program planet

      if(pgopen('/xwin')<=0)stop
      call pgenv(-10.0,10.0,-10.0,10.0,1,0)
      call pgsfs(2)

      r=5.0
      x_old=r
      y_old=0.0

      d_theta=2*3.14159/360000
      do i=1, 100000000
        theta = theta + d_theta
        x = r*cos(theta)
        y = r*sin(theta)

        call pgbbuf

          call pgsci(0)
          call pgcirc(x_old,y_old,0.2)

          call pgsci(1)
          call pgcirc(x,y,0.2)

        call pgebuf

        x_old = x
        y_old = y
      end do

      call pgclos
      end