Twice a year, near the winter and summer solstices, the orbit ofspace station nearly parallels the terminator—the fuzzy line separatingday from night on the surface below. For a period of about a week, welive in what seems like perpetual twilight, being in neither fulldaylight nor full night. Our orbit follows the terminator, so that spacestation is constantly sunlit. From this vantage I can see both day andnight simply by swiveling my head from left to right. But the night isnot really dark, and the day is lit by low-angle rays from the Sun.
Geographic relief casts long shadows, and imparts stark contrast tofeatures that are typically overlooked. Small ripples in sand dunes makehigh contrast striations across the bright desert landscape that looklike Nature’s way of drawing with pen and ink. Geographic relief playstricks on you. First you see the Grand Canyon as this deep scar.Blink your eyes and it is now a rippling bump. Thunderstorms castshadows that look like they come from some new type of ray beam weapon.Airliners, their path defined by contrails, leave glimmering lines likesnail trails in the morning dew. The gardens of Earth appear to havequite an infestation of snails.
The Moon sets in a counterintuitive way. From this vantage it movesnearly parallel to the horizon. Once I saw it slowly set, only toreappear in a few minutes. The Moon was visible for nearly the wholeorbit.
The night side is equally fascinating. The atmosphere on edge glowswith a vibrant electric blue. Did van Gogh paint this scene? I can seeat least five, maybe six distinct layers of blue—perhaps a visualdisplay of the classic atmospheric strata. Just past the terminator,rays of sunlight can be seen projected above the darkened limb of theEarth.
The most striking aspect of our atmosphere is not the palette ofelectric blue colors but the thinness of it all. Our atmosphere is adiaphanous veil; thin, fragile, transparent, and the only thing thatprotects us from the harsh vacuum of space. Too much atmosphere, and theplanet is choked and suffocated. Too little, and it is exposed to theharshness of cosmic space. My vantage on the station gives me a deepappreciation of this fact.