• Question: when does sky become space?

    Asked by anon-188322 to Warren, Shanti, Pizza Ka Yee, Paul, Nadine, Alex on 7 Nov 2018.
    • Photo: Alex Reid

      Alex Reid answered on 7 Nov 2018: last edited 7 Nov 2018 5:50 pm

      Hi thanks for your question. This is not my area so I was very tempted to first say ‘at night’! However, jokes aside, I then remembered I did see Tim Peake (the first British astronaut on the ISS) speak when he came to visit us at the University of York. If I recall he got this exact same question, and I (think) he said it space is most commonly said to start at 100km above sea level. There are different opinions on when space actually starts though, which brings up a more general issue we often face as scientists. In order to measure things we have to define them, and there are lots of different ways you could define the sky and space. That 100km number seems nice and round number, so it may have been decided more out of convenience than due to a specific distinction between sky and space.

    • Photo: Paul Matusz

      Paul Matusz answered on 11 Nov 2018:

      Hi , I think this question is directed to physicists.. 😉

    • Photo: Nadine Mirza

      Nadine Mirza answered on 15 Nov 2018:

      Hey bekki!
      I believe, as Alex said, it is 100km above sea level and this is called the Kármán line, after the physicist Theodore von Kármán. He discovered that at this height the atmosphere becomes to thin for a standard air craft to fly. To be able to fly at this height an aircraft would have to be moving faster than orbital velocity to have enough lift under its wings to keep it in the air. Orbital velocity is the minimal speed required to keep something in orbit.
      So essentially, to get past this line you need to upgrade yourself from an aircraft to a spaceship.

Comments