By the Numbers: Astronaut Scott Kelly's Year in Space

— -- U.S. astronaut Scott Kelly will return to Earth this week after spending a year on the International Space Station.

For most of us earthlings, 340 days in space is pretty hard to imagine. It entails:

1. 143,846,525 miles of space travel
2. 5,440 orbits
3. 10,260 sunrises and sunsets
4. 640 hours on a treadmill to stay in shape
5. 20 medical tests

The sunsets seem to be a favorite for Kelly, 52, who has become known for posting beautiful photos of them from orbit.

This is Kelly's fourth mission, bringing his lifetime total to 520 days in space. NASA hopes the medical tests conducted on Scott Kelly and his twin brother, retired astronaut Mark Kelly, over the course of the mission will help them understand the effect of space travel on the body.

Scott Kelly's journey home started Monday when he handed over command to fellow astronaut Tim Kopra.

Kelly is expected to land in Kazakhstan tonight and return to Houston Wednesday.