The Eye on the Sky Project | What Makes Shadows? Observing Light | Creating a Sundial & What Makes Day & Night
There is an infamous fury critter from west central Pennsylvania, who legend insists can foretell the duration of winter based on if he sees or doesn't see his shadow. A rather dubious distinction for expert weather prognostication entrusted to a woodchuck.
However, what creates an annual hoopla on every 2nd of February is based on a few scientific principles of how we observe light. If we can step away from the forecast map for a moment, we can better consider what causes the cast shadow, groundhog or otherwise.
Shadows cast across the ground, or against another surface, have long attracted our attention. There have been superstitions surrounding seeing your shadow or not being able to see it. You can appreciate the benefit of shadows on a hot, sunny day.
For instance, trees cast shadows that where we seek solace from the blistering effects of the sun. Buildings cast massive shadows that relegate parts of inner cities to limited sunlight at best. There are superstitious benefits to having your shadow blocked by a larger object.
Mystical beliefs of days-gone-by insisted that shadows were actually demons chasing after us. If you're hidden under the gigantic umbrella shadow of a massive tree, these demonic pursuits can never happen.
There are dozens of odd superstitious surrounding shadows, most of them not very flattering to the unnecessarily demonized casting of one's reflection by a source of light. One ancient Greek legend insisted that anyone who walked into a sacred sanctuary would lose their shadow and subsequently die within the next year.
On a good note, some theorize shadows as being angels that follow you around to protect you from otherwise bad spirits. Many of these shadowy superstitions make for interesting conversation.
Nevertheless, they don't give much account for what actually causes your shadow. So what does cause shadows, whether it's your own silhouette, or the one shaped like Punxsutawney Phil?
You've certainly noticed a variety of shadows on super sunny days. However, there are other things that cause shadows. The one consistency between them is that they are all in some form a type of light.
Shadows have three points or objects that are necessary. One is the source of light. Since the prevalence of shadows caused by our largest source of light is the most predominate, we'll use the sun for our example.
Sunlight, or all light beams for that matter, continues in a straight line. While light rays can bend using transparent objects or prisms, nontransparent objects block those rays of light. Translucent objects are those items that allow restricted light to pass.
Now, when a nontransparent object is placed between the source of light, the sun in our example and another object like the sidewalk, the object casts a shadow. Nontransparent or opaque objects block the light.
You've also certainly noticed that shadows are not always the same size. Rarely is the shadow the exact duplicate of the object between the light source and the third object. We've all witnessed our late afternoon shadows that cast a long and ominous silhouette across the ground.
There is the converse phenomenon of a small shadow, barely visible at times, when the sun is positioned directly overhead. The reason behind different sizes of shadow involves the angle of projection for the light source.
If you stand in a lamp-lit room without any other source of light, you would notice that the shadows cast from any given point in the room will always be the same. This is not the case with shadows cast by the sun as the light source.
Since the sun is always moving, the size and positioning of your shadow will move as well. If you stood in the same sunny spot all day long, you'd watch as your shadow started out as long and tall, got gradually smaller, and then started to grow again.
As the earth rotated, the angle of the sun casting light on that spot would also move second-by-second. Not only would your shadow grow smaller and then larger, it would flip 180 degrees from one side of you to the other as the sun's light rays passed over your head.
There will two points during the day when your shadow will be its longest. This happens once in the morning, and again once at dusk. The lower the sun's angle of light is cast on the earth at each of these points is what causes your shadow to reach a maximum size.
Standing in exactly the same spot for a full day may seem an odd way to perform an experiment showing how shadows shift as the sun's position with the earth changes. You could use the welcome shadow cast by a large tree on a hot sunny day.
When you visit this tree for shade in the morning, you'll find you need to stand in a particular spot to be in the shade. Come back later in the afternoon, and you'll find that if you returned to the same spot, you'd be standing in the hot sun.
The shift in the light beams hitting the middle object, in this example the big shade tree, has cast the shadow in a completely different spot. So, shadows are created by light.
The source and angle of the light source dictate how intense and how large the shadows are. Keep in mind, the third surface where the shadow is cast will also affect how vivid the shadow is.
Shadows on a smooth, white wall will be more distinct from shadows cast across a dull grass field. Shadows have always been a part of our lives, and they always will be, as long as there's a big source of light.
Sometimes your shadow will seem to chase you. But don't worry; it's not a scary demon trying to capture your soul. We all cast a shadow, as long as we're placed between a light source and an object.
We just wonder whether Punxsutawney Phil is actually shadow superstitious. He may have no care about projecting the weather at all. He just thinks his shadow is chasing him, so he flees back down into his hole.