Night

Night, or nighttime, is the period of darkness when the Sun is below the horizon. While one side of the Earth is lit by daylight, the other side is in darkness. Earth's rotation makes the Sun appear to rise and set each day. Although dark, the night sky can still be lit by moonlight, the soft glow of airglow, the twinkle of starlight, and sometimes by light pollution.

Living things change their behavior when night falls. Many animals, called nocturnal animals, are more active at night and have special ways to see in the dark or use other senses to find food. During sleep, many daytime animals, including mammals and birds, experience dreams. Plants and tiny water organisms also change what they do at night, storing energy or working differently without sunlight.

In the past, night was often seen as a risky time, when it was harder to see and dangers could hide in the shadows. This fear of darkness still affects many people today, especially children. Different cultures have told stories about night creatures like werewolves, witches, ghosts, and goblins, showing how people felt about the unknown during dark hours. As lighting improved over time, people could stay active later, creating new parts of life such as nightlife with bars, clubs, and evening events that bring communities together.

Etymology

The word night comes from the Old English word niht. This is a Germanic word, similar to the German word nacht. Many European languages have words for night that come from the same ancient Indo-European root, thought to mean either "to perish" or "empty".

The term fortnight, meaning fourteen days, comes from an old way of measuring time by nights instead of days. The letters "gh" in night were added to represent an old English letter called yogh, which could not be printed with early printing presses. Over time, English speakers stopped saying this sound, so "gh" is now silent, just like in the word light.

Astronomy

A planet's rotation causes nighttime and daytime. When a place on Earth faces away from the Sun, it experiences night. The Sun appears to set in the West and rise in the East because of Earth's rotation. Many celestial bodies, including other planets in our solar system, also have night.

Earth

The length of night on Earth changes depending on the season. Nights are longer in winter, with the winter solstice being the longest night. Nights are shorter in summer, with the summer solstice being the shortest. Earth's orbit around the Sun is tilted at 23.44 degrees. Nights are longer when a hemisphere faces away from the Sun and shorter when it faces toward the Sun. This means the longest night in the Northern Hemisphere is the shortest night in the Southern Hemisphere.

Night length changes less near the equator. The difference between the longest and shortest night grows as you move toward the poles. At the equator, night lasts about 12 hours all year. The tropics have little change in day and night length. At the 45th parallel, the longest winter night is about twice as long as the shortest summer night. Inside the polar circles, night can last all 24 hours on the winter solstice. The length of this polar night grows closer to the poles. Utqiagvik, Alaska, the northernmost place in the United States, has 65 days of polar night. At the pole itself, polar night lasts 179 days from September to March.

Over the year, there is more daytime than nighttime because of the Sun's size and atmospheric refraction. The Sun is not just a single point. From Earth, the Sun looks like a small circle in the sky. When the center of the Sun drops below the western horizon, half of the Sun is still visible. Similarly, when the center of the Sun rises over the eastern horizon, half of it is already visible. This shortens night by about three minutes in temperate zones. Atmospheric refraction bends sunlight, so the Sun stays visible a little after it has actually gone below the horizon. This shortens night by about six minutes. After sunset, scattered sunlight leaves a glow in the sky during twilight.

Twilight

Twilight is the time between daylight and darkness when the Sun is below the horizon. Civil twilight happens when the Sun is between 0° and 6° below the horizon. During this time, bright planets and stars like Venus and Sirius can be seen. Nautical twilight continues until the Sun is 12° below the horizon, when the horizon is just visible enough for navigation. Astronomical twilight lasts until the Sun is 18° below the horizon, after which no sunlight is visible. The time when the Sun is 18° or more below the horizon is called astronomical night.

Like night itself, the length of twilight changes with latitude. At the equator, day turns to night quickly. Near the poles, the change can take weeks. Twilight lasts longest at the summer solstice and shortest near the equinoxes. Moonlight, starlight, airglow, and light pollution can add a soft glow to the night sky, called skyglow. Skyglow gets stronger each year because of more artificial lighting.

Other celestial bodies

Night happens on other planets and moons in the Solar System. The length of night depends on how fast the planet or moon spins and how long its year is. The lunar phases we see from Earth are caused by night on the Moon. The Moon has longer nights than Earth, lasting about two weeks. This is half of the Moon's cycle through its phases. The Moon always shows the same face to Earth. The side facing away from Earth is called the far side of the Moon, and the side facing Earth is the near side of the Moon. During lunar night on the near side, Earth looks 50 times brighter than a full moon from Earth. Since the Moon has no atmosphere, night comes on suddenly without twilight.

Night varies on different planets in our Solar System. Mars has a dusty atmosphere that creates a long twilight with colors from purple to blue, sometimes making glowing noctilucent clouds. Venus and Mercury have long nights because they spin very slowly. Venus spins once every 243 Earth days. Because of its unusual spin direction, nights on Venus last just over 58 Earth days. Venus's thick atmosphere stays so hot it could melt lead all night. Its winds change direction from day to night, blowing from the equator to the poles during the day and from the poles to the equator at night. On Mercury, the closest planet to the Sun, temperatures drop by over 1,000 °F (538 °C) after sunset.

The pattern of day and night matters for whether a planet could support life. Shorter nights usually mean a warmer planet. On an Earth-like planet, longer days and nights might help life by making the planet cooler and less cloudy. But if a planet spins very slowly, the temperature difference between day and night becomes very large. Some faraway planets, like those around TRAPPIST-1, are tidally locked. This means they spin exactly once per orbit, so one side always faces the star and has constant day, while the other side has constant night. Scientists think life on these planets would most likely develop in the twilight zone between the day and night sides.

Biology

Living things respond to the darkness of night in many ways. Light and darkness help control our daily cycles, called circadian rhythms. These cycles are guided by an internal "biological clock" that changes with light exposure.

Animals that are active at night, called nocturnal animals, have special ways to see in the dark. They have more rod cells in their eyes, which help them see in dim light. Some night animals even have a special layer behind their eyes called the tapetum lucidum that helps them see better. Insects can see in very low light, and some use the moon or stars to find their way. However, too many lights at night can confuse these animals.

Many animals, including humans, sleep at night. During sleep, our brains go through different stages, and we may have dreams. Some animals, like fungi and plants, also change their activities based on the night. Fungi grow more at night, and plants use stored energy instead of making new energy from sunlight. Special plants called succulents open their pores at night to store carbon dioxide for use during the day.

Culture

History and technology

Before factories and electric lights, people were more afraid of the night. They couldn’t see well, so they might fall into holes or get lost. People also worried about getting into fights or being robbed when it was dark. In old times, thieves sometimes used tricks to steal from houses, and fires were a big danger because lights like candles could easily start blazes.

When streetlights were invented, they made it safer and more comfortable to be out after sunset. At first, these lights used oil or gas, but later, electric lights made it even brighter. This change allowed people to work, go to school, or enjoy activities that used to happen only during the day.

Fear of the dark

Even with bright lights, many people still feel uneasy when it’s dark, especially children. Stories about scary things that might happen at night have been told for a long time. Some adults also feel nervous walking alone after dark, particularly in places that seem unsafe.

Folklore and religion

Many cultures have special stories about the night sky. Some people believe the Milky Way is a path for spirits or a road to places beyond our world. Different cultures have goddesses and gods connected to the night, often linking it to rest, dreams, or mysterious forces.

Nightlife

Nightlife refers to fun activities that many people enjoy after the sun goes down. This can include going to bars, clubs, movies, or concerts. Nightlife is popular with adults and often includes special events or gatherings. In cities, nightlife is important for tourism and the local economy. It has also been a place where people come together for cultural and social movements throughout history.

Art

Literature

Night is often used in stories to show mystery, secrets, and danger. One famous play, Rhesus, uses night as a time of confusion when the hero Odysseus sneaks into the enemy camp. Writers through history have used night to describe hidden feelings and magic. Modern stories often use night to show places like hospitals where many important events happen.

Night fell, while Helga Crane in the rushing swiftness of a roaring elevated train sat numb. It was as if all the bogies and goblins that had beset her unloved, unloving, and unhappy childhood had come to life with tenfold power to hurt and frighten.

— Lella Larsen, Quicksand

Film and photography

Filming at night is tricky because cameras don't see as well as our eyes in the dark. Old movies often faked night by filming during the day and making everything look blue. Modern movies can film at night using special lights. Taking pictures at night can be beautiful. Longer picture times let photographers add light to make cool effects, and special camera settings help capture moving things without blurring.

Painting

Artists have painted night for thousands of years. Early night sky paintings used special symbols. Later, artists used dark colors to show night scenes. Some famous painters made night look very real by using strong lights and deep shadows. Others used special brown and blue shades to show darkness. Today, painters show night in many ways, from old symbols to modern city lights.