Nightfall, published in 1990, is an apocalyptic novel by American science fiction authors Isaac Asimov and Robert Silverberg. The novel is an expansion of Asimov’s short story of the same title, which he wrote and published in 1941 in an issue of Astounding Science Fiction. The magazine’s editor, John W. Campbell, encouraged Asimov to write a story about the mass psychology of people who see the stars only once every 1,000 years, alluding to a quote by the American philosopher Ralph Waldo Emerson. The story was immensely popular and became a calling card for Asimov’s early writing career.

Nightfall—like the short story of the same title—concerns a planet whose inhabitants are unaware of the universe beyond their six neighboring suns, which cast sunlight on the planet at all times of the day. As an eclipse settles over the planet, the local astronomers ponder the ways the darkness will affect their people psychologically, sparking fears of societal collapse and widespread destruction. The novel goes on to show the aftermath of such a collapse, inviting questions about science and its relationship with faith, public psychology, and the impact of human disasters.

This study guide refers to the hardcover first edition of the novel, published in 1990 by Doubleday.

Content Warning: The source material for this guide depicts sexual violence and references alcohol use disorder and mental health conditions. In addition, the novel uses outdated and offensive terms for mental health conditions, such as “madness” to describe chaos and uncertainty, which are replicated in this guide only in direct quotes from the source material.

Plot Summary

The novel is told in three parts. It takes place on Kalgash, a fictional planet that has six suns. Because at least one of Kalgash’s six suns is present in the sky at any given time, the planet’s people have never experienced darkness or seen the stars.

Part 1, entitled “Twilight,” introduces several main characters, all of whom are linked by separate discoveries that foreshadow a cataclysmic event later on referred to as the Darkness or Nightfall.

Siferra 89, an archaeologist, uncovers evidence of past civilizations that were destroyed by a great fire. Among the ruins of these civilizations is a collection of tablets that explain how each city had been destroyed by a holy fire called Stars, which were sent by the gods.

Meanwhile, a psychologist named Sheerin 501 investigates reports about a theme park attraction that causes heightened distress among its visitors. He experiences the ride itself, a tunnel that plunges visitors into total darkness. This causes him to experience claustrophobia and distress.

Finally, Beenay 25, an astronomer, observes an anomaly in Kalgash’s orbit, forcing him to doubt the Theory of Universal Gravitation put forward by his mentor, Athor 77. Through close consultation with Theremon 762, a friend who writes columns for the city newspaper, and Athor himself, Beenay discovers that the anomaly points to the existence of a previously-unknown planetary body in their solar system. Upon closer examination, Beenay realizes that this satellite will cause an eclipse when Kalgash’s smallest sun is alone in the sky, casting all of human civilization on the planet into a period of extended darkness.

Siferra, Sheerin, and Beenay come together at Saro University. As they discuss their separate findings, they come to realize that the eclipse aligns with the prophecy forwarded by a religious cult known as the Apostles of Flame. Once every 2,049 years, the eclipse will cause civilization to collapse into chaos. Fearing this outcome, Athor decides to work together with an emissary of the Apostles, Folimun 66, to prepare the people of Kalgash for the impending eclipse in one year’s time.

Part 2, which adopts the title of the novel, jumps forward to the day of the eclipse and largely preserves the material of Asimov’s original short story. Athor and the astronomers have failed to prepare Kalgash for the impending cataclysm. This is largely due to Theremon’s interference, as he rejected the scientists’ authority when they began collaborating with the Apostles of Flame.

Theremon comes to the observatory, where the scientists have gathered to watch the eclipse. He remains skeptical, however, of any destructive outcome. Folimun likewise infiltrates the observatory, determined to destroy any evidence of the group’s scientific findings. He warns them of an approaching mob that will come to destroy the observatory as well. As the eclipse approaches, each of the scientists downplays the devastating effects of the event. None of them are prepared, however, when Nightfall finally occurs, sending much of the nearby city into chaos. The mob storms the observatory, killing Athor and other scientists in the process.

Part 3, entitled “Daybreak,” picks up immediately after the end of the Darkness. Siferra, Beenay, Sheerin, and Theremon survive the assault on the observatory, albeit separate from one another in a post-apocalyptic Kalgash. The nearby city of Saro is either burned down or placed under the control of the Apostles. Factions have sprung up across the surrounding forest area, each one vying for control while trying to restore the pre-eclipse government. The academics who sought shelter from the eclipse have likewise abandoned their hideout to travel south to Amgando National Park, where other academics plan to form a community of their own. Sheerin and Beenay make the journey to Amgando as well. However, Sheerin is killed by a group of settlers. Meanwhile, Beenay chooses to remain at a border checkpoint when his romantic partner, Raissta 717, is injured.

Theremon seeks out Siferra and the two decide to travel to Amgando together. They encounter Beenay and learn of an army organized by the Apostles of Flame. The army is moving toward Amgando in an attempt to destroy the surviving academic community. Theremon and Siferra continue on their journey in hopes of warning the scientists. However, they are intercepted by the army, which is led by Folimun. Folimun reveals that he is the true leader of the Apostles. He has devised a plan that will ensure the reconstitution of society through religious totalitarianism. Theremon is convinced that Folimun’s plan is effective. He hopes that in several generations’ time, their descendants will lead the shift away from theocracy to a more secular society governed by reason. With the combined knowledge that the astronomers and the Apostles have produced, they can better prepare future generations for the eclipses to come.