Chris Hadfield became famous not just for doing his job but because he told the world all about it, as he orbited the Earth 250 miles (400km) above its surface.
While he was commander of the International Space Station (ISS), Colonel Hadfield estimates that he took 45,000 photographs of the Earth. He tweeted a number of these, as well as videos of him brushing his teeth, washing his hands and singing David Bowie's Space Oddity (pictured, right).
And although his Instagram account describes him as a "former Canadian astronaut and spaceship commander" and his Twitter handle is @Cmdr_Hadfield, Colonel Hadfield also refers to himself as a teacher.
"When you are asked to do something really rare or unique on behalf of other people, you are basically an emissary of other people," he tells TESS. "You are seeing the world in a way no one else gets to and starting to understand what it's like to meet the planet itself. It is a really important part of that responsibility to share it in the best way you can."
He estimates that he has spoken to at least 1,000 schools over his 35-year career as an astronaut. "I've been a teacher my whole life," he says. "I've taught people to fly, I've taught spacewalking, I've taught leadership, I've taught crew resource management, I've taught robotics and I'm a professor at the University of Waterloo in Canada.
"I tie in using Skype to talk to elementary and middle schools on a weekly basis with schools primarily across Canada - we call the programme `On the Lunch Pad'."
Colonel Hadfield recently toured the UK promoting his latest book, You Are Here: around the world in 92 minutes. As he visited bookshops and schools everywhere from Glasgow to Bath, he also found time to answer pupils' questions through social media (see panel, opposite).
One such question was: "What was the most difficult thing about adjusting to life in space?" The answer? "Tying your laces on your trainers. Because both hands and one foot are busy, so there's nothing to keep you stable and you float all around the spaceship."
This small, quotidian annoyance demonstrates that, despite having an extraordinary job, astronauts are just like the rest of us - something that Colonel Hadfield is keen to underline to the students he engages with.
"I think invariably young people have more interesting questions than adults," he tells TESS. "The reason being that most adults have decided they are not going to fly in space, so questions are not particularly penetrating, whereas a young person still has it as a possibility so they are much more specific."
In his TED talk "What I learned from going blind in space" (bit.lySpaceTED), Colonel Hadfield speaks about when he first flew in space, in a 1995 space shuttle mission. Clad in his spacesuit and crawling into the spaceship on his hands and knees, he realised that what he had chosen to do when he was nine years old was now actually about to happen.
"You have taken the dreams of that nine-year-old boy, which were impossible and dauntingly scary, and figured out a way to reprogram your primal fear," he says. "That enabled me to come back with a set of experiences and a level of inspiration for other people that never could have been possible otherwise."
Colonel Hadfield has inspired thousands of children and adults, and his attitude to science education is optimistic. "Our level of worldwide scientific literacy has never been higher," he says. "When you look at the number of people who have access to education and access to the internet, it is tremendously enabling; anybody who has any curiosity can look up any fact they want to pursue. It really bodes well."
And, he adds, he will never forget his own inspiring teachers. "Every single one of us is for ever indebted to the people who have taught us," he says. "If someone has taken the time to teach you something, you now have a debt and you owe it to make sure that someone else gets an education as least as good as your own. It is the only way that we can have the quality of life that really enables people to succeed."