Space: the final frontier.
It lies beyond an invisible line, high above the earth, that so few men (and even fewer women) have ever crossed.
It's a mystery to most, but also a source of constant wonder and inspiration.
But where exactly is space? Where do we stop and where does it begin? At the Kármán Line apparently, though you'd be forgiven for never having heard of it. It's the name of that invisible line, high up in the sky, which acts as a (sort of) boundary to separate us from everything else.
So how high exactly is this boundary? The Kármán Line is at an approximate altitude of 100km (328,084ft) above the earth – not the kind of place you want to be if you suffer from vertigo.
It's probably worth noting that the Kármán line isn't actually a real line. You can't see it – it's not, in the technical sense, actually there. It's a measurement of distance, a theoretical spherical boundary where our planet's atmosphere stops and the rest of the universe begins.
(A quick aside: science boffins will know that the earth's atmosphere doesn't actually stop at a certain point, but rather gets progressively thinner the higher you get. But as we're straying into seriously technical territory here, it's probably best to leave the explanation at that.)
So what's it all about then, this Kármán line? Well for a start it was named after Hungarian-American mathematician, aerospace engineer and physicist Theodore von Kármán (who appears to have been a very clever chap). Kármán calculated that above an altitude of around 100km the atmosphere becomes too thin for aeronautical purposes (that's flying to you and me).
He also worked out that at this line (or at least around it – the measurement is not exactly 100km, but it was decided that a nice round number would be easier for everyone to remember) planes would have to "fly faster than orbital velocity in order to derive sufficient aerodynamic lift". At least, that's how Nasa's website explains it.
The Fédération Aéronautique Internationale (FAI), the internationally-recognised body for recording aeronautic achievements which has 100 member countries, recognises the Kármán Line as an altitude of 100km and so it has become an accepted boundary to space for the purposes of world records and many treaties.
Why are we talking about it now though? It's a good question. Usually the Kármán Line doesn't come up in everyday conversation, unless that is you're an astronaut or just really, really into space facts.
This week though, we were all getting excited about Sir Richard Branson's commercial space flights, which just so happen to venture over the 100km altitude mark, to about 350,000ft. That means, in essence, that the Virgin Galactic flights will cross the Kármán Line into space.
Presumably, for the 500 or so people who have already paid $200,000 for their space flight ticket, this is a very exciting fact.
The Kármán Line
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