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: Alain Gerbault logbook
    From: Lars Bergman
    Date: 2019 Jan 10, 11:59 -0800

    Paul,

    Further to my previous post, where I was puzzled of why Gerbault calculated both COLAT + DEC and COLAT - DEC, now I believe I know why: To calculate the azimuth to be able to plot the LOP.

    Using the same formula as for hour angle, but changing a few variables, it is "readily seen" that

    hav(AZ) = sec(LAT) · sec(ALT) / [sec(s) · sec(90° - (s - DEC))],
    where s = (COLAT + DEC + ALT) / 2,

    and you get the log of the numerator = 0.1277 + log sec(10°8') + 0.1277 + log sec(17°57') = 0.2839,
    s = 52°36', and log denominator = 0.1277 + log sec(52°36') + 0.1277 + log sec(44°47') = 0.6208,
    using the same strange table as before, resulting in 9.6631. This gives azimuth as N85°W, and the direction of the LOP N5°E / S5°W.

    You could thus use the same table and the same set-up for calculating both hour angle and azimuth.

    Another thing I noticed, is that RAMS of 32m1s indicates a GMT of 31 March 3h something, civil time, so it seems Gerbault is still using the old style of astronomical days, in 1925, the year that NA switched to civil days. But it must have been pitch dark when sighting this evening.

    Lars

       
    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