Expedition 42 astronauts on the International Space Station enjoying their Thanksgiving meal in 2014.
Clockwise from top: cosmonauts Anton Shkaplerov and Elena Serova, NASA astronauts Terry Virts and Butch Wilmore and ESA astronaut Samantha Cristoforetti with cosmonaut Alexander Samoukutyaev centre.
From the brain’s point of view, living in space is very stressful. The signals from an astronaut’s body in space go haywire in weightlessness. The inner ear reports that it is falling, but the eyes show that nothing is moving.
As fluid shifts to the head, the brain usually interprets this extra pressure as a sign it is upside down – but in space there is no up or down. The body clock might signal that it is tired after a day’s work on the International Space Station, but astronauts experience 16 sunrises and sunsets every 24 hours.