Shadows: Definition, Formation, and Characteristics

If you go outside on a sunny day, you will be followed by a dark ghost-like creature. What exactly is it? It’s your Shadow! It can be seen trailing you or moving behind you multiple times throughout the day; even while you read this, there is a chance that a shadow of some portion of your body can be seen someplace.

But shadows are generated by more than just humans; from a small pen to a large, old banyan tree, shadows are formed by even a mosquito. What if you were now told that our planet, too, casts a shadow? Take a walk outside and find your own! The night sky is nothing more than the earth’s shadow. Earth’s shadow extends almost \(1.4\;\text{million}\,\text{km}\) into space.

To learn more about shadows and their formation, let us read further.

What is a Shadow?

A shadow refers to a region or space that is devoid of light because of the blocking of the path of light by an opaque object. The intensity and position of the light source determine the intensity and type of the shadow formed. To understand this, let us take a natural light source, for example, the sun. Start early morning, and throughout the day, watch how your shadow changes. From early morning till noon, you will find your shadow to be elongated and less dark. At noon, your shadow will be short and deep dark. From late afternoon till evening, shadow again would be less intense and much longer.

A shadow is formed when the light rays hit an opaque object (the objects that do not allow the light to pass through them). A shadow may seem like a reflection, but it is not. Thus in simple terms, a shadow is associated with the absence of light. When the light cannot get through an object, the surface on the other side of that object, either the ground or a wall, will have less light reaching it.

Requirements for Shadow Formation

An area of darkness formed by an opaque object obstructing light is called a shadow.
The following are the requisites to form a shadow:

1. a source of light
2. an opaque object
3. a screen or surface behind the object.

A shadow will not be formed in the absence of any one of the following things. That is why we cannot see a shadow in the dark. The shadow of an object can give us an idea about its shape, although it can be misleading too. For example, the shadow of a ball appears circular, much like a ball, but the shadow of a cone looks like a triangle on the screen. The shape of the shadow of an object only depends on the direction from which light is falling on it.

Learn about Diffraction of Light here

Formation of a Shadow

Shadows are formed when the path of light rays is obstructed. The position of the source of light determines the size of the shadow. When the object is closer to the source of light, the size of the shadow produced is large. When the object is shifted away from the source of light, the size of the shadow becomes small. Shadows are formed on the opposite side of the light source. We can not obtain shadows using transparent objects because they allow light to pass through them. An opaque object blocks the light falling on it, and hence an area of darkness is created on the other side of the opaque object away from the source of light. In fact, shadows are created by a translucent object, although they will be fainter compared to the ones created by an opaque object. 

Shadow Formation: An Activity

To obtain a shadow and study its characteristics, let us perform an experiment with the things available in our homes.
Materials Required: Collect a few opaque objects (like a book, an apple, a ball, a glass container) of different shapes and sizes, a light source like a torch, a candle and a lamp and a white screen which could either be a wall or a piece of cardboard covered with white paper).

1.  Place the bulb in front of a wall at a certain distance from it.
2. Place an object (whose shadow you want to study) between the bulb and the wall.
3. Turn on the bulb and trace an outline of the shadow that you obtain on the wall.
4. Now shift the bulb away from the object and trace down the shadow.
5. Shift the bulb close to the object and trace down your observation.
6. Replace the torch first with a candle, then with a lamp and trace all the shadows.
7. Perform all the above steps for different objects and note the colour and the size of the shadow.

You will observe that the shadows are only formed for only opaque objects, and these become bigger when the light source is moved closer to the object and smaller when the light source is moved away from it. The intensity of the light source determines the intensity and colour of the shadow.

Characteristics of a Shadow

From the above activity, we can conclude that the following are the characteristics of a shadow:

1. Irrespective of the colour of the object used to make the shadow; It is always black.
2. A shadow only depicts the shape or outline of the object and not the details.
3. The size of a shadow depends on the distance between the object and the source of light and between the object and the screen.

4. The change in the size (or length) of the light source changes the clarity of the shadow. For example, at noon, the shadows formed are more defined in nature than those formed late afternoon or early morning shadows, which are slightly blurred with edges not defined very well. This is because when the light source, i.e. the sun, is wider during these times.
5. There are two types of Light sources: point or non-point (extended) in nature. A point source of light forms a simple shadow called an umbra, while in the case of an extended light source, the shadow consists of three parts: the umbra, penumbra, and antumbra.

Umbra is the innermost and darkest part of the shadow. In this part, the light source is completely blocked.
Penumbra is the faintly dark part of a shadow in which an object obstructs only a portion of the light source.
Antumbra is the part of a shadow from which the object’s body appears entirely within the disc of the light source.
6. Generally, shadows formed on surfaces are two-dimensional; they can also produce a three-dimensional effect. For example, the three-dimensional effect can be observed when a shadow is cast on dense mist or fog.

Seasons and Shadows

We experience four seasons summer, spring, autumn and winter, although a significant shift in the sunlight is experienced in summers and winters only. The seasons too, have a role to play in determining the shape and size of a shadow. During summer, the days are bright and sunny; hence the shadows of objects will be sharp. Due to a large amount of water vapour in the rainy season, the light gets obstructed, and we get blurry shadows. In winter, days are colder, the light is less intense, and shadows will be faint. Our location is tilted towards the sun during the summer, so our midday shadows are very short. Our location is tilted away from the sun during the winter, so our midday shadows are longer.

The Solar and Lunar Eclipse

Solar eclipse: During a solar eclipse moon comes in between earth and the sun. Thus, the light travelling from the sun towards earth gets obstructed, and we get the moon’s shadow on the earth in the form of a solar eclipse.

Lunar Eclipse: During a lunar eclipse, the earth comes in between the moon and the sun. Thus, the light rays travelling from the sun towards the moon get obstructed, and we get the earth’s shadow on the moon in the form of a lunar eclipse.
Depending upon the positions of these heavenly bodies, we can get partial or total eclipses.

Summary

A shadow refers to a region of space devoid of light because of an opaque object blocking the path of light. The intensity and position of the light source determine the intensity and type of the shadow formed. Shadows are formed when the path of light rays is obstructed. The position of the source of light determines the size of the shadow. When the object is closer to the source of light, the shadow produced is large. When the object is shifted away from the source of light, the size of the shadow becomes small. Shadows are formed on the opposite side of the light source. There are two types of Light sources: point or non-point (extended) in nature. A point source of light forms a simple shadow called an umbra, while in the case of an extended light source, the shadow consists of three parts: the umbra, penumbra, and antumbra. Solar and lunar eclipses are a few examples of shadows formed by heavenly bodies.

Frequently Asked Questions on Shadows

Q.1. Can we observe shadows at night?
Ans: With a light source like the moon, streetlight, or torch, we can observe shadows at night.

Q.2.  Why only opaque materials form shadows?
Ans: Opaque materials do not allow the light to pass through them and hence form a dark shadow. Translucent objects also form shadows, but those are faint compared to those made by an opaque object.

Q.3. Is the shadow of an object the same as its image?
Ans: No shadow and an image are different things. Image is formed by the real or virtual intersection of light rays, whereas a shadow is formed when light rays get obstructed.

Q.4. What is a shadow?
Ans: A shadow is a region devoid of light formed by an opaque object’s obstruction of the path of light.

Q.5. When the source of light is brought closer to the object, what happens to its shadow?
Ans: The shadow of the object becomes elongated when the source of light is brought close to it.

Learn Construction of Pinhole Camera here

We hope you find this article on ‘Shadows‘ helpful. In case of any queries, you can reach back to us in the comments section, and we will try to solve them.