a or more in tly namedbut very erratic temperatures can vary by a to nig must be said t “temperature” at suc becomes a someional concept. temperature is really just a measure of tivity of molecules. At sealevel, air molecules are so t one molecule can move only tiniest distance—aboutto be precise—before banging into anotrillions ofmolecules are constantly colliding, a lot of  gets exc at t of t fifty miles or more, t any t and act. So alteractions bettle  transference. tellitesand spaces  any man-made objectorbiting at t level  into flame.

    Even so, spaceso take care in ter atmospicularly on return trips toEarttle Columbia demonstrated all too tragically in February 2003.

    Altmosp comes in at too steep an angle—more t 6 degrees—or too sly it can strike enougo generate drag of anexceedingly combustible nature. Conversely, if an incoming ve ttoo s could o space, like a pebble skipped across er.

    But you needn’t venture to tmospo be reminded of ime in a lofty city  o rise too many t from sea level before your body begins toprotest. Even experienced mountaineers, s of fitness, training, and bottledoxygen, quickly become vulnerable at  to confusion, nausea, exion, frostbite,ite, and a great many otumbling dysfunctions. In aic s o it  designed to operateso far above sea level.

    “Even under t favorable circumstances,” ter ten ofconditions atop Everest, “every step at t altitude demands a colossal effort of  force yourself to make every movement, reacuallytene