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    Re: Lunar Distances with Alex's SNO-T
    From: Fred Hebard
    Date: 2006 Oct 31, 15:33 -0500

    I remembered where it was!
    
    On Oct 31, 2006, at 3:23 PM, Alexandre E Eremenko wrote:
    
    >
    >
    > Fred,
    > Thanks a lot.
    > How did you find my appartment,
    > by the address or by co-ordinates?
    > :-)
    >
    > Alex.
    >
    > On Tue, 31 Oct 2006, Fred Hebard wrote:
    >
    >>
    >>
    >> Alex,
    >>
    >> It's full featured.  There's a search box, and you can change the
    >> size and zoom of the map, and look at maps of different scale.  It
    >> starts out with the 7.5' series maps.  The captions are cut off, but
    >> the contours have elevation in feet above sea level marked here and
    >> there, always on the darker lines, and you can count the divisions
    >> between.  Your apartment in West Lafayette has the 670 contour
    >> running through the middle.  The fine contours there are at 10 foot
    >> intervals.
    >>
    >> Fred
    >>
    >> On Oct 31, 2006, at 12:51 PM, Alexandre E Eremenko wrote:
    >>
    >>>
    >>>
    >>> Thanks, Fred.
    >>> This seems to be a demo with limited features,
    >>> and I am not sure where on the map elevation
    >>> is shown, and in which units.
    >>> Can you give an example?
    >>>
    >>> Alex
    >>>
    >>> On Tue, 31 Oct 2006, Fred Hebard wrote:
    >>>
    >>>>
    >>>>
    >>>> Alex,
    >>>>
    >>>> The website, http://www.topozone.com/ has topographic maps covering
    >>>> the U.S., from which you can extract your elevation to the
    >>>> nearest 20
    >>>> feet or so, which is close enough.
    >>>>
    >>>> Fred
    >>>>
    >>>> On Oct 31, 2006, at 10:33 AM, Alexandre E Eremenko wrote:
    >>>>
    >>>>>
    >>>>>
    >>>>> Jean-Philippe,
    >>>>> Thanks.
    >>>>> I have no problems with conversion of units,
    >>>>> (though it is sometimes annoying with pressure
    >>>>> for which at least 5 different units are commonly used:
    >>>>> psi(=punds/square inch), millibar(=1000 dynes/square centimeter),
    >>>>> Pascal (not to be confused with psi:-),
    >>>>> inches of mercury and
    >>>>> millimeters of mercury.
    >>>>> And I almost forgot the sixth unit: the atmosphere:-)
    >>>>>
    >>>>> Most barometers on e-bay use one or two of these units,
    >>>>> so one has to hand a conversion table besides the barometer:-)
    >>>>>
    >>>>> Is there a convenient source on the web to find one's altitude
    >>>>> over the sea level, (I mean for those unfortunate ones
    >>>>> who do not live on a sea shore)?
    >>>>>
    >>>>> Alex.
    >>>>>
    >>>>> On Tue, 31 Oct 2006, 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  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
    >>>>>>>>>
    >>>>>>>>
    >>>>>>>>
    >>>>>>>>>
    >>>>>>>
    >>>>>>>
    >>>>>>>>
    >>>>>>
    >>>>>>
    >>>>>>
    >>>>>>
    >>>>>>
    >>>>>>
    >>>>>> JPP
    >>>>>>
    >>>>>> ---------------------------------
    >>>>>> Get your email and see which of your friends are online -
    >>>>>> Right on
    >>>>>> the  new Yahoo.com
    >>>>>>
    >>>>>>>
    >>>>>
    >>>>>
    >>>>>>
    >>>>
    >>>>
    >>>>>
    >>>
    >>>
    >>>>
    >>
    >>
    >>>
    >
    >
    > >
    
    
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