(Curiosity) 62 miles from the end of the world

Take a deep breath.

Now, repeat.

It gets harder and harder to do that the higher you go, but there’s never a point where the atmosphere just stops. Like an aging celebrity, it just kind of faaaaaaades away….. which raises the question, where does the world end and space begin?

By convention, we call that the Kármán Line, which is 100 km. (62 mi.) above sea level. It’s named after Theodore von Kármán (1881–1963), a Hungarian-American aeronautical engineer who was the first to calculate that above this height the atmosphere is so thin that the speed necessary to maintain sufficient aerodynamic lift surpasses orbital velocity. In other words, at that point you may as well trade your wings for rockets.

For reference, we live in the troposphere, the portion of the atmosphere that extends to about 16 km. (10 mi.) above sea level — but only at the equator. At the poles, it ends a mere 8 km. (5 mi.) up. The stratosphere, where we send weather balloons and where we’d like to send our in-laws, extends from there to about 50 km. (31 mi.) above sea level — again, depending where you are on the planet. The mesosphere, where most meteors flare up, extends to about 85 km. (53 mi.) above sea level.

The thermosphere, which includes the Kármán Line, extends to about 690 km., or 429 mi. This is where most of our rockets go and where the International Space Station (400 km./ 250 mi.) hangs out, as well as the northern and southern auroras, which are at about the same height as the Kármán Line.

But “space” at that point is not a complete void. In fact, trace gases continue fading to about 10,000 km. (6,214 mi.) above sea level, which means the radius of the atmosphere is 50% larger than the radius of the Earth! (Mean: 6,371 km./ 3,959 mi., although it’s less at the poles and more at the equator.)

But then, even deep space isn’t a total void. There’s all kinds of stuff out there — dust, radiation, virtual particles, alien microbes, the remnants of Krypton, my hopes and dreams, etc. — it’s just that all that stuff is relatively far between, which is why everybody down here likes Kármán’s definition — except NASA, which actually puts the boundary lower.

What all that means is, if you take a map and draw a circle around your house with a 62-mile radius, everything outside it is further away than outer space. If you live in Los Angeles proper, you are closer to outer space than to San Bernardino, or even parts of Orange County. Where I live, I’m closer to outer space than to any major city by a factor of three.

Look up and think about that.