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
    Name or NavList Code:
    Email:
       
    Reply
    Re: Skyfield
    From: Lars Bergman
    Date: 2018 Oct 23, 14:00 -0700

    John H.,

    I am fully aware that the Nautical Almanac of today is not that accurate.

    But it was different in 1915. For the Moon, RA and declination were given for each hour. Also given were the variation in 10 minutes, given to 0.001 seconds of time and 0.01 seconds of arc respectively, providing full information for performing a quadratic interpolation for times in between. For the Moon, "The numbers (which contain Newcomb's Correction to Hansen's Tables) represent the position of the Moon, with respect to the true equinox and the equator, as it would appear from the centre of the Earth at the respective Greenwich times."

    My point is that the differences, as shown by Robin, between Skyfield and NA is showing a very regular pattern, indicating some kind of systematic "error" somewhere, it is not random noise. Different coordinate system? Time offset? I don't know.

    Lars

       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    Get a NavList ID Code

    Name:
    (please, no nicknames or handles)
    Email:
    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:

    Email Settings

    NavList ID 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