Night
Aiton's Encyclopedia (1910)
that portion of time during which the sun is below the horizon, from sunset to sunrise. God saw the light was good; And light from darkness by the hemisphere Divided: light the day, and darkness night He named, says Milton. As a matter of fact, day is an ambiguous term. It covers the time from sunrise to sunset or from midnight to midnight indifferently, but night is restricted to the period of darkness. At every moment one-half of the world has nights. The nights are twelve hours long on the equator. The length of night for any locality in the northern hemisphere equals the length of day for the same date and corresponding latitude in the southern hemisphere . The total length of the nights for a given locality equals the total length of the days for the same locality and is the same for all parts of the world. The Arctic and Antarctic regions with their long winter night have no more night than equatorial regions. The check that comes to growing vegetation at nightfall is a topic falling rather under the subjects of LIGHT and BOTANY. For man, night is a period of natural rest, but many animals are more active by night than by day. Nature has endowed many insects, fishes, reptiles, birds, and beasts with eyes that are adapted to the faint light of evening and morning. Many nocturnal animals are distressed if caught abroad in full daylight. In a figurative sense, night is used to designate a period of intellectual ignorance, as the night of the Middle Ages . The poet speaks also of the night of sorrow, the long night of death, and eternal night. See Day ; Light Spectral lemur. Egyptian jumping-mouse. Night-lemur. Eyes of nocturnal animals Hawk-owl. Nocturnal animals Spectral lemur. Eyes of nocturnal animals
What Has Changed in the Last Century
The astronomy in Aiton's 1910 entry is still exact: nights of twelve hours at the equator, half the globe dark at any moment, and the same total of darkness everywhere over a year. What has changed is that darkness itself has become scarce. A 2016 survey of artificial sky brightness found that about 83 per cent of the world's people live under light-polluted skies and roughly a third of humanity, including some 80 per cent of North Americans, can no longer see the Milky Way. Aiton's remark that "for man, night is a period of natural rest" has also been overtaken by circadian biology: the hormone melatonin was identified in 1958, and in 2007 the World Health Organization's cancer agency classified shift work that disrupts the body clock as a probable human carcinogen.
Written for this edition, 2026.