Investigate why shadows change size during the day. Physical processes - Light - The Sun as a light source Learning Points Shadows change size during the day because of the position of the Sun. When the Sun is overhead shadows are short. At dusk and at dawn shadows are long. A Twig Curriculum Film. Delivering key learning points. Get straight to the facts in just three minutes – directly linked to core learning, Twig's curriculum films will fit neatly into your lesson plans.