beginfig(1);
     u := 1cm; 
     a := 6u; 
     b := 3.5u;
     pair sun; 
     sun := (-1.75u,0); 
     path E[], p[], area[];
     E1 = fullcircle xscaled a yscaled b;
     E2 = E1 scaled 1.1;
     p1 = sun -- (4.9u*dir(10) shifted sun);
     p2 = sun -- (4.5u*dir(18) shifted sun);
     p3 = sun -- (2u*dir(73) shifted sun);
     p4 = sun -- (1.6u*dir(150) shifted sun);
     area1 = buildcycle(p1,E1,p2);
     area2 = buildcycle(p3,E1,p4);
     fill area1 withcolor 0.8[blue,white];
     fill area2 withcolor 0.8[blue,white];
     draw p1; 
     draw p2; 
     draw p3; 
     draw p4; 
     draw E1; 
     draw sun withpen pencircle scaled 6bp;
     numeric t[];
     t1 = ypart (p1 intersectiontimes E2);
     t2 = ypart (p2 intersectiontimes E2);
     t3 = ypart (p3 intersectiontimes E2);
     t4 = ypart (p4 intersectiontimes E2);
     drawarrow subpath (t1,t2) of E2;
     drawarrow subpath (t3,t4) of E2;
     label.urt(btex $\Delta t$ etex, point((t1+t2)/2) of E2);
     label.ulft(btex $\Delta t$ etex, point((t3+t4)/2) of E2);
 endfig;
 
 end;