Welcome to the NavList Message Boards.


A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Add Images & Files
    Re: Calculating Twilight
    From: Bill B
    Date: 2014 Sep 20, 14:58 -0400

    On 9/20/2014 1:56 PM, Frank Reed wrote:
    > if you avoid lights, you'll be able to see the horizon earlier than
    > normal. In evening twilight, this is harder to arrange since it takes
    > about fifteen minutes to become properly dark-adapted. That fifteen
    > minute period happens to be roughly the pace of the transition from
    > light to dark in twilight, so in evening twilight, by the time you're
    > dark-adapted it's probably too late...
    I carry an eye patch in my sextant case to dark adapt my shooting eye if
    necessary. The downside is monocular vision, so caution must be
    exercised if moving about the craft.
    Dark adaption is not always beneficial. Many years ago Frank pointed out
    an article which explained the larger the pupil aperture, the more a
    point source point source became a spiked object. I would suggest being
    guided by the magnitude and location of the preselected bodies. In the
    case of Polaris, a definite yes. Venus, not so much.
    On September 19th (International Talk Like a Pirate Day) it should
    always be worn.

    Browse Files

    Drop Files


    What is NavList?

    Join NavList

    (please, no nicknames or handles)
    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 Settings

    Posting Code:

    Custom Index

    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