Why Earth gets more daylight than darkness over a year
If Earth were an airless world lit by a point of light, day and night would split the year evenly. They don't. The Sun's width and the bending of light by our atmosphere steal several minutes from every night, so across a year the planet enjoys more daytime than darkness.
Night simply means the Sun is below your horizon, but the details are fussy. The Sun covers about half a degree of sky, so sunset technically begins when its centre touches the horizon while half the disc still shows; that trims around three minutes from a temperate night. Refraction matters more. Air bends sunlight over the horizon, keeping the Sun visible after it has geometrically set and cutting about six more minutes. Then comes twilight in three stages, civil, nautical and astronomical, ending only when the Sun sinks 18 degrees below the horizon.
Length varies hugely with place. At the equator night stays close to 12 hours all year and dusk is quick. At the 45th parallel the longest winter night is about twice the shortest summer one. Utqiagvik in Alaska gets 65 days of polar night, and at the pole itself darkness lasts 179 days, from September to March.
Other worlds do it differently. The Moon's nights last about two weeks and arrive abruptly, with no air to make twilight; from the near side, Earth hangs in the dark sky some 50 times brighter than a full Moon looks to us. Venus turns so slowly, and backwards, that its nights last just over 58 Earth days, yet its thick atmosphere keeps the surface hot enough to melt lead throughout. On Mercury the temperature plunges by more than 538 degrees Celsius after dark.
The word carries old baggage too. Night comes from Old English niht, part of a family of related words across nearly every European language, including Latin nox, behind equinox and nocturnal. Its deepest root may have meant to perish. Early peoples counted time in nights, which is why fortnight survives as a shortening of fourteen nights. The silent gh stands in for an old letter, yogh, that printing presses imported from the continent lacked.
Source: Night
