The angle at which the sun shines on stationary objects changes during the day as a result of the Earth’s rotation. For example, when the sun is close to the horizon in the early morning, it throws long shadows when an object blocks its light. In contrast, when the sun is directly overhead in the middle of the day, shadows get shorter because the light’s angle has shifted.
The angle at which the sun’s rays impact the Earth varies throughout the course of the day, while the sun’s position in the sky fluctuates throughout the course of the year. In the summer, the sun traces a very high arc in the sky, whereas in the winter, the sun traces a very low arc, barely rising over the horizon at extreme latitudes. This change in its direction also causes variations in temperature and day duration throughout the year.
The theory behind a sundial is that the changing position of the sun during the day causes a change in the shape of the shadows its light casts. A sundial employs a central item that casts shadows to cast shadows in a circular pattern that varies throughout the day.
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