Emily and Charlotte Brontë, insomniacs both, would walk together in circles around the dining room table until they were tired enough to sleep. When Emily died and Charlotte suffered alone, her insomnia worsened; she added to her route, often wandering down neighborhood streets and into the cemetery until daybreak.

In Japanese tradition, ghosts and spirits are more likely to appear at dusk or dawn than in the middle of the night. “In order for people to see them and be frightened by them,” wrote folklorist Kunio Yanagita, “emerging in the pitch-dark after even the plants have fallen asleep is, to say the least, just not good business practice.”

“Darkness has come upon me,” a hymn in the Rig Veda laments. “O Dawn, banish it like a debt.” The morning light is here asked, suggested translator Wendy Doniger, to act as a collection agency—to “make good what darkness had incurred or ‘exact’ the darkness from night as one would exact money.”

Astronomers theorizing the existence of small moons orbiting larger moons have proposed calling them “moonmoons.” The planet Kepler-1625b, which has a Neptune-sized moon distantly orbiting it, was cited as “sort of the best-case scenario for a moonmoon.”

A longtime practice of European peasants was to bring cows and sheep inside for the night. If one could ignore “the nastiness of their excrements,” a late seventeenth-century visitor to Ireland opined, “the sweetness of their breath” and “the pleasing noise they made in ruminating or chewing the cud” might lull a person to sleep. A visitor to the Hebrides noted, however, that while urine was regularly collected and discarded, the dung was removed only once a year.

“You don’t need a brain to sleep” was a central takeaway for a team of biologists who found that Cassiopea, a genus of upside-down jelly­fish, display signs of sleep deprivation when disturbed by water pulses at twenty-minute intervals throughout the night.

In August 2018 data scientist David Bamman examined how authors recently interviewed in the New York Times’ By the Book column answered the question “What’s on your nightstand?” Women mentioned male and female authors almost equally; men mentioned male authors more than 79 percent of the time. “Don’t read in bed,” advised Fran Lebowitz. “It’s too stimulating. Watch TV instead. It’s boring.”

Asked whether it was night or day that first emerged when the universe came into existence, sixth-century-bc Greek philosopher Thales of Miletus replied, “Night, earlier by a day.”

Poet Edward Fairfax kept a 1621 account of his daughter Helen’s terrible nightmares, describing an incident in which she complained about a demonic white cat that “has been long upon me and drawn my breath.” The cat, she said, “has left in my mouth and throat so filthy a smell that it does poison me.”