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    Re: Lunar Distances with Alex's SNO-T
    From: Alexandre Eremenko
    Date: 2006 Oct 31, 15:23 -0500

    
    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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