Meet the Time-Travelling Twins
When astronaut Scott Kelly got back from his year-long stay on the ISS, he was technically 0.01 second younger than his twin brother Mark Kelly who stayed on Earth. This is because of the combined time-dilation effects of low-gravity and high-speed.
1.) The further away you are from Earth, the slower time passes, because there’s less gravity.
2.) Time also moves slower when you move faster and the International Space Station is travelling at 5 miles per second.