Astronauts on the International Space Station age slightly slower than people on Earth.

This phenomenon is rooted in Albert Einstein's 1905 theory of special relativity, which dictates that time is not absolute. When an object moves at high velocities relative to another observer, time for the moving object slows down. The International Space Station (ISS) travels at approximately 7.66 kilometers per second, or roughly 17,130 miles per hour, to maintain its orbit around Earth.While velocity makes the astronauts younger through velocity time dilation, gravity plays a conflicting role. According to general relativity, time moves faster in weaker gravitational fields. Since the ISS is further from Earth's mass, time should technically speed up for astronauts. However, at the ISS's specific altitude of about 250 miles, the effects of high speed outweigh the effects of reduced gravity.The net result is that time passes slower for the crew. For every six months spent in orbit, an astronaut ages roughly 0.005 to 0.007 seconds less than a person on the surface. This effect has been precisely measured using atomic clocks, which are accurate to within billionths of a second. Russian cosmonaut Sergei Krikalev, who spent over 803 days in space, is technically 0.02 seconds younger than he would have been if he never left Earth.These calculations are vital for modern technology like Global Positioning System (GPS) satellites. GPS satellites orbit much higher than the ISS and move at different speeds, meaning their internal clocks must be constantly adjusted for relativity to ensure location accuracy. Without accounting for these tiny fractions of a second, GPS coordinates would drift by several kilometers every single day.