I've loved airplanes for as long as I can remember, but it wasn't until my late 20s that I started training to become a commercial airline pilot. My adult life before then consisted of a master's degree and about a third of a PhD (I like to say I did the ‘P'), followed by a stint as a management consultant — career tracks that at least allowed me to fly regularly as a passenger, one usually too excited by the window seat to sleep.

I often regret my late start as a professional pilot. Many of my colleagues started to fly as much as a decade earlier than me, and will have many more years of work they truly love. If there's an upside to starting late, though, it's that I'm still utterly amazed by many things about my professional world — by which I mean both aviation and the planet I'm paid to fly a 747 over and around.

I decided to write Skyfaring, a book about flying, in order to set down for myself some of the remarkable details of the job I'd dreamed of since childhood. I guess I hoped, too, that these details would be of interest to readers who travel so often that flight has become an uninteresting experience for them. Here are six of the more amazing things I've learned, or relearned, in the 15 years that I've been flying.

1) Our world is round

This is told or demonstrated to you as a child and then … well, it's not something you forget, of course. But it's something that I, at least, put in a box filled with facts that I know about the world, and that I may even know how to prove, but that I don't really experience or have reason to think about when I drive to the supermarket or go for a run through the woods.

Since I became a pilot, though, the roughly spherical shape of the earth has become something that I interact with, and even see, much more directly.

A great circle route is the shortest path between two points on a sphere — imagine extending a string between two cities on a desktop globe. In the northern hemisphere, these routes, modified by the wind and other considerations, often take us far closer to the North Pole than most of us are likely to otherwise go (here's a fun great circle mapping tool to play with).

For example, on flights between London and Los Angeles, we typically cross Greenland and icy Hudson Bay (where Hudson himself was abandoned, after a mutiny). Places that, imaginatively at least, seem entirely at odds with the temperate cities we're flying between.

When I started flying routes like this regularly, my intuitive sense of the planet changed completely. In my employer's flight planning office, surrounded by banks of humming computers, stands a pleasing relic of a former age of flight planning: a huge globe with — yes! — a string attached to it. That's basically what my mental map of the world feels like now.

The curiosities of light and darkness on long-haul flights offer additional, quite beautiful clues to our planet's shape. On summer "overnight" flights between London and Tokyo, for example, the sky may never get dark. Instead, the sun will remain up, moving behind us and then around, across the north of the sky, round and round until it meets us in the east, at our morning appointment in Japan. And when we see the sun due north of us, and wonder whether it is yesterday (or tomorrow?) that we see over the top of the world, the only way to make sense of it all is to picture something round — an apple, say — slowly turning in the beam of a flashlight.

By the way, at dusk or dawn (which can last for hours in an airliner) you may see a clearly delineated, barely curved shadow on the sky above the horizon. That's the shadow of the earth on the sky — one of the few opportunities, for the non-astronauts among us, to observe more or less directly the shape of our planet.

2) Most of our overcrowded, over-stressed planet is … uninhabited

The American nature writer Barry Lopez wrote that the far North reveals "in startling ways the complacency of our thoughts about land in general". I would say that long-haul flying has a similar effect.

I grew up in a small town in New England, not far from a handful of medium-sized cities such as Albany and Hartford and a few hours from big urban centers like Boston and New York. I suppose I learned a little about biomes and geography in high school science classes. But my fundamental, experienced sense of the world was based, unsurprisingly, on what I saw: a mix of farms, forests, towns and suburbs, with the occasional patch of wilderness or big city, and beaches somewhere along the edge. That's the world that many other Americans know, too; for many of us, indeed, it is the world.

It was certainly my world. Or at least it was until I became a long-haul pilot. Suddenly, as part of my work, I started spending long hours over Siberia, the Sahara, northern Canada, and central Australia, over tundra or taiga, deserts or towering snowy peaks, over vast lands that are only barely inhabited; and of course, entire days or nights over the waters that cover around 70 percent of the earth. A few years ago I came across a fascinating statistic I made certain to include in my book: that the portion of the earth's surface on which an unclothed human could survive for 24 hours is around 15 percent. I don't know how accurate that number is, but from the cockpit of a 747 it sounds (and certainly looks) about right.

It's a particularly odd thing to contemplate at a time when environmental concerns have never been greater. In the cockpit, at night, up-shining cities are among my favorite sights. But over most of the world, sailing under the dome of stars, we see only the occasional light below us, if we see any at all.

3) The weight of a plane is the main variable in how it feels to fly

I'm occasionally asked if one 747 feels the same as another. It does. But the feel of a plane changes with its weight. And the weight of a jet varies greatly, both between flights and during a flight.

A 747 flying from the East Coast to London — with not many customers on board, say, and not too many boxes of lobsters or advanced medical equipment (if we're departing from Boston!) in the cargo holds, and with the fuel tanks only a third full for this relatively short flight — seems to practically jump off the runway, and it's light to the touch once we're in the sky. On the other hand, a fully loaded jet leaving Singapore for a long flight to London, with enough fuel to fight the winter headwinds the whole way, takes much more power and runway to get airborne, and it has a pleasant, quite stately feel in our hands.

Before I became a pilot it also never occurred to me that a plane might lose a third or more of its weight between takeoff and landing. That that jet leaving Singapore might start the night and its flight at 390 metric tons, and reach morning in London at 250 tons — the difference being the fuel burned along the way. Throughout the flight, then, the feel of the jet, as well as other characteristics such as the most efficient speeds and altitudes to fly at, are changing. It's no surprise, then, that entering the aircraft weight into the flight computers is one of our most critical and rigorously scripted pre-flight procedures.

4) There are rivers in the sky

It's easy to forget, when you're in your backyard under clear skies on a windless day, that the world above you is almost certainly in motion. Indeed, in an airliner at high altitude, it's a very rare moment when the weathervane-like digital pointer on our main navigation screen indicates no wind at all. Through this already-moving landscape of air cut the jet streams — vast, racing rivers, howling, if only we could hear them, at 100 or 200 miles per hour or more. These jet streams strengthen or weaken; they migrate and twist over the planet. I'm a fan of the maritime world and of its charming echoes in the aeronautical realm (think of terms like deck, air-liner, purser, port and starboard…) And so I find it endlessly pleasing that as the winds and currents shaped the journeys of ships in the old days, similarly today, over the Atlantic, pilots routinely sail hundreds of miles out of their way to avoid a headwind, or to catch a tailwind that will speed us across the sea.

In my book I speculate a little on how culture and mythology might have accounted for the jet streams, if only we could see them. Although they're among the most physically dramatic phenomena on earth, they were all but unknown to us until the age of aviation. How might we have worshipped them, or beaten drums to summon or scatter them, if they were a prominent feature of the daylight sky? Or if these air-rivers' remarkably clean-cut edges or shimmering, racing depths were somehow visible at night? At the very least, I suggest, we would have named them. Maybe someday we will.

5) Geographically speaking, the sky is like a whole other planet encasing our own

Wherever you're reading this, the air above you is charted and named. It is its own total, round world, complete with landmarks ("airmarks," perhaps we should call them) and borders, paths, and an ever-deeper history. To discover this world, and to work in it, is one of the great joys of being a pilot. Two features of particular interest are waypoints, which are named positions in the sky, sometimes connected to one another to form airways; and what I like to call sky countries, the enormous, often beautifully named divisions of the planet's airspace which only occasionally line up with the earthly borders below.

Waypoints typically have five-letter, pronounceable names, so they can be easily articulated and understood over the radio. The names are sometimes random, but many, especially American ones, are not, which is one of the most fun aspects of flying over the United States. Just a few examples: Near Boston is NIMOY — Leonard was born in Beantown. Near Detroit is MOTWN. Near St Louis, for some Eurythmics-related reason I couldn't for the life of me pin down while researching my book, are ANNII and LENXX. There are hundreds of good ones.

"Sky countries" (a loose term I use in the book for various types of administrative divisions of airspace) are a more sublime wonder. Their borders define the geography of the sky, and our crossings of them compose the rhythm of a long-haul flight. Every long-haul pilot knows the sky country of Maastricht. Though named for a small Dutch city, it covers some of the planet's busiest upper airspace, that over northwest Europe. Boston covers New England, appropriately enough, but most of New York state, too. Farther afield are Dushanbe and Arkhangelsk, Magadan and Petropavlovsk-Kamchatsky. Names that still seem, at least to a guy from a small town in New England, almost impossibly exotic. It's a tough call, but my two favorite sky countries are in Africa: Dakar Terrestre and, just off the West African coast, its sky-sibling Dakar Oceanique.

6) Everywhere is going on at once

I came up with the term "place lag" to refer to the way that airliners can essentially teleport us into a moment in a far-off city; getting us there much faster, perhaps, than our own deep sense of place can travel. I could be in a park in London one afternoon, running, or drinking a coffee and chatting to the dog-walkers. Later I'll go to an airport, meet my colleagues, walk into a cockpit, and take off for Cape Town. I'll fly over the Pyrenees and Palma and see the lights of Algiers come on at sunset, then sail over the Sahara and the Sahel. I'll cross the equator, and dawn will come to me as I parallel the Skeleton Coast of Namibia, and finally I'll see Table Mountain in the distance as I descend to the Mother City.

Then, less than an hour after the long-stilled wheels of the 747 were spun back to life by the sun-beaten surface of an African runway, I'll be on a bus heading into Cape Town, sitting in rush hour traffic, on an ordinary morning in which, glancing down through the windshield of a nearby car, I'll see a hand lift a cup of coffee or reach forward to tune the radio. And I'll think: All this would still be going on if I hadn't flown here. And that's equally true of London, and of all the other cities I passed in the long night, that I saw only the lights of. For everyone, and every place, it's the present.

I know, this sounds obvious. But when I started to fly it became, like the roundness of the earth, the sort of fact I came to really feel as well as know. In the book I compare it to a geographic form of the feeling you sometimes have when looking at an old photo, when you suddenly realize that, at the moment the photo was taken, it felt as much like the present to everyone in it as the present moment does to you. There's a passage in A Tale of Two Cities that nails this heady sense of all the world's lives and moments: "A solemn consideration, when I enter a great city by night, that every one of those darkly clustered houses encloses its own secret; that every room in every one of them encloses its own secret…" It's a sentiment I recall when I arrive in Delhi, say, at 1 o'clock in the morning, and drive into the vast, quiet metropolis, where nearly everyone is sensibly sleeping. It's something I ponder, too, when I'm flying at night, and I suddenly see the lights of a town far below, and then watch as the dark earth they're resting on slowly turns away.

Mark Vanhoenacker is a pilot and writer. He flies the Boeing 747 from London to major cities around the world. He is the author of Skyfaring: A Journey with a Pilot.

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