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: Using a sextant from the bottom of a canyon
    From: Frank Reed
    Date: 2013 Jul 4, 15:25 -0700

    Don,

    You wrote:
    "Of course there is some parallax error associated with sighting a cliff top a few hundred meters away, but the collective wisdom of this forum should be able to work out the necessary correction."

    I would say that the parallax correction cancels out as long as you don't move much. If we maintain the sextant within 10cm of the same position between observations and if the surrogate horizon is 500m away, then the change in its angular altitude would be less than 0.7 minutes of arc. Another problem would be making sure that the sextant is vertical and that the angles are measured in a common vertical arc. If the canyon edge is sloping in angle relative to the true horizon, then "swinging the arc" relative to it might lead to some error.

    It's a great idea though, and it's got me thinking of a variant for sextant enthusiasts who do not happen to find themselves at the bottoms of canyons and instead are stuck in suburbia on an early summer day at local noon. If you have a good, straight roofline to your south it would be analogous to the top edge of the canyon wall (and also straight and possibly very close to horizontal so verticality might be less of a problem). In this case, it might make more sense to measure the angle from the reflected Sun in the A.H. to the roofline and then from the roofline to the true Sun. Around noon, the "hang" at constant altitude is long enough that you could alternate a couple of sights like this and add up to get the Noon altitude. This might work really well.

    -FER

    ----------------------------------------------------------------
    NavList message boards and member settings: www.fer3.com/NavList
    Members may optionally receive posts by email.
    To cancel email delivery, send a message to NoMail[at]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