This patch of earth, longitude 117 degrees west, latitude 33 degrees 2 minutes north, passes away from the sun. The sun's light, leaning in from the west, reaches us through denser and denser layers of atmosphere, which block all but the reds and oranges of its spectrum. Fifteen to 20 minutes after the sun sets, from areas of the city with an unobstructed view of the eastern horizon, an arc of purple haze can be seen to the east: the earth's shadow. The moon is revealed. The bright star in the western sky this time of year is Regulus. To the southeast is Antares. The Summer Triangle is overhead. The animal kingdom awakens at the cocktail hour, emerges into the dusk. Raccoons, striped skunks, and possums, forced into urban areas by development in North and East Counties, then trapped here in canyons isolated by construction, move up from the brush and venture into streets and yards. They encounter death by automobile tire or battle domestic cats turned out for the night. Crows and gray foxes hunt small gray mice, cotton-tailed rabbits, squirrels. Meadow voles -- brown-and-white spotted creatures resembling large hamsters -- emerge from the tunnels they've burrowed beneath the lawns of Golden Triangle industrial parks, also searching for food.

Electricity consumption drops between 3 p.m. and 7 p.m. as computers, lights, air-conditioning units are turned off, office buildings deserted. At SDG&E's control center, resource schedulers and power-supply coordinators monitor the energy load flow, make adjustments to the output of "base load units" and turn off "cycling units." The constant buying and selling of energy (from as far away as Canada, Texas) slacks off. Soon after, there is a minor spike in consumption -- on one recent day, consumption rose from 1940 megawatts at 7 p.m. to 2091 megawatts at 8:30 p.m. -- as workers settle in at home and begin using electric appliances, turn on televisions, cook meals. By 9 p.m., consumption begins again to drop and continues to fall steadily until it reaches a "valley" between 3 and 4 a.m. By 5 a.m., people have begun to wake up, make toast, turn on radios, percolate coffee, shave; usage climbs steadily until its daily peak around 2 p.m.

After dark, the valleys, mesas, mountains, and desert cool. The air above them cools, and the ocean winds, no longer sucked in by the hot air rising over land, blow inland and die. Land and ocean temperatures roughly equalize.

A skeleton of freeways binds the city with rushing white and red pinpoints. The steady sigh-and-ebb of cars on the interstates and highways dwindles. Around 11 p.m., the last train from Los Angeles slides down the city's profile. The last jets, except the 2 a.m. Federal Express flight, shock into their landings at Lindbergh Field.

The roofs of houses and apartment buildings shift downward as their surfaces cool, no longer heated by light protons from the sun. Radon gas wafts from paintwork, floorboards, and ceilings. Evening baths, showers, toothbrushings, defecations, dishwasher cycles, lawn-waterings taper off after 9 p.m., causing the sewage rushing through pipes beneath the ground to slow to a gentle, bedtime pace. Nearly all 190,000,000 gallons of sewage that glide efficiently out to the Point Loma sewage treatment facility each day have already passed through the system.

People sleep. Stale arguments are left hanging over marriage beds. The innocent drift off to unconsciousness, hands between legs. Hidden and resting in warm, tight wall spaces and meter boxes and drains, cockroaches register the quiet dark and begin to move out, antennae waving. Fast-moving German roaches head up the walls. The larger, shiny, black Oriental roaches climb from drains. They look for decaying vegetable matter, for water, for others of their kind with which to breed -- 20 young per female per month.

Plants breathe on in the dark. Photosynthesis suspended until dawn, the plants use oxygen to burn food, give off carbon dioxide. A hidden, microscopic war continues in lawns and gardens. Female moths loose potent scents detectable by the males of their kind. Camped in narrow ornamental planters outside office buildings and apartment complexes, male crickets vibrate transparent wings -- stridulate their shrill note -- attracting females with an odor emanating from a gland exposed when the wings are elevated for song. The females chew on the gland. Hunting cats and skunks snap up the crickets.

In isolated boxes of light around the dark city, workers on graveyard shifts drill holes in circuit boards, mop floors, colorize movies, x-ray broken bones, and cut away mangled tissue from gunshot wounds; sell beer, milk, and cat food to nighthawks. Night workers become subject to psychosomatic occupational disorders of various neuroses, digestive ulcers. Their biological rhythms are no longer synchronized, as in other mammals, with the alteration of daylight and darkness. Their heartbeats, body temperatures, the secretion of their digestive juices cannot be forced to change day for night.

Insomniacs, criminals, and drunks walk the streets. Between 9 p.m. and 2 a.m. Priority One calls -- those relating to life-threatening situations or crimes in progress -- decline from an early-evening high. Reports of alcohol-related traffic accidents rise, car thefts drop slightly, burglaries taper off. After 2 a.m., the number of rapes reported increases. Priority One calls reach their lowest point. Off-work domestics and restaurant workers sit hugging their shopping bags to their breasts at bus stops, waiting for the last bus of the night. Transients roll up in their blankets in the urine-reeking shelters of downtown storefronts.

Between 10 p.m. and 6 a.m., only 10 percent of the water the system's 1.6 million customers consume each day is used. During peak demand hours, water flows back out of reservoirs. This augments the filtration plants' output. At night, water continues to flow from the plants through the pipes but builds up in the system's 16 water storage facilities (the stand-pipes and standing reservoirs, like the aqua tower in North Park). System pressure builds in preparation for the next morning.

The air smells of wet earth and grass. Jasmine bushes release their scent, and the white flowers of other night-blooming plants open, waiting to be pollinated by the moths that fly at night and mistake them for the females of their species. Transvestite prostitutes amble slack-legged along El Cajon Boulevard, waiting to be gathered into cars whose occupants willingly mistake them for the females of their species.

The swells and waves of the ocean continue to roll in, calm and relentless. Bioluminescent organisms spark in the breakers. Plankton rise through the water to feed. Lobsters crawl out from the crevices of rocks to feed. Grunion move in to lay eggs and fertilize them. In the rocks along Mission Bay and the harbor, rats sinuate their way toward discarded food wrappers and restaurant kitchens.

Cloud masses form, the marine layer builds up, and what used to be known as el velo de la luz (the veil of light) moves inland, shrouds the sky. It's a box lid that shuts us in or a blanket that protects us from the limitless darkness.

Sleeping humans and some birds and reptiles enter REM sleep, D-sleep. In the area of the humans' brain stems called the raphé system, large neurons reduce their activity. Pulse rates, respiratory rates, blood pressures rise and fall, muscle tone lowers. Cerebral cortexes are activated, sensory images flood the sleeping mind. Neurons in the brain stem release norepinephrine, serotonin, acetylcholine into the forebrain. It is speculated that changes in the proportion of these chemicals, along with certain activity in the forebrain, produce nightmares. In former times these were attributed to intercourse with incubi.

The wakeful ear is pricked by snapping twigs, by the scrabblings of roof rats leaving attics and palm trees to sniff out snails, fruit rinds, rotting meat. Cars peel out angrily from alleys. Backfires or gunshots? Dark reddish-brown American cockroaches fly out from palm trees and sewer drains to crawl on the sidewalks downtown. Garbage-pickers discreetly heave squeaking dumpster lids up, foraging for breakfast, income, and outerwear. Refrigerators click on and hum. Creaks and yowls from neighbors' bedrooms reach guilty ears, muffled and enticing: people beg to be taken, call for God.

-- Mary Lang