verbatimtex
%&latex
\documentclass{article}
\usepackage{fourier}
\begin{document}
etex

path axe;
axe = (0,-60)--(0,60);

beginfig(1);
	for i:=0 upto 12:
	    yy := 50 - (25 / 3 * i);
	    xx := - sqrt(3600 - yy * yy) - 10;
	    drawarrow (-100,yy)--(xx,yy) withcolor (1,1,0);
	endfor;

	fill fullcircle scaled 100 withcolor (1,1,.3);
	fill (halfcircle--cycle) rotated -90 scaled 100 withcolor (.3,.2,.1);

	draw axe;

	for i:=1 upto 7:
	    yy  := 50 - i * 12.5;
	    xx  := sqrt(2500 - yy * yy);
	    draw (xx,yy)--(-xx,yy) withpen pencircle scaled .5pt
		    withcolor .6white;
	endfor;

	label.urt(btex $N$ etex,(0,50));
	label.lrt(btex $S$ etex,(0,-50));
endfig;

beginfig(2);

	for i:=0 upto 12:
	    yy := 50 - (25 / 3 * i);
	    xx := - sqrt(3600 - yy * yy) - 10;
	    drawarrow (-100,yy)--(xx,yy) withcolor (1,1,0);
	endfor;

	fill fullcircle scaled 100 withcolor (1,1,.3);
	fill (halfcircle--cycle) rotated -90 scaled 100 withcolor (.3,.2,.1);

	draw axe rotated 23;

	for i:=1 upto 7:
	    yy  := 50 - i * 12.5;
	    xx  := sqrt(2500 - yy * yy);
	    draw ((xx,yy)--(-xx,yy)) rotated 23 withpen pencircle scaled .5pt
		withcolor .6white;
	endfor;

	label.urt(btex $N$ etex,(0,50) rotated 23);
	label.lrt(btex $S$ etex,(0,-50) rotated 23);
endfig;

beginfig(3);

    for i:=0 upto 12:
	yy := 50 - (25 / 3 * i);
	xx := - sqrt(3600 - yy * yy) - 10;
	drawarrow (-100,yy)--(xx,yy) withcolor (1,1,0);
    endfor;

    fill fullcircle scaled 100 withcolor (1,1,.3);
    fill (halfcircle--cycle) rotated -90 scaled 100 withcolor (.3,.2,.1);

    draw axe rotated -23;
    for i:=1 upto 7:
	yy  := 50 - i * 12.5;
	xx  := sqrt(2500 - yy * yy);
	draw ((xx,yy)--(-xx,yy)) rotated -23 withpen pencircle scaled .5pt
		withcolor .6white;
    endfor;

    label.urt(btex $N$ etex,(0,50) rotated -23);
    label.lrt(btex $S$ etex,(0,-50) rotated -23);
endfig;

end