An astronaut set out in a spaceship from Earth orbit to travel to a distant star in our galaxy. The spaceship travelled at a speed of 0.8 c. When the spaceship reached the star, the on-board clock showed the astronaut that the journey took 20 years.
An identical clock remained on Earth. What time in years had elapsed on this clock when seen from the astronaut’s spaceship?
An identical clock remained on Earth. What time in years had elapsed on this clock when seen from the astronaut’s spaceship?