How come when you see your shadow, it is always taller than you actually are? asks Camryn Leddy, a student at Long Island Lutheran Middle and High School in Brookville, N.Y.On a sunny day a shadow is like a patch of night. Try to jump on your shadow, and it jumps with you, ever out of reach of your feet.

A shadow appears when an object gets in the way of streaming light. The less light that can pass through an object, the more solid its shadow. So your body casts a solid dark shadow, while the shadow of a bottle of water is fainter and more translucent.

Any light source can make a shadow, from the sun and moon to a lamp or flashlight. The larger the source, the fuzzier the shadow. Which is why a lamp with a shade creates fuzzier shadows than does a bare lightbulb.

On a cloudy, overcast day, it's as if the sun were wearing a lampshade. With the whole sky acting as a diffuse light source, your body's shadow will be so spread out and fuzzy that you can't see it on the ground.

If the sun is so huge, capable of holding a million planet Earths, how come it casts such sharp shadows? While the sun is enormous, it is also enormously distant: 93 million miles away. So the sun appears as a rather small light source in the sky.

Combine the intensely bright sun with your solid body, and the result is a black, well-defined shadow on the sidewalk.

Because the sun's position in the sky changes throughout the day, the length of your shadow changes, too. So even though your shadow is indeed sometimes longer than your body, it is often shorter, too. To see this for yourself, simply go outdoors several times from early morning until noon (or from noon until evening). Your shadow will be longer when the sun is low in the sky, shorter when the sun is higher.

Near sunrise and sunset, you'll cast the longest, skinniest shadow. Near noon, your shadow will be its shortest. And if the sun is directly overhead, your shadow will sadly dwindle to nothing. In fact, some recommend a handy shadow test for covering up or applying sunscreen: If your shadow is shorter than you are, you're more likely to get sunburned.

Want to know how long your shadow would be on a sunny day -- without even stepping outside?

Try the Shadow Length Calculator, which can be found at http://tinyurl.com/882d28y.

Wondering how tall that tree is? Simply measure its shadow and then use this calculator: http://tinyurl.com/7unr5pl.

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