Night

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For other uses, see Night (disambiguation).

The night sky over a lake
Night sky over a bog in Estonia, with light pollution visible on the horizon

Night or nighttime is the period of ambient darkness when the Sun is below the horizon.

The word can be used in a social sense as the time between bedtime and morning. In common communication, it is a farewell (sometimes lengthened to "good night"), mainly when someone is going to sleep or leaving.[1]

Astronomical night is the period between astronomical

equinoxes
. And as seen from latitudes greater than 72° north or south of the equator, complete darkness does not occur in both equinoxes because, although the Sun sets, it is never more than 18° below the horizon.

The opposite of night is

umbra
, where the night is darkest.

Natural illumination at night is still provided by a combination of moonlight, planetary light, starlight, zodiacal light, gegenschein, and airglow. In some circumstances, aurorae, lightning, and bioluminescence can provide some illumination. The glow provided by artificial lighting is sometimes referred to as light pollution because it can interfere with observational astronomy and ecosystems.

Duration and geography

On Earth, an average night is shorter than daytime due to two factors. Firstly, the Sun's apparent disk is not a point, but has an angular diameter of about 32 arcminutes (32'). Secondly, the atmosphere refracts sunlight so that some of it reaches the ground when the Sun is below the horizon by about 34'. The combination of these two factors means that light reaches the ground when the center of the solar disk is below the horizon by about 50'. Without these effects, daytime and night would be the same length on both equinoxes, the moments when the Sun appears to contact the celestial equator. On the equinoxes, daytime actually lasts almost 14 minutes longer than night does at the equator, and even longer towards the poles.

The drainage basin of the Nile river and delta at night

The

low latitudes before and after an equinox. In the Northern Hemisphere, Denmark experiences shorter nights in June than India. In the Southern Hemisphere, Antarctica sees longer nights in June than Chile. Both hemispheres experience the same patterns of night length at the same latitudes, but the cycles are 6 months apart so that one hemisphere experiences long nights (winter) while the other is experiencing short nights (summer
).

In the region within either polar circle, the variation in daylight hours is so extreme that part of summer sees a period without night intervening between consecutive days, while part of winter sees a period without daytime intervening between consecutive nights.[2]

Beyond Earth

waning moon

The phenomenon of day and night is due to the rotation of a

retrograde rotation and orbital motion around the Sun.[4] Mercury has the longest day-night cycle as a result of its 3:2 resonance between its orbital period and rotation period - this resonance gives it a day-night cycle that is 176 days long.[5] A planet may experience large temperature variations between day and night, such as Mercury, the planet closest to the sun.[6]

The day-night cycle is one consideration for planetary habitability or the possibility of extraterrestrial life on distant exoplanets.[7] Some exoplanets, like those of TRAPPIST-1, are tidally locked. Tidally locked planets have equal rotation and orbital periods, so one side experiences constant day, and the other side constant night. In these situations, astrophysicists believe that life would most likely develop in the twilight zone between the day and night hemispheres.[8][9]

Effects on life

Biological

The disappearance of sunlight, the primary

carbon fixation which allows some photosynthetic plants to store carbon dioxide in their tissues as organic acids during the night, which can then be used during the day to synthesize carbohydrates. This allows them to keep their stomata closed during the daytime, preventing transpiration of water
when it is precious.

Social

Further information: Nightlife and Timeline of lighting technology
Regent Street, London, England, at 10:00 pm

The first constant electric light was demonstrated in 1835.[10] As artificial lighting has improved, especially after the Industrial Revolution, nighttime activity has increased and become a significant part of the economy in most places. Many establishments, such as nightclubs, bars, convenience stores, fast-food restaurants, gas stations, distribution facilities, and police stations now operate 24 hours a day or stay open as late as 1 or 2 a.m. Even without artificial light, moonlight sometimes makes it possible to travel or work outdoors at night.

cinemas, and shows. These venues often require a cover charge for admission. Nightlife entertainment is often more adult
-oriented than daytime entertainment.

Cultural and psychological

Nótt, the personification of night in Norse mythology, rides her horse in this 1887 painting by Peter Nicolai Arbo.
National Museum in Warsaw
, Poland)
Vincent van Gogh's 1889 painting The Starry Night[12]

Night is often associated with danger and evil, because of the psychological connection of night's all-encompassing darkness to the fear of the unknown and darkness's hindrance of a major sensory system (the sense of sight). Nighttime is naturally associated with vulnerability and danger for human physical survival. Criminals, animals, and other potential dangers can be concealed by darkness. Midnight has a particular importance in human imagination and culture.

Upper Paleolithic art was found to show (by André Leroi-Gourhan) a pattern of choices where the portrayal of animals that were experienced as dangerous were located at a distance from the entrance of a cave dwelling at a number of different cave locations.[13]

The belief in magic often includes the idea that magic and magicians are more powerful at night. Séances of spiritualism are usually conducted closer to midnight. Similarly, mythical and folkloric creatures such as vampires, ghosts and werewolves are described as more active at night. In almost all cultures, legendary stories warn of the night's dangers.

The cultural significance of the night in Islam differs from that in Western culture. The Quran was revealed during the Night of Power, the most significant night according to Islam. Muhammad made his famous journey from Mecca to Jerusalem and then to heaven in the night. Another prophet, Abraham, came to realize the supreme being in charge of the universe at night.

People who prefer nocturnal activity are called

night owls.[14]

See also

References

  1. ^ "Definition of good night". merriam-webster.com. Retrieved 31 December 2019.
  2. ^ "Day Length". University Of Guelph. Archived from the original on 27 May 2021. Retrieved 27 May 2021.
  3. ^ Seidelmann, P. K.; Abalakin, V. K.; Bursa, M.; Davies, M. E.; et al. (2001). "Report of the IAU/IAG Working Group on Cartographic Coordinates and Rotational Elements of the Planets and Satellites: 2000". HNSKY Planetarium Program. Archived from the original on 26 December 2018. Retrieved 2 February 2007.
  4. ^ Williams, Matt (7 February 2017). "How Long is a Day on Venus?". Universe Today. Retrieved 14 February 2024.
  5. ^ "Space Topics: Compare the Planets: Mercury, Venus, Earth, The Moon, and Mars". Planetary Society. Archived from the original on 28 July 2011. Retrieved 12 April 2007.
  6. ^ "Mercury: Facts - NASA Science". science.nasa.gov. Retrieved 14 February 2024.
  7. ^ Clery, Daniel (1 November 2017). "Earth-sized alien worlds are out there. Now, astronomers are figuring out how to detect life on them". Science. American Association for the Advancement of Science. Retrieved 29 February 2024.
  8. ^ Walla, Emily (10 April 2019). "Powerful Particles and Tugging Tides May Affect Extraterrestrial Life". University of Arizona News.
  9. ^ Lewis, Briley (5 April 2023). "Aliens could be hiding in 'terminator zones' on planets with eternal night". Space.
  10. ^ Matulka, Rebecca; Wood, Daniel (22 November 2013). "The History of the Light Bulb". Department of Energy. Archived from the original on 25 May 2021. Retrieved 25 May 2021.
  11. ^ "Nightlife – Definition of nightlife by Merriam-Webster". merriam-webster.com.
  12. MoMA
    . Retrieved May 23, 2021.
  13. ISBN 9780191025266
    . Retrieved 26 May 2021. The source doesn't state whether the location "painted in the depths" had natural light or no natural light.
  14. ^ Klein, Stefan (2008). Time. p. 20.

Further reading

Culture

External links

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