Teaching Notes

To help students understand the time delay in Step 4, you can have each group simulate the transmission of radio waves to and from the Moon. Divide each group into two, separated by five or ten meters. Ask two students in each group to represent the radio waves. One student on “Earth” will whisper a few words to a “radio wave,” who will then walk to the “Moon.” In the same way, a reply reaches Earth, after a delay equal to the time for both students to walk the distance between the groups. Ask the students to compare this simulation to Galileo’s attempt to measure the speed of light (for Galileo, the delays were too short to measure). Play the video to allow students to make their observations.

Astronomical distances are certainly a difficult topic for students. Although the units of light travel-time are unfamiliar, they emphasize the great expanse of distances in space, with light-years separating us from the next-nearest star, compared to light-hours between us and the edge of the solar system. You can have the students set up a calendar for a light beam heading toward the next-nearest star. They can give the dates for the beam’s transmission on the Earth, the date the beam would go by the Moon, by the Sun, by Pluto, and finally the date it would reach the next-nearest star. (Of course the alignment of these objects is imagined.)