An astronaut travels at 0.93c. As one hour passes for her how much time passes for an observer on earth?

Answer 1

In general, suppose you have a spaceship going at velocity v relative to Earth.

For an observer on Earth, clocks in the spaceship's frame of reference will appear to run slow by the factor

√(1 - (v/c)²)

So the observer on Earth needs to wait 1/√(1 - 0.93²) = 2.72 hours to observe clocks in the

spaceship's frame of reference to advance 1 hour.

The situation is symmetrical: The astronaut sees the Earth's clocks as running slow

and it takes her 2.72 hours to see the Earth's clocks advance 1 hour.