On Saturday, I introduced you to the Kármán Line. It is named after Theodore Von Kármán, a Hungarian physicist who made a lot of contributions to the fields of aeronautics (think airplanes) and astronautics(think spaceships). He spearheaded a study that tried to determine an altitude where planes could no longer fly, or at least would have to go so fast as to essentially reach escape velocity. He came up with a number that rounded off to 100 kilometers (62 miles) above sea level. That figure has almost been universally accepted as the "start of space." Works for me.

Below that boundary, you essentially have all the air around the earth. So here's an interesting question: At what altitude are you halfway through the atmosphere?

Seems like a pretty simple answer at first blush. If the atmosphere is 62 miles thick, then the halfway point must be 31 miles up. But that doesn't work, and on Tuesday I'll tell you why.

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