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    Re: The Usps Aries Calculator
    From: Gary LaPook
    Date: 2010 Nov 08, 19:46 -0800

    The modification to the 2102-D that I posted last year added the date
    and time scales so that it can be set like the usual planisphere.
    
    http://www.fer3.com/arc/m2.aspx?i=107982&y=200904
    
    gl
    
    On 11/8/2010 3:55 PM, Frank Reed wrote:
    >
    > Alan, you wrote:
    > "Having run a couple of LHA's on it, the LHA I got with it was about
    > 15 Degrees greater than the calculated LHA Aries."
    >
    > Whenever you encounter a 15 degree difference, you should immediately
    > ask yourself two questions: did I forget to correct for DST? or did I
    > use the wrong time zone? Fifteen degrees corresponds to one hour's
    > worth of the Earth's rotation. It almost has to be one of those two
    > errors.
    >
    > If you find a discrepancy that's more on the order of a dozen or two
    > dozen minutes of time or a few degrees in angle, then it's likely that
    > the Zone Time to Local Time correction is off, possibly done
    > backwards. Here you can get it right by thinking --thinking outside
    > the black box, you might say :). The stars rise from the east, set
    > towards the west. So suppose you work out how the sky should appear
    > from the center of your time zone. In your present case, for example,
    > you said you're in Pittsburgh. That's close to 80 degrees West. The
    > center of the Eastern Time zone is at 75 W, running very close to
    > Philadelphia. Those five degrees difference in longitude correspond to
    > 20 minutes in time (15 degrees per hour).
    >
    > So let's suppose you want to set a star finder, whether the
    > navigators' H.O.2102-D or a common planisphere star finder, to show
    > the sky for Pittsburgh. You can set it for Eastern Time easily enough,
    > but then you will have to adjust by 20 minutes to show the sky in
    > Pittsburgh. Which way? Well, Pittsburgh is west of Philadelphia, and
    > the stars rise from the east, so the stars "get there" (to Pittsburgh)
    > twenty minutes later. That means that if I've set a star finder for
    > 7pm (center of time zone, Philadelphia's sky), then I won't see the
    > sky like that from Pittsburgh until 7:20pm.
    >
    > While there's a fair amount of calculation and technical jargon
    > involved in setting up the navigators' Rude Star Finder, the common
    > planisphere couldn't be simpler: you rotate the disk until the time
    > and the date line up. Any child can do it --literally! The only tricky
    > operation, usually ignored, is the correction for LMT from Zone Time
    > (like the 20 minutes from Philadelphia to Pittsburgh above). Common
    > planispheres don't include azimuth-altitude overlays, but these can be
    > printed easily on an ordinary inkjet printer.
    >
    > A really nice innovation in the common planisphere was invented and
    > marketed by David Chandler starting almost twenty years ago. His
    > planispheres are double-sided. One side shows the view facing north.
    > When you flip it over, without any change in adjustment, you have the
    > view facing south. This avoids the high distortion near the edge
    > usually found in planispheres. If you're trying to learn the star
    > patterns and constellations, and not merely calculate their positions,
    > these double-sided planispheres are a great tool. The constellations
    > have the right shapes. You can find Chandler's "Night Sky"
    > planispheres for various latitudes at amazon.com by searching for
    > "Night Sky Small Star Finder" (also available in Large size).
    >
    > -FER
    >
    >
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