// Author: John Bowman
size(10cm,0);

real r=1;
real R=3.8;

int step=30;
path p=arc(0,r,0,step);
path P=arc(0,R,step,0);
for(int h=0; h < 360; h += step) {
  transform t=rotate(90-h);
  tensorshade(t*p--t*P--cycle,
              new pen[] {white,white,hsv(h-step,1,1),hsv(h,1,1)});
}

for(int h=0; h < 360; h += 30) {
  pair v=R*dir(90-h);
  draw(Label(string(h)+"$^\circ$",EndPoint),(v--1.05v));
}

draw(circle(0,r));
draw(circle(0,R));