You are in a spaceship, traveling directly away from the Moon with a speed of 0.9c. A light signal is sent in your direction from the surface of the Moon.
(a) As the signal passes your ship, do you measure its speed to be greater than, less than, or equal to 0.1c?
(b) Choose the best explanation from among the following:
I. The speed you measure will be greater than 0.1c; in fact, it will be c, since all observers in inertial frames measure the same speed of light.
II. You will measure a speed less than 0.1c because of time dilation, which causes clocks to run slow.
III. When you measure the speed you will find it to be 0.1c, which is the difference between c and 0.9c?