Say what you’ll about death and taxes, but only two things are certainties on any given day: the sun is going to rise, and the sun is going to set. (Although that doesn’t technically, actually happen—rotation of the earth and all that. But I digress!) Some of your more observant students may have noticed that, at each sunrise and sunset, there are a few extra moments when the sun can be seen before it has actually crested, or after it has actually sunk behind, the horizon. How does that work? This handy dandy Demo Science science demo will help you explain this phenomenon to your charges.
Shine A Light
Let me start out by stating that this experiment is easier to prepare than to execute. Sorry. Anyway, supplies-wise, you’ll need a jar (with lid) completely filled—as in to. The. Brim—with water and tightly sealed, a lamp sans lampshade, and several books with which to create simple platforms. Also a table or your desk, cleared of obstructions.
Stack a few books on one side of the table, and put the lamp behind the stack (probably on the floor, because lamp) and turn it on. Make sure your stack o’ books is tall enough to completely obscure the light bulb, along with as much as possible of the light it gives off, from your view if you’re sitting on the other side of the table, say in a student’s desk.
Next, make another stack of books roughly the same height as and in front of the first—your stacks o’ books may need height adjustments to make this experiment work as it should, so be sure to have a few extras of varying thickness available.
Lay the filled jar on its side atop book stack #2, with its rounded edge toward the lamp (if the lamp is at the “North” end of the table, the ends of the jar should be aligned East-West). Have your students look through the jar to observe the light of the lamp. What do they see?
The Sunny Side of Science
Though it’s totally obscured by books, you should be able to see the light of the lamp. The rounded side of the jar refracts the light, just like Earth’s atmosphere does, bending it to make it visible “around” the obstacle.
The refracted light creates a mirage similar to those seen in deserts, on hot pavement, and in the sunset/sunrise sky. Because the sun is closer to the horizon at these times, and its light is coming in “sideways” (as opposed to from “above” as it does at noon, say), that light must pass through more of Earth’s atmosphere than it does at other times of the day. This additional atmosphere bends the sun’s rays, making the sun appear above the horizon before actual sunrise and after actual sunset.