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    Re: Biruni and the radius of the Earth by dip
    From: Fred Hebard
    Date: 2011 Jan 5, 10:40 -0500

    be careful too of the angle unit, radians versus degrees.
    On Jan 5, 2011, at 10:27 AM, Apache Runner wrote:
    > Maybe I am misunderstanding.   Let me look at the formula again -
    > on that website you had, there was a crude figure of merit for what
    > I thought was refraction that was 1.75 moa * sqrt(h)   where h is
    > in meters.   It seemed to be for refraction and it gives 40 moa if
    > I plug into it.
    > Where did you get 6 moa from?
    > On Wed, Jan 5, 2011 at 10:17 AM, Marcel Tschudin
    >  wrote:
    > John, you wrote:
    > > Both the dip and the refraction are in the 40 arc minute region
    > for a 500 m
    > > peak, ....
    > Could there be a misunderstanding? From a 500m high peak the horizon
    > has a geometrical dip (without refraction) of about 40 moa. The
    > refraction increases this geometrical dip by e.g. 6 moa leading to an
    > observed dip of e.g. 46 moa. In this case we deal with the
    > "terrestrial" refraction which is considerably smaller than the
    > "astronomical" refraction since in the "terrestrial" case the length
    > of the ray path through the atmosphere is much shorter.
    > Marcel
    > --
    > Keeping up with the grind

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