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: Obscure Nautical Almanac star
    From: Frank Reed
    Date: 2021 Jan 3, 10:43 -0800

    Rob van Gent, you wrote:
    "Did you factor in the cos δ correction?"

    Yes, but thank you for the reminder! Even ignoring the proper motion in RA, the proper motion for beta Hydri in Dec in Stellarium is roughly double what it should be. Is it actually wrong? Are they displaying it wrong? Are they possibly applying a factor of 15 or of cos δ backwards in the displayed values but not in the actual coordinate work? Is there some serious problem with their astrometry code?? 

    This afternoon I looked at another case: the angular distance between Capella and Rigel and the change in that distance between 1 Jan 1821 and 1 Jan 2021. Rigel has nearly zero proper motion, and Capella's rather substantial motion is nearly due south torwards Rigel. So this should be easy, and all sources should agree very closely. Precession doesn't enter into it. Stellarium shows a change in angular distance of 1.47 minutes of arc. Better sources (SOLEX, USNO ICE, mine) show changes of 1.42 minutes of arc. That's close, but rather strange. Stranger still, the change in the distance in Stellarium does not seem to match the proper motion values in Stellarium! 

    I should emphasize that I'm just poking around and reporting what I'm seeing after minimal experimentation, so double-check anything I have said here. 

    Frank Reed

       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    NavList is a community devoted to the preservation and practice of celestial navigation and other methods of traditional position-finding. We're a group of navigators, navigation enthusiasts and hobbyists, mathematicians and physicists, and historians interested in all aspects of navigation but primarily those techniques which are non-electronic.

    To post a message, if you are already signed up as a NavList member, start a new discussion or reply to any posted message and use your posting code (this is a simple low-security password assigned when you join). You may also join by posting. Your first on-topic messsage automatically makes you a member, and a posting code will be assigned and emailed to you for future posts.

    Uniquely, the NavList message boards also permit full interaction entirely by email. You can optionally receive individual posts or daily digests by email, and any member can post messages by email (bypassing the web site) by sending to our posting address which is "NavList@NavList.net". This functionality is similar to a traditional Internet mailing list: post by email, read by email, reply by email. Most members will prefer the web interface here for posting and replying to messages.

    NavList is more than an online community... more about that another day.

    © Copyright notice: please note that the rights to all messages and posts in this discussion group are held by their respective authors. No messages or text or images extracted from messages may be reproduced without the explicit consent of the message author. Email me, Frank Reed, if you have any questions.

    Join / Get 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