHA if the topocenter is very close to a pole
    and at 0 longitude.
    For instance, at 2014 March 19 at 1700 UT1, compare Moon LHA from N89 59
    59 W000 00 00 to a GHA computed by subtracting the geocentric apparent
    RA from Greenwich apparent sidereal time.
    220 01 11.6  topocentric LHA
    220 01 11.5  RA - GAST
    I converted LHA from hours to degrees.
    If you set the topocenter at exactly 90 north, MICA's LHA is a couple
    degrees in error. Of course one could argue that LHA and azimuth are
    undefined at a pole. However, my software does the common sense thing
    and computes as if you were on the specified longitude and an
    infinitesimal distance away from the pole. That happens with no extra
    effort by the programmer if the coordinate transformations utilize
    vectors and rotation matrices.
    I filter out messages with attachments or HTML.

    Browse Files

    Drop Files


    What is NavList?

    Join NavList

    (please, no nicknames or handles)
    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 Settings

    Posting Code:

    Custom Index

    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