I haven’t picked a book apart in a while, so have some mildly-disjointed thoughts on Asimov & Silverberg’s 1989 novel, mostly focused on the somewhat-ropey astronomy, but looking at a few other things as well...
"Nightfall" is a late-1980s novel-length expansion of the 1950s story of the same name. The basic premise is, "what about a world with no night?"
The planet Kalgash (Lagash in the short story - no relation to Ur or Sumer insofar as I know!) orbits the G-type star Onos, which is in turn one part of a complex multiple system containing six stars in total. With that many stars, there is always one in the sky somewhere. The other five suns are Trey and Patru (a co-orbiting pair of A-type stars), Tanu and Sitha (another co-orbiting pair, this time B stars) and lastly Dovim, a red dwarf. You can see several oddities immediately - note that the stars have neatly sorted themselves by spectral type! And there's only the one red dwarf (Dovim, implied to be an early-M-type object), when you'd expect loads as a) star formation is an efficient machine for making red dwarfs and b) ~75-80% of all stars are red dwarfs.
As for the system architecture, I've struggled to come up with anything sensible. The below scribbling would make (some) sense, but fails the "always a sun in the sky from anywhere on Kalgash" test, as Dovim will often "fall behind" Onos on its orbit around the barycentre:
Presumably Onos has to pass quite regularly between the Patru/Trey and Sitha/Tano pairs - what this implies for Kalgash's climate and thermal balance I'll leave as an exercise for the reader! Also, the formation history of this system must be weird. Kalgash's complex biosphere implies an age of several billion years, but A and B stars have far shorter life expectancies. Is Onos actually a star that formed elsewhere, which was captured into the system later on?
Anyway. Kalgash orbits Onos, supposedly alone, and there is no night - even if it's only reddish inadequate Dovim, there's always a sun in the sky. Always. Forever. And this sentence is 100% certified to contain no lies, evasions or elided truths of any kind. *Ahem.*
The native Kalganians - supposedly some sort of non-terrestrial non-humanoid life, though the book flip-flops this many times - apparently cope very poorly with darkness. Even as little as 15 minutes in complete dark is apparently enough to induce permanent psychosis. This makes it just as well that Kalgash is a loner object, with no moons or nearby planets or other local bodies that could cause eclipses ... ooops.
Basically, the plot of the novel concerns some scientists who discover evidence of Mass Effect-style periodicities in the collapses of historical civilisations on Kalgash. About every 2000 years, *something* happens that seems to cause people to go collectively go mad and burn down any settlement they might be living in at the time. It seems to be sudden - it stops as soon as it starts - but the destruction is near-complete. And guess what? It's almost 2000 years since the last time civilisation toasted itself.
Meanwhile, Kalganian astronomers have recently developed a theory of universal gravitation, based on studying the motions of the suns (plausible; you'd have a lot of data to work with there). Only there's a problem. Kalgash itself is stubbornly not-quite-conforming to the predictions of the models, and in fact the deviations seem to be getting larger. The theory seems to be wrong - what horror! what sadness! gravity fails!
Or does it? In fact some Kalganian theorists notice something odd - you can explain the planet's motion perfectly if you assume the presence of a second planetary-mass object. Once you plug this in, you can figure out where this body would have to be. The results are ... worrying. You see, this hypothetical Kalgash Two is apparently closing in on Kalgash-Prime. It won’t collide with Kalgash Prime, but it will get close enough to block out sunlight.
Now, the book isn't 100% clear whether Kalgash-Two is a moon or another planet. I think it has to be a planet - its orbit apparently takes 2000 years, which would certainly take a moon entirely outside Kalgash's Hill sphere; Onos would have "snatched it away" onto a stellar orbit. Another oddity is that no-one can see Kalgash-Two - even here on Earth you can see the Moon clearly by day, and given what we know of the dynamics of this system, Two would present a large disk when it enters opposition with Kalgash-Proper. In the book it's speculated that Two's surface rock might be bluish in colour, which might "camouflage" it against the sky. I'm dubious about this - yes, Turquoise-The-Mineral Is A Thing, but an entire planet made of it? To me, this feels a bit "off", geologically.
Anyway, the astronomers realise that if it exists, Kalgash-Two is only a matter of weeks away from by-passing Kalgash itself. And when it does, it will arrive when half the planet has a rare "one-sun" day. That sun is, of course, the red runt Dovim itself, and Two will pass between Kalgash and Dovim. Depending on how big Two is, it could entirely block the sun out. Things are about to get dark! The other five suns will all be on the other side of the planet, but Kalgash rotates, so the other hemisphere will apparently get a taste of darkness too.
Now, note how odd the dynamics of this eclipse are. Apparently the umbra - the region of full shadow - is bigger than Kalgash itself, and the eclipse takes an entire Kalganian rotational period to pass. The book never - IIRC - tells us how fast Kalgash spins. It's certainly possible that a Kalganian "day" is far shorter than a terrestrial one, but it's implied to be at least a dozen or so hours. (The suns don't "move" fast enough against the sky for anything less.) So just how big is Kalgash-Two? To create an eclipse lasting multiple hours, it must be large. Honestly I think it would be hard to do this at a size smaller than that of a gas giant. Is something bigger than Jupiter swinging by, just outside the Roche limit? (No-one on Kalgash notes any seismic events - there's no upsurge in tremors, no disruption to tides or odd behaviour from gravimeters, like you would expect if a super-Jovian body was closing in on you, which is an inconsistency.)
Anyway, sure enough, Kalgash Two shows up on queue. Suddenly the reddish gloom of a one-sun day starts to darken, and the horrified masses look up to see a massive bite eating into the side of Dovim! Rapidly and with maximum fuss, the sun goes out! Basically what happens next is like "Pitch Black", except with mad people instead of cannibalistic alien monsters.
You'll note I haven't said a lot about the characters yet. There's not a lot to say - they're all very much "straight from central casting". They aren't objectionable, but they're not particularly memorable either. The plot itself has two threads - the astronomers' growing concerns about the impending disaster, which in turn puts them into conflict with a politically-influential cult, who claim to be preparing for the imminent return of "the stars". While the book is formulaic and the characters are fairly-average, it is a fun read; the pages turn without too much difficulty!
In case anyone's wondering about where exactly the authorities are in all of this, well, on eclipse night they prove completely useless. If I remember correctly, the government fails to take any warnings seriously and officials dismiss the astronomers as cranks. Basically they’re running on “January to March 2020″ rules - sadly I can no longer dismiss this pattern of behaviour as unrealistic, depressing as that is!
When the night itself arrives, IIRC, the staff at the local power company manage to go mad ahead of almost everyone else (apparently there were no bulbs inside the turbine hall, or something) and their rampage plunges Saro City into the worst-timed power outage ever. Also, making matters worse, Saro probably didn't have any municipal lighting (because why would it?) and apparently most people don't have much in the way of torches or candles at home. So the darkness-maddened people react by torching everything that will burn (fire = light = MASS PYROMANIA!). How they're all able to find matches while a) utterly-demented and b) fumbling around in the dark ... yeah, that never gets explained.
Now we arrive at another oddity: on the night itself, people actually are able to see. They can see the stars without any trouble - which makes no sense. Why would their eyes be evolved to function in low-light conditions? But see the stars they do. There are several pages of the astronomers (those who survive the first few hours of the eclipse-chaos) boggling at the sheer scale of the universe they find themselves in. (In fairness, this is quite a cinematic moment ... basically the ~400 years of the Copernican revolution, which wasn't really "complete" here until Hubble demonstrated that the Great Nebula of Andromeda was a physically-separate galaxy in the 1920s? Kalgash's scientists get the entire thing, mainlined into their stunned brains in about 1 hour.
Their disorientation is certainly understandable.
Incidentally, there's another astronomical oddity here. Kalgash Two should be visible - a dark disc blocking out the sky in the direction where Dovim "should" be - but no-one remarks on it. Also, Two seems to have no atmosphere at all, because Kalgash-Proper doesn't experience any total-lunar-eclipse style blood-Moon. (What exactly is Two? It has to be at least as large as a gas giant, but it's also airless? What is this thing? Is it a planet at all?) Anyway, the eclipse does eventually end, after a few hours. While there are survivors, society has essentially collapsed. The damage is roughly the same as a median-scenario Great Powers nuclear exchange would be here on Earth (except minus the craters and radioactivity).
Just think - if the utilities provider for Saro City hadn't pulled an ERCOT, it's quite possible they could have got through the night without a mass casualty event. While people would have been frightened, if they'd had working lights to huddle around while Two passes by overhead, they might have been able to ride it out. But that didn't happen, of course. (If I was a cynic, I might say the real story of "Nightfall" is the cost of inept/crony-coddling infrastructure policies when the once-in-a-century event pays you its rare-but-inevitable visit.)
Anyway, the ending of the book, unfortunately, is pure Silverberg.
That is to say, it's rushed, lazy and addresses none of the themes, character-development or even some of the earlier plot-events of the book. On the last two pages of the book, the surviving scientists decide to join forces with the menacing theocratic star-cult, because apparently religious totalitarianism is somehow the only way to save the world, post-nightfall. Yeaaaaaaaaaaaah.
Incidentally, here we see some of the typical narrative ticks of a certain sort of mid-century SF writer. Note how any sort of change (nightfall! social chaos!) just *has* to be BAD and SCARY, and they instantly seek refuge in anti-democratic authoritarianism. You see this tick a lot in so-called "Golden Age" writers - it's almost a trope of their behaviour. (It's also interesting given the cross-links between people like Heinlein and the military/industrial complex, or Pournelle and the GOP.)
So the TL;DR summary ... "Nightfall" is a novel that follows the spirit of hard SF (if not the letter, as seen above) and has some iffy ideological/mimetic moments ... but, it works as a potboiler and (disappointing ending aside) is definitely a fun read. Just don't expect the celestial mechanics to be in any way workable.
“Consider, for instance, the matter of education. Throughout history, it has been assumed that education, in any formal sense, is for the young only. Education usually stops when the young man or woman has learned enough to support himself somehow or has mastered the rudiments of those clichés that will make it possible for him to carry on polite conversation. Individuals, once past their youth, if they continue to wish to learn, must generally do so on their own time and by their own efforts. If they attempt the task in any organized fashion, they are competing with the young and do so, in our youth-centered society, at a psychological disadvantage.
With education confined to youth only, they retain the attitudes, beliefs, and clichés suitable to their youthful, and only, years of education, so that they become the Archie Bunkers whose outmoded ways of thought amuse young people and convince them that there is something inherently stupid about old people. It is a vicious cycle in which we deprive the post-youth of socially approved opportunities to learn, allow the faculty of learning to atrophy, conclude that “old dogs cannot learn new tricks,” and then use the conclusion to justify a continuation of the procedure that makes the conclusion inevitable.”
They drank beer and reminisced as men will who have met after long separation. They called to mind the days under fire. They remembered sergeants and girls, both with exaggeration. Deadly things became humorous in retrospect, and trifles disregarded for ten years were hauled out for airing.
Including, of course, the perennial mystery.
"How do you account for it?" asked the first. "Who started it?"
The second shrugged. "No one started it. Everyone was doing it, like a disease. You, too, I suppose."
The first chuckled.
The third one said softly, "I never saw the fun in it. Maybe because I came across it first when I was under fire for the first time. North Africa."
"Really?" said the second.
"The first night on the beaches of Oran. I was getting under cover, making for some native shack and I saw it in the light of a flare ----"
George was deliriously happy. Two years of red tape and now he was finally back in the past. Now he could complete his paper on the social life of the foot soldier of World War II with some authentic details.
Out of the warless, insipid society of the thirtieth century, he found himself for one glorious moment in the tense, superlative drama of the warlike twentieth.
North Africa! Site of the first great sea-borne invasion of the war! How the temporal physicists had scanned the area for the perfect spot and moment. This shadow of an empty wooden building was it. No human would approach for a known number of minutes. No blast would seriously affect it in that time. By being there, George would not affect history. He would be that ideal of the temporal physicist, the "pure observer".
It was even more terrific than he had imagined. There was the perpetual roar of artillery, the unseen tearing of planes overhead. There were the periodic lines of tracer bullets splitting the sky and the occasional ghastly glow of a flare twisting downward.
And he was here! He, George, was part of the war, part of an intense kind of life forever gone from the world of the thirtieth century, grown tame and gentle.
He imagined he could see the shadows of an advancing column of soldiers, hear the low cautious monosyllables slip from one to another. How he longed to be one of them in truth, not merely a momentary intruder, a "pure observer".
He stopped his note taking and stared at his stylus, its microlight hypnotizing him for a moment. A sudden idea had overwhelmed him and he looked at the wood against which his shoulder pressed. This moment must not pass unforgotten into history. Surely doing this would affect nothing. He would use the older English dialect and there would be no suspicion.
He did it quickly and then spied a soldier running desperately toward the structure, dodging a burst of bullets. George knew his time was up, and, even as he knew it, found himself back in the thirtieth century.
It didn't matter. For those few minutes he had been part of World War II. A small part, but part. And others would know it. They might not know they knew it, but someone perhaps would repeat the message to himself.
Someone, perhaps that man running for shelter, would read it and know that along with all the heroes of the twentieth century was the "pure observer", the man from the thirtieth century, George Kilroy. He was there!
