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Spectral color

2025-11-02T03:24:33Z

2604:3D08:9476:BE00:1558:7B75:A113:A172:

{{short description|Color evoked by a single wavelength of light in the visible spectrum}}
{{Use American English|date=March 2021}}
{{Use mdy dates|date=March 2021}}
{{more citations needed|date=December 2009}}
[[File:WhereRainbowRises.jpg|thumb|A [[rainbow]] is a [[dispersion (optics)|decomposition]] of white light into ''all'' of the spectral colors.]]
[[File: Laser Pointer.jpg|thumb|Laser beams are monochromatic light, thereby exhibiting spectral colors.]]

A '''spectral color''' is a [[color]] that is evoked by [[monochromatic radiation|monochromatic light]], i.e. either a [[spectral line]] with a single [[wavelength]] or [[frequency]] of [[light]] in the [[visible spectrum]], or a relatively narrow [[spectral band]] (e.g. [[laser]]s). Every wave of visible light is perceived as a spectral color; when viewed as a [[continuous spectrum]], these colors are seen as the familiar [[rainbow]].
'''Non-spectral colors''' (or '''extra-spectral colors''') are evoked by a combination of spectral colors.

== In color spaces==
[[File:CIE1931xy blank.svg|right|thumb|
{{center|'''[[CIE 1931 color space#The CIE xy chromaticity diagram|CIE xy chromaticity diagram]]'''}}
The spectrum colors are the colors on the horseshoe-shaped curve on the outside of the diagram. All other colors are not spectral: the bottom line is ''the [[line of purples]]'', whilst within the interior of the diagram are unsaturated colors that are various mixtures of a spectral color or a purple color with [[white]], a grayscale color. White is in the central part of the interior of the diagram, since [[Additive colors|when all colors of light are mixed together, they produce white]].]]

In [[color space]]s which include all, or most spectral colors, they form a part of boundary of the set of all real colors. When considering a three-[[dimension]]al color space (which includes [[luminance]]), the spectral colors form a [[surface (mathematics)|surface]]. When excluding luminance and considering a two-dimensional color space ([[chromaticity diagram]]), the spectral colors form a [[curve]] known as the '''spectral locus'''. For example, the spectral locus of the [[CIE 1931 color space#CIE xyY|CIE xy]] chromaticity diagram contains all the spectral colors (to the eye of the standard observer).

A trichromatic color space is defined by three [[primary color]]s, which can theoretically be spectral colors. In this case, all other colors are inherently non-spectral. In reality, the spectral bandwidth of most primaries means that most color spaces are entirely non-spectral. Due to different chromaticity properties of different spectral segments, and also due to practical limitations of light sources, the actual [[color distance|distance]] between RGB pure [[color wheel]] colors and spectral colors shows a complicated dependence on the [[hue]]. Due to the location of R and G primaries near the 'almost flat' spectral segment, [[RGB color space]] is reasonably good with approximating spectral orange, yellow, and [[bright green|bright (yellowish) green]], {{anchor|×}}but is especially poor in reproducing the visual appearance of spectral colors in the vicinity of central green, and between green and blue, as well as extreme spectral colors approaching [[Infrared|IR]] or [[ultraviolet|UV]].

Spectral colors are universally included in [[color science|scientific]] color spaces such as CIE 1931, but industrial and consumer color spaces/models such as sRGB, CMYK, and [[Pantone Matching System|Pantone]], do not typically include any spectral colors. Exceptions include [[Rec. 2020]], which uses three spectral colors as primaries (and therefore only includes precisely those three spectral colors), and color spaces such as the [[ProPhoto RGB color space]] which use imaginary colors as primaries.

In color spaces such as [[CIELUV]], a spectral color has maximal [[Colorfulness#Saturation|saturation]]. In [[Helmholtz–Kohlrausch effect#Helmholtz color coordinates|Helmholtz coordinates]], this is described as 100% [[Colorfulness#Excitation_purity|purity]].

===In dichromatic color spaces===
In [[Dichromacy|dichromatic]] [[color vision]] there is no distinction between spectral and non-spectral colors. Their entire gamut can be represented by spectral colors.{{NoteTag|This is true for dichromats with [[photoreceptor cell]]s with overlapping [[spectral sensitivity]] curves. If the spectral sensitivity curves do not overlap, then all colors (except the ones that only excite one type of conecell) would be non-spectral. However, there are no known vision systems where the [[cone cell|cones']] spectral sensitivity curves do not overlap.}}

== Spectral color terms ==

The spectrum is often divided into ''[[color term]]s'' or names, but aligning boundaries between color terms to a specific wavelength is very subjective.

The first person to decompose white light and name the spectral colors was [[Isaac Newton]], in the 1660s.<ref>{{Cite web |title=Newton and the Science of Color |url=https://www.thecolumbiasciencereview.com/blog/newton-and-the-science-of-color |access-date=2025-05-02 |website=Columbia Science Review |language=en}}</ref> Early in the study of radiometry, Newton was not able to measure the wavelength of the light, but his experiments were repeated contemporarily to estimate wavelengths where his color term boundaries probably lay.<ref name=mclaren/> [[Isaac Newton|Newton's]] color terms included red, orange, yellow, green, blue, indigo, and violet; this color sequence is still used to describe spectral colors colloquially and a [[mnemonic]] for it is commonly known as "[[Roy G. Biv]]".

In modern divisions of the spectrum, [[Indigo#Isaac Newton's classification of indigo as a spectral color|indigo is often omitted]] and [[cyan]] is often included. Some have argued that Newton's indigo would be equivalent to modern blue, and his blue equivalent to cyan. However, his nonintuitive choices can be better explained. In the table below, note how wavelength is not proportional to hue (which is approximately perceptually uniform). Color systems such as [[ISCC-NBS]] attempt to divide the spectrum into sections that appear perceptually uniform. On the other hand, Newton's sections are approximately uniform in size as they would have physically appeared in the diffracted spectrum, i.e. each about 40nm "wide". In this theory, the sections were divided without influence of his own perception, and each section was then given a name that best suited its ''average'' color. In contrast, the sections in the [[ISCC-NBS]] spectrum vary greatly in wavelength range, but are more consistent in the [[hue]] degree range. Both instances deviate from the [[color term#Basic color terms|basic color terms]] used in English, only some of which are spectral colors.

The table below includes several definitions where the spectral colors have been categorized in [[color term]]s. The [[hue]] that a given monochromatic light evokes is approximated at the right side of the table.

{| class="wikitable" style="text-align: center;"
|+Spectral color classifications
!scope="col"|[[wavelength|nm]]
!scope="col"|[[Isaac Newton|Newton]][[#×|*]]<ref name=mclaren>{{cite journal |last1=McLaren |first1=K. |title=Newton's indigo |journal=Color Research & Application |date=1985 |volume=10 |issue=4 |pages=225–229 |doi=10.1002/col.5080100411}}</ref>
!scope="col"|[[ISCC-NBS]][[#×|*]]<ref>{{cite journal |last1=Kelly |first1=Kenneth L. |title=Color Designations for Lights |journal=Journal of the Optical Society of America |date=1 November 1943 |volume=33 |issue=11 |pages=627 |doi=10.1364/JOSA.33.000627}}</ref>
!scope="col"|Malacara<ref>{{cite book |last1=Malacara |first1=Daniel |title=Color vision and colorimetry : theory and applications |date=2011 |publisher=SPIE |location=Bellingham, Wash. |isbn=9780819483973 |edition=2nd}}</ref>
!scope="col"|[[CRC Handbook of Chemistry and Physics|CRC Handbook]]<ref>{{cite book |last1=Bruno |first1=Thomas J. |title=CRC handbook of fundamental spectroscopic correlation charts |date=2006 |publisher=CRC Press |location=Boca Raton, FL |isbn=9780849332500}}</ref>
!scope="col"|[[Hue]][[#×|*]]
|-
|380
| rowspan="5" bgcolor="#7F00FF" |'''Violet'''
| rowspan="6" bgcolor="#7F00FF" |'''Violet'''
| rowspan="5" bgcolor="#7F00FF" |'''Violet'''
| rowspan="7" bgcolor="#7F00FF" |'''Violet'''
|250°
|-
|390
|250°
|-
|400
|250°
|-
|410
|249°
|-
|420
|249°
|-
|430
| rowspan="2" bgcolor="#3F00FF |'''Indigo'''
| rowspan="7" bgcolor="#0000FF" |'''Blue'''
|249°
|-
|440
| rowspan="5" bgcolor="#0000FF" |'''Blue'''
|247°
|-
|450
| rowspan="4" bgcolor="#1DA2DF" |'''Blue'''
| rowspan="5" bgcolor="#0000FF" |'''Blue'''
|245°
|-
|460
|242°
|-
|470
|238°
|-
|480
|226°
|-
|490
| rowspan="4" bgcolor="#00FF00" |'''Green'''
| rowspan="1" bgcolor="#00FFFF" |'''Blue-Green'''
|190°
|-
|500
| rowspan="5" bgcolor="#00FF00" |'''Green'''
| rowspan="2" bgcolor="#00FFFF" |'''Cyan'''
| rowspan="7" bgcolor="#00FF00" |'''Green'''
|143°
|-
|510
|126°
|-
|520
| rowspan="5" bgcolor="#00FF00" |'''Green'''
|122°
|-
|530
| rowspan="5" bgcolor="#FFFF00"|'''Yellow'''
|117°
|-
|540
|113°
|-
|550
| rowspan="3" bgcolor="#88FF00" |'''Yellow-Green'''
|104°
|-
|560
|93°
|-
|570
| rowspan="1" bgcolor="#FFFF00" |'''Yellow'''
| rowspan="2" bgcolor="#FFFF00" |'''Yellow'''
|62°
|-
|580
| rowspan="4" bgcolor="#FF8800" |'''Orange'''
| rowspan="1" bgcolor="#FFFF00" |'''Yellow'''
| rowspan="5" bgcolor="#FF8800" |'''Orange'''
|28°
|-
|590
| rowspan="2" bgcolor="#FF8800" |'''Orange'''
| rowspan="3" bgcolor="#FF8800" |'''Orange'''
|14°
|-
|600
|7°
|-
|610
| rowspan="13" bgcolor="#FF0000" |'''Red'''
|5°
|-
|620
| rowspan="8" bgcolor="#FF0000" |'''Red'''
| rowspan="13" bgcolor="#FF0000" |'''Red'''
|3°
|-
|630
| rowspan="11" bgcolor="#FF0000" |'''Red'''
|2°
|-
|640
|1°
|-
|650
|1°
|-
|660
|1°
|-
|670
|0°
|-
|680
|0°
|-
|690
|0°
|-
|700
| rowspan="6" bgcolor="#000000" |
|0°
|-
|710
|0°
|-
|720
|0°
|-
|730
|0°
|-
|740
| rowspan="2" bgcolor="#000000" |
| rowspan="2" bgcolor="#000000" |
|0°
|-
|750
| rowspan="1" bgcolor="#000000" |
|
|}

==Extra-spectral colors==

Among some of the colors that are {{em|not}} spectral colors are:

* [[Grayscale]] (achromatic) colors, such as [[white]], [[grey|gray]], and [[black]].
* Any color obtained by mixing a gray-scale color and another real color (either spectral or not), such as [[pink]] (a mixture of a [[red]]dish color and white), or [[brown]] (a mixture of [[Orange (color)|orange]] and black or gray).
* [[Violet (color)|Violet]]-[[red]] colors, which include colors in the [[line of purples]] (such as [[magenta]] and [[Rose (color)|rose]]), and other variations of purple and red.
* [[Impossible color]]s, which cannot be seen under normal viewing of light, such as over-saturated colors or colors that are seemingly brighter than white.
* [[Metallic color]]s which reflect light by effect.

== Notes ==
{{NoteFoot}}

== References ==
{{Reflist}}

{{-}}
{{Color topics}}

{{DEFAULTSORT:Spectral Color}}
[[Category:Color]]

Ice crystal

2025-11-02T01:20:00Z

2604:3D08:9476:BE00:1558:7B75:A113:A172: /* Formation */

{{Short description|Water ice in symmetrical shapes}}
{{Refimprove|date = March 2022}}
[[File:Ice crystals 3.jpg|thumb|A close-up of growing ice crystals displaying typical hexagonal symmetry]]

'''Ice crystals''' are solid [[water]] (known as [[ice]]) in [[crystal structure|symmetrical]] shapes including [[hexagonal crystal family|hexagonal]] columns, hexagonal plates, and [[dendrite (crystal)|dendritic crystals]].<ref name=":0">{{cite web |date= |title=ice crystal |url=https://glossary.ametsoc.org/wiki/Ice_crystal |website=Glossary of Meteorology |publisher=[[American Meteorological Society]] |access-date=2023-03-29}}</ref> Ice crystals are responsible for various [[atmospheric optics|atmospheric optical]] displays and [[cirrus cloud|cloud formations]].<ref name=":0" /><ref name=":1">{{cite web |title=Ice Crystal Halos |url=https://its.caltech.edu/~atomic/snowcrystals/halos/halos.htm |website=its.caltech.edu |access-date=2023-03-30}}</ref>

== Formation ==
[[File:Hexagonal Ice Crystals.svg|thumb|An example of a hexagonal plate (top) and a hexagonal column (bottom), typical ice crystal shapes]]
At ambient temperature and pressure, [[Properties of water|water molecules]] have a V shape. The two [[hydrogen]] atoms bond to the [[oxygen]] atom at a 105° angle.<ref name=":3">{{Cite web |last=Puiu |first=Tibi |date=2015-03-27 |title=Sandwiching water between graphene makes square ice crystals at room temperature |url=https://www.zmescience.com/science/chemistry/graphene-square-ice-0534534/ |access-date=2023-03-30 |website=ZME Science |language=en-US}}</ref> Ice crystals have a hexagonal [[Crystal structure|crystal lattice]], meaning the water molecules arrange themselves into layered [[Hexagon|hexagons]] upon freezing.<ref name=":0" />

Slower crystal growth from colder and drier atmospheres produces more hexagonal symmetry.<ref name=":1" /> Depending on environmental [[temperature]] and [[humidity]], ice crystals can develop from the initial hexagonal prism into many symmetric shapes.<ref>{{Cite book |last=Visconti |first=Guido |title=Fundamentals of physics and chemistry of the atmosphere |date=2001 |publisher=Springer |isbn=3-540-67420-9 |location=Berlin |oclc=46320998}}</ref> Possible shapes for ice crystals are columns, [[Needle ice|needles]], plates and [[Dendrite (crystal)|dendrites]]. Mixed patterns are also possible.<ref name=":0" /> The symmetric shapes are due to [[Deposition (chemistry)|depositional]] [[Crystal growth|growth]], which is when ice forms directly from water vapor in the atmosphere.<ref>{{Cite web |title=Sublimation and deposition - Energy Education |url=https://energyeducation.ca/encyclopedia/Sublimation_and_deposition#:~:text=An%20example%20of%20deposition%20is,as%20the%20formation%20of%20frost. |access-date=2023-04-10 |website=energyeducation.ca}}</ref> Small spaces in atmospheric [[Dust|particles]] can also collect water, freeze, and form ice crystals.<ref>{{Cite web |last=Utah |first=University of |title=We've been thinking of how ice forms in cirrus clouds all wrong |url=https://phys.org/news/2019-04-weve-ice-cirrus-clouds-wrong.html |access-date=2023-03-30 |website=phys.org |language=en}}</ref><ref>{{Cite web |title=How ice crystals form in clouds |url=https://analyticalscience.wiley.com/do/10.1002/micro.2104/ |access-date=2023-03-29 |website=Wiley Analytical Science Magazine|doi= }}</ref> This is known as [[nucleation]].<ref>{{Cite web |last=UCL |date=2016-12-09 |title=Understanding how ice crystals form in clouds |url=https://www.ucl.ac.uk/news/2016/dec/understanding-how-ice-crystals-form-clouds |access-date=2023-04-10 |website=UCL News |language=en}}</ref> [[Snowflake|Snowflakes]] form when additional vapor freezes onto an existing ice crystal.<ref>{{Cite web |title=Growth Rates and Habits of Ice Crystals between −20° and −70°C - Google Search |url=https://www.google.com/search?q=Growth+Rates+and+Habits+of+Ice+Crystals+between+%E2%88%9220%C2%B0+and+%E2%88%9270%C2%B0C |access-date=2024-03-10 |website=www.google.com}}</ref><ref>{{Cite web |title=How do snowflakes form? Get the science behind snow |url=https://www.noaa.gov/stories/how-do-snowflakes-form-science-behind-snow |access-date=2023-03-30 |website=www.noaa.gov |date=19 December 2016 |language=en}}</ref>[[File:Снежинка на разноцветном фоне.JPG|thumb|Further freezing of water on an ice crystal produces [[Snowflake|snowflakes]].]]
=== Trigonal and cubic crystals ===
[[Supercooling|Supercooled]] water refers to water below its [[Melting point|freezing point]] that is still liquid.<ref>{{Cite web |date=2014-12-20 |title=Supercool Clouds |url=https://earthobservatory.nasa.gov/images/84916/supercool-clouds#:~:text=Supercooling%20may%20sound%20exotic,%20but,of%20about%20-15%20degrees%20C. |access-date=2023-04-10 |website=earthobservatory.nasa.gov |language=en}}</ref> Ice crystals formed from supercooled water have [[Stacking fault|stacking defects]] in their layered hexagons. This causes ice crystals to display [[trigonal]] or [[Ice Ic|cubic]] symmetry depending on the temperature. Trigonal or cubic crystals form in the upper atmosphere where supercooling occurs.<ref>{{Cite journal |last1=Murray |first1=Benjamin J. |last2=Salzmann |first2=Christoph G. |last3=Heymsfield |first3=Andrew J. |last4=Dobbie |first4=Steven |last5=Neely |first5=Ryan R. |last6=Cox |first6=Christopher J. |date=2015-09-01 |title=Trigonal Ice Crystals in Earth's Atmosphere |journal=Bulletin of the American Meteorological Society |language=EN |volume=96 |issue=9 |pages=1519–1531 |doi=10.1175/BAMS-D-13-00128.1 |bibcode=2015BAMS...96.1519M |s2cid=120907603 |issn=0003-0007|doi-access=free }}</ref><ref>{{Cite web |title=Cubic ice (ice Ic) structure |url=https://water.lsbu.ac.uk/water/cubic_ice.html |access-date=2023-04-10 |website=water.lsbu.ac.uk}}</ref>

=== Square crystals ===
Water can pass through [[Lamination|laminated]] sheets of [[Graphite oxide|graphene oxide]] unlike smaller molecules such as [[helium]]. When squeezed between two layers of [[graphene]], water forms square ice crystals at room temperature. Researchers believe high pressure and the [[van der Waals force]], an [[Force|attractive force]] present between all molecules, drives the formation. The material is a new crystalline phase of ice.<ref name=":3" /><ref>{{Cite journal |last1=Algara-Siller |first1=G. |last2=Lehtinen |first2=O. |last3=Wang |first3=F. C. |last4=Nair |first4=R. R. |last5=Kaiser |first5=U. |last6=Wu |first6=H. A. |last7=Geim |first7=A. K. |last8=Grigorieva |first8=I. V. |date=2015 |title=Square ice in graphene nanocapillaries |url=https://www.nature.com/articles/nature14295 |journal=Nature |language=en |volume=519 |issue=7544 |pages=443–445 |doi=10.1038/nature14295 |pmid=25810206 |arxiv=1412.7498 |bibcode=2015Natur.519..443A |s2cid=4462633 |issn=1476-4687}}</ref>

== Weather phenomena ==
[[File:Refraction-of-light Winter-Halo-2020.jpg|thumb|A [[Halo (optical phenomenon)|halo]] created by light reflecting off of ice crystals in cirrus clouds. This specific halo is called a [[46° halo]].]]
Ice crystals create optical [[Phenomenon|phenomena]] like [[diamond dust]] and [[Halo (optical phenomenon)|halos]] in the sky due to light reflecting off of the crystals in a process called [[scattering]].<ref name=":0" /><ref name=":1" /><ref name=":2">{{Citation |last=Gedzelman |first=S. D. |title=OPTICS, ATMOSPHERIC {{!}} Optical Phenomena |date=2003-01-01 |url=https://www.sciencedirect.com/science/article/pii/B0122270908002840 |encyclopedia=Encyclopedia of Atmospheric Sciences |pages=1583–1594 |editor-last=Holton |editor-first=James R. |access-date=2023-03-30 |place=Oxford |publisher=Academic Press |language=en |doi=10.1016/b0-12-227090-8/00284-0 |isbn=978-0-12-227090-1|url-access=subscription }}</ref>

[[Cirrus cloud|Cirrus clouds]] and [[ice fog]] are made of ice crystals.<ref name=":0" /><ref>{{Cite web |title=Ice fog |url=https://glossary.ametsoc.org/wiki/Ice_fog |access-date=2023-03-29 |website=Glossary of Meteorology |publisher=American Meteorological Society}}</ref> Cirrus clouds are often the sign of an approaching [[warm front]], where warm and moist air rises and freezes into ice crystals.<ref>{{Cite web |title=Cirrus Clouds {{!}} Center for Science Education |url=https://scied.ucar.edu/image/cirrus-clouds |access-date=2023-03-30 |website=scied.ucar.edu}}</ref><ref>{{Cite web |title=Cirrus clouds |url=https://www.metoffice.gov.uk/weather/learn-about/weather/types-of-weather/clouds/high-clouds/cirrus |access-date=2023-03-30 |website=Met Office |language=en}}</ref> Ice crystals rubbing against each other also produces [[lightning]].<ref>{{Cite news |last=Plait |first=Phil |date=2016-11-16 |title=Ice Crystals Above Clouds Dance to the Tune of Electricity |language=en-US |work=Slate |url=https://slate.com/technology/2016/11/ice-crystals-above-clouds-dance-and-flash-according-to-electric-fields.html |access-date=2023-03-30 |issn=1091-2339}}</ref><ref>{{Cite web |last=Canada |first=Environment and Climate Change |date=2011-04-15 |title=How lightning works |url=https://www.canada.ca/en/environment-climate-change/services/lightning/science/how-lightning-works.html |access-date=2023-03-30 |website=www.canada.ca}}</ref> The crystals normally fall horizontally,<ref>{{Cite journal |last1=Stillwell |first1=Robert A. |last2=Neely |first2=Ryan R. |last3=Thayer |first3=Jeffrey P. |last4=Walden |first4=Von P. |last5=Shupe |first5=Matthew D. |last6=Miller |first6=Nathaniel B. |date=2019-11-27 |title=Radiative Influence of Horizontally Oriented Ice Crystals over Summit, Greenland |journal=Journal of Geophysical Research: Atmospheres |language=en |volume=124 |issue=22 |pages=12141–12156 |doi=10.1029/2018JD028963 |bibcode=2019JGRD..12412141S |s2cid=210640681 |issn=2169-897X|doi-access=free }}</ref> but [[Electric field|electric fields]] can cause them to clump together and fall in other directions.<ref>{{Cite web |last=Libbrecht |first=Kenneth G. |title=Electric Snow Crystal Growth |url=https://www.its.caltech.edu/~atomic/snowcrystals/electric/electric.htm |access-date=2023-03-30 |website=www.its.caltech.edu}}</ref><ref>{{Cite journal |last1=Latham |first1=J. |last2=Saunders |first2=C. P. R. |date=1964 |title=Aggregation of Ice Crystals in Strong Electric Fields |url=https://www.nature.com/articles/2041293a0 |journal=Nature |language=en |volume=204 |issue=4965 |pages=1293–1294 |doi=10.1038/2041293a0 |bibcode=1964Natur.204.1293L |s2cid=8747928 |issn=1476-4687|url-access=subscription }}</ref>

== Detection ==
[[Image:Snow crystals.jpg|thumb|[[Dendrite (crystal)|Dendritic]] ice crystals imaged with a [[scanning electron microscope]]. The [[false color|colors are computer generated]].]]The [[Aerospace engineering|aerospace industry]] is working to design a radar that can detect ice crystal environments to discern hazardous flight conditions. Ice crystals can melt when they touch the surface of warm aircraft, and refreeze due to environmental conditions. The accumulation of ice around the engine damages the aircraft.<ref>{{Cite web |last=Heidman |first=Kelly |date=2015-08-11 |title=Flight Campaign Studies Radar Detection of Ice Crystal Icing |url=http://www.nasa.gov/image-feature/flight-campaign-studies-radar-detection-of-ice-crystal-icing |access-date=2023-03-30 |website=NASA}}</ref><ref>{{Cite journal |last1=Lukas |first1=Jan |last2=Badin |first2=Pavel |date=2019-06-10 |title=High Altitude Ice Crystal Detection with Aircraft X-band Weather Radar |url=https://www.sae.org/publications/technical-papers/content/2019-01-2026/ |journal=SAE International Journal of Advances and Current Practices in Mobility |language=English |volume=2 |issue=1 |pages=256–264 |doi=10.4271/2019-01-2026 |s2cid=182542723 |issn=2641-9637|url-access=subscription }}</ref> Weather forecasting uses differential reflectivity [[Weather radar|weather radars]] to identify types of [[precipitation]] by comparing a droplet's horizontal and vertical lengths.<ref>{{Cite web |last=US Department of Commerce |first=NOAA |title=Dual-Pol Products |url=https://www.weather.gov/jan/dualpolupgrade-products |access-date=2023-03-30 |website=www.weather.gov |language=EN-US}}</ref> Ice crystals are larger in the horizontal direction<ref name=":2" /> and are thus detectable.

== See also==
* [[Snow]]
* [[Snowflake]]
* [[Ice spike]]
* [[Ice lens]]
* [[Icicle]]

==References==
{{reflist}}

== External links ==
* [https://snowcrystals.com/ SnowCrystals.com!], at [[Caltech]]
* [https://web.archive.org/web/20080316222148/http://amsglossary.allenpress.com/glossary/search?id=ice-crystal1 American Meteorological Society Glossary]

{{ice}}
{{Authority control}}

[[Category:Water ice|Crystal]]
[[Category:Snow or ice weather phenomena|Crystal]]
[[Category:Clouds, fog and precipitation]]
[[Category:Atmospheric optical phenomena]]

Empennage

2025-11-01T19:41:59Z

2604:3D08:9476:BE00:1558:7B75:A113:A172:

{{Short description|Tail section of an aircraft containing stabilisers}}
{{Use mdy dates|date=March 2023}}
{{Use British English|date=March 2023}}
[[File:Aircraft tail.JPG|thumb|upright=1.14|The empennage of an [[Atlas Air]] [[Boeing 747-200]]]]The '''empennage''' ({{IPAc-en|ˌ|ɑː|m|p|ᵻ|ˈ|n|ɑː|ʒ}} or {{IPAc-en|ˈ|ɛ|m|p|ᵻ|n|ɪ|dʒ}}), also known as the '''tail''' or '''tail assembly''', is a structure at the rear of an aircraft that provides stability during flight, in a way similar to the feathers on an [[arrow]].<ref name="Crane">Crane, Dale: ''Dictionary of Aeronautical Terms, third edition'', p. 194. Aviation Supplies & Academics, 1997. {{ISBN|1-56027-287-2}}</ref><ref name="GroundUp">Aviation Publishers Co. Limited, ''From the Ground Up'', p. 10 (27th revised edition) {{ISBN|0-9690054-9-0}}</ref><ref name="airlines">{{cite web|url = http://www.airlines.org/ATAResources/Handbook/Pages/AirlineHandbookChapter5HowAircraftFly.aspx |title = ATA Airline Handbook Chapter 5: How Aircraft Fly|access-date = 5 March 2013|last = Air Transport Association|author-link = Air Transport Association|date = 10 November 2011|archive-url=https://web.archive.org/web/20111110141033/http://www.airlines.org/ATAResources/Handbook/Pages/AirlineHandbookChapter5HowAircraftFly.aspx|archive-date=10 November 2011}}</ref> The term derives from the [[French language]] verb {{lang|fr|empenner}} which means "[[Fletching|to feather]] an arrow".<ref name=OxfordEtymology>{{cite web|title=Empennage|url=http://oxforddictionaries.com/definition/english/empennage|archive-url=https://web.archive.org/web/20120722152506/http://oxforddictionaries.com/definition/english/empennage|url-status=dead|archive-date=July 22, 2012|publisher=Oxford Dictionaries|work=Oxford Dictionaries Online|access-date=5 March 2013}}</ref> Most aircraft feature an empennage incorporating vertical and horizontal stabilising surfaces which stabilise the [[flight dynamics]] of [[Yaw (rotation)|yaw]] and [[pitch (flight)|pitch]],<ref name="Crane" /><ref name="GroundUp" /> as well as housing [[flight control surface|control surface]]s.

In spite of effective control surfaces, many early aircraft that lacked a stabilising empennage were virtually unflyable. Even so-called "[[tailless aircraft]]" usually have a tail fin (usually a [[vertical stabiliser]]). Heavier-than-air aircraft without any kind of empennage (such as the [[Northrop B-2]]) are rare, and generally use specially shaped [[airfoil]]s whose trailing edge provide pitch stability, and rearwards [[swept wing]]s, often with [[dihedral (aeronautics)|dihedral]] to provide the necessary [[Aircraft principal axes|yaw]] stability. In some aircraft with swept wings, the airfoil section or angle of incidence may change radically towards the tip.

==Structure==
[[file:Empennage components.png|alt=|thumb|The major components of an airplane's empennage.]]
Structurally, the empennage consists of the entire tail assembly, including the [[Vertical stabiliser|tailfin]], the [[tailplane]] and the part of the [[fuselage]] to which these are attached.<ref name="Crane" /><ref name="GroundUp" /> On an airliner this would be all the flying and control surfaces behind the [[rear pressure bulkhead]].

[[File:flight_dynamics_with_text.svg|lang=en|thumb|[[Aircraft principal axes|Yaw, pitch, and roll]] in an aircraft.]]

The front (usually fixed) section of the [[tailplane]] is called the ''horizontal stabiliser'' and is used to provide pitch stability. The rear section of the tailplane is called the [[elevator (aircraft)|elevator]], and is a movable [[aerofoil]] that controls changes in pitch, the up-and-down motion of the aircraft's nose. In some aircraft the horizontal stabiliser and elevator are one unit, and to control pitch the entire unit moves as one. This is known as a ''[[stabilator]]'' or ''full-flying stabiliser''.<ref name="Crane" /><ref name="GroundUp" />

The [[fin|vertical tail structure]] has a fixed front section called the ''[[vertical stabiliser]]'', used to control yaw, which is movement of the fuselage right to left motion of the nose of the aircraft. The rear section of the vertical fin is the ''[[Rudders#Aircraft rudders|rudder]]'', a movable aerofoil that is used to turn the aircraft's nose right or left. When used in combination with the [[aileron]]s, the result is a banking turn, a ''coordinated turn'', the essential feature of aircraft movement.<ref name="Crane" /><ref name="GroundUp" />

Some aircraft are fitted with a tail assembly that is hinged to pivot in two axes forward of the fin and stabiliser, in an arrangement referred to as a ''movable tail''. The entire empennage is rotated vertically to actuate the horizontal stabiliser, and sideways to actuate the fin.<ref name="GroundUp14">Aviation Publishers Co. Limited, ''From the Ground Up'', p. 14 (27th revised edition) {{ISBN|0-9690054-9-0}}</ref>

The aircraft's [[cockpit voice recorder]], [[flight data recorder]] and [[emergency locator transmitter]] (ELT) are often located in the empennage, because the aft of the aircraft provides better protection for these in most aircraft crashes.

== Trim ==
In some aircraft [[trim (aircraft)|trim]] devices are provided to eliminate the need for the pilot to maintain constant pressure on the elevator or rudder controls.<ref name="GroundUp14" /><ref name="Reichmann">Reichmann, Helmet: ''Flying Sailplanes'', p. 26. Thompson Publications, 1980.</ref>

The trim device may be:

*a [[trim tab]] on the rear of the elevators or rudder which act to change the aerodynamic load on the surface. Usually controlled by a cockpit wheel or crank.<ref name="GroundUp14" /><ref name="T52-14E">[[Transport Canada]]: ''Flight Training Manual 4th Edition'', p. 12. Gage Educational Publishing Company, 1994. {{ISBN|0-7715-5115-0}}</ref>
*an [[adjustable stabilizer|adjustable stabiliser]] into which the stabiliser may be hinged at its spar and adjustably jacked a few degrees in incidence either up or down. Usually controlled by a cockpit crank.<ref name="GroundUp14" /><ref name="Crane524">Crane, Dale: ''Dictionary of Aeronautical Terms, third edition'', p. 524. Aviation Supplies & Academics, 1997. {{ISBN|1-56027-287-2}}</ref>
*a [[bungee cord|bungee]] trim system which uses a spring to provide an adjustable preload in the controls. Usually controlled by a cockpit lever.<ref name="GroundUp14" /><ref name="Reichmann" />
*an [[anti-servo tab]] used to trim some elevators and stabilators as well as increased control force feel. Usually controlled by a cockpit wheel or crank.<ref name="GroundUp14" />
*a [[servo tab]] used to move the main control surface, as well as act as a trim tab. Usually controlled by a cockpit wheel or crank.<ref name="GroundUp14" />

Multi-engined aircraft often have [[trim tab]]s on the rudder to reduce the pilot effort required to keep the aircraft straight in situations of asymmetrical thrust, such as single engine operations.<ref name="T52-14E" />

==Tail configurations==
Aircraft empennage designs may be classified broadly according to the fin and tailplane configurations.

The overall shapes of individual tail surfaces (tailplane planforms, fin profiles) are similar to [[wing configuration#Wing planform|wing planforms]].

===Tailplanes===
{{main article|tailplane}}
The tailplane comprises the tail-mounted fixed horizontal stabiliser and movable elevator. Besides its [[wing configuration#Wing planform|planform]], it is characterised by:
*Configuration – [[Tailless aircraft|tailless]] or [[canard aircraft|canard]].
*Location of tailplane – mounted high, mid or low on the fuselage, fin or tail booms.
*Fixed stabiliser and movable elevator surfaces, or a single combined [[stabilator]] or "[all]-flying tail".<ref>Anderson, John D., ''Introduction to Flight'', 5th ed, p. 517</ref> ([[General Dynamics F-111 Aardvark]])

Some locations have been given special names:
*'''Conventional tail''' – The [[vertical stabiliser]] and [[horizontal stabiliser]]s are mounted to the rear of the fuselage. This is the simplest configuration that performs all three aspects of the function of a tail: trim, stability, and control.<ref name="sadraey289">Mohammad H. Sadraey, ''Aircraft Design: A Systems Engineering Approach'', Wiley 2013, p.289</ref> Around 60% of current aircraft designs<ref name="sadraey289"/> — and about 80% ever<ref>Snorri Gudmundsson, ''General Aviation Aircraft Design: Applied Methods and Procedures'', Elsevier Science 2013, p.483</ref> — incorporate this type of tail. Examples are found on aircraft of every size and role, from general aviation types like the ubiquitous [[Cessna 172]] to the largest airliners ever flown, such as the [[Airbus A380]]. Examples of this type of tail were in use as early as the [[Blériot VII]] of 1907.
*'''[[Cruciform tail]]''' – The horizontal stabilisers are placed midway up the vertical stabiliser, giving the appearance of a [[cross]] when viewed from the front. Cruciform tails are often used to keep the horizontal stabilisers out of the engine wake, while avoiding many of the disadvantages of a [[T-tail]]. Examples include the [[Hawker Sea Hawk]] and [[Douglas A-4 Skyhawk]].
*'''[[T-tail]]''' – The horizontal stabiliser is mounted on top of the fin, creating a "T" shape when viewed from the front. T-tails keep the stabilisers out of the engine wake, and give better pitch control. T-tails have a good [[glide ratio]], and are more efficient on low-speed aircraft. However, the T-tail has several disadvantages. It is more likely to enter a [[Stall (flight)#Deep stall|deep stall]], and is more difficult to recover from a spin. For this reason a small secondary stabiliser or '''tail-let''' may be fitted lower down where it will be in free air when the aircraft is stalled.<ref>Ralph D. Kimberlin, ''Flight Testing of Fixed Wing Aircraft'', AIAA 2003, p.380.</ref> A T-tail must be stronger, and therefore heavier than a conventional tail. T-tails also tend to have a larger [[radar cross section]]. Examples include the [[Gloster Javelin]] and [[McDonnell Douglas DC-9]].

{| align=center style="text-align:center;"
|-
|[[File:tail fuselage mounted.svg|150px|alt=" "]] Fuselage mounted
|[[File:tail cruciform.svg|150px|alt=" "]] Cruciform
|[[File:tail T.svg|150px|alt=" "]] T-tail
|[[File:tail plane flying.svg|210px|alt=" "]] Flying tailplane
|}

===Fins===
{{Main|Vertical stabilizer}}
The fin comprises the fixed vertical stabiliser and rudder. Besides its [[wing configuration#Wing planform|profile]], it is characterised by:
*Number of fins – usually one or two.
*Location of fins – on the fuselage (over or under), tailplane, tail booms or wings

Twin fins may be mounted at various points:
*'''[[Twin tail]]''' A twin tail, also called an '''H-tail''', consists of two small vertical stabilisers on either side of the horizontal stabiliser. Examples include the [[Antonov An-225 Mriya]], [[B-25 Mitchell]], [[Avro Lancaster]], and [[ERCO Ercoupe]].
*'''[[Twin-boom aircraft|Twin boom]]''' A twin boom has two fuselages or booms, with a vertical stabiliser on each, and a horizontal stabiliser between them. Examples include the [[Northrop P-61 Black Widow]], [[P-38 Lightning]], [[de Havilland Sea Vixen]], [[Sadler Vampire]], and [[Edgley Optica]].
*'''Wing mounted''' midwing as on the [[F7U Cutlass]] or on the wing tips as on the [[Handley Page Manx]] and [[Rutan Long-EZ]]

{| align=center style="text-align:center;"
|-
|[[File:tail twin tailplane mounted.svg|150px|alt=" "]] Tailplane mounted
|[[File:tail twin boom.svg|150px|alt=" "]] Twin tail boom
|[[File:tail twin wing mounted.svg|150px|alt=" "]] Wing mounted
|}

Unusual fin configurations include:
*'''No fin''' – as on the [[McDonnell Douglas X-36]]. This configuration is sometimes incorrectly referred to as "tailless".
*'''Multiple fins''' – examples include the [[Lockheed Constellation]] (three), [[Bellanca 14-13]] (three), and the [[Northrop Grumman E-2 Hawkeye]] (four).
*'''Ventral fin''' – underneath the fuselage. Often used in addition to a conventional fin as on the ([[North American X-15]] and [[Dornier Do 335]]).

{| align=center style="text-align:center;"
|-
|[[File:tail fin triple.svg|150px|alt=" "]] Triple fins
|[[File:tail fin ventral.svg|210px|alt=" "]] Ventral fin
|}

===V, Y and X tails===
An alternative to the fin-and-tailplane approach is provided by the [[V-tail]] and [[X-tail]] designs. Here, the tail surfaces are set at diagonal angles, with each surface contributing to both pitch and yaw. The control surfaces, sometimes called [[ruddervator]]s, act differentially to provide yaw control (in place of the rudder) and act together to provide pitch control (in place of the elevator).<ref name="Crane" />

*'''V tail:''' A V-tail can be lighter than a conventional tail in some situations and produce less drag, as on the [[Fouga Magister]] trainer, [[Northrop Grumman RQ-4 Global Hawk]] RPV and [[X-37]] spacecraft. A V-tail may also have a smaller radar signature. Other aircraft featuring a V-tail include the [[Beechcraft Bonanza|Beechcraft Model 35 Bonanza]], and [[Davis DA-2]]. A slight modification to the V-tail can be found on the [[Sonex Aircraft Sonex|Waiex]] and [[Monnett Moni]] called a Y-tail.
*'''Inverted V tail:'''The unmanned [[General Atomics MQ-1 Predator|Predator]] uses an inverted V-tail as do the [[Lazair]] and [[Aerocar Mini-IMP|Mini-IMP]].
*'''Y tail''': A V-tail with an added lower vertical fin (generally used to protect an aft propeller), as [[LearAvia Lear Fan]]
*'''X tail:''' The [[Lockheed XFV]] featured an "X" tail, which was reinforced and fitted with a wheel on each surface so that the craft could sit on its tail and take off and land vertically.

{| align=center style="text-align:center;"
|-
|[[File:tail V.svg|150px|alt=" "]] V-tail
|[[File:Tail inverted V.svg|150px|alt=" "]] Inverted V-tail
|[[File:tail X.svg|150px|alt=" "]] X-tail
|}

===Outboard tail===

[[File:Spaceship One at Smithsonian.jpg|thumb|SpaceShipOne at the US National Air and Space Museum]]
An outboard tail is split in two, with each half mounted on a short boom just behind and outboard of each wing tip. It comprises outboard horizontal stabilisers (OHS) and may or may not include additional boom-mounted [[vertical stabilizer|vertical stabilisers]] (fins). In this position, the tail surfaces interact constructively with the wingtip vortices and, with careful design, can significantly reduce drag to improve efficiency, without adding unduly to the structural loads on the wing.<ref>Kurt W. Muller; "Analysis of a Semi-Tailless Aircraft Design" (Master's thesis), Naval Postgraduate School, US, 2002.[http://apps.dtic.mil/dtic/tr/fulltext/u2/a402729.pdf] {{Webarchive|url=https://web.archive.org/web/20221123054514/http://apps.dtic.mil/dtic/tr/fulltext/u2/a402729.pdf |date=November 23, 2022 }}</ref>

The configuration was first developed during World War II by [[Richard Vogt (aircraft designer)|Richard Vogt]] and George Haag at [[Blohm & Voss (aircraft)|Blohm & Voss]]. The [[Skoda-Kauba SL6]] tested the proposed control system in 1944 and, following several design proposals, an order was received for the [[Blohm & Voss P 215]] just weeks before the war ended.<ref>Zdenek Titz and Jaroslav Zazvonil; "Kauba's Dwarfs", ''Flying Review International'', Nov 1965, pp.169-172.</ref><ref>Pohlmann, Hermann. ''Chronik Eines Flugzeugwerkes 1932-1945. B&V – Blohm & Voss Hamburg – HFB Hamburger Flugzeugbau'' (in German). Motor Buch Verlag, 1979 {{ISBN|3-87943-624-X}}.</ref> The outboard tail reappeared on the [[Scaled Composites SpaceShipOne]] in 2003 and [[SpaceShipTwo]] in 2010.<ref>Benjamin Darrenougue; "Aircraft Configurations With Outboard Horizontal Stabilizers" (Final year project report), Queens University Belfast, 14 May 2004.[http://hdarrenougue.free.fr/html/report.pdf]</ref>

===Tailless aircraft===
{{main article|Tailless aircraft}}
[[File:DH 108 Swallow tg283.jpg|thumb|The [[de Havilland DH 108|DH108 ''Swallow'']]]]

A '''tailless aircraft''' (often '''tail-less''') traditionally has all its horizontal control surfaces on its main wing surface. It has no [[horizontal stabiliser]] {{Ndash}}either tailplane or [[Canard (aeronautics)|canard]] foreplane (nor does it have a second wing in [[tandem wing|tandem]] arrangement). A "tailless" type usually still has a vertical stabilising fin ([[vertical stabiliser]]) and control surface ([[rudder]]). However, [[NASA]] adopted the "tailless" description for the novel [[McDonnell Douglas X-36|X-36 research aircraft]] which has a canard foreplane but no vertical fin.{{Citation needed|date=September 2011}}

The most successful tailless configuration has been the tailless [[delta wing|delta]], especially for combat aircraft.{{Citation needed|date=September 2011}}

== See also ==
* [[Trijet]]
* [[S-duct]]
* [[Tail-sitter]]

==References==
{{Reflist}}

{{Aircraft components}}

[[Category:Aircraft components]]