It has been ages since we learned about the human body. This little lesson was long overdue. Considering how easy it was to put together, I'm embarrassed we haven't explored the human anatomy more.
I think the eyes are fascinating - the way the pupils open and close to allow in the right amount of light, the way we see everything upside down but our brain flips the image right-side up, how our eyelashes are a defense mechanism to keep dust and dirt out, the science behind tears - all of it is amazing!
If your child hasn't figured out how cool our seeing mechanisms really are, this little experiment will convince them in less than a minute!
What You Need
Timer or watch with a second hand
Cut several star shapes out of the colored papers. Cut rectangles out of the colored paper too. You'll be putting the stars in the center of the colored rectangles, so make sure they're big enough. Attach the stars making various color combinations. Use a marker to make a black dot in the center of each star.
Now make a small black dot in the middle of the white paper.
Make an Afterimage
Now pick one of the colored rectangles and put it side-by-side with the white paper.
Set a timer for 30 seconds and stare at the black dot inside the star on the colored paper. When the timer goes off, switch your gaze to the black dot on the white paper.
Like magic, you'll see the ghosted image of the star you stared at, but the color will not be the same. It will be the complementary color. This is an afterimage.
Try staring at different colored stars. What color is the afterimage?
How and Why It Works
At the back of the eye, in the retina, there are two types of photoreceptor cells - rods and cones. These cells communicate color to the brain.
When you stare at the star for a long time, the cones and rods become tired. The result is an afterimage.
This great activity came from Karin Halvorson's extraordinary book Inside the Eyes. It's loaded with details and definitions, but presented in such an engaging way, kids are bound to be drawn in. The activities that support the information are interesting, use many everyday objects you're likely to already have on hand, and truly make learning hands on.
Want to see more afterimages? Check out this great book by Eric Carle!