Out of the shadows

John Stringer sheds some light on the art and science behind a rich vein of creative ideas. Photography by Colin Crisford.

After Peter Pan lost his shadow he asked Wendy to sew it to his feet. Like many children, he believed that shadows had a life of their own. Research has shown that a seven-year-old might think that shadows hide inside objects. When the sun comes out, or a lamp is switched on, the shadow is pushed out by the light and strikes the ground. That's why the shadow is the same shape as the object. But an 11-year-old should know that an object that gets in the way of a light source will cast a shadow. Most children of this age can predict where their own shadow is likely to fall. But they may struggle with deciding where the shadow of a tree will be when the sun comes out. And only a few will be able to link shadows to light travelling in straight lines, to objects blocking these lines, and so to shadows resembling the objects that cast them.

Shadows are often associated with threat and fear. In books, plays, films, cartoons and pictures of all kinds, shadows threaten and oppress. They are naturally associated with night and gloom. "Shadows of the evening steal across the sky", as an old hymn goes.

Shadows also suggest death. Macbeth whispers, "Hence, horrible shadow!" to Banquo's ghost and reminds us later that, "Life's but a walking shadow".

You can be a "shadow of your former self"; and being shadowed by someone can feel threatening. But shadows also have a lighter side. On February 2 each year, according to American rural tradition, the groundhog leaves its hibernation burrow to see whether winter is over. If the sun is shining and the groundhog sees its shadow, six more weeks of cold weather are to follow, so it returns to its burrow. In some Eastern countries, the expression "May your shadow never grow smaller!" is a friendly way of bidding farewell.

The metaphorical battle between light and dark - as in "Heaven's light forever shines,Earth's shadows fly" from Shelley's poem "Adonais" - is richly exploited in myth and story.

What is a shadow?

A shadow is created when the passage of light is blocked by an opaque object. Beyond the object is darkness. Sometimes the darkness is not complete. A lighter area, or penumbra, may surround the darker umbra. This semi-shadow is caused when there is a large source of light and some of the light spills over the object into the shadow area. Translucent and transparent objects may cast a muted shadow - even glass can stop enough light to cast a faint but clear shadow.

The size of a shadow depends on the distance between the light source and the object blocking its rays. Its length is also affected by the angle between the light source, the object, and the surface on to which the shadow falls. This is why the Earth's rotation causes shadows to change in length through the day. Long morning and evening shadows are cast when the Sun is low in the sky.

Young children can be forgiven for believing that the Sun moves around the Earth. According to legend, when forced to retract his heretical discovery and to declare that the Earth stands still, Galileo Galilei is said to have whispered to himself, "But yet it moves".

Paint with shadows

Shadows are often used to emphasise light. They also give depth and contrast to our view of the world. Medieval paintings were curiously flat - later use of shadows and perspective added tone, shape and depth.

Artists who were interested in the power of contrasting light and dark placed artificial light sources in deep areas of darkness. Rembrandt was a master of this dramatic technique.

The invention of photography and motion pictures gave shadows a new and exciting purpose. From the earliest days of film-making they have been used to create moments of suspense (is something hidden in the dark?), relief (phew! there isn't really) and surprise (oh-oh, there was something hiding there after all), motifs that are still used by movie directors today.

PUPIL ACTIVITIES

* Add shadows to pictures you paint. Think carefully about where the light source is, and place the shadows accordingly.

* Silhouettes: using chalk on black paper, draw round the shadow cast by a seated partner and cut out the silhouette.

* Sculpture: light models or objects so that their shadows add dramatic effect.

* Photography: use a digital camera to take pictures of shadows. Place objects so that light and shadow give them tone and form.

PUPIL ACTIVITIES

* Collect and define sayings about light and shadow: "shadow of a doubt", "shadow cabinet" and so on.

* In pairs, use your shadows on the ground to make a creature with two heads, three legs and four arms.

* Make shadow puppets: you need a light source, opaque puppets, a sheet or thin paper for a screen. Tell a story where one character grows bigger or smaller, or where one swallows another.

* Trace a shadow: put a traffic cone in the playground, chalk round its shadow every hour and record your findings.

* Make a shadow clock: chalk or paint an arc in the playground around a centre spot. Mark it with the hours. Whoever stands on the spot becomes the human gnomon of a sundial.

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