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    Re: Learn the stars, by phone
    From: Frank Reed
    Date: 2009 May 22, 16:07 -0700

    Brad, you wrote:
    "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."
    Yes, probably. The actual accuracy available in the device is mostly a 
    question of which chipsets are available to the device designers at a 
    reasonable price (reasonable to them). What price do you pay for 0.01 
    degrees? How much cheaper is 0.1 degrees? And would we ever need any more in 
    such devices in the first place?
    And you wrote:
    "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."
    Global magnetic variation data, with rate of change, too, is widely available. 
    This is not a difficult aspect of the design of a device like this, and I 
    don't think it results in much "approximation" except in high magnetic 
    latitudes. You're right, of course, that it can't be "infinitely fine" but 
    that's not required. How about 0.1 degree accuracy in the calculation?
    And you added:
    "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."
    Well sure. It's just a little bit of calculation inside the device. This is 
    not complicated. These little machines probably have more calculating power 
    than the first computer you ever owned.
    And you wrote:
    "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 
    Well, it sounds like you've come up with another speculative model for the 
    'magnetic error message' here, but this couldn't be how it works. Think about 
    it: the device doesn't say, "Now point at the north star" or any other marker 
    that could determine true direction. It ONLY has the magnetic field for 
    direction in the horizontal plane. It then calculates variation/declination 
    and gets true azimuth from that. I still don't have a better idea for how it 
    detects nearby magnetic interference other than detecting field gradients. 
    The Earth's field is basically uniform over short distances while the field 
    from a magnetic object nearby would vary measurably.
    And Brad, you wrote:
    "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 
    Ha. Whoa there, cowboy... You didn't think anyone was suggesting NAVIGATING 
    with a SkyScout, did you? Of course, this is "upside down", much as using a 
    2012-D star finder is upside down.
    And you wrote:
    "They may make the connection that it is Celestial turned inside out, but they may not."
    Yes, of course. So the question then is, 'can we provide some sort of software 
    application (and remember, these smart phones can be programmed by us, or 
    people like us) that would "inspire" an interest in celestial navigation?' 
    Being able to identify stars is a lot of fun that used to require some rather 
    dull star chart work. With devices like this it's a snap, and it's genuinely 
    fun, and if we can create some sort of custom software that points people in 
    the right direction, then out of the potential millions and millions of 
    people who would have access to such software, there are bound to be 
    thousands and thousands who would discover celestial navigation that never 
    would have gotten near it before.
    You concluded:
    "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!"
    Sure, there ya go. Something like that might make a nice little lesson in software like this.
    So again, if every high-end cell phone in two years has directional 
    capabilities like the present SkyScout, how can we leverage that to get 
    people interested in celestial navigation.
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