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
Add Images & Files
    Name or NavList Code:
    Email:
       
    Reply
    A meridian-passage latitude from Jupiter
    From: David Pike
    Date: 2017 May 12, 00:48 -0700

    Isn’t it strange that you sometimes stumble upon something quite by accident that should have been obvious to you years ago, but you never noticed, because you never needed to use it?  Wednesday evening was our first clear evening for some time, so I decided to spend an hour in the “Astrovan” checking the accuracy of my Smith’s “2b and 2c pendulous reference periscopic sextants against Jupiter, which was one of the few bodies easily visible in moon glow and local light pollution.  As the hour passed, I noticed that the difference between successive observations was tending towards zero as the azimuth approached 180, so I thought “What if I tried a simple mer-pass calculation?”  The details were as follows:

    Sextant: Smith’s Mk2c Serial No 148KHI/73 last serviced 5
    th June 1997 by Fenns of Farnborough

    Date: Wednesday 10th May 2017

    Time: 2hrs44min UTC

    Hs  32° 33.3’ +1.0’ error on the 30° stop – 1.5’ refraction.  Ho=32° 32.8’        

    Mer-pass Latitude = 90°-(Ho+declination S) = 90°-(32° 32.8' + 4° 19.1') = 52° 08.1’N
    Actual Latitude = 53
    °10.2’N difference 2.1nm

    For the mariners and astronomers +/- 3nm in the air and  +/- 1nm on the ground would be considered very good for a freshly serviced aircraft sextant, so 2nm for one last serviced in 1997 and delivered by post via a number of dealers is quite good.

    From the Air Almanac: The actual mer-pass time was:

    21hrs 40min LHA Jupiter = GHA-LongW=359°55' – 000°32' = 359°23'
    37’arc=2min 28secs time. Actual mer-pass time was 21hrs 42min 28secsUTC
    DaveP

       
    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