public void createStars(int number)
    {
      GreenfootImage background = new getBackground
      for (int i = 0; i < number; i++)
      {
           int x = Greenfoot.getRandomNumber(getWidth());
           int y = Greenfoot.getRandomNumber(getHeight());
           int color = 120 - Greenfoot.getRandomNumber(100);
           background.setColor(new Color(color,color,color));
           background.fillOval(x, y, 2, 2);
           addObject(new Asteroid(),x,y);
      }
      }