function theta = mars_angle( d ) % % Find the angle (in degrees) at which Mars appears in the sky % on day d of the year 2000. Pe = 365.256; % period of Earth orbit (days) Pm = 686.980; % period of Mars orbit (days) d0 = 187; % day of 2000 on which Mars crosses angle 0 Re = 1.496e8; % radius of Earth orbit (km) Rm = 2.279e8; % radius of Mars orbit (km) phi_e = 2*pi*d/Pe; phi_m = 2*pi*(d-d0)/Pm; xe = Re*cos( phi_e ); ye = Re*sin( phi_e ); xm = Rm*cos( phi_m ); ym = Rm*sin( phi_m ); % disp('xm - xe = ') % disp(xm - xe) % disp('ym - ye = ') % disp(ym - ye) theta = atan( ( ym - ye )/( xm - xe ) ); % theta = atan2( ( ym - ye ), ( xm - xe ) ); theta = 180*theta/pi; % convert from radians to degrees