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    Re: Bubble horizon
    From: Jim Dullea
    Date: 2002 Dec 17, 09:19 -0500

    Does this mean that since I would be placing the center of the observed body
    on/in the bubble that there would be no semi-diameter correction only a
    refraction correction say, for the sun?  Would seem that upper or lower limb
    corrections are no longer required.
    Jim Dullea
    Tech Marine Business, Inc
    202 675-7782
    -----Original Message-----
    From: Navigation Mailing List [mailto:NAVIGATION-L@LISTSERV.WEBKAHUNA.COM]
    On Behalf Of Robert Eno
    Sent: Tuesday, December 17, 2002 8:40 AM
    Subject: Re: Bubble horizon
    Happy to respond. I find the results are more accurate if the size of the
    bubble is slightly larger than the body being observed; in the case of the
    sun or moon, the diameter of the bubble should be just enough to encircle
    those bodies. In the case of stars and planets, it is a fine balance. If the
    bubble is too small, I find that it becomes sluggish and lags, thus the
    accuracy drops off. It should be lively enough to move freely with the
    slightest movement of the observer. I am finding it hard to encapsulate this
    in words. It is one of those things which one must experience first-hand in
    order to fully grasp the concept.
    ----- Original Message -----
    From: Dr. Geoffrey Kolbe 
    Sent: Tuesday, December 17, 2002 3:52 AM
    Subject: Re: Bubble horizon
    > Robert Eno wrote:
    > >To make a long story short, unless you can adjust the size of the bubble,
    > >you will experience errors; sometimes gross errors.
    > I, and I am sure some others on the list, would be grateful to Robert if
    > could make this short story a little longer. Why is the size of the bubble
    > critical? Is Robert concerned that the damping of the bubble movement is a
    > function of bubble size, or that the accuracy with which the celestial
    > object can be centered in the bubble is a function of bubble size, or some
    > other consideration?
    > To answer George Huxtable's question on the sort of accuracy one should
    > expect from a bubble sextant. I have a Link A-12 aircraft sextant (still
    > available from Celestaire, last time I looked,) and I would expect an
    > altitude measurement to be within +/- one minute. I am disappointed if I
    > two minutes out and I cannot remember the last time I was more than two
    > minutes out.
    > Geoffrey Kolbe.

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