  function E = Earth(t)
% E is a column 2-vector with the property that Earth is located
% at (E(1),E(2)) at time t.
  E = zeros(2,1); PE = 147.098; AE = 152.097; tE = 70; rhoE = 365.24;
  theta = 2*pi*(t + tE)/rhoE;
  E(1) = (PE-AE)/2 + ((PE+AE)/2)*cos(theta);
  E(2) = sqrt(PE*AE)*sin(theta);