private void createStars(int number) 
    {
        GreenfootImage background = 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);
        }
    }