The changing law of shadow in a day

The change rule of shadow in a day is from long to short and then to long.

When the sun just rises, the shadow of the object is the longest, on the west side of the object. As the sun rises, the shadow will become shorter and shorter, and gradually move to the northwest. At noon, the shadow is the shortest, facing north, and then the sun sets in the west, and the shadow will become longer and longer, facing east.

1. Sunrise: At sunrise, the sun just rises from the horizon and is located at a lower position above the earth. At this time, the shadow of the object will be very long, because the sun shines on the object and the ground at a small angle, resulting in a long projection.

2. Morning: As the sun rises, the shadow becomes shorter. When the angle of the sun becomes larger, the sun shines on the object at a more vertical angle, making the shadow cast by the object shorter and shorter.

3. Noon: Noon is the moment when the sun's altitude angle is highest. At this time, the sun shines directly on the ground, and the light shines almost vertically on the object, so the projection shadow of the object is the shortest. In some cases, such as near the equator, the sun may hardly see its shadow at noon.

4. Afternoon: In the afternoon, the height angle of the sun gradually decreases, and the angle of sunlight projection increases, making the shadow of the object gradually longer.

5. Evening: Near sunset, the angle of the sun becomes lower again, similar to sunrise, and the shadow cast by objects becomes very long.

The causes of shadows

1. Propagation of light: The light emitted by the sun is electromagnetic wave, which travels in a straight line in a vacuum, and will be refracted and scattered when it meets substances. Air molecules in the earth's atmosphere will scatter sunlight, which will change the direction of light during its propagation.

2. Object occlusion: When the sun shines on an object, the object will block part of the light, so that the light cannot directly reach other areas. This part of the light blocked by the object forms a shadow.

3. Ray tracing: Sunlight travels along a straight line and is blocked or refracted when it meets an object. When light shines on an object, the object will project its outline and details, forming a shadow area, that is, a shadow.