How High Is The Sky?

A view of the earth from space
NASA

So how thick is what we call sky?

Well, you'd think, looking up, that there's so much blue up there it's got to go on for hundreds and hundreds of miles.

But it doesn't.

Looking at this photo, you can see that the ring of atmosphere around the earth is cellophane thin...a wisp of gas.

It's a little thinner at the poles and thicker near the equator, but the "sky" is about 250 miles wide (or up), the distance, roughly, between New York City and Washington, D.C.

Which means — if Amtrak could run a "Sky Chief" straight up and handle the spin — you could chug to the very edge of space in three and a half hours.

But that's not the cool part.

In the 1940's, the great illustrator Eric Sloane did a cross-section of the atmosphere that surrounds our planet. He observed that we live in a sea of air, and we, like lobsters, are at the bottom:

Drawing number 9 from Eric Sloane's Weather Book
Eric Sloane/Dover Publications

Then he took a closer look at that bottom piece, the first three miles, which is called the "troposphere," the slice of sky that contains weather.

When most of us look up, we don't think of the thinning blue sheet of gases that taper off into space, we think of storms and clouds and rain and tornados and lightning; the stuff that makes looking up interesting. For us, sky equals weather. So, Eric Sloane slyly switched the question "How High Is the Sky?" to a more user friendly "How High is the Weather?" His answer I found deeply surprising. We live in a compact neighborhood. Everything we see above us, the vast stretches of clouds, no matter how high they look, are not that far away — no further than the horizon. Ours is a geometrically small world, says Eric. Here is his startling (to me) formula:

Drawing number 12 from Eric Sloane's Weather Book
Eric Sloane/Dover Publications

...What's more, Sloane wrote that about half of all the air (the gas molecules we breathe) and 90 percent of the moisture is crammed into the first 18,000 feet of sky. That's the lowest layer of the first layer of sky, so the habitable zone of air is extraordinarily narrow. Like lobsters, we are stuck at the bottom of our ocean.

However, as the drawing below shows, folks who live at the equator get twice as much "sky" above them and therefore — if you believe the two cloud pictures on the lower left — Ecuadorians and toucans get to look at taller clouds than Siberians and polar bears.

Drawing number 13 from Eric Sloane's Weather Book
Eric Sloane/Dover Publications

These images come from Eric Sloane's Eric Sloane's Weather Book. Like Donald Trump, Eric didn't mind multiple mentions of his own name, but boy could he draw. This book was great when I was a boy. And it's just as great today.

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