Question

Spaceship flies past mars with a speed of 0.985c rela- tive to the surface of the planet. when the spaceship is directly overhead, a signal light on the martian surface blinks on and then off. an observer on mars measures that the signal light was on for 75.0 ms. (a) does the observer on mars or the pilot on the space- ship measure the proper time?

Answer 1

The proper time would be the time measured in the rest frame of the event, so in this case the observer on mars would measure the proper time.