float angle,angleD;

void setup() {
  size(400,400);
  angle=0;
  angleD=6;
  ellipseMode(CENTER_DIAMETER);
}

void loop() {
//  background(200);
  ellipse(200+cos(radians(angle))*100,
    200+sin(radians(angle))*100, 20,20);
  angle=angle+angleD;
}