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Encyclopedia > Twilight
Twilight in Pittsburgh, PA
Twilight in Pittsburgh, PA
Twilight in Denmark, just after sunset
Twilight in the midwestern US featuring Venus as a brilliant "evening star" and the crescent moon
Twilight in the midwestern US featuring Venus as a brilliant "evening star" and the crescent moon
Finland - Lapland at midnight in July
Finland - Lapland at midnight in July
Twilight in Acapulco with Long time Exposure
Twilight in Acapulco with Long time Exposure
Early twilight in California, before sunset
Early twilight in California, before sunset
Twilight over the Mediterranean Sea, Israel, just after sunset
Twilight over the Mediterranean Sea, Israel, just after sunset

Twilight is the time before sunrise or after sunset when sunlight scattered in the upper atmosphere illuminates the lower atmosphere and the surface of the Earth is between light and dark. Image File history File links Merge-arrows. ... Dusk in Breaux Bridge, Louisiana, USA. Dusk outside a plane on cruise. ... Look up twilight in Wiktionary, the free dictionary. ... Image File history File links Size of this preview: 600 × 599 pixelsFull resolution‎ (800 × 799 pixels, file size: 121 KB, MIME type: image/jpeg) Light Study - Twilight Photo - Pittsburgh, PA Dec 03 additional images located [1] File historyClick on a date/time to view the file as it appeared at... Image File history File links Size of this preview: 600 × 599 pixelsFull resolution‎ (800 × 799 pixels, file size: 121 KB, MIME type: image/jpeg) Light Study - Twilight Photo - Pittsburgh, PA Dec 03 additional images located [1] File historyClick on a date/time to view the file as it appeared at... Image File history File links Download high resolution version (1350x900, 381 KB)Picture of Lillebælt in the twilight. ... Image File history File links Download high resolution version (1350x900, 381 KB)Picture of Lillebælt in the twilight. ... Image File history File links Download high resolution version (1958x1380, 356 KB)Picture of a beautiful evening sky featuring the cresent moon next to the planet Venus over a grain elavator. ... Image File history File links Download high resolution version (1958x1380, 356 KB)Picture of a beautiful evening sky featuring the cresent moon next to the planet Venus over a grain elavator. ... ImageMetadata File history File links Download high resolution version (2048x1536, 934 KB) Finland, Lapland: midnight twilight, 22:09CET/23:09EET, July 31st 2005 File links The following pages link to this file: Twilight ... ImageMetadata File history File links Download high resolution version (2048x1536, 934 KB) Finland, Lapland: midnight twilight, 22:09CET/23:09EET, July 31st 2005 File links The following pages link to this file: Twilight ... Lappi, or the Province of Lapland is one of the Provinces of Finland, and a part of the larger geographical area of Lapland, which spans over four countries. ... Image File history File linksMetadata Download high-resolution version (3072x2048, 2323 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Exposure (photography) Twilight Metadata This file contains additional information, probably added from the digital camera or scanner used... Image File history File linksMetadata Download high-resolution version (3072x2048, 2323 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Exposure (photography) Twilight Metadata This file contains additional information, probably added from the digital camera or scanner used... Image File history File linksMetadata Size of this preview: 800 × 533 pixelsFull resolution (3456 × 2304 pixel, file size: 3. ... Image File history File linksMetadata Size of this preview: 800 × 533 pixelsFull resolution (3456 × 2304 pixel, file size: 3. ... Image File history File links Metadata Size of this preview: 800 × 600 pixelsFull resolution‎ (2,048 × 1,536 pixels, file size: 843 KB, MIME type: image/jpeg) File historyClick on a date/time to view the file as it appeared at that time. ... Image File history File links Metadata Size of this preview: 800 × 600 pixelsFull resolution‎ (2,048 × 1,536 pixels, file size: 843 KB, MIME type: image/jpeg) File historyClick on a date/time to view the file as it appeared at that time. ... Mediterranean redirects here. ... A typical sunrise, in New Zealand A sunrise through clouds over Oakland, California. ... A composite image showing the terminator dividing night from day, running across Europe and Africa. ... Prism splitting light High Resolution Solar Spectrum Sunlight in the broad sense is the total spectrum of the electromagnetic radiation given off by the Sun. ... Scattering is a general physical process whereby some forms of radiation, such as light, sound or moving particles, for example, are forced to deviate from a straight trajectory by one or more localized non-uniformities in the medium through which it passes. ... Air redirects here. ... This article is about Earth as a planet. ...


The collateral adjective of "twilight" is crepuscular (for daylight it is "diurnal" and for night, "nocturnal"). The term is most frequently encountered when applied to certain species of insects and mammals that are most active during that time. Collateral adjective refers to an adjective with the same meaning as a noun but derived from a different root. ... Adult Firefly or Lightning Bug – a Crepuscular Beetle Photuris lucicrescens Crepuscular is a term used to describe animals that are primarily active during the twilight. ... Orders Subclass Apterygota Archaeognatha (bristletails) Thysanura (silverfish) Subclass Pterygota Infraclass Paleoptera (Probably paraphyletic) Ephemeroptera (mayflies) Odonata (dragonflies and damselflies) Infraclass Neoptera Superorder Exopterygota Grylloblattodea (ice-crawlers) Mantophasmatodea (gladiators) Plecoptera (stoneflies) Embioptera (webspinners) Zoraptera (angel insects) Dermaptera (earwigs) Orthoptera (grasshoppers, etc) Phasmatodea (stick insects) Blattodea (cockroaches) Isoptera (termites) Mantodea (mantids) Psocoptera... Subclasses & Infraclasses Subclass †Allotheria* Subclass Prototheria Subclass Theria Infraclass †Trituberculata Infraclass Metatheria Infraclass Eutheria Mammals (class Mammalia) are warm-blooded, vertebrate animals characterized by the presence of sweat glands, including those that produce milk, and by the presence of: hair, three middle ear bones used in hearing, and a neocortex...

Contents

Definitions

The following guidelines have been established and widely accepted. (For these definitions, an ideal horizon 90° from the zenith is used. The altitudes of the sun below the horizon are "true geometric" altitudes, that is, refraction by the atmosphere and other small factors influencing the observed position of the Sun are not to be accounted for.) Image File history File links Broom_icon. ... In broad terms, the zenith is the direction pointing directly above a particular location (perpendicular, orthogonal). ... For the property of metals, see refraction (metallurgy). ...


Civil twilight

This begins in the morning when the center of the Sun is less than 6° below the horizon (the point of civil dawn), and ends at sunrise. Evening civil twilight begins at sunset and ends when the center of the Sun is more than 6° below the horizon (the point of civil dusk).
The brightest stars appear during civil twilight, as well as planets, such as Venus which is known as the 'morning star' and/or 'evening star'. During this period there is enough light from the Sun so that artificial sources of light are not needed to carry on outdoor activities. This concept is sometimes enshrined in laws, like when drivers of automobiles must turn on their headlights, or if the crime of burglary is to be treated as night-time burglary, or in the daytime, with the latter determination resulting in a lesser penalty —although a fixed period of time (most commonly 30 minutes after sunset or before sunrise) will form the basis for the application of these 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 good 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 good atmospheric conditions in the absence of moonlight or other illumination. Sol redirects here. ... Horizon. ... Sol redirects here. ... For other uses, see Venus (disambiguation). ...


Nautical twilight

This is defined as the time when the center of the Sun is more than 6° below the horizon but less than 12°.


At this time, sailors can take reliable star sights 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) and EENT (end evening nautical twilight) are used and considered when planning military operations. A military unit may treat BMNT and EENT with heightened security (i.e. a process called "stand to" in which everyone pulls security). This is partially due to tactics dating back to the French and Indian War, when warriors on both sides would use BMNT and EENT to launch attacks.


Astronomical twilight

This is defined as the time when the center of the Sun is more than 12° below the horizon but less than 18°.
Most casual observers would consider the entire sky already 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 objects such as nebulae and galaxies can only be properly observed beyond the limit of astronomical twilight. Conceptually, the dimmest stars ever visible to the naked eye —those of the sixth magnitude— will appear in the evening once the Sun falls more than 18° below the horizon (i.e. when astronomical dusk occurs) and disappear when the Sun moves to within 18° of the horizon in the morning (when astronomical dawn occurs); however, due to 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. This article is about the astronomical object. ... The Triangulum Emission Nebula NGC 604 The Pillars of Creation from the Eagle Nebula For other uses, see Nebula (disambiguation). ... For other uses, see Galaxy (disambiguation). ... The apparent magnitude (m) of a star, planet or other celestial body is a measure of its apparent brightness as seen by an observer on Earth. ... This time exposure photo of New York City shows sky glow, one form of light pollution. ...


Within the polar circles, 24-hour daylight is encountered in summer, and twilight literally lasts for weeks (in the polar fall and spring). In high latitudes outside the polar circles, 24-hour daylight is not seen, but twilight can extend from sunset to sunrise, a phenomenon often referred to as 'white nights'. Above roughly 60.5°N or S (e.g. Anchorage, Helsinki, Tallinn, Saint Petersburg and Oslo), civil twilight lasts all night at midsummer, while above about 54.5°N or S (e.g. Copenhagen, Moscow, Gdańsk, Glasgow, Belfast, Vilnius, Szczecin and Hamburg), nautical twilight lasts all night at midsummer. Astronomical twilight can last all night for several weeks as far from the poles as 48.5°N or S (e.g. London, Vancouver, Kraków, Prague, Frankfurt and Punta Arenas). The polar circle in Finland, 1975. ... Look up daylight in Wiktionary, the free dictionary. ... For other uses, see Summer (disambiguation). ... This article is about the geographical term. ... White night is a night on which it never gets completely dark, because the sun does not descend completly far below the horizon. ... This article is about the city in the U.S. state of Alaska. ... Location of Helsinki in Northern Europe Coordinates: , Country Province Region Uusimaa Sub-region Helsinki Charter 1550 Capital city 1812 Government  - Mayor Jussi Pajunen Area  - Total 187. ... County Area 159. ... Saint Petersburg (Russian: Санкт-Петербу́рг, English transliteration: Sankt-Peterburg), colloquially known as Питер (transliterated Piter), formerly known as Leningrad (Ленингра́д, 1924–1991) and... This article is about the capital of Norway. ... For other uses, see Copenhagen (disambiguation). ... For other uses, see Moscow (disambiguation). ... For alternative meanings of GdaÅ„sk and Danzig, see GdaÅ„sk (disambiguation) and Danzig (disambiguation) Motto: Nec temere, nec timide (No rashness, no timidness) Coordinates: , Country Voivodeship Powiat city county Gmina GdaÅ„sk Established 10th century City Rights 1263 Government  - Mayor PaweÅ‚ Adamowicz Area  - City 262 km²  (101. ... For other uses, see Glasgow (disambiguation). ... This article is about the city in Northern Ireland. ... Not to be confused with Vilnius city municipality. ... Stettin redirects here. ... This article is about the city in Germany. ... This article is about the capital of England and the United Kingdom. ... For other uses, see Vancouver (disambiguation). ... For other uses, see Krakow (disambiguation). ... For other uses, see Prague (disambiguation). ... For other uses, see Frankfurt (disambiguation). ... City of Punta Arenas Punta Arenas in Tierra del Fuego Sunrise view of the Strait of magellan Punta Arenas is the main city on the Strait of Magellan and the capital of the Región de Magallanes y la Antártica Chilena, Chile, and depending on the definition of city...


Twilight 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 at all) can last for several hours (with none at the poles within a month on either side of the winter solstice), while at the equator, it can go from day to night in as little as 20 minutes. This is because at low latitudes the earth's movement is perpendicular to the observer's horizon. Thus a location on the equator will pass through the various twilight zones directly and quickly. As one gets closer to the Arctic and Antarctic circles, the earth's surface moves toward the observer's horizon from a lower angle. The observer's earthly location will pass through the various twilight zones less directly, taking more time. At temperate-zone latitudes, twilight is shortest at or near both equinoxes, slightly longer around the time of the winter solstice, and much longer in late spring and early summer. This article is about the geographical term. ... The red line indicates the 10°C isotherm in July, commonly used to define the Arctic region border Satellite image of the Arctic surface The Arctic is the region around the Earths North Pole, opposite the Antarctic region around the South Pole. ... Greek ἀνταρκτικός, opposite the arctic) is a continent surrounding the Earths South Pole. ... World map showing the equator in red In tourist areas, the equator is often marked on the sides of roads The equator marked as it crosses Ilhéu das Rolas, in São Tomé and Príncipe. ...


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.[1] Adjectives: Martian Atmosphere Surface pressure: 0. ...


See also

Dusk in Breaux Bridge, Louisiana, USA. Dusk outside a plane on cruise. ... Look up daylight in Wiktionary, the free dictionary. ... The blue hour Commerzbank Tower in Frankfurt, Germany, at the blue hour The blue hour comes from a French expression (lheure bleue) which refers to the hour experienced between the hours of daylight and darkness. ... Green flashes and green rays are rare optical phenomena that occur shortly after sunset or before sunrise, when a green spot is visible for a short period of time above the sun, or a green ray shoots up from the sunset point. ... Dawn in Peng Chau, Hong Kong. ...

References

  1. ^ NASA-Jet Propulsion Laboratory: Winter Solstice on Mars: Rovers Look Forward to A Second Martian Spring, August 7, 2006

External links

Wikimedia Commons has media related to:
Twilight

  Results from FactBites:
 
Twilight (683 words)
Twilight (formally named Dawn by TakiCorb, but the other name stuck) was one of the first colony projects of the first federation era.
The twilight zone was colonised by tweaks, overseeing the construction of large climate controlled habitats for TakiCorb.
The Twilight culture is traditionally based around a complex animist religious philosophy involving the sun, the planet, the weather and the concept of flying (sailing on the intense winds is a common sport and form of religious worship).
  More results at FactBites »

 
 

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