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: Bubble Sextant as Dip Meter
    From: David Pike
    Date: 2015 Oct 24, 12:03 -0700
    Gary you wrote - Dip from 40,000 feet is 3 04' so, in theory, it might be possible to measure a celestial altitude of three degrees below horizontal from a B-52 on its way to the Soviet Union. Of course, due to extinction, the only body that can be observed below horizontal is the sun. To support this
    military mission, HO 249 shows computed altitudes as low as minus 8° 16' at lat 71°, dec 6 °contrary, LHA 98°! You'd have to be flying at 261,000 feet to measure an altitude that low, (bombing from the Space Shuttle?)

    Such low values would be usable with the RAF Mk2T Periscopic Sextant.  T was for twilight facility.  This sextant incorporated a polarization analyser to assist in polar navigation.  The 2T used the fact that when the Sun is at low altitude or just below the horizon, sky light from the zenith is largely plane polarized.  You couldn’t get a celestial position line, but you could get a bearing.  It was claimed that under practical conditions azimuth bearings accurate to about 1.75° were possible when the Sun’s altitude was between 20° above and 6° below the horizon even when the Sun was obscured by cloud, provided there was a clear sky in the zenith region. I never used the 2T, but I’d rather like to have one.  I’m not sure if the analyser was inside the sextant or an add-on to the eyepiece.  Neither am I sure if the sextant could also be used normally.  The interesting thing is you didn’t set the sextant to the altitude of the Sun; you set it to about 70°. A facsimile of the AP for the RAF Mks 2, 2A, 2B, and 2T periscopic sextants is available from Paul Brewer on ebay for a few $s.  DaveP  

     

       
    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