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    Re: Computer space required to get 1" accuracy
    From: Frank Reed
    Date: 2010 Apr 7, 10:14 -0700

    Antoine, you wrote:
    "In order to fully agree about such "starting conditions" before I undertake this research, may I summarize this "friendly challenge" of yours under the following form ?
    - We are to define a daily array of numerical data in order to get a 1 arc second accuracy on the coordinates of the SUN + Moon + 4 Navigational Planets through linear interpolation."

    Yes. There's a bit of ambiguity here in the way I've defined things. Should the maximum error be limited to 0.5 arcseconds so that the coordinates when rounded to the nearest arcsecond are correct or whould the maximum be 1.0 arcseconds? Take your pick.

    Note that you don't need the full x,y,z coordinates. For terrestrial navigation, you need celestial (ecliptic) longitude, celestial latitude, and horizontal parallax. You need enough daily data so that you can do plain linear interpolation to get the instantaneous positions.

    In my own code, I originally forgot to include the Sun's SD in the database (equivalently, I assumed the Sun's HP was constant). So that's the one observable quantity that's calculated. It's actually more efficient since the Sun's SD variation repeats annually with no measurable difference.


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