Light pollution is a well-recognized problem, severing human beings who live in urban areas (alas, the vast majority of us these days) from our primordial right to look up into the sky and gaze in wonder at endless twinkling points of light when the sun goes down. What if something was done about it? Certainly starting from the early 20th century we could envision an alternate history where greater care was taken to preserve the night sky for future generations to enjoy…a development that likely did occur in the science-fictional alternate history I write my stories in. What would that even look like?
A go-to gauge of how pristine or polluted the night sky is is the Bortle dark-sky scale, which ranges from Bortle 1 (excellent dark-sky site; e.g. Badwater Basin) to Bortle 9 (inner-city sky; e.g. Manhattan). You can dig into the details, but long story short: 80% of Americans today can’t even see the Milky Way from home, let alone in its full glory. Could this distressing situation have been prevented from coming about? Perhaps.
It’s well-known that lights that illuminate regions to the side and (especially) upward of the source are the worst contributors to light pollution; the universal adoption of opaque shields that ensure that the only light that escapes is pointed directly downward would cut light pollution substantially.
Less well-known is that broad-spectrum and especially white to bluish lighting is another contributor; light at higher frequencies (i.e. bluer colors) scatters more in the atmosphere, enlarging the characteristic light domes that make cities visible from dozens to even hundreds of miles away, and broader-spectrum bluer lighting interferes the most with human night vision. This is why dark-sky regulations historically prescribed sodium-vapor lighting for outdoor spaces: these lights emit only a very narrow spectrum, and the color they do emit is yellowish, helping to mitigate the effects of light pollution. LEDs have often been much brighter and broader-spectrum, but LED lights that replicate the characteristic yellow spectrum of sodium-vapor lights are available and used.
However, sodium vapor is not ideal; ideally the light would be not only narrow-spectrum, but the spectrum it emits would be red. Ideally deep in the red section of the visible light spectrum. With the advent of LEDs, lamps that emit only this sort of light have become cheap and readily available, potentially unlocking a full notch on the Bortle scale’s worth of improvement from even sodium lamps, if implemented universally.
In my science-fictional alternate history, LEDs become available early in the 20th century (thank you, Oleg Losev), so implementing such a regulation would be simple, especially if there was widespread voluntary public buy-in…which, courtesy of the space craze that goes global starting in the 1920s and 1930s, there just might be. The early advent of spacefaring civilization (the first man in space circa 1940, with lunar landings following circa 1950 and on to Mars circa 1960) as well as epic space-opera movies on IMAX-tier screens, among other factors such as space telescopes detecting all the hitherto-invisible planets of the Kuiper Belt and god-knows-how-many beyond our solar system, greatly stimulates public interest in stargazing and astronomical observation.
Helping too is vehicle headlights and instrument clusters as well as industrial and commercial lighting settling on dimmer red illumination, so as to not interfere with human night vision, similar to what you saw in real life with airplanes (and sometimes still see in other contexts in science-fiction movies, largely because of the cool factor). Highways where the lights are all characteristically red won’t emit nearly as much light pollution, greatly expanding the accessibility of dark skies in the countryside and even the deepest suburbs.
A world lit in red LEDs forced down, which perhaps only activate when needed (e.g. motion detection technology), would lead to dramatic improvements in night-sky visibility. Even in the inner cities Bortle 7 to Bortle 6 would become typical: on clearer nights the Milky Way might become visible near the zenith, even if only subtly, the Andromeda Galaxy would become dimly apparent, and the brightest constellations could be seen in their entirety. Clouds would still be noticeably brighter than the surrounding sky, but toward the zenith the background sky would actually look somewhat dark, as opposed to the characteristic washed-out greyish tone seen today.
Suburbs today are typically Bortle 5, where the Milky Way is usually visible but subtle and the zodiacal light might be barely noticeable on the best nights; the sky looks washed-out, but all the brightest stars are fully visible. As opposed to inner-city skies, where deep-sky objects are invisible even with a telescope, you can see the Orion Nebula with binoculars from a typical suburb. In this timeline, however? The combined effects of the dark-sky initiative open up visibility dramatically, to Bortle 3 in a typical suburban area: Bortle 3 is currently characteristic of rural skies.
The suburbs of this timeline would experience striking zodiacal light in the spring and autumn, with even its color being visible somewhat. Light pollution could still be seen at the horizon, with clouds seeming noticeably brighter than the surrounding sky, but overhead clouds would appear truly dark, as silhouettes against the starry night. The Milky Way would be striking year-round and visible in its entirety, but it would only look truly complex when it’s at peak visibility directly overhead. The Andromeda Galaxy is easily visible, with the Triangulum Galaxy becoming a naked-eye object with averted vision. Globular clusters become visible to the naked eye.
This isn’t truly dark skies yet, but the idea that with modern illumination, properly controlled, the sky could be this visible from even just a few miles outside the city cores is wild. Certainly this is a universe where instead of only 20% of Americans being able to see the Milky Way much at all, nearly 100% of Americans could; it’s faintly visible even from downtowns, and obviously striking to even the most untrained of eyes in the suburbs, where most Americans currently live.
Rural areas, currently Bortle 3 in the more developed parts of the United States, would enjoy Bortle 2 skies almost universally, which is the beginning of what’s considered a truly dark night sky. At Bortle 2, the zodiacal light is distinctly yellowish and can even cast shadows, the airglow becomes weakly visible, the gegenschein becomes observable, the Milky Way on the best nights looks highly structured, Triangulum is an easy naked-eye object, and a panoply of globular clusters and Messier objects become visible. Clouds even near the horizon appear only as silhouettes against the night sky.
In this timeline even in the more populous eastern part of the United States, the entire countryside experiences a truly dark night sky at Bortle 2. Where it gets really fancy is that there’s a migration out of urban and into rural areas in this timeline, as suburban sprawl is transformed by better transportation technology into rural sprawl, quarter-acre lots transformed into acreages, hour-long commutes that previously opened up 50 miles of traverse instead extending into the hundreds of miles. By the early 21st century an absolute majority of the American population is once again rural, with the median American living in a site of less population density…and far less bright light sources from commercial and industrial developments.
In these settings, with residential lighting at night red and directed downward, and even the brightest highways appearing as dim red ribbons that cast little light domes, an absolute majority of Americans could once again enjoy truly dark night skies: Bortle 2.
The deeper countryside would enjoy the greatest of all the dark skies: Bortle 1. At Bortle 1 airglow is readily visible, the zodiacal light is easily visible and colorful, the gegenschein is readily visible, the Milky Way casts obvious shadows, the number of stars becomes so great that the fainter constellations are barely recognizable amid a twinkling sea of light, Triangulum is easily visible to the naked eye, many globular clusters being easily visible, and with Venus and Jupiter being bright enough to affect dark adaptation on a moonless night (!).
Today Bortle 1 skies, considered the truly excellent dark-sky sites, are confined to only a few areas in the contiguous United States, adjacent to (or within) wildernesses and far from the light domes of cities: Death Valley is perhaps the best-known, but Yellowstone also qualifies, to use two examples of such sites I’ve been to.
In this timeline, however? Bortle 1 conditions become much more widespread; basically anywhere far from a major city would qualify, including the deeper countryside in the eastern United States. Quite a few sites in Appalachia, for instance, might become truly excellent dark-sky sites. In the rural western United States Bortle 1 might even become the norm (as opposed to Bortle 2); humidity scatters light more, and light domes are more visible in flatter regions, so even with a much larger population pouring into the rural western US the mountainous terrain and dry climate should be more conducive to darker skies (this is the reason why Death Valley is Bortle 1 despite not being all that far from Las Vegas or even Los Angeles; a similarly remote site in the lower Midwest wouldn’t be as pristine).
For the excellent dark-sky sites like Death Valley there might be some subtle improvement in this timeline, but the impact wouldn’t be noticeable to the human eye; the standout is the drastic expansion of Bortle 1 and especially Bortle 2 conditions closer to the city centers, at precisely the time when the population is exiting the city centers as a place to live. This is a world where the vast majority of American children could experience skies at home that are the preserve of only the most remote areas today.
In a world like the one where I write in, where children are raised free-range and toward early independence, where school attendance is not expected, and where even adults have little need to work jobs, hiking or biking out to a picturesque spot deep into the night to lie down under the blanket of twinkling stars and gaze the night away might be a normal feature of childhood. Kids’ bedrooms on second stories might be expected to have a balcony attached, where a big telescope could be set up, lights red or even off altogether, peering deeply into the universe’s wonders, natural and perhaps artificial.
For this is a world where humanity is a spacefaring civilization by the 21st century. Already the paltry step forward we’ve taken with Starlink has rattled the astronomical community with the bright visibility of satellites, sunlit in orbit, interfering with observations of the natural universe…but this could easily be mitigated, especially in a more advanced world, with very dark absorbent coatings (several exist even today, such as Vantablack). Satellites could swarm in the hundreds of thousands above us, but from the surface they’d be invisible, bar perhaps the odd occultation or two.
Spaceships too might have their hulls’ reflections and illuminations all but eliminated, but one source of spaceborne light pollution that’s difficult to mitigate is the engines: rocket engines tend to burn brightly, after all, and this tendency extends to more advanced methods such as nuclear pulse propulsion. Even then, if engines were oriented so their emissions pointed directly behind the vessel they were propelling (which would be a desirable trait anyway, as it increases efficiency and minimizes radiation exposure for the crew), the vast majority of emissions from even a crowded orbital space would be invisible for earthbound observers. It’s likely also possible to tailor the spectrum of engine emissions so much less is emitted in the visible portion, improving matters still further (this is already the case for nuclear pulse propulsion, which emits mainly hard radiation as opposed to visible light, but it’s so powerful the flashes still tend to be pretty bright to the human eye).
Still, the mitigation measures outlined above would ensure a more or less pristine sky for the Earth’s Bortle 1 zones; instead of the sky being marred by scintillating satellites swarming all over and flashes of nuclear pulse drives and rocket motors, there would just be the odd flash or two as a heavy nuclear ship happened to be oriented in the right direction, rocket motors perhaps forming steady bright stars at worst, but more often just being briefly visible as they turned in their orbital trajectories. More of a futuristic counterpart of natural meteors, amounting to an attraction for observers, much more so than a hindrance.
The overall vibe of the modal American household would be much more rugged, and not just because the sky is truly dark outside; these star-studded skies by the 21st century would commonly be accompanied by the sound of wolves howling in the distance, as rewilding initiatives make their force felt: agricultural yields improve to the point where much less land is needed to feed the population, so the vast majority of rural land not directly used for dwelling space reverts to nature. Reforestation in places like the eastern United States becomes more pronounced. Wolves could move in from the north even without deliberate release, reclaiming territory currently occupied by the spreading packs of coyotes.
Between the dark skies, the thick woods, and the sound of wolves howling in the distance (not to mention the possibility of encounters, which would require said kids to be armed for their own protection as they wandered across the countryside), it would be a much more wild, and perhaps more wholesome, existence, with subtle futuristic touches like red LED lighting, advanced computing and robotics, and the odd flash or two from a starship bound for Alpha Centauri visible in the pristine sky.
So fascinating I’m tempted to write a vignette about it right now; it’s not a motif you see a lot in science fiction or in future visions in general, but it’s one I truly love, and would like for my own children and grandchildren to experience some day. Maybe, in some way, I could evoke the ancestral memory, and help the future along…now there’s a thought…