If your students have ever watched a sunset (or a sunrise), they may have noticed (as you surely have) that the sun is actually visible for a few minutes after it sets (and a few minutes before it rises). “What kind of sorcery is this?” your more, shall we say, interesting students may ask. (*cough* Kevin! *cough cough*) It’s not sorcery, of coursery—it’s science!
Here’s a handy dandy lil’ experiment that will show them how this phenomenon shakes out.
A Jarful of Sunshine
For this Demo Science science demo, you’ll need a jar with a tight-fitting lid, enough water to completely fill said jar (like, right to the tippy-tip-top), a lamp sans shade, and a few textbooks.
Stack your textbooks on one side of a table or desk, then position the lamp behind the books (i.e., on the opposite side of the books from your students). Turn the lamp on and make sure that your book pile is tall enough that you can’t see the lightbulb from the low(er) viewpoint of your students (crouch or squat down to stinky kid level to get a proper view).
Then, place your jar o’ water on its side in front of the books (a pencil on each side should stop it from rolling about your tabletop). The jar should be level with the stack o’ books, so you might need a few more books to prop up the jar.
Stay eyelevel with the jar and books, look directly at both, and observe. If everything’s set up right, you should still be able to see the light, even though it’s “blocked” by the books. How the science does that happen?
Refraction in Action, Jackson
The rounded sides (side? it’s only one all the way ‘round, really) of the jar acts as an analog of Earth’s atmosphere, refracting (bending) the light and bringing it into view. This refraction causes a mirage type thing, not unlike those you see in the desert, at sea, or on the highway on hot day.
A rising or setting sun shoots its rays to the earth at sharp angles, instead of the full thickness of our atmosphere, as it does at noon. This bends the rays of the sun at rise/set, making it possible to “see” the sun before it rises/after it sets.