I updated it. 248 bytes,and it enters and exits eclipse correctly.
Graphics 640,480Repeat;o=320;p=240For i#=0To 360f#=Sin(i)*128s=Sgn(Cos(i))For x#=0To 8Step .04b#=(x^2)-64a#=((8-x)^2)-64For e=a To -a;c#=Rnd((e/2)+f+(b*(b/400)))*6SetColor 64-c,c,c;Plot o+e*s,p+b;Plot o+e*s,p-b;Next;Next;Flip;Next;Until Keyhit(27)