23 Most fascinating facts about shadow

 1. A shadow is a dark (real image) area where light from a light source is blocked by an opaque object.

2. A shadow happens when an object blocks the sun’s rays.

3. Shadows are longer in the winter because of the angle of the sun.

4. A person's shadow is longest in the early morning and in the late afternoon.

5. When the sun is directly above us i.e in mid noon, there is little or no shadow because the light from the sun is falling upon us from all the sides and there is hardly any dark region.

6. Shadow occupies all of the three-dimensional volume behind an object with light in front of it.

7. The cross section of a shadow is a two-dimensional silhouette, or a reverse projection of the object blocking the light.

8. The outlines of the shadow zones can be found by tracing the rays of light emitted by the outermost regions of the extended light source.

9. The wider the light source, the more blurred the shadow becomes.

10. A point source of light casts only a simple shadow, called an "umbra".

11. For a non-point or "extended" source of light, the shadow is divided into the umbra, penumbra and antumbra.

12. The umbra region does not receive any direct light from any part of the light source, and is the darkest.

13. A viewer located in the umbra region cannot directly see any part of the light source.

14. By contrast, the penumbra is illuminated by some parts of the light source, giving it an intermediate level of light intensity.

15. A viewer located in the penumbra region will see the light source, but it is partially blocked by the object casting the shadow.

16. If two penumbras overlap, the shadows appear to attract and merge. This is known as the Shadow blister effect.

17. If there is more than one light source, there will be several shadows, with the overlapping parts darker. 

18. A long time ago, people observed the way shadows were formed by the sun and utilized that principle in making the world’s most primitive clocks, the sundials.

19. Some objects, such as glass, are transparent. Light can shine through them. Some light shines through translucent objects, such as a balloon or sheet of wax paper. Light cannot shine through opaque object and is blocked by them and creates shadow of that opaque object. 

20. The smaller the angle between an elongated object and the direction of the light is, the shorter the shadow is. 

21. On the other hand, the smaller the angle between the direction of the light and the surface on which the shadow occurs is, the longer the shadow is.

22. If the object is close to the light source, the shadow is large. 

23. For a person or object touching the surface, like a person standing on the ground, or a pole in the ground, these converge at the point of touch.