Source : saisons3C.mp

saisons3C.mp
verbatimtex
%&latex
\documentclass{article}
\usepackage{fourier}
\begin{document}
etex

beginfig(1);

% excentricité, demi-grand axe, demi-petit axe
numeric e,a,b;
e = 0.2;
a = 100;
b = a * sqrt(1 - e * e) ;

% ellipse
path el;
el = (fullcircle xscaled 2a yscaled 2b) rotated -78;

pair S,T;
% soleil vrai
S = point 5.2 of el;
% terre
T = (sqrt(a**2-b**2),0) rotated -78;

% axes
draw ((-1.1a,0) -- (1.1a,0)) shifted T;
draw ((0,-a) -- (0,1.3a)) shifted T;

draw el;
% ligne des apsides
draw ((-a,0)--(a,0)) rotated -78;

% marque des angles
path t[];
t1 = reverse (((fullcircle scaled 30 rotated -78) shifted T)
cutafter (T--(T shifted (20,0))));
t2 = ((fullcircle scaled 20 rotated -78) shifted T) cutafter (T--S);
drawarrow t2;
drawarrow t1;
draw T--S;

% le soleil
label(btex $S$ etex, 1.1S);
draw S withpen pencircle scaled 6pt withcolor (1,1,0);

label.urt(btex $v$ etex,point 3 of t2);
label.lrt(btex $\varpi$ etex,point 1 of t1);
label.urt(btex $\gamma$ $0^{\tiny\circ}$ etex,(.92a,0)shifted T);
label.urt(btex $90^{\tiny\circ}$ etex,(0,(1+e)*a)shifted T);
label.ulft(btex $180^{\tiny\circ}$ etex,(-a,0)shifted T);
label.llft(btex $270^{\tiny\circ}$ etex,(0,(-1+e)*a)shifted T);
dotlabel.llft(btex $T$ etex, T);
dotlabel.urt(btex $A$ etex, (-a,0) rotated -78);
dotlabel.llft(btex $P$ etex, (a,0) rotated -78);
endfig;

end