twilight
American Heritage Dictionary:
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twi·light
(twī'līt') 
n.
n.
- The diffused light from the sky during the early evening or early morning when the sun is below the horizon and its light is refracted by the earth's atmosphere.
- The time of the day when the sun is just below the horizon, especially the period between sunset and dark.
- Dim or diffused illumination.
- A period or condition of decline following growth, glory, or success: in the twilight of his life.
- A state of ambiguity or obscurity.
[Middle English twilighte : Old English twi-, two, half + Old English līht, light; see light1.]
Wiley Book of Astronomy:
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Twilight
The interval that follows sunset and comes before sunrise, during which the sky is partially illuminated by light from the Sun. Twilight lengthens with the distance of the observer from the equator, and is shortest as seen from anywhere on Earth at the equinoxes. Astronomical twilight is defined to begin in the morning and to end in the evening, when the center of the Sun is geometrically 18° below the horizon. Before the beginning of astronomical twilight in the morning and after the end of astronomical twilight in the evening, the Sun does not contribute at all to sky illumination. This corresponds to the older definition, going back to ancient times, that hinged on the ability to discern a sixth magnitude star (at the limit of naked-eye visibility) at the zenith. Civil twilight and nautical twilight are defined in exactly the same way but with 6° and 12°, respectively, in place of the 18° for the astronomical variety.
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The period between sunset and darkness in the evening, and between darkness and sunrise in the morning. The characteristic light is caused by atmospheric scattering, which transmits sunlight to the observer for some time after sunset and before sunrise. It depends geometrically on latitude, longitude, and elevation of the observer, and on the time of year. Physically it depends also on local conditions, particularly the weather.
Roget's Thesaurus:
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twilight
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The periods of incomplete darkness following sunset and preceding sunrise. Twilight is designated as civil, nautical, or astronomical, as the darker limit occurs when the center of the sun is 6 degrees, 12 degrees, or 18 degrees, respectively, below the celestial horizon.
See the Introduction, Abbreviations and Pronunciation for further details.
Oxford Companion to the Photograph:
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twilight
As well as being evocative in its own right, twilight is the key to many of the best so-called ‘night’ shots. Subjects are differentiated against the sky, whereas in true night they often merge into blackness, except in cities where light pollution means that not even the night is ever fully dark. It is often possible, by looking closely at a picture, to determine whether it was a true night shot or a dusk shot.
As soon as the sun has set, contrast falls and the light becomes very blue, which is obvious in colour; but in black-and-white the result of a generous exposure looks like an overcast day. Reducing exposure creates a much more nightlike effect. Light levels change rapidly, so the exposure required to create a particular effect can change very quickly, especially in southern climes where twilight is shorter than in the north.
Dusk can also be faked, in the style of the movie maker's nuit americaine. This is achieved by a combination of heavy filtration (blue for colour, red for black-and-white) and underexposure. Done properly, nuit americaine can be quite convincing, as long as it is not let down by heavy shadows which seldom look like genuine moonlight. An overcast day, when street lights and car headlights stand out brightly, is often the most convincing. In the heyday of pictorial photography, combination prints of lowering skies and heavy overexposure often created much the same effect.
— Roger W. Hicks
Bibliography
- Hicks, R., Low Light and Night Photography: A Practical Handbook (1989).
- ‘Fotografie und Daemmerung’,
Fotogeschichte , 89 (2003)
Oxford Dictionary of Dance:
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Twilight
Ballet in one act with choreography by van Manen, music by Cage, and designs by Vroom. Premiered 20 June 1972 by the Dutch National Ballet at Stadsschouwburg in Amsterdam with Radius and Ebbelaar. The ballet is set to Cage's Perilous Night and tells of a man and a woman who are engaged in an aggressive and confrontational relationship. It was revived for the Royal Ballet in 1973.
Columbia Encyclopedia:
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Twilight
twilight, period between sunset and total darkness or between total darkness and sunrise. Total darkness does not occur immediately when the sun sinks below the horizon because light from the sun that strikes the atmosphere is scattered (both by the air itself and by suspended matter, e.g., dust and smoke). Civil twilight ends when the center of the sun is 6° below the horizon. Although it is still not very dark, it is necessary to use artificial light to carry out most activities. Nautical twilight ends when the sun's center is 12° below the horizon; at about this time the light is too dim for the user of a sextant to see a sharp horizon. Astronomical twilight ends when the sun's center is 18° below the horizon; by this time even the faintest stars overhead can be seen. (Similar definitions apply to morning twilight.) During twilight, Venus or Mercury is often seen as the evening star or morning star. The length of twilight depends on latitude and the time of year. Twilight is generally shorter at the equator, where the sun's path toward the horizon is more nearly vertical than at higher latitudes; typically, astronomical twilight may last for 1 hr at the equator and 11/2 hr in New York City.
The Dream Encyclopedia:
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Twilight
Twilight is usually thought of as a peaceful and colorful time of day. In a dream it may signify that someone is well along in years or represent an end to old conditions or circumstances.
McGraw-Hill Dictionary of Aviation:
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twilight
The period of incomplete darkness following sunset and preceding sunrise. Twilight is designated as civil, nautical, or astronomical, as the darker limit occurs when the center of the sun is 6°, 12°, and 18°, respectively, below the celestial horizon. The period of civil twilight before sunrise is known as morning civil twilight and after the sunset as evening civil twilight. The air almanac lists the local mean times of the beginning of morning civil twilight and the end of evening civil twilight in exactly the same format as sunrise and sunset tables. The twilight tables are printed on the right-hand pages facing the sunrise and sunset tables, with each pair covering the same block of calendar dates.
Random House Word Menu:
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categories related to 'twilight'
- Cyclical Events - twilight: hour after sunset; crepuscule
- Fixed Times - twilight: period of dimming light just after sunset
See crossword solutions for the clue Wikipedia on Answers.com:
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Twilight
For other uses, see Twilight (disambiguation).
Twilight is the time between dawn and sunrise or between sunset and dusk, during which sunlight scattering in the upper atmosphere illuminates the lower atmosphere, and the surface of the earth is neither completely lit nor completely dark. The sun itself is not directly visible because it is below the horizon. Owing to the distinctive quality of the ambient light at this time, twilight has long been popular with photographers and painters, who refer to it as the "blue hour", after the French expression l'heure bleue. Twilight is technically defined as the periods between sunset and sunrise during which there is natural light provided by the upper atmosphere, which receives direct sunlight and scatters part of it towards the earth's surface.[1]
The collateral adjective for twilight is crepuscular; it is most frequently encountered when applied to certain insects, fishes and mammals that are most active during that time.
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Contents
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Definitions
Twilight is defined according to the solar elevation angle 
, which is the position of the geometric center of the sun relative to the horizon. There are three established and widely accepted subcategories of twilight: civil twilight (brightest), nautical twilight, and astronomical twilight (darkest).[2]
| Definition | Sun's centre relative to mathematical horizon[3] |
|---|---|
| Day | 0° ≤ |
| Sun's lower limb at horizon | = 0° 15' |
| Center of Sun's disk at horizon | = 0° |
| Sun's upper limb at horizon | = −0° 15' |
| Solar twilight | 0° ≤ < 6° |
| Civil twilight | −6° ≤ < 0° |
| Nautical twilight | −12° ≤ < −6° |
| Astronomical twilight | −18° ≤ < −12° |
| Night | < −18° |
(For these definitions, an ideal horizon 90° from the zenith is used.)
Civil twilight
Morning civil twilight begins when the geometric center of the sun is 6° below the horizon (civil dawn) and ends at sunrise. Evening civil twilight begins at sunset and ends when the geometric center of the sun reaches 6° below the horizon (civil dusk).
The brightest stars appear during the civil twilight, as well as planets, such as Venus, which is known as the "morning star" or "evening star". During this period there is enough light from the sun that artificial sources of light may not be needed to carry on outdoor activities. This concept is sometimes enshrined in laws, for example, when drivers of automobiles must turn on their headlights (called lighting-up time in the UK); when pilots may exercise the rights to fly aircraft; or if the crime of burglary is to be treated as nighttime burglary, which carries stiffer penalties in some jurisdictions. A fixed period (most commonly 30 minutes after sunset or before sunrise) is typically used in such statutes, rather than how many degrees the sun is below the horizon. Civil twilight can also be described as the limit at which twilight illumination is sufficient, under clear weather conditions, for terrestrial objects to be clearly distinguished; at the beginning of morning civil twilight, or end of evening civil twilight, the horizon is clearly defined and the brightest stars are visible under clear atmospheric conditions.
Nautical twilight
Nautical twilight is the time when the center of the sun is between 6° and 12° below the horizon. In general, nautical twilight ends when navigation via the horizon at sea is no longer possible.[3]
During nautical twilight, sailors can take reliable star sightings of well-known stars, using a visible horizon for reference. The end of this period in the evening, or its beginning in the morning, is also the time at which traces of illumination near the sunset or sunrise point of the horizon are very difficult, if not impossible, to discern (this often being referred to as "first light" before civil dawn and "nightfall" after civil dusk). At the beginning of nautical twilight in the morning (nautical dawn), or at the end of nautical twilight in the evening (nautical dusk)—under good atmospheric conditions and in the absence of other illumination—general outlines of ground objects may be distinguishable, but detailed outdoor operations are not possible, and the horizon is indistinct.
Nautical twilight has military considerations as well. The initialisms BMNT (begin morning nautical twilight, i.e. nautical dawn) and EENT (end evening nautical twilight, i.e. nautical dusk) are used and considered when planning military operations. A military unit may treat BMNT and EENT with heightened security, e.g. by "standing to", in which everyone assumes a defensive position. This is partially due to tactics dating back to the French and Indian War (part of the Seven Years' War of 1756–1763), when combatants on both sides would launch attacks at nautical dawn or dusk.
Astronomical twilight
Astronomical twilight is the time when the center of the sun is between 12° and 18° below the horizon. From the end of astronomical twilight in the evening to the beginning of astronomical twilight in the morning, the sky (away from urban light pollution) is dark enough for all astronomical observations.
Most casual observers would consider the entire sky fully dark even when astronomical twilight is just beginning in the evening or just ending in the morning, and astronomers can easily make observations of point sources such as stars, but faint diffuse items such as nebulae and galaxies can be properly observed only beyond the limit of astronomical twilight. In some places, especially those with sky glow, astronomical twilight may be almost indistinguishable from night. Theoretically, the dimmest stars ever visible to the naked eye—those of the sixth magnitude—will become visible in the evening once the sun falls more than 18° below the horizon (i.e., at astronomical dusk) and become invisible when the sun moves to within 18° of the horizon in the morning (at astronomical dawn). However, because of light pollution, some localities—generally those in large cities—may never have the opportunity to view even fourth-magnitude stars, irrespective of the presence of any twilight at all.[1]
Length
The length of twilight after sunset and before sunrise is heavily influenced by the latitude of the observer. In the Arctic and Antarctic regions, twilight (if there is any) can last for several hours. There is no civil twilight at the poles within a month on either side of the winter solstice. At the poles, civil twilight can be as long as two weeks, while at the equator, conditions can go from day to night in as little as twenty minutes. This is true because at low latitudes the sun's apparent movement is perpendicular to the observer's horizon. As one gets closer to the Arctic and Antarctic circles, the sun's disk moves toward the observer's horizon at a lower angle. The observer's earthly location will pass through the various twilight zones less directly, taking more time.
Within the polar circles, twenty-four hour daylight is encountered in summer, and in regions very close to the poles, twilight can last for weeks on the winter side of the equinoxes. Outside the polar circles, where the angular distance from the polar circle is less than the angle which defines twilight (see above), twilight can continue through local midnight near the summer solstice (June in the Northern Hemisphere, December in the Southern Hemisphere). The precise position of the polar circles—and thus of the regions where twilight can continue through local midnight—varies slightly from year to year with Earth's axial tilt. The lowest latitudes at which the various twilights can continue through local midnight are approximately 60.561° (60° 33’ 43”) for civil twilight, 54.561° (54° 33’ 43”) for nautical twilight and 48.561° (48° 33’ 43”) for astronomical twilight.[4][5]
These are the largest cities, of their respective countries, where the various twilights can continue through local solar midnight:
- Civil twilight from sunset to sunrise: Arkhangelsk, Tampere, Umeå, Trondheim, Mid Yell, Tórshavn, Reykjavik, Nuuk, Whitehorse, Anchorage and Baltasound.
- Nautical twilight from civil dusk to civil dawn: Petropavl, Moscow, Vicebsk, Vilnius, Riga, Tallinn, Wejherowo, Flensburg, Helsinki, Stockholm, Copenhagen, Oslo, Newcastle upon Tyne, Glasgow, Belfast, Letterkenny, Edmonton, Grande Prairie, Juneau, Ushuaia and Puerto Williams.
- Astronomical twilight from nautical dusk to nautical dawn: Hulun Buir, Erdenet, Astana, Samara, Kiev, Minsk, Warsaw, Košice, Northernmost points of Hungary, Zwettl, Prague, Berlin, Paris, Luxembourg City, Brussels, Amsterdam, London, Cardiff, Dublin, Winnipeg, Calgary, Vancouver, International Falls, Bellingham, Rio Gallegos and Punta Arenas.
Although Helsinki, Oslo, Stockholm, Tallinn and Saint Petersburg do not actually receive civil twilight from sunset to sunrise, they do have noticeably lighter skies at night (known as white nights) around the summer solstice.
During the winter solstice there are various twilights that can go through solar noon. Here are the highest latitudes that twilight go through solar noon 73.439° ( 73° 26' 17" ) for Civil twlight,79.439°( 79° 26' 17" ) for Nautical twlight,85.439°( 85° 26' 17 ) for Astronomical twlight.
These are the cities where twilights can continue through solar noon:
- Astronomical twilight from dawn to dusk: Alert, Canada
On other planets
Twilight on Mars is longer than on Earth, lasting for up to two hours before sunrise or after sunset. Dust high in the atmosphere scatters light to the night side of the planet. Similar twilights are seen on Earth following major volcanic eruptions.[6]
In Hinduism
Twilight is sacred in Hinduism. It is called गोधूळिवेळ in Marathi or गोधूलिवेला godhūlivelā in Hindi—literally "cow dust time". Many rituals including Sandhyavandanam and Puja are performed at twilight. Hindus believe that this time is ideal for study and education.[7]
Gallery
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Twilight after sunset in Parbhani
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Nautical twilight in Acapulco, with visible stars and horizon
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Astronomical twilight at Prague Castle
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The red skies seen during Twilight in Madurai, Tamil Nadu, India.
See also
- BMCT
- Dawn
- Dusk
- Earth's shadow, visible at twilight
- Gloom
- Green flash
- Polar night
- Sunrise
- Sunset
References
- ^ a b "Definitions from the US Astronomical Applications Dept (USNO)". http://aa.usno.navy.mil/faq/docs/RST_defs.php. Retrieved 2011-07-22.
- ^ "Rise, Set, and Twilight Definitions". US Naval Observatory. United States Navy. http://www.usno.navy.mil/USNO/astronomical-applications/astronomical-information-center/rise-set-twi-defs.
- ^ a b Van Flandern, T.; K. Pulkkinen (1980). "Low precision formulae for planetary positions". Astrophysical Journal, Supplement Series 31 (3). Bibcode 1979ApJS...41..391V.
- ^ "Length of Day and Twilight (Formulas)". www.gandraxa.com. http://www.gandraxa.com/length_of_day.xml. Retrieved 2011-08-26.
- ^ Herbert Glarner's website, reference 2. "Civil Twilight" "6°", "Nautical Twilight" "12°". "90°-Axis(23.439°)-12°=54.561°.
- ^ NASA-Jet Propulsion Laboratory: Winter Solstice on Mars: Rovers Look Forward to A Birtha Williams Sanford Crisanthemum Barbra Layota Martian Spring, August 07, 2006.
- ^ Jossleyn Hennessy (1955). "ch. VII Education in the villages "Cow-dust time"". India democracy and education. Orient Longmans. p. 127. http://books.google.co.uk/books?id=fGEXAAAAIAAJ.
Bibliography
- Mateshvili, Nina; Didier Fussen; Filip Vanhellemont; Christine Bingen; Erkki Kyrölä; Iuri Mateshvili; Giuli Mateshvili (2005). "Twilight sky brightness measurements as a useful tool for stratospheric aerosol investigations". Journal of Geophysical Research 110 (D09209): D09209. Bibcode 2005JGRD..11009209M. doi:10.1029/2004JD005512.
External links
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Wikiquote has a collection of quotations related to: Twilight |
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Look up twilight in Wiktionary, the free dictionary. |
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Wikimedia Commons has media related to: Twilight |
- Twilight Calculator Compute twilight times.
- Definition of Twilight US Naval Observatory.
- Twilight time calculator
- Formulae to calculate twilight duration by Herbert Glarner.
- The colors of twilight and sunset
- HM Nautical Almanac Office websurf Compute twilight times.
- Geoscience Australia "Sunrise and sunset times" Compute twilight times.
"Twilight". Collier's New Encyclopedia. 1921.- Beach, Chandler B., ed. (1914). " Twilight". The New Student's Reference Work. Chicago: F. E. Compton and Co.. Wikisource
- An Excel workbook with VBA functions for twilight (dawn and dusk), sunrise, solar noon, sunset, and solar position (azimuth and elevation) by Greg Pelletier, translated from NOAA's online calculator for sunrise/sunset
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Translations:
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Twilight
Dansk (Danish)
n. - tusmørke, skumring, dunkel, halvmørke
Nederlands (Dutch)
(avond- of ochtend) schemering, nadagen (laatste periode), schemergebied
Français (French)
n. - (lit, fig) crépuscule
Deutsch (German)
n. - Dämmerung, Zwielicht
Ελληνική (Greek)
n. - λυκόφως, μισοσκόταδο, (μτφ.) δύση, παρακμή
Italiano (Italian)
aurora, crepuscolo
Português (Portuguese)
n. - crepúsculo (m), penumbra (f), compreensão (f) ou conhecimento imperfeito (m)
Русский (Russian)
вечерние сумерки, упадок
Español (Spanish)
n. - crepúsculo, ocaso, media luz
Svenska (Swedish)
n. - skymning, mörkning, halvdager, halvmörker, dunkel
中文（简体）(Chinese (Simplified))
微明, 微光, 薄暮, 黄昏
中文（繁體）(Chinese (Traditional))
n. - 微明, 微光, 薄暮, 黃昏
한국어 (Korean)
n. - 어스름, 미광, 중간 상태
日本語 (Japanese)
n. - 薄明かり, たそがれどき, 衰退期
العربيه (Arabic)
(الاسم) حمرة ألأفق عند غروب ألشمس
עברית (Hebrew)
n. - דמדומי-ערב, נצנוצי-שחר, בין-הערביים, תקופת-שקיעה, מצב של חוסר-בהירות
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American Heritage Dictionary
The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.
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