Shadows change direction
Imagine that you are lying on the grass on a sunny afternoon. The sunlight is shining on one side of your body. The light rays, however, are not passing through your body because you are made of opaque materials. This means that the rays are blocked so on the other side of your body there is an absence of light rays. The place where the light rays are absent is dark. The dark area on the ground next to you is called your shadow.

If you had looked at your shadow as you lay there, you would have been able to make out your head and shoulders. The rest of your body and legs may have formed an uneven outline to the shadow and you may not have been able to tell where your knees were. However, the moment you moved your knees, your shadow changed and you could spot them. In fact every time you moved your body your shadow changed. When you sat up, you could make out your head and body easily in your shadow. When you stood up, you could see the shadow of your legs and feet too.

As you changed position from lying down to standing up, you made a discovery. Your shadow always began at the part where your body touched the ground. There was no gap between your body and the shadow. When you were laid down, your shadow ran all the way from your head to your feet. When you sat up, the shadow was in contact with the sides of your legs as you stretched them out across the grass. When you stood up, the shadow was in contact with your feet. Finally, you wondered what would happen if you raised one foot? Would the shadow still be stuck to it? When you tried your experiment, you found that only the foot on the ground remained in contact with your shadow.

As you moved about, you made another discovery about your shadow. It always matched what your body was doing. If you raised your arm, the arm on the shadow was raised. If you ran, your shadow went with you. If you rolled up in a ball and turned your head so you could see your shadow, it looked like a ball too. All this may seem obvious but sometimes people forget about it when they are drawing pictures. They draw shadows and objects with gaps between them or they draw shadows which do not match the objects. Next time you are drawing a picture, remember to put the shadows in the right place.

There is something else that some people do when drawing shadows. When they draw shadows of people they put faces on them and perhaps features of clothes such as buttons or pockets. It is possible that they confuse a shadow with a reflection. A shadow is a place where there is no light, so no details, such as parts of the face or parts of the clothes, can be seen. A reflection occurs at a shiny surface where large amounts of light from a person bounce off. This light appears to be coming from inside the mirror and it shows all the details of the person and their clothes.

When you were outside on a sunny afternoon there were two other things you noticed about your shadow. The first thing was that no matter where you went, the Sun was on one side of your body and the shadow was on the other. This was because your body blocked the rays of light from the Sun. The second thing you noticed was that the length of the shadow changed during the afternoon. In the early afternoon your shadow was not much longer than you. By late afternoon the shadow had stretched and was much longer. The reason for this was the height of the Sun.

When the Sun is high in the sky in the early afternoon the light rays almost shine down on top of you and this makes a small squashed shadow close to your body. When the Sun is low in the sky in the late afternoon the light rays strike you from one side and this makes your shadow long and thin.

Next time you are out on a sunny day look at your shadow. See how it changes as you move, notice that you cannot see your face or clothes in your shadow and see how it changes in length as the Sun rises and sinks in the sky.

Are there any other kinds of materials besides opaque materials?
Yes. There are translucent materials and transparent materials. Translucent materials let a small amount of light pass through them. The light rays, which pass through the translucent material, are scattered. This means that you cannot see clearly through translucent material. Transparent materials let a large amount of light through. The light rays are not scattered. This means that you can see clearly through transparent materials.

Do transparent and translucent materials cast shadows?
Yes, they do. A large amount of light is reflected from the surface of a translucent material. This means that only a small amount of light passes through. This reduction in the number of light rays leaving the translucent materials produces a pale shadow of the material. Only a small amount of light is reflected by a transparent material. This means that a large amount passes through. As there is only a very small reduction in the amount of light passing through the material, only a very pale shadow is produced.

What happens to your shadow if you walk around a light?
Think about being at a campfire. If you stand up and face the fire your face is lit up and the heat warms it. Turn away and you see your shadow pointing away from the fire. If you walk around the campfire your shadow goes with you but it always points away from the fire.

If you stand with your hands on your hips you can see patches of light in your shadow. Why is this?
When you stand with your hands on your hips you make gaps between your body and your arms. Some light rays can get through the gaps and shine onto the ground. They make the light patches in your shadow.

What would happen to my shadow if I stood under a light?
It would be very small and squashed up close to your body.

What would happen to my shadow as I walked away from the light?
It would become longer.

Can a shadow be half on the floor and half on a wall?
Yes, it can. Shadows are not just found on the ground or on a wall. Half a shadow can be on the ground and the other half on a wall. The important thing about how shadows form is that they form when light is blocked. It does not matter whether the blocked light would have shone on the ground or on a wall so a shadow will form wherever light is blocked.

Can shadows be cast at night outside?
Yes, they can. Streetlights cast shadows. As they are high in the air and sometimes overhead they may produce short shadows which you do not notice easily. Also the light from one street lamp can shine into an area where a shadow has formed from another street lamp and this makes the shadow paler. Out in the countryside the Moon may reflect so much light from the Sun that the light can cast shadows.