How do you sleep in zero gravity?
The crew on the International Space Station (ISS) kip in sleeping bags attached to the wall with Velcro or cables. On average, crew members get six hours of sleep a night, but as there is no ‘up’ or ‘down’ in weightless conditions, many suffer from sleep disorders. These are made worse by the fact that the ISS experiences 16 sunrises and sunsets every 24 hours. This frequent switching between day and night disturbs the production of the hormone melatonin, which regulates our circadian rhythms. Another cause of sleep deprivation are solar lightning strikes, which the astronauts can still see with their eyes closed.