If the object they hit is opaque, the light cannot pass through, and a shadow forms. Simply speaking, a shadow is an absence of light. If light cannot get through an object, the surface on the other side of that object for example, the ground or a wall will have less light reaching it. There are many sources of light — stars like our Sun, candle flames, light bulbs, glow-worms and computer screens produce light. All of this light travels in a straight line until it hits something.
Sometimes, it travels a short distance — like when we switch on the lamp. Other times, light travels thousands of years — like the light from stars we see in the Milky Way. It is easy to see our shadows when we are outdoors in the sunshine on a clear, bright sunny day, but do shadows form when an object blocks light from other sources?
The answer is yes, but they may be difficult to see if the light source is not very bright has a low light intensity. Shadows are also more definite sharper where there is contrast between the shadow and the lit surface, for example, a shadow on a white wall will be more easily seen. The size of the light source can sharpen or blur the shadow. A small spotlight like a cellphone torch forms a more distinct shadow than an overhead room light, but the sharpness of the shadow changes when the torch moves away from the object.
A shape of an object always determines the shape of its shadow. However, the size and shape of the shadow can change. These changes are caused by the position of the light source. When we are outside on a sunny day, we can see how our shadows change throughout the day. When the Sun is low on the horizon, the shadows are long. When the Sun is high in the sky, the shadows are much shorter. We can create the same effects indoors by changing the position of a torch as it shines on an object.
Although the shadow effects are the same, the reasons for the moving light source are very different. However, as you move to either side, part of the light source becomes visible. That's the penumbra. If you move further to the side until you can see all of the lamp's surface, you have left the penumbra.
If the diameter of the light source exceeds that of the object, an antumbra appears. Rule: If the diameter of the light source is larger than the diameter of the object , a 3rd type of shadow appears where the cone-shaped umbra ends: the antumbra. In this experiment, the light source is another round lamp, but this time it has twice the ball's diameter.
Imagine once more that you are looking at the lamp from behind the ball. As long as you are fairly close to it, the ball's apparent size exceeds the lamp's apparent size. You are within the umbra, and the lamp is invisible. However, as you move away from the ball, its apparent size decreases. At some point, the basketball will appear smaller than the lamp. A ring of light will appear around the ball as the outer rim of the lamp comes into view. You have just entered the basketball's antumbra.
Our solar system resembles the set-up of the last experiment. Search form Search. Home About What is Inquiry Science? The Sun, lamps, flashlights, and fires are all sources of light. Shadows need a light source and an object. Shadows show the shape of an object.
What is Light? All objects reflect or absorb the seven different colors of light. Objects appear to be different colors based on what colors they reflect. What is a Shadow? A shadow is light blocked by an object.
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