What Do You Mean the Sun is Already Set?

Objective: To understand why the sun can be seen a few minutes before it actually rises and a few minutes after it sets below the horizon.

Standards: Objects in the Sky (sky object properties, locations, and movements), Earth in the Solar System (position, properties of the sun and earth), Light, Heat, Electricity, and Magnetism (light refraction), and Transfer of Energy (light transmission, refraction).

Materials: a tightly covered jar filled completely with water, unshaded lamp, and a few textbooks.

Procedure: (1) Place a stack of a few textbooks on one side of a table. (2) Put the lamp behind this stack of books. Make sure that the stack of books is high enough so that you cannot see the light from where you are sitting or crouching at the table. (3) Place the filled jar on its side in front of the stack of books. The jar should be about level with the stack of books so you will probably need to place the jar on top of a smaller stack of books. (4) Remaining eye level with the jar and stack of books, look at both of them.

Science Behind It: Even though the level of the light is below the stack of books, you should still be able to see the light. This happens because the rounded side of the jar acts like the Earth’s atmosphere by bending or refracting the light. By doing this, it brings the light into view. If this does not happen, carefully adjust the level of the jar so this can occur. In refracting the light, the jar creates a mirage similar to those observed in the desert, at sea, on hot pavement, and in the sky. The light waves from the rising or setting sun must pass through a greater thickness of atmosphere than they do at noon. Because of this, the rays of sun are bent and at sunrise when the sun appears to moving up and over the horizon, an image or mirage of the sun can be seen on the horizon before the sun actually reaches it. Similarly at sunset, we continue to see an image of the sun briefly after the sun has technically set.