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    Re: Learn the stars, by phone
    From: Brad Morris
    Date: 2009 May 22, 15:02 -0400

    The Skyscout just has two flat lenses, through which you observe the object. 
    You are expected to observe the object in the center of the objective, a 
    reticle would have been nice, but is not part of the kit.
    
    When we talk about pointing accuracy, I think we must bifurcate the discussion 
    to azimuth and elevation.  Since the inclination of the Skyscout is far more 
    readily obtained than the azimuth, I would suggest that the elevation is of a 
    very high accuracy, much finer than the 0.5 degrees.  There are several 
    electronic devices which can provide inclination, here are several 
    http://www.leveldevelopments.com/inclinometer-sensors.htm Note that the 
    quoted resolution is on the order of 1/100 th of a degree.
    
    The azimuth is a far different matter.  The internal magnetic variation map 
    (absolutely required for the device to work) cannot be infinitely fine in 
    resolution, leading to an approximation right from the start.  Why is it 
    required?  Since the variation of the compass will clearly affect object 
    identification, we have no choice but to account for it. If your variation 
    was 10 degrees, then the object pointed at would be wrong by 10 degrees, thus 
    mis-identification would occur. Next, we must sense the local magnetic field, 
    determine (via gps) where in the variation map we are, and then compare to 
    see if we are in range (yielding that 'magnetic error message') and finally 
    determine azimuth by correction.
    
    To me, this azimuth solution sounds much like the longitude method whereby the 
    longitude would be found by the variation of the compass.   If the variation 
    was mapped to a very fine level AND we had a way to sense azimuth, then we 
    probably could get a fairly good approximation to longitude.  Problems: the 
    variation map changes all the time, the sensitivity isn't there and local 
    disturbances would yield some highly wrong results.
    
    ------
    
    On the topic though, of attracting Celestial Navigators because they have the 
    Skyscout or a Smart Phone is upside down.  If you have a Skyscout, you have a 
    GPS, no need for Celestial.  If you have a Smart Phone, between the cell 
    tower localization and the probable on board GPS, you have no need for 
    Celestial.
    
    They may make the connection that it is Celestial turned inside out, but they may not.
    
    But that can be turned to our advantage.  Suppose the display would show a 
    graphic, explaining how the object's light intersects the earth's sphere and 
    showing that classic circle of equal altitudes.  Then click on the next 
    object, with its circle of equal altitudes shown super-imposed on the same 
    sphere, showing the intersection!  In other words, Sumner's Lines of 
    Position, graphically, based on the objects the user selects!  That brings 
    the attention to how celestial "could" have shown the same thing...
    
    Best Regards
    Brad
    
    
    
    
    
    
    
    
    -----Original Message-----
    From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf Of frankreed@HistoricalAtlas.com
    Sent: Friday, May 22, 2009 1:53 PM
    To: NavList@fer3.com
    Subject: [NavList 8381] Re: Learn the stars, by phone
    
    
    I wrote previously that the SkyScout has a pointing accuracy of 0.5-1.0 
    degrees. George found a FAQ saying 2-3 degrees. If we were talking about a 
    sextant or other measuring instrument, those statements would be 
    contradictory, but we're not.
    
    Under good operating conditions, I wouldn't be surprised if the SkyScout has a 
    pointing accuracy at the high end of accuracy. And under marginal operating 
    conditions (for example, just before its software complains about magnetic 
    interference), I wouldn't be suprised if the pointing accuracy is near the 
    low end of accuracy. For a device with no magnification, none of this makes 
    any difference, of course.
    
    It will be interesting to see if the mobile phone engineers who are attempting 
    to add this pointing capability to a device with a more hostile environment, 
    both internally and externally, can get reasonable accuracy out of it. They 
    have a lot more money than Celestron (now there's an understatement!), and 
    they've had a few more years to work on it, but we will have to wait and see.
    
    -FER
    
    
    
    
    
    
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