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.”

“The difference between us is very marked,” wrote Frederick Douglass to Harriet Tubman in 1868. “Most that I have done and suffered in the service of our cause has been in public, and I have received much encouragement at every step of the way. You, on the other hand, have labored in a private way. I have wrought in the day—you in the night.”

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.”

Psychologists at the University of California recognized a lack of sleep “as a social repellent” and its effect contagious: “People who come in contact with a sleep-deprived individual, even through a brief one-minute interaction, feel lonelier themselves as a result.”

According to his nephew, Pliny the Elder liked to rise in the middle of the night and study by lamplight. “Admittedly, he fell asleep very easily,” Pliny the Younger wrote, “and would often doze and wake up again during his work.”

The practice of yobai, “night crawling,” was common in rural communities in medieval Japan, and continued into the twentieth century. A young man would visit a young woman’s house after dark, disguising his features with a cloth to avoid embarrassment should his advances be rejected. These premarital liaisons could become formal if a child were conceived.

In 2005 the British Cheese Board attempted to dispel the idea that eating cheese before bed causes nightmares. No evidence of this “evil myth” was reported among two hundred volunteers, though eating Stilton was found to lead to “crazy” dreams, while eating cheddar often led to dreams of celebrities. “We hope that people will think positively about eating cheese before bed,” said the board secretary.

A study of sixty-two mammalian species found that animals around the world have shifted into more nocturnal lives. “Humans are now this ubiquitous, terrifying force on the planet,” said lead author Kaitlyn Gaynor, “and we are driving all the other mammals back into the night-time.” The Southeast Asian sun bear, formerly diurnal, now spends as much as 70 percent more time awake at night to avoid humans.

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.”