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
    Name or NavList Code:
    Re: Lunar trouble, need help
    From: Kent Nordström
    Date: 2008 Jun 16, 11:31 +0200
    Sorry for misprinting. The sun's apparent time shall be 15-59-47.5. The calculation of MT-GMT is correct.
    Kent N
    ----- Original Message -----
    Sent: Monday, June 16, 2008 5:04 AM
    Subject: [NavList 5472] Re: Lunar trouble, need help

    Thanks Frank.
    That is perhaps what I did.  I can't be sure at this point.  Unfortunately, since I don't have reduction tables or programs at sea, I can't clear my sights until I return to port, and by that time, I have forgotten some of the fine details.  I will try and remember to do an IC check on the sextant tonight, it might be the source of some error since I haven't checked in awhile.
    On a slightly different subject, what is your sign convention on your lunar program?  When I get a positive error in longitude, is that east or west of the DR position?  I am trying to deterimine the position north or Hawaii and am running into trouble with sign convention.
    In a message dated 6/16/2008 8:33:48 A.M. West Pacific Standard Time, frankreed@HistoricalAtlas.net writes:

    Hi Jeremy.

    I have a little working theory on your lunars. I suspect that you took what
    I call "Inside Limb" lunar distances rather than "Near Limb" lunars. With
    Near Limb lunars, you bring the Moon over to the Sun so that they just touch
    with the two disks side-by-side with no overlap and no gap between them.
    With an 'Inside Limb' shot you bring the Moon's disk inside the Sun's disk
    and bring it into contact with the far limb (note that this is not what is
    meant by a "Far Limb" lunar in which you bring a star at night over to the
    limb opposite the star). Assuming that this is the case, we can convert your
    Inside shot to a Near shot by subtracting twice the Sun's semi-diameter
    which would be 31.5'. Then the average error in the set is 0.8 minutes of
    arc (which may indeed be due to an error in index correction as Jim
    suggested) and the standard deviation of that set is around 0.25'. Shooting
    an "Inside" lunar is not normal practice, but if you've never seen lunars
    done or diagramed, there's no way that you would know that. I think it's
    harder to shoot those alignments than a standard Near Limb lunar.

    Of course, this is just a speculation. If you're quite sure you shot these
    lunars by bringing the Moon and Sun side-by-side, then the problem must lie

    PS: If you select "Far Limb" lunar in my online calculator for a Sun sight,
    you get a result that really doesn't mean anything since Far lunars actually
    don't make any sense when the other body is the Sun. Maybe I will change
    that to calculate Inside Limb lunars.

    Navigation List archive: www.fer3.com/arc
    To post, email NavList@fer3.com
    To , email NavList-@fer3.com

    Browse Files

    Drop Files


    What is NavList?

    Get a NavList ID Code

    (please, no nicknames or handles)
    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 Settings

    NavList ID Code:

    Custom Index

    Start date: (yyyymm dd)
    End date: (yyyymm dd)