1. At its closest approach (called "lunar perigee"), the moon is around 360,000 km from the Earth. If astronauts on the moon want to send a message to NASA via radio, how long will it take the message to reach mission control?

2. The farthest human-made object from the Earth right now is Voyager 1, a space probe that has left our solar system. It is currently almost 2 x 1010 km from Earth. How long would it take for NASA to send a radio message to Voyager 1 and hear a response? Remember that the radio signal has to reach Voyager 1, and then Voyager 1 must send its response back to Earth.

3. Galileo tried to measure both the speed of sound and light. He did this by standing on a hill while an assistant stood on another, far away hill that Galileo could see. Galileo made a loud noise, and when the assistant heard the noise, he made a loud noise back. Galileo timed how long it took for the returning sound to reach him, and then he calculated the speed of sound. Galileo tried to do the same thing for light by shining a lamp and having his assistant shine a lamp back at him, but Galileo was not able to calculate the speed of light. He thought it might even be instantaneous.

a. If the hills were 3 km apart, how long would it have taken Galileo to hear the returning sound? Assume the speed of sound is 340 m/s.

b. How long would it have taken him to see the returning light?

c. Why do you think Galileo could not calculate the speed of light?