Движение Земли вокруг Солнца

uses graphABC;
type zvezda=record
            x,y:integer;
            end;
     mas=array[1..500] of zvezda;
var x0,y0:integer;
procedure fon(a:mas); //звездное небо
var i:integer;
begin
clearwindow(clBlack);
for i:=1 to 500 do
setpixel(a[i].x,a[i].y,clWhite);
end;
procedure gas;  //гаснущие звезды
var i:integer;
begin
setbrushcolor(clBlack);
for i:=1 to 50 do
circle(10+random(windowwidth-20),10+random(windowheight-20),10);
end;
procedure solnce; //солнце
begin
setbrushcolor(clYellow);
circle(x0,y0,40);
end;
procedure zemlya(x,y:integer); //земля
begin
setbrushcolor(clBlue);
circle(x,y,10);
end;
var a:mas;
    k,r1,r2,x,y:integer;
    u:real;
begin
randomize;
setwindowsize(600,400);
centerwindow;
for k:=1 to 200 do
 begin
  a[k].x:=1+random(windowwidth-2);
  a[k].y:=1+random(windowheight-2);
 end;
x0:=windowwidth div 2;
y0:=windowheight div 2;
r1:=x0 div 2+50;
r2:=y0 div 2-50;
u:=0;
k:=0;
lockdrawing;
repeat
fon(a);
inc(k);
if k mod 10=0 then gas;
x:=x0+round(r1*cos(u));
y:=y0-round(r2*sin(u));
zemlya(x,y);
sleep(100);
solnce;
sleep(50);
u:=u+0.1;
redraw;
until false;
end.