From: Adam Anderson <adam.anderson@theglass.com.au>
Newsgroups: alt.uu.math.misc,de.sci.astronomie,de.sci.mathematik,sci.math,uk.education.maths,uk.sci.astronomy
Subject: Re: Calculating the angle between Sun and a Geostationary Satellite
Date: Wed, 21 Mar 2001 22:55:49 +1100
Organization: Contract IT PTY LTD
Message-ID: <3AB896C5.8787DCBA@theglass.com.au>
References: <%Jtq6.3124$tR1.28825@news1.oke.nextra.no>

What you are referring to is generically called a syzygy (a good word for
hangman).

If you are interested in a commercial product to do this please contact
Ian Dick
ID & Associates Pty Limited
Ph:+61 2 49366566
Fx:+61 2 49366602
email:igmdick@mail.newcastle.edu.au

Bobben wrote:
> 
> I'm interessed in calculating the angle between the sun, earthlocation
> and a geostationary orbit(GSO) satellite.   This angle can be used to find
> outages on a GSO satellite caused by the sun.
> 
> There will be an outage whenever this angle is less  than
> (0.266_deg +AntennasBeamwidth_in_degrees)
> 
> I have theese orbital parameters of the sun:
> ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
> '''''''''
> w=282.9404
> e=0.016709
> ecl=23.4393
> M=356.0470 + (360/365.25)*T
> RSUN=149504200 km
> Rearth=6378 km
> H=35786 km
> 
> T= Days  (could be time in days since 0.0.2000 )
> 
> E=M+ e*Sin(M)*(1+Cos(M))
> 
> Y1=RSUN*(Cos(E)-e)
> Y1=RSUN*(SQRT(1-e*e))*Sin(E)
> 
> V=ATAN2(Y1,X1)
> R=SQRT(X1*X1+Y1*Y1)
> 
> lonsun=V+w
> 
> Suns equatorial coordinates:
> '''''''''''''''''''''''''''''''''''''''''''''''''''''''''
> Xsun=R*Cos(lonsun)
> Ysun=R*Sin(lonsun)*cos(ecl)
> Zsun=R*Sin(lonsun)*sin(ecl)
> 
> Earth equatorial coordinates:
> '''''''''''''''''''''''''''''''''''''''''''''''''''''''''
> Xearth=Rearth*Cos(Latitude_earth)*Cos(Longitude_earth +360*T)
> Yearth=Rearth*Cos(Latitude_earth)*Sin(Longitude_earth +360*T)
> Zearth=Rearth*Sin(Latitude_earth)
> 
> The geost. satellite equatorial coordinates:
> ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
> '''''''
> Xsat=(Rearth+H) * Cos(Longitude_Satellite + 360*T)
> Ysat=(Rearth+H) * Sin(Longitude_Satellite + 360*T)
> Zsat=0
> 
> Now I have some formulas that uses vector calculations.
> 
> EarthSunvector * EarthSatellitevector =
> |Earthsunvector|*|EarthSatellitevector| * Cos(alfa)
> 
> A=Xsun-Xearth
> B=Xsat-Xearth
> C=Ysun-Yearth
> D=Ysat-Yearth
> E=Zsun-Zearth
> F=Zsat-Zearth
> 
> Earthsunvector*EarthSatellitevector  =A*B +C*D + E*F
> |Earthsunvector|=Sqrt(A*A+C*C+E*E)
> |EarthSatellitevector|=Sqrt(B*B+D*D+F*F)
> 
> Alfa= Acos(  (A*B +C*D + E*F)/(Sqrt(A*A+C*C+E*E)*Sqrt(B*B+D*D+F*F)))
> 
> Where Alfa is the off_axis angle of the sun viewed from the earthlocation.
> 
> I have tested this with a time where there is supposed to be suninterference
> on the GSO satellite
> and the alfa angle is about 150 degrees so it can't be the angle I'm looking
> for.  I would expect the sun to
> be less than 1 deg. from the satellite as seen from the earth.
> 
> If somebody know how to calculate the correct angle between the satellite
> and sun seen from a earthlocation I would like
> to know.
> 
> Jens


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