What are shadows, exactly?  How are shadow, penumbra and antumbra formed?  - Incredibilia.ro

Shadows are all around us; we see them almost constantly. But have you stopped to think about what exactly they are and how we can define them?

The easiest way to describe shadows is as “dark areas where an object blocks light coming from a certain source.” This object must be opaque, which means that it is impenetrable to electromagnetic radiation, especially light.

Normally, shadows occupy the entire three-dimensional volume of the space behind the object (seen from the direction of the light source). If we looked at a cross section of a shadow, we would see that it looks like a flat silhouette. A shadow is an inverse projection of any object that is placed in front of a light source.

Light sources

Light sources are separated into point sources and non-point sources. A shadow that is projected by a point source of light is simple and is called a shadow. If we talk about a pointless light source, the shadow has three parts. These parts are the shadow, the penumbra and the shadow.

The shadow is the darkest part of a shadow, the one that is in the innermost part of it. The penumbra is the region where only part of the light is hidden. Finally, the antumbra is the region in which the body that blocks the light source appears entirely inside the same light source, namely its disk.

A shadow that is projected by a point source of light is simple and is called a shadow.
A shadow that is projected by a point source of light is simple and is called a shadow. Photo: iStock

If the light source is wide, the shadows will be dim. These will become more and more blurred as we increase the width of the light source. An interesting phenomenon is the blistering shadow effect. This happens when two shadows overlap with each other and the shadows begin to merge.

Light scattering

The outlines of shadows can be found if we follow the rays of light coming from the outside areas of the light source. The shadow is the darkest part because it does not receive light directly from the source. If we were in the shadows, we would not be able to see the parts of the light source directly.

The light source partially illuminates the penumbra, so we could see it if we sat there. However, the view of the light source would still be blocked by any of the objects responsible for the shadow.

With more light sources we get more shadows. The places where they overlap are darker and may even be a different color than usual. Once we start to diffuse the light, the shadows become softer and softer and lose their contours until they disappear completely.

The shadows of outer space are extremely clear, with clearly visible boundaries and contours between light and dark. This is because there are no atmospheric effects that diffuse light.

If a person touched the spot where a shadow is projected, the two shadows would also converge exactly where the point of contact is. Shadows are distorted, but they still show the exact silhouette of an object.

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