1. How many seconds does it take light to get from the Sun to Earth (the distance from the sun to the earth is 150000000 km)? How many minutes?

2. When the Apollo spacecraft landed on the moon, astronauts placed a reflector on the surface so scientists on Earth could aim a laser beam at the reflector. When they did this, they measured the time for the light to go from Earth to the moon and back to be 2.56 seconds. By doing this, they were able to calculate accurately the distance between the moon and Earth. What is the distance in kilometers? In miles?

3. In 1989 the spacecraft Voyager I passed the planet Pluto, and headed out of our Solar System. Pluto is about 3.6 billion miles from Earth! As it left the solar system, Voyager I was still sending radio signals (which travel at the speed of light) back to astronomers. How many minutes did it take the radio signals from Voyager I to get back to Earth?

4. Our fastest spacecraft are able to travel at 70,000 mph. How long would it take such a spacecraft to travel a distance equal to one light-year?

5. Telephone companies now use light to send phone conversations over fiber optic cables. Suppose you were talking to someone on the other side of the planet, say in Japan, about 12,000 miles away. How long would it take the light signal to get there?

6. Before fiber optic cables were invented, engineers tried to send telephone calls between continents by bouncing microwaves (also a form of light!) off satellites orbiting 22,600 miles from Earth. How long would it take the microwave signal to go up to the satellite and back?

7. Human ears are sensitive to time delays greater than 0.1 seconds. Can you explain why telephone companies decided to replace the microwave satellites with fiber optic cables? (Hint: why did people complain about the phone service from the microwave satellites?)

8. The FUSE satellite will be operated by a control center at Johns Hopkins University in Baltimore, Maryland. The satellite will be controlled by a ground station antenna located in Puerto Rico, 1800 miles from Baltimore. The FUSE satellite will orbit 480 miles above Earth. Do you think the astronomers at Johns Hopkins will notice any delay when they communicate with the satellite? Give evidence to support your answer.