NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Lunar Distances with Alex's SNO-T
From: Jean-Philippe Planas
Date: 2006 Oct 31, 06:52 -0800
Fred Hebard <Fred@acf.org> wrote:
From: Jean-Philippe Planas
Date: 2006 Oct 31, 06:52 -0800
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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