ESA astronaut Alexander Gerst working on an experiment in the microgravity glovebox on the International Space Station. On his forehead he has a specially-developed thermometer called ThermoLab that measures his temperature continuously.
He Tweeted this image during his six-month Blue Dot mission with the text: "Dual Science – wearing a circadian rhythm sensor while working in the glovebox."
The International Space Station is a collaboration between five space agencies, sharing resources and time to run out-of-this-world experiments.
Read more about Alexander’s six-month Blue Dot mission at http://www.esa.int/Our_Activities/Human_Spaceflight/Blue_dot
Follow Alexander here: http://alexandergerst.esa.int/