“I have a little shadow that goes in and out with me…”, so goes the poem ‘My Shadow‘ by Robert Louis Stevenson. My 2-year-old likes to chase her shadow when we go out walking but my elder daughter wants to know where shadows come from…
The key to understanding shadows is light, because shadows are made when something blocks out the light.
You might remember from my post about rainbows that light is made up of waves and that light-waves travel in straight lines. So, if something gets in the way of those light-waves, then they will stop travelling. If that happens, you will see a dark patch where there is no light and we call this ‘no light’ a shadow.
You can test this out by doing an experiment: Find a torch and take it into a dimly lit room. Point the torch at the wall and you’ll see a circle of light coming from the torch. Put your hand in between the torch and the wall, you’ll see a shadow of the shape of your hand on the wall. That’s because the light from the torch can’t travel through your hand, so there is a patch of ‘no light’ or shadow where the light has been blocked.
The same thing happens outside when the Sun is shining. You might have noticed your shadow on a sunny day? If you stand with the Sun behind you, you will see a shadow of the shape of you on the ground. That’s because you are blocking the light from the Sun from getting onto the ground in front of you.
So, a shadow is made when something gets in the way of lightwaves!