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    Re: Lunar Distances with Alex's SNO-T
    From: Fred Hebard
    Date: 2006 Oct 31, 15:14 -0500

    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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