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: The Bygrave
    From: Brad Morris
    Date: 2009 Jul 24, 11:53 -0400

    Hi Hanno Ix

     

    See my answers interspaced below

     

    Best Regards

    Brad

     

     

    From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf Of hannoix---.net
    Sent: Friday, July 24, 2009 11:37 AM
    To: NavList@fer3.com
    Subject: [NavList 9212] Re: The Bygrave

     


    May I please ask some questions?

    1. I am not a sailor. So, what are the useful ranges of a Bygrave? In  other terms, what are the critical trigonometrical/nautical Regardssituations where the knowledge of angles >89deg or angles <1deg  is important?

     

    Suppose your celestial body is the sun.  If reducing for a meridian crossing (sun on your line of longitude), then the hour angle T is 0 (less than 1 degree).  As a practical matter, the Bygrave is quite compressed under 5 degrees for the LogCosine scale, so reductions when the sun is close to your meridian suffer from accuracy issues.

     

    If reducing when the sun is directly east or west of you, when the hour angle is 90 degrees (sunrise, sunset) similar issues result.



    2. Are there practical approximations by polynomials etc. for such extreme cases?

     

    Just use the standard azimuth and altitude equations that can be directly reduced using a calculator.


    3. More generally: Are we aiming at historical replicas of the Bygrave, MHR, etc.  or are we seeking at a modern implemetation of the idea? Or both?

     

    Depends upon who you talk to.  Due to cost, we probably won’t be looking at historical replicas. 

    4: Similarly: Are we interested in the Bygrave just because it is so interesting - which it is! - or are we looking for the very simplest means to do accurate sight reduction? For the latter, there might be attractive alternatives.

     

    HO229 offers accuracies to 0.1 arc-minutes, about 10-20X the accuracy of the Bygrave.  It is heavier, larger and requires tabular lookup instead of slide rule manipulation. 

     

    Others will have different preferences for tabular reduction or for computer aided reduction.  The beauty of the Bygrave is the small size, small weight and rapidity of reduction

    Regards</table


     



    "Confidentiality and Privilege Notice
    The information transmitted by this electronic mail (and any attachments) is being sent by or on behalf of Tactronics; it is intended for the exclusive use of the addressee named above and may constitute information that is privileged or confidential or otherwise legally exempt from disclosure. If you are not the addressee or an employee or agent responsible for delivering this message to same, you are not authorized to retain, read, copy or disseminate this electronic mail (or any attachments) or any part thereof. If you have received this electronic mail (and any attachments) in error, please call us immediately and send written confirmation that same has been deleted from your system. Thank you."

    --~--~---------~--~----~------------~-------~--~----~
    NavList message boards: www.fer3.com/arc
    Or post by email to: NavList@fer3.com
    To unsubscribe, email NavList-unsubscribe@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