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    Re: Lunar Distances with Alex's SNO-T
    From: Gary LaPook
    Date: 2006 Oct 31, 10:06 -0800
    A rule of thumb is that pressure drops off approximately one inch of mercury per thousand feet of altitude.

    http://www.digitaldutch.com/atmoscalc/tableoptions1.htm

    1976 Standard Atmosphere

    Altitude
    [ft]
    Temperature
    [Fahrenheit]
    Pressure
    [inches of mercury]
    Density
    [slug/ft3]
    Speed of sound
    [knot]
    0 59 29.921261 0.002377 661.479316
    1000 55.43384 28.855692 0.002308 659.201365
    2000 51.86768 27.821061 0.002241 656.915514
    3000 48.30152 26.816676 0.002175 654.621682
    4000 44.73536 25.841855 0.002111 652.319784
    5000 41.1692 24.895929 0.002048 650.009734
    6000 37.60304 23.978238 0.001987 647.691446
    7000 34.03688 23.088131 0.001927 645.364829
    8000 30.47072 22.224971 0.001868 643.029794
    9000 26.90456 21.388129 0.001811 640.68625
    10000 23.3384 20.576986 0.001755 638.334101

    http://www.digitaldutch.com/atmoscalc/



    Gary LaPook
    jean-philippe planas wrote:
    If you know the elevation of your observation spot as well as the atmospheric pressure reduced to sea level (QNH for the pilots) you can determine the local pressure (QFE for the pilots) knowing the fact that every 28 ft of altitude the pressure decreases by 1 millibar in the lower standard atmosphere . I'll look for the formula in inches of mercury if its the way the weather channel provides this info.
    JPP

    Fred Hebard <Fred@acf.org> wrote:

    That's correct! I started looking into this, but gave up.
    Hopefully, the physicists will jump in here.

    On Oct 31, 2006, at 8:59 AM, Alexandre E Eremenko wrote:

    >
    >
    > Fred,
    > I see, this sounds reasonable.
    > But then I need a barometer, or to correct
    > the pressure from the Weather channel for
    > my altitude, because,
    > if I understand correctly, the pressure broadcast
    > for the weather prediction is reduced to the sea level.
    >
    > Alex
    >
    > On Tue, 31 Oct 2006, Fred Hebard wrote:
    >
    >>
    >>
    >> Alex,
    >>
    >> Use the actual pressure. That is the determinant for the refraction
    >> correction. The elevation above sea level has an insignificant
    >> effect on parallax, when you consider that the radius of the earth is
    >> about 3400 nautical miles, but significantly reduces refraction via
    >> the effect on barometric pressure.
    >>
    >> Fred
    >>
    >> On Oct 31, 2006, at 8:27 AM, Alexandre E Eremenko wrote:
    >>
    >>> Related question: the barometric pressure in the refraction formula.
    >>> Should I use the actual pressure at my observation site,
    >>> or should I "reduce it to the sea level"?
    >>> The actual pressure at my site reflects not only the deviation
    >>> from the standard atmosphere but also my altitude over the sea
    >>> level.
    >>>
    >>> Alex
    >>>
    >>
    >>
    >>>
    >
    >
    > >



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