Re: Geostationary apparent declination

Date: Mon Oct 17 2005 - 04:45:47 EDT

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    Jeff wrote in
    > ... The math gets way to complicated for proper
    > calculation of the declination off the local
    > meridian. But it will be *smaller* ...
    Not much - I find thinking in Cartesian coordinates easier.
    Replace computation of Rs and ThetaD by:
    TheD = ARCTAN(h/(SQRT(Xsat^2+Ysat^2)))
    Xsat = Rg*COS(Longi)-Re*COS(ThetaL)
    Ysat = Rg*SIN(Longi)
    Longi = Satellite longitude relative local meridian.
    In Excel, with H2 (, H3, H4...) = Longi
    (and Re,Rg,ThetaL,h in A2 to D2) this becomes:
    where X = I2 (, I3, I4...) :
    and Y = J2 (, J3, J4 ...) :
    This spreadsheet (I hope I did it right) is at
    (in Excel 5.0 format to be compatible with more users).
    To be more correct, Re should be your local Earth radius,
    and ThetaL your geocentric latitude, both of which are smaller.
    At 60 degrees, the diffs are about -13 km, -0.2 degrees;
    less near the equator.
    There is a more advanced spreadsheet by Drew (AlJanah?)
    Subscribe/Unsubscribe info, Frequently Asked Questions, SeeSat-L archive:

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