As the ISS orbits the Earth in 90 minutes, there is no 24-hour rhythm of day and night that we on Earth are accustomed to. During one orbit, The ISS is in the sunlight for 45 minutes and for another 45 minutes in the Earth’s shadow during one orbit. Despite this, astronauts try to keep an artificial 24-hour rhythm as close as possible to what they are used to on Earth. By using GMT as a reference, they try to get eight hours of sleep during “night-time” and to work eight hours during weekdays. The rest of the day they spend eating, exercising, relaxing and having fun.

Astronaut Philippe Perrin floats near the Microgravity Science Glovebox in the Destiny laboratory on the ISS.

On Saturdays, the astronauts usually work a fourhour day, while Sundays are their day off. Sometimes, though, there are experiments to be checked and maintenance work to be carried out.