An Etymological Dictionary of Astronomy and Astrophysics

To oscillate with a continuing periodic change relative to a fixed reference point or state of equilibrium. → oscillate.

Etymology (EN): From L. vibratus, p.p. of vibrare “to move quickly to and fro, shake” (cf. Lith. wyburiu “to wag the tail,” Dan. vippe, Du. wippen “to swing,” O.E. wipan “to wipe”).

Etymology (PE): Šividan “to vibrate, move to and fro, to tremble,” related to šodan, šow- “to go; to become;” Av. šiyav-, š(ii)auu- “to move, go,” šiyavati “goes,” šyaoθna- “activity; action; doing, working;” O.Pers. šiyav- “to go forth, set,” ašiyavam “I set forth;” Skt. cyu- “to move to and fro, shake about; to stir,” cyávate “stirs himself, goes;” Gk. kinein “to move;”
Goth. haitan “call, be called;” O.E. hatan “command, call;” PIE base *kei- “to move to and fro.”

To oscillate with a continuing periodic change relative to a fixed reference point or state of equilibrium. → oscillate.

Etymology (EN): From L. vibratus, p.p. of vibrare “to move quickly to and fro, shake” (cf. Lith. wyburiu “to wag the tail,” Dan. vippe, Du. wippen “to swing,” O.E. wipan “to wipe”).

Etymology (PE): Šividan “to vibrate, move to and fro, to tremble,” related to šodan, šow- “to go; to become;” Av. šiyav-, š(ii)auu- “to move, go,” šiyavati “goes,” šyaoθna- “activity; action; doing, working;” O.Pers. šiyav- “to go forth, set,” ašiyavam “I set forth;” Skt. cyu- “to move to and fro, shake about; to stir,” cyávate “stirs himself, goes;” Gk. kinein “to move;”
Goth. haitan “call, be called;” O.E. hatan “command, call;” PIE base *kei- “to move to and fro.”

1. The act of vibrating. The state of being vibrated.
   

2. A continuing → periodic  → oscillation relative to a fixed reference point or → equilibrium state.

See also: Verbal noun from → vibrate.

1. The act of vibrating. The state of being vibrated.
   

2. A continuing → periodic  → oscillation relative to a fixed reference point or → equilibrium state.

See also: Verbal noun from → vibrate.

Of or pertaining to → vibration. → vibrational mode.

See also: → vibration; → -al.

Of or pertaining to → vibration. → vibrational mode.

See also: → vibration; → -al.

The energy due to the vibration of the molecules making up atoms (→ molecular vibration). A molecule in space can have energies in various forms: → rotational energy, vibrational energy, or electronic energy. These energies of molecules are → quantized and a particular molecule can exist in different rotational and vibrational → energy levels. The molecules can move from one level to another level only by a jump involving a finite amount of energy. → Quantum mechanics predicts that any molecule can never have zero vibrational energy, that is atoms can never be completely at rest relative to each other. The harmonically oscillating molecules can undergo vibrational changes determined by simple selection rules obtained from → Schrödinger equation.

See also: → vibrational; → energy.

The energy due to the vibration of the molecules making up atoms (→ molecular vibration). A molecule in space can have energies in various forms: → rotational energy, vibrational energy, or electronic energy. These energies of molecules are → quantized and a particular molecule can exist in different rotational and vibrational → energy levels. The molecules can move from one level to another level only by a jump involving a finite amount of energy. → Quantum mechanics predicts that any molecule can never have zero vibrational energy, that is atoms can never be completely at rest relative to each other. The harmonically oscillating molecules can undergo vibrational changes determined by simple selection rules obtained from → Schrödinger equation.

See also: → vibrational; → energy.

The frequency at which the atoms in a molecule vibrate. The frequencies of → molecular vibrations in diatomic molecules are in the order of 10^-12 to 10^-14 Hz. In such molecules, the only → vibrational mode available is along the bond. More complicated molecules have many types of vibration and stretching modes.

See also: → vibrational; → frequency.

The frequency at which the atoms in a molecule vibrate. The frequencies of → molecular vibrations in diatomic molecules are in the order of 10^-12 to 10^-14 Hz. In such molecules, the only → vibrational mode available is along the bond. More complicated molecules have many types of vibration and stretching modes.

See also: → vibrational; → frequency.

Any of the ways in which a → molecule vibrates. Each vibrational mode has a different → frequency frequency. The number of vibrational modes of a molecule is determined by the number of atoms in it. The number of vibrational modes for a non-linear molecule is 3N - 6, where N is the number of atoms making up the molecule. For a linear molecule it is 3N - 5.

See also: → vibrational; → mode.

Any of the ways in which a → molecule vibrates. Each vibrational mode has a different → frequency frequency. The number of vibrational modes of a molecule is determined by the number of atoms in it. The number of vibrational modes for a non-linear molecule is 3N - 6, where N is the number of atoms making up the molecule. For a linear molecule it is 3N - 5.

See also: → vibrational; → mode.

A transition between two → quantized  → levels of a → molecule that have different vibrational energies.

See also: → vibrational; → transition.

A transition between two → quantized  → levels of a → molecule that have different vibrational energies.

See also: → vibrational; → transition.

A slight change in the → energy level of a → molecule due to → vibrational transition and/or → rotational transition.

See also: → vibrational; → rotational; → transition.

A slight change in the → energy level of a → molecule due to → vibrational transition and/or → rotational transition.

See also: → vibrational; → rotational; → transition.

A person or thing that suffers harm or death, from another or from some adverse act or circumstance.

Etymology (EN): M.Fr. victime, from L. victima “sacrificial animal.”

Etymology (PE): Lišé, from Mid.Pers. lyš- / rêš- “to wound, hurt;” Pers. riš, rêš “wound;” Av. raēš- “to get hurt, suffer damage;” cf. Skt. reṣ “to get harmed.”

A person or thing that suffers harm or death, from another or from some adverse act or circumstance.

Etymology (EN): M.Fr. victime, from L. victima “sacrificial animal.”

Etymology (PE): Lišé, from Mid.Pers. lyš- / rêš- “to wound, hurt;” Pers. riš, rêš “wound;” Av. raēš- “to get hurt, suffer damage;” cf. Skt. reṣ “to get harmed.”

A series of 532 years, arising from the cycles of the Sun and Moon multiplied into one another. It was used by the Western churches for many years, in computing the time of Easter, till the → Gregorian calendar was established.

See also: Named after Victorius (a French clergyman), who invented the period about the middle of the 5th century.

A series of 532 years, arising from the cycles of the Sun and Moon multiplied into one another. It was used by the Western churches for many years, in computing the time of Easter, till the → Gregorian calendar was established.

See also: Named after Victorius (a French clergyman), who invented the period about the middle of the 5th century.

1. (n.) The visual part of a television broadcast.
   Something that has been recorded on videotape, especially a movie or music performance.
   
2. (adj.) Of or pertaining to the electronic apparatus for producing the television picture.

Etymology (EN): From L. video “I see,” from videre→ vision.

Etymology (PE): Didâré, didâri, from didâr “vision, sight,” verbal noun from didan “to see” (Mid.Pers. ditan “to see, regard, catch sight of, contemplate, experience;” O.Pers. dī- “to see;” Av. dā(y)- “to see,” didāti “sees;” cf. Skt. dhī- “to perceive, think, ponder; thought, reflection, meditation,” dādhye; Gk. dedorka “have seen”).

1. (n.) The visual part of a television broadcast.
   Something that has been recorded on videotape, especially a movie or music performance.
   
2. (adj.) Of or pertaining to the electronic apparatus for producing the television picture.

Etymology (EN): From L. video “I see,” from videre→ vision.

Etymology (PE): Didâré, didâri, from didâr “vision, sight,” verbal noun from didan “to see” (Mid.Pers. ditan “to see, regard, catch sight of, contemplate, experience;” O.Pers. dī- “to see;” Av. dā(y)- “to see,” didāti “sees;” cf. Skt. dhī- “to perceive, think, ponder; thought, reflection, meditation,” dādhye; Gk. dedorka “have seen”).

A → lunisolar calendar used now in Vietnam mainly for determining seasonal holidays and cultural events. It is in fact the → Chinese calendar computed for Hanoi. It has 12 months of 29 or 30 days each (→ synodic month) and the year totals 355 days. The → lunar year is therefore 11 days shorter than its solar counterpart. To keep up with the solar pace, every 19 years seven extra months are added to the calendar.
In practice, approximately every third year an → embolismic month is included. The New Year, called Tet, begins at the second → new moon after the → winter solstice. The Vietnamese calendar has some minor differences with the Chinese calendar. For example, it uses the cat and buffalo instead of the Chinese rabbit and cow respectively in the → zodiac.

See also: From Vietnam “Viets of the South,” from Viet the people’s name + nam “south;” → lunar; → calendar.

A → lunisolar calendar used now in Vietnam mainly for determining seasonal holidays and cultural events. It is in fact the → Chinese calendar computed for Hanoi. It has 12 months of 29 or 30 days each (→ synodic month) and the year totals 355 days. The → lunar year is therefore 11 days shorter than its solar counterpart. To keep up with the solar pace, every 19 years seven extra months are added to the calendar.
In practice, approximately every third year an → embolismic month is included. The New Year, called Tet, begins at the second → new moon after the → winter solstice. The Vietnamese calendar has some minor differences with the Chinese calendar. For example, it uses the cat and buffalo instead of the Chinese rabbit and cow respectively in the → zodiac.

See also: From Vietnam “Viets of the South,” from Viet the people’s name + nam “south;” → lunar; → calendar.

1. An instance of seeing or beholding; visual inspection.
   

   2. Sight; vision (Dictionary.com).

Etymology (EN): M.E. v(i)ewe, from M.Fr. veue “sight,” from V.L. *viduta, from *vidutus, from L. visus, p.p. of videre “to see,” → vision.

Etymology (PE): Did, → vision.

1. An instance of seeing or beholding; visual inspection.
   

   2. Sight; vision (Dictionary.com).

Etymology (EN): M.E. v(i)ewe, from M.Fr. veue “sight,” from V.L. *viduta, from *vidutus, from L. visus, p.p. of videre “to see,” → vision.

Etymology (PE): Did, → vision.

The maximum angle at which a display, such as a TV screen, can be viewed with acceptable visual performance.

Etymology (EN): Viewing, from view, M.E. v(i)ewe (n.); M.Fr. veue “sight,” feminine p.p. of veoir “to see,” from L. videre “to see,” → vision; → angle.

Etymology (PE): Zâviyé, → angle; did→ vision.

The maximum angle at which a display, such as a TV screen, can be viewed with acceptable visual performance.

Etymology (EN): Viewing, from view, M.E. v(i)ewe (n.); M.Fr. veue “sight,” feminine p.p. of veoir “to see,” from L. videre “to see,” → vision; → angle.

Etymology (PE): Zâviyé, → angle; did→ vision.

The numeral system based on → twenty.

Etymology (EN): From L. vigesimus, variant of vicesimus, vicensimus “twentieth,” from vigniti “twenty” + → -al.

The numeral system based on → twenty.

Etymology (EN): From L. vigesimus, variant of vicesimus, vicensimus “twentieth,” from vigniti “twenty” + → -al.

The gradual reduction in energy through an optical system as the off-axis angle increases, resulting from limitations of the clear apertures of elements within the system.

Etymology (EN): From vignette “an unbordered picture, often a portrait, that shades off into the surrounding color at the edges;” “softening the edges of a picture in vignette style;” from Fr. vignette, O.Fr., diminutive of vigne “vineyard;” from L. vinea “vine, vineyard,” from vinum “wine.”

Etymology (PE): Labe-puš, literally “limb covering,” from labé “limb,” from lab “lip;” (Mid.Pers. lap; cf. L. labium; O.E. lippa; E. lip; Ger. Lefze) + puš present stem of pušidan “to cover; to put on” (Mid.Pers. pôšidan, pôš- “to cover; to wear;” cf. Mid.Pers. pôst; Mod.Pers. pust “skin, hide;” O.Pers. pavastā- “thin clay envelope used to protect unbaked clay tablets;” Skt. pavásta- “cover,” Proto-Indo-Iranian *pauastā- “cloth”).

The gradual reduction in energy through an optical system as the off-axis angle increases, resulting from limitations of the clear apertures of elements within the system.

Etymology (EN): From vignette “an unbordered picture, often a portrait, that shades off into the surrounding color at the edges;” “softening the edges of a picture in vignette style;” from Fr. vignette, O.Fr., diminutive of vigne “vineyard;” from L. vinea “vine, vineyard,” from vinum “wine.”

Etymology (PE): Labe-puš, literally “limb covering,” from labé “limb,” from lab “lip;” (Mid.Pers. lap; cf. L. labium; O.E. lippa; E. lip; Ger. Lefze) + puš present stem of pušidan “to cover; to put on” (Mid.Pers. pôšidan, pôš- “to cover; to wear;” cf. Mid.Pers. pôst; Mod.Pers. pust “skin, hide;” O.Pers. pavastā- “thin clay envelope used to protect unbaked clay tablets;” Skt. pavásta- “cover,” Proto-Indo-Iranian *pauastā- “cloth”).

A small group of dwellings in a rural area, usually ranking in size between a hamlet and a town.

Etymology (EN): M.E. village, from O.Fr. village, from L. villaticus, ultimately from L. villa “country house,” related to vicus “village, group of houses,” vecinus “neighbor;” cf. Mid.Pers. wis “village,” Manichean Mid.Pers. wys “to repose;” Khotanese bäsā “house;” O.Pers. viθ- “settlement;” Av. vis- “to enter;” cf. Skt. vis- “house;” Albanian vis- “place;” Gothic weihs “village;” E. suffix wich, -wick (as in Norwich and Brunswick); Iranian dialects/languages Xonsâri hos “house, home;” Lori, Laki hoš, höš, hovš “house, home;” Baluci ges “house, home;” Kermânshahi, Ilâmi, Lori huz “clan, family, tribe;” Parachi γos, γus “house, home;” Wakhi wiš- / wišt- “to set [of sun];” Yaghnavi wes-, ves- “to go down;” PIE *ueik- “to settle (down).”

Etymology (PE): Deh, dehkadé, from Mid.Pers. dêh “village, settlement, country;” loaned into Armenian deh “district;” O.Pers./Av. dahyu- “country.”

A small group of dwellings in a rural area, usually ranking in size between a hamlet and a town.

Etymology (EN): M.E. village, from O.Fr. village, from L. villaticus, ultimately from L. villa “country house,” related to vicus “village, group of houses,” vecinus “neighbor;” cf. Mid.Pers. wis “village,” Manichean Mid.Pers. wys “to repose;” Khotanese bäsā “house;” O.Pers. viθ- “settlement;” Av. vis- “to enter;” cf. Skt. vis- “house;” Albanian vis- “place;” Gothic weihs “village;” E. suffix wich, -wick (as in Norwich and Brunswick); Iranian dialects/languages Xonsâri hos “house, home;” Lori, Laki hoš, höš, hovš “house, home;” Baluci ges “house, home;” Kermânshahi, Ilâmi, Lori huz “clan, family, tribe;” Parachi γos, γus “house, home;” Wakhi wiš- / wišt- “to set [of sun];” Yaghnavi wes-, ves- “to go down;” PIE *ueik- “to settle (down).”

Etymology (PE): Deh, dehkadé, from Mid.Pers. dêh “village, settlement, country;” loaned into Armenian deh “district;” O.Pers./Av. dahyu- “country.”

A star located in the → Virgo constellation, also called ε Virginis. It is a yellow → giant of apparent magnitude 2.83 and → spectral type G8 III. Vindemiatrix lies about 102 → light-years from Earth, has a luminosity 83 times the → solar luminosity, and a → surface temperature about 5,000 K.

Etymology (EN): L. Vindemiatrix “grape-harvestress,” feminine of vindemiator “grape-hervester,” translation of Gk. names Protrugeter, Protrugetes, and Trugeter used by Ptolemy, Plutarch, and other Gk. authors. The first of these words denoted “Fruit-plucking Herald.” In Gk. trugos is the process of collecting the grapes. It has been argued that the first visibility of the star in morning light was the time of gathering the grapes. The original Gk. name was translated in Ar. as al-Mutaqaddim lil-Qaţāf (المتقدم للقطاف) “Harvest Precursor,” and later to Almuredin maybe with the same meaning, but the etymology is not clear.

Etymology (PE): Angurcin “grape harvester,” from angur “grape” (related to quré “unripe grape,” angordé “a single grape, a berry;” cf. Skt. ankurá- “buds, sprout, shoot, blossom, swelling”) + cin present stem of cidan “to gather, collect,” related to gozidan “to choose, select”
(Mid.Pers. cyn- “to gather, collect;” Av. ci- “to heap up, gather”

A star located in the → Virgo constellation, also called ε Virginis. It is a yellow → giant of apparent magnitude 2.83 and → spectral type G8 III. Vindemiatrix lies about 102 → light-years from Earth, has a luminosity 83 times the → solar luminosity, and a → surface temperature about 5,000 K.

Etymology (EN): L. Vindemiatrix “grape-harvestress,” feminine of vindemiator “grape-hervester,” translation of Gk. names Protrugeter, Protrugetes, and Trugeter used by Ptolemy, Plutarch, and other Gk. authors. The first of these words denoted “Fruit-plucking Herald.” In Gk. trugos is the process of collecting the grapes. It has been argued that the first visibility of the star in morning light was the time of gathering the grapes. The original Gk. name was translated in Ar. as al-Mutaqaddim lil-Qaţāf (المتقدم للقطاف) “Harvest Precursor,” and later to Almuredin maybe with the same meaning, but the etymology is not clear.

Etymology (PE): Angurcin “grape harvester,” from angur “grape” (related to quré “unripe grape,” angordé “a single grape, a berry;” cf. Skt. ankurá- “buds, sprout, shoot, blossom, swelling”) + cin present stem of cidan “to gather, collect,” related to gozidan “to choose, select”
(Mid.Pers. cyn- “to gather, collect;” Av. ci- “to heap up, gather”

Any of various plants, especially the grapevine, having long flexible stems that creep along the ground or climb by clinging to a support by means of tendrils, leafstalks, etc (Dictionary.com).

Etymology (EN): M.E., from O.Fr. vigne “vine, vinyard,” from L. vinea “vine, vineyard,” from vinum “wine,” from PIE *win-o- “wine.”

Etymology (PE): Mow, tâk, raz “vine,” Persian words of unknown origin.

Any of various plants, especially the grapevine, having long flexible stems that creep along the ground or climb by clinging to a support by means of tendrils, leafstalks, etc (Dictionary.com).

Etymology (EN): M.E., from O.Fr. vigne “vine, vinyard,” from L. vinea “vine, vineyard,” from vinum “wine,” from PIE *win-o- “wine.”

Etymology (PE): Mow, tâk, raz “vine,” Persian words of unknown origin.

To break, infringe, or transgress (a law, rule, agreement, promise, instructions, etc.). → parity violation.

Etymology (EN): M.E., from L. violatus p.p. of violare “to treat with violence, violate,” from violentus “violent, " from vis “force, violence.”

Etymology (PE): Enâhidan infinitive from enâh, from Av. aēnah- “violence, mischief, crime, outrage,” from aēn- “to do violence to, to violate, to injure, to offend;” cf. Skt. énas- “offence, mischief, crime, sin;” Gk. ainos “terrible.”

To break, infringe, or transgress (a law, rule, agreement, promise, instructions, etc.). → parity violation.

Etymology (EN): M.E., from L. violatus p.p. of violare “to treat with violence, violate,” from violentus “violent, " from vis “force, violence.”

Etymology (PE): Enâhidan infinitive from enâh, from Av. aēnah- “violence, mischief, crime, outrage,” from aēn- “to do violence to, to violate, to injure, to offend;” cf. Skt. énas- “offence, mischief, crime, sin;” Gk. ainos “terrible.”

The act of violating. The state of being violated. → parity violation

See also: Verbal noun from → violate.

The act of violating. The state of being violated. → parity violation

See also: Verbal noun from → violate.

Intense in force, effect; severe; extreme.

See also: → optically violent variable (OVV) quasar, → violent galaxy, → violent interstellar environment, → violent relaxation, → violent star formation.

Etymology (EN): M.E., from O.fr. violent, from L. violentus “vehement, forcible.”

Etymology (PE): Surâ, from Av. sūra- “strong, powerful, mighty;” cf. Skt. śūra- “strong, powerful, valiant.”

Intense in force, effect; severe; extreme.

See also: → optically violent variable (OVV) quasar, → violent galaxy, → violent interstellar environment, → violent relaxation, → violent star formation.

Etymology (EN): M.E., from O.fr. violent, from L. violentus “vehement, forcible.”

Etymology (PE): Surâ, from Av. sūra- “strong, powerful, mighty;” cf. Skt. śūra- “strong, powerful, valiant.”

A type of galaxy that releases a tremendous amount of energy, on the average
10⁵⁸ ergs, compared with a supernova release of 10⁴⁹ ergs. Violent galaxies include quasars and exploding galaxies. About 1 percent of the galaxies are classified as violent. The nearest violent galaxy is Cen A.

See also: → violent; → galaxy.

A type of galaxy that releases a tremendous amount of energy, on the average
10⁵⁸ ergs, compared with a supernova release of 10⁴⁹ ergs. Violent galaxies include quasars and exploding galaxies. About 1 percent of the galaxies are classified as violent. The nearest violent galaxy is Cen A.

See also: → violent; → galaxy.

A description of the interstellar medium justified by the presence of supersonic shock waves, massive star winds, turbulence, supernova explosions, etc.

See also: → violent; → interstellar; → environment.

A description of the interstellar medium justified by the presence of supersonic shock waves, massive star winds, turbulence, supernova explosions, etc.

See also: → violent; → interstellar; → environment.

A process in which a dynamical system made up of many objects (star cluster, galaxy cluster) rapidly relaxes from a chaotic initial state to a quasi-equilibrium.

See also: → violent; → relaxation.

A process in which a dynamical system made up of many objects (star cluster, galaxy cluster) rapidly relaxes from a chaotic initial state to a quasi-equilibrium.

See also: → violent; → relaxation.

The concept of star formation pertaining to a variety of systems (OB associations, giant H II regions, H II galaxies, massive star clusters, etc.) that are believed to have formed large numbers of stars in a very short time.

See also: → violent; → star formation.

The concept of star formation pertaining to a variety of systems (OB associations, giant H II regions, H II galaxies, massive star clusters, etc.) that are believed to have formed large numbers of stars in a very short time.

See also: → violent; → star formation.

A color at the opposite end of the visible spectrum from red, an effect of light with a wavelength between 4000 and 4500 Å. → ultraviolet.

Etymology (EN): M.E., from O.Fr. violete, diminutive of viole “violet,” from L. viola, akin to Gk. ion “violet.”

Etymology (PE): Banafš “violet,” related to banafšé “violet flower;” Mid.Pers. vanafšak “violet flower.”

A color at the opposite end of the visible spectrum from red, an effect of light with a wavelength between 4000 and 4500 Å. → ultraviolet.

Etymology (EN): M.E., from O.Fr. violete, diminutive of viole “violet,” from L. viola, akin to Gk. ion “violet.”

Etymology (PE): Banafš “violet,” related to banafšé “violet flower;” Mid.Pers. vanafšak “violet flower.”

A layer of particles in the upper Martian atmosphere that scatter and absorbs electromagnetic radiation at shorter wavelengths, making the atmosphere opaque to blue, violet, and ultraviolet light.

See also: → violet; → layer.

A layer of particles in the upper Martian atmosphere that scatter and absorbs electromagnetic radiation at shorter wavelengths, making the atmosphere opaque to blue, violet, and ultraviolet light.

See also: → violet; → layer.

The Maiden. A large constellation of the Zodiac, situated at the celestial equator with 13h right ascension, 2° south declination. The brightest star is the first magnitude → Spica, and there are seven others brighter than fourth magnitude. Because of the presence of a background galaxy cluster, → Virgo cluster, this constellation is especially rich in galaxies. Eleven of the brighter galaxies are listed in the → Messier catalog.
Abbreviation: Vir; Genitive: Virginis.

Etymology (EN): L. virgo “maiden, unwedded girl or woman.”

Etymology (PE): Dušizé “maiden, virgin;” Mid.Pers. dôšizag “maiden, virgin,” related to duxtar, duxt “daughter” (O.Pers. *duxçi-;
Av. dugədar-, duγdar-; cf.
Skt. duhitár-, Gk. thygater;
E. daughter; Ger. Tochter; PIE base *dhug(h)əter-); Manichean Mid.Pers. duxš “princess, girl of noble birth;” O.Pers. duxši- (Elamite du-uk-ši-iš) “royal princess” + diminutive suffix -izag, -izé (as in suffixed Fr. demoiselle, from V.L. *dominicella, from domin(a) “lady” + -i- + -cella diminutive suffix).

The Maiden. A large constellation of the Zodiac, situated at the celestial equator with 13h right ascension, 2° south declination. The brightest star is the first magnitude → Spica, and there are seven others brighter than fourth magnitude. Because of the presence of a background galaxy cluster, → Virgo cluster, this constellation is especially rich in galaxies. Eleven of the brighter galaxies are listed in the → Messier catalog.
Abbreviation: Vir; Genitive: Virginis.

Etymology (EN): L. virgo “maiden, unwedded girl or woman.”

Etymology (PE): Dušizé “maiden, virgin;” Mid.Pers. dôšizag “maiden, virgin,” related to duxtar, duxt “daughter” (O.Pers. *duxçi-;
Av. dugədar-, duγdar-; cf.
Skt. duhitár-, Gk. thygater;
E. daughter; Ger. Tochter; PIE base *dhug(h)əter-); Manichean Mid.Pers. duxš “princess, girl of noble birth;” O.Pers. duxši- (Elamite du-uk-ši-iš) “royal princess” + diminutive suffix -izag, -izé (as in suffixed Fr. demoiselle, from V.L. *dominicella, from domin(a) “lady” + -i- + -cella diminutive suffix).

The most powerful radio source in the constellation Virgo, among the thousands of galactic systems comprising the → Virgo Cluster. Optically, it is an elliptical galaxy (M87) with a luminous blue jet about 1500 pc long. It is also an X-ray source (3C 274, Virgo X-1, 2U 1228+12).

See also: → Virgo.

The most powerful radio source in the constellation Virgo, among the thousands of galactic systems comprising the → Virgo Cluster. Optically, it is an elliptical galaxy (M87) with a luminous blue jet about 1500 pc long. It is also an X-ray source (3C 274, Virgo X-1, 2U 1228+12).

See also: → Virgo.

The largest and nearest galaxy cluster to the Local Group. The Virgo cluster spans 120 square degrees on the sky and contains on the order of 2,000 galaxies. It is located at a distance of about 60 million light-years. It is an irregular cluster with no central concentration. The giant elliptical galaxy M87 is the most massive in the cluster.

See also: → Virgo; → cluster.

The largest and nearest galaxy cluster to the Local Group. The Virgo cluster spans 120 square degrees on the sky and contains on the order of 2,000 galaxies. It is located at a distance of about 60 million light-years. It is an irregular cluster with no central concentration. The giant elliptical galaxy M87 is the most massive in the cluster.

See also: → Virgo; → cluster.

A → Michelson interferometer using → laser beams designed to detect → gravitational waves. It consists of two 3-km-long arms, which house the various machinery required to form a → laser interferometer. The gravitational waves searched for have frequencies between 10 Hz and 10 kHz. Virgo has been designed and built by a collaboration between the French Centre National de la Recherche Scientifique (CNRS) and the Italian Istituto Nazionale di Fisica Nucleare (INFN). It is now operated and improved in Cascina, a small town near Pisa on the site of the European Gravitational Observatory (EGO), by an international collaboration of scientists from France, Italy, the Netherlands, Poland, and Hungary.

The initial Virgo detector observed the sky between 2007 and 2011 together with the two interferometers of the → Laser Interferometer Gravitational-Wave Observatory (LIGO), located in the United States. Virgo underwent a major upgrade after a long shutdown period. The “Advanced Virgo” overhaul lasted 5-year and costed 23 million Euros. The upgraded observatory was inaugurated on 20 February 2017 and, notably, detected the → GW170817 event.

See also: Named after the → Virgo cluster of galaxies whose stellar explosions it aims to detect; → interferometer.

A → Michelson interferometer using → laser beams designed to detect → gravitational waves. It consists of two 3-km-long arms, which house the various machinery required to form a → laser interferometer. The gravitational waves searched for have frequencies between 10 Hz and 10 kHz. Virgo has been designed and built by a collaboration between the French Centre National de la Recherche Scientifique (CNRS) and the Italian Istituto Nazionale di Fisica Nucleare (INFN). It is now operated and improved in Cascina, a small town near Pisa on the site of the European Gravitational Observatory (EGO), by an international collaboration of scientists from France, Italy, the Netherlands, Poland, and Hungary.

The initial Virgo detector observed the sky between 2007 and 2011 together with the two interferometers of the → Laser Interferometer Gravitational-Wave Observatory (LIGO), located in the United States. Virgo underwent a major upgrade after a long shutdown period. The “Advanced Virgo” overhaul lasted 5-year and costed 23 million Euros. The upgraded observatory was inaugurated on 20 February 2017 and, notably, detected the → GW170817 event.

See also: Named after the → Virgo cluster of galaxies whose stellar explosions it aims to detect; → interferometer.

The irregular supercluster that contains the Virgo cluster and the Local Group. At least 100 galaxy groups and clusters are located within its diameter of 110 million light-years. It is one of millions of superclusters in the observable Universe.

See also: → Virgo; → supercluster.

The irregular supercluster that contains the Virgo cluster and the Local Group. At least 100 galaxy groups and clusters are located within its diameter of 110 million light-years. It is one of millions of superclusters in the observable Universe.

See also: → Virgo; → supercluster.

Of or pertaining to the interactive forces between components of a system, such as particles or molecules in a gas or stars in a cluster.
→ virial equation of state, → virial equilibrium, → virial mass, → virial parameter, → virial radius, → virial temperature, → virial theorem, → virialization.

Etymology (EN): From L. vires, plural of vis “strength,” and by extension
“force” or “energy,” first used by Rudolf Clausius in the investigation of problems in molecular physics.

Etymology (PE): Viriyâl, loan from E., as above.

Of or pertaining to the interactive forces between components of a system, such as particles or molecules in a gas or stars in a cluster.
→ virial equation of state, → virial equilibrium, → virial mass, → virial parameter, → virial radius, → virial temperature, → virial theorem, → virialization.

Etymology (EN): From L. vires, plural of vis “strength,” and by extension
“force” or “energy,” first used by Rudolf Clausius in the investigation of problems in molecular physics.

Etymology (PE): Viriyâl, loan from E., as above.

In thermodynamics, a generalized → equation of state obtained when the → compression factor Z is expanded in terms of a power series, e.g.: Z = 1 + B(T) / V_m + C(T) / V_m² + …

See also: → virial; → equation of state.

In thermodynamics, a generalized → equation of state obtained when the → compression factor Z is expanded in terms of a power series, e.g.: Z = 1 + B(T) / V_m + C(T) / V_m² + …

See also: → virial; → equation of state.

The condition of a physical system which obeys the → virial theorem.

See also: → virial; → equilibrium.

The condition of a physical system which obeys the → virial theorem.

See also: → virial; → equilibrium.

The mass of a cluster of stars or galaxies in statistical equilibrium derived by using the → virial theorem.

See also: → virial; → mass.

The mass of a cluster of stars or galaxies in statistical equilibrium derived by using the → virial theorem.

See also: → virial; → mass.

A dimensionless parameter that measures the ratio of thermal plus kinetic energies to gravitational energy of a physical system, such as a molecular cloud. The virial parameter is expressed as: α_vir = 5σ²R / GM, where R and M are the radius and mass of the cloud respectively, σ is the one-dimensional → velocity dispersion inside the cloud, and G the → gravitational constant. It indicates whether a cloud could be bound or not. For molecular clouds that are confined by their surface pressure and for which self-gravity is unimportant, α_vir is much larger than unity, whereas α_vir
is ~ 1 when the gravitational energy of a clump becomes comparable to its kinetic energy. See, e.g., Bertoldi & McKee, 1992 (ApJ 395, 140). See also → virial theorem.

See also: → virial; → parameter.

A dimensionless parameter that measures the ratio of thermal plus kinetic energies to gravitational energy of a physical system, such as a molecular cloud. The virial parameter is expressed as: α_vir = 5σ²R / GM, where R and M are the radius and mass of the cloud respectively, σ is the one-dimensional → velocity dispersion inside the cloud, and G the → gravitational constant. It indicates whether a cloud could be bound or not. For molecular clouds that are confined by their surface pressure and for which self-gravity is unimportant, α_vir is much larger than unity, whereas α_vir
is ~ 1 when the gravitational energy of a clump becomes comparable to its kinetic energy. See, e.g., Bertoldi & McKee, 1992 (ApJ 395, 140). See also → virial theorem.

See also: → virial; → parameter.

The radius centered on a galaxy containing matter at 200 times the → critical density of the Universe.

See also: → virial; → radius.

The radius centered on a galaxy containing matter at 200 times the → critical density of the Universe.

See also: → virial; → radius.

The mean temperature at which a gravitationally → bound system would satisfy the → virial theorem. For a system of mass M and radius R with constant density, the gravitational energy per unit mass is W = GM/R. The kinetic energy per unit mass is E = (3/2)kT_vir/μ, where k is → Boltzmann’s constant and μ the mean molecular weight. According to the virial theorem, E = W/2, which leads to the virial temperature
T_vir = (1/3)(GM/kR).

See also: → virial; → temperature.

The mean temperature at which a gravitationally → bound system would satisfy the → virial theorem. For a system of mass M and radius R with constant density, the gravitational energy per unit mass is W = GM/R. The kinetic energy per unit mass is E = (3/2)kT_vir/μ, where k is → Boltzmann’s constant and μ the mean molecular weight. According to the virial theorem, E = W/2, which leads to the virial temperature
T_vir = (1/3)(GM/kR).

See also: → virial; → temperature.

A general equation applicable to a gravitationally → bound system of equal mass objects (stars, galaxies, etc.), which is stable against → dynamical disruption.
It states that in such a system the average → gravitational potential energy (W_vir) is twice the average → kinetic energy (K_vir) of the system: W_vir = -2K_vir. This general proposition, first derived by Rudolf Clausius (1822-1888),
has important applications in a variety of fields ranging from statistical mechanics to astrophysics. See also → virialization, → virial equilibrium, → virialized.

See also: → virial; → theorem.

A general equation applicable to a gravitationally → bound system of equal mass objects (stars, galaxies, etc.), which is stable against → dynamical disruption.
It states that in such a system the average → gravitational potential energy (W_vir) is twice the average → kinetic energy (K_vir) of the system: W_vir = -2K_vir. This general proposition, first derived by Rudolf Clausius (1822-1888),
has important applications in a variety of fields ranging from statistical mechanics to astrophysics. See also → virialization, → virial equilibrium, → virialized.

See also: → virial; → theorem.

The process whereby a system of gravitationally interacting particles attains stability. The comparable mass components interact with each other, but the whole system does not expand or collapse. Virialization occurs when the → potential energy is twice the negative → kinetic energy:

• W_vir = 2 K_vir (→ virial theorem). In the case of a → galaxy cluster,
  when the cluster is virialized the merging process and the collapse of matter have finished and the formation process of the galaxy cluster is considered to be done. A cluster has formed by → hierarchical clustering. Virialized clusters, in other words finished clusters, can be found by looking at their radius and density. A cluster is virialized when it satisfies the condition:

R_vir ~ R_max/2,

where R_vir is the radius when the cluster is virialized and
R_max is the radius when the collapse starts. From this condition it follows that the object is 8 times denser at virialization than when the collapse started.

See also: Verbal noun of → virialize.

The process whereby a system of gravitationally interacting particles attains stability. The comparable mass components interact with each other, but the whole system does not expand or collapse. Virialization occurs when the → potential energy is twice the negative → kinetic energy:

• W_vir = 2 K_vir (→ virial theorem). In the case of a → galaxy cluster,
  when the cluster is virialized the merging process and the collapse of matter have finished and the formation process of the galaxy cluster is considered to be done. A cluster has formed by → hierarchical clustering. Virialized clusters, in other words finished clusters, can be found by looking at their radius and density. A cluster is virialized when it satisfies the condition:

R_vir ~ R_max/2,

where R_vir is the radius when the cluster is virialized and
R_max is the radius when the collapse starts. From this condition it follows that the object is 8 times denser at virialization than when the collapse started.

See also: Verbal noun of → virialize.

To undergo → virialization.

See also: → virial; → -ize.

To undergo → virialization.

See also: → virial; → -ize.

That has undergone → virialization.

See also: Past participle of → virialize.

That has undergone → virialization.

See also: Past participle of → virialize.

1. General: Having the efficacy without the material part; unreal but capable of being considered as real for some purpose.
   

2. Computers: Simulated by a computer (for reasons of experiment or
   convenience) of an entity that lacks some elements of total reality.

Etymology (EN): M.E., from M.L. virtualis, from L. virtus “manliness, excellence, potency, efficacy,” from vir “man, human, husband, soldier,” cf. Mid.Pers. vīr, wīr “man, hero;” Av. vīra- “man, human;” Skt. vīrá- “man, hero;”
Lith. vyras “man, husband;” O.Ir. fer “man;” Goth. wair “man;” O.E. wer “man.” In Roman philosophy, virtue became associated with virility and strength of character.

Etymology (PE): Virâgin from vir “intellect, mind, memory,” variants bar, bir (Mid.Pers. vir, varm, vârom “mental faculty, memory, mind;” Av. vārəma, vārəm “according to one’s wishes,” from var- “to choose”) + -âgin a
suffix denoting “consisting of, similarity, possession.”

1. General: Having the efficacy without the material part; unreal but capable of being considered as real for some purpose.
   

2. Computers: Simulated by a computer (for reasons of experiment or
   convenience) of an entity that lacks some elements of total reality.

Etymology (EN): M.E., from M.L. virtualis, from L. virtus “manliness, excellence, potency, efficacy,” from vir “man, human, husband, soldier,” cf. Mid.Pers. vīr, wīr “man, hero;” Av. vīra- “man, human;” Skt. vīrá- “man, hero;”
Lith. vyras “man, husband;” O.Ir. fer “man;” Goth. wair “man;” O.E. wer “man.” In Roman philosophy, virtue became associated with virility and strength of character.

Etymology (PE): Virâgin from vir “intellect, mind, memory,” variants bar, bir (Mid.Pers. vir, varm, vârom “mental faculty, memory, mind;” Av. vārəma, vārəm “according to one’s wishes,” from var- “to choose”) + -âgin a
suffix denoting “consisting of, similarity, possession.”

In → analytical mechanics, any infinitesimal change in the configuration of a material system, consistent with any constraints acting on the system at a given instant. If the constraints are stationary (→ scleronomous), then the actual displacement of the system, in an
infinitesimal length of time dt, coincides with one of its virtual displacements. In the case of time-dependent (→ rheonomous) constraints, the actual displacement of the system does not coincide with any of the virtual ones, since the conditions imposed by the constraints vary during the time dt.

See also: → virtual; → displacement.

In → analytical mechanics, any infinitesimal change in the configuration of a material system, consistent with any constraints acting on the system at a given instant. If the constraints are stationary (→ scleronomous), then the actual displacement of the system, in an
infinitesimal length of time dt, coincides with one of its virtual displacements. In the case of time-dependent (→ rheonomous) constraints, the actual displacement of the system does not coincide with any of the virtual ones, since the conditions imposed by the constraints vary during the time dt.

See also: → virtual; → displacement.

Optics: An image formed inside an instrument at the point where diverging rays would cross if they were extended backward into the instrument. Such an image cannot be obtained on a screen placed at its apparent position, since the rays do not pass through that point. → real image.

See also: → virtual; → image.

Optics: An image formed inside an instrument at the point where diverging rays would cross if they were extended backward into the instrument. Such an image cannot be obtained on a screen placed at its apparent position, since the rays do not pass through that point. → real image.

See also: → virtual; → image.

An international initiative by the astronomical community to allow global electronic access to the available astronomical data archives of space and ground-based observatories. It also aims to enable data analysis techniques through a coordinating entity that provides common standards, wide-network bandwidth, and state-of-the-art analysis tools. The Virtual Observatory is also intended for re-using data for scientific objectives different from the original ones, in order to optimize the science return of astronomical observations. The Virtual Observatory’s capabilities are enabled through the use of standard protocols for registering the existence and location of data and for requesting data that satisfies the user’s interests. These standards are developed on an international basis through the → IVOA. The cornerstone of the Virtual Observatory is → interoperability.

See also: → virtual; → observatory.

An international initiative by the astronomical community to allow global electronic access to the available astronomical data archives of space and ground-based observatories. It also aims to enable data analysis techniques through a coordinating entity that provides common standards, wide-network bandwidth, and state-of-the-art analysis tools. The Virtual Observatory is also intended for re-using data for scientific objectives different from the original ones, in order to optimize the science return of astronomical observations. The Virtual Observatory’s capabilities are enabled through the use of standard protocols for registering the existence and location of data and for requesting data that satisfies the user’s interests. These standards are developed on an international basis through the → IVOA. The cornerstone of the Virtual Observatory is → interoperability.

See also: → virtual; → observatory.

A subatomic particle that, according to the uncertainty principle, comes into being out of energy fluctuations of the “vacuum” and lasts for extremely short periods of time. An electron-positron pair can exist only about 4 x 10^-21 seconds. The lifetime increases as the mass and energy involved decreases. Virtual particles are real and have measurable effects, but cannot be directly observed, according to the uncertainty principle. → vacuum polarization.

See also: → virtual; → particle

A subatomic particle that, according to the uncertainty principle, comes into being out of energy fluctuations of the “vacuum” and lasts for extremely short periods of time. An electron-positron pair can exist only about 4 x 10^-21 seconds. The lifetime increases as the mass and energy involved decreases. Virtual particles are real and have measurable effects, but cannot be directly observed, according to the uncertainty principle. → vacuum polarization.

See also: → virtual; → particle

In → analytical mechanics, an element of work performed in a → virtual displacement by the → forces acting on all n particles of a → holonomic system with s degrees of freedom (→ degree of freedom).

See also: → virtual; → work.

In → analytical mechanics, an element of work performed in a → virtual displacement by the → forces acting on all n particles of a → holonomic system with s degrees of freedom (→ degree of freedom).

See also: → virtual; → work.

In → analytical mechanics, a principle whereby it is necessary and sufficient for the equilibrium of any material system with ideal constraints that the sum of the elements of work, performed by the applied forces acting on the system in any virtual displacement, be equal to zero (if all constraints are bilateral) or less than zero (if some of the constraints are unilateral).

See also: → virtual; → work; → principle.

In → analytical mechanics, a principle whereby it is necessary and sufficient for the equilibrium of any material system with ideal constraints that the sum of the elements of work, performed by the applied forces acting on the system in any virtual displacement, be equal to zero (if all constraints are bilateral) or less than zero (if some of the constraints are unilateral).

See also: → virtual; → work; → principle.

1. An ultramicroscopic (20 to 300 nm in diameter), metabolically inert, infectious agent that replicates only within the cells of living hosts, mainly bacteria, plants, and animals: composed of an RNA or DNA core, a protein coat, and, in more complex types, a surrounding envelope (Dictionary.com).
   

2. → computer virus.

See also: From L. virus “poison, sap of plants, slimy liquid, a potent juice,” ultimately from PIE *ueis- “fluidity, slime, poison;” cf. Pers. bīš “a poisonous plant;” Mid.Pers. wiš “poison;” Av. viš-, viša- “poison;” Skt. visa- “venom, poison, poisonous;” L. viscum “sticky substance, birdlime;” Gk. ios “poison,” ixos “mistletoe, birdlime;” O.C.S. višnja “cherry;” O.Irish fi “poison;” Welsh gwy “poison.”

1. An ultramicroscopic (20 to 300 nm in diameter), metabolically inert, infectious agent that replicates only within the cells of living hosts, mainly bacteria, plants, and animals: composed of an RNA or DNA core, a protein coat, and, in more complex types, a surrounding envelope (Dictionary.com).
   

2. → computer virus.

See also: From L. virus “poison, sap of plants, slimy liquid, a potent juice,” ultimately from PIE *ueis- “fluidity, slime, poison;” cf. Pers. bīš “a poisonous plant;” Mid.Pers. wiš “poison;” Av. viš-, viša- “poison;” Skt. visa- “venom, poison, poisonous;” L. viscum “sticky substance, birdlime;” Gk. ios “poison,” ixos “mistletoe, birdlime;” O.C.S. višnja “cherry;” O.Irish fi “poison;” Welsh gwy “poison.”

An instrument used to measure the → viscosity of a liquid. Same as viscosimeter.

See also: → viscosity; → -meter.

An instrument used to measure the → viscosity of a liquid. Same as viscosimeter.

See also: → viscosity; → -meter.

Same as → viscometer.

See also: → viscosity; → -meter.

Same as → viscometer.

See also: → viscosity; → -meter.

The property of a → fluid that resists the force tending to cause the fluid to flow. Viscosity may be thought of as the internal → friction of two fluid layers which flow parallel to each other at different speeds. The cause of viscosity is the transport of → momentum by the molecules from one layer to the other. Viscosity is given by η = φ.u.λ.ρ, where φ is a coefficient which depends on the nature of the interaction between the molecules, u is the average velocity of thermal motion of the molecules, λ is the → mean free path, and ρ the → density of the fluid. Also called → dynamic viscosity or → absolute viscosity. See also → kinematic viscosity.

See also: Noun from → viscous; → -ity.

The property of a → fluid that resists the force tending to cause the fluid to flow. Viscosity may be thought of as the internal → friction of two fluid layers which flow parallel to each other at different speeds. The cause of viscosity is the transport of → momentum by the molecules from one layer to the other. Viscosity is given by η = φ.u.λ.ρ, where φ is a coefficient which depends on the nature of the interaction between the molecules, u is the average velocity of thermal motion of the molecules, λ is the → mean free path, and ρ the → density of the fluid. Also called → dynamic viscosity or → absolute viscosity. See also → kinematic viscosity.

See also: Noun from → viscous; → -ity.

Having the property of → viscosity. See also: → viscous dissipation, → viscous decretion disk, → viscous fluid, → viscous force, → nonviscous.

Etymology (EN): M.E., from M.Fr. viscous, from L. viscosus “sticky,” from viscum “anything sticky; mistletoe.”

Etymology (PE): From vošk “a kind of sticky gum” + -sân suffix of similarity, from sân “way, manner.”

Having the property of → viscosity. See also: → viscous dissipation, → viscous decretion disk, → viscous fluid, → viscous force, → nonviscous.

Etymology (EN): M.E., from M.Fr. viscous, from L. viscosus “sticky,” from viscum “anything sticky; mistletoe.”

Etymology (PE): From vošk “a kind of sticky gum” + -sân suffix of similarity, from sân “way, manner.”

A model for explaining several observational features of → circumstellar disks around → Be stars. According to this model, the central star provides → angular momentum to the disk at the innermost radius, and then it is redistributed over the whole disk via → viscosity. Thus, in isolated Be stars, the equatorial disk can spread out to a large distance as long as the star can give angular momentum to the disk.

The VDD model, first introduced by Lee et al. (1991, MNRAS, 250, 432) and further developed by several other researchers, is now widely accepted as the best physical model for describing the circumstellar disks of Be stars. Among the growing evidence supporting the VDD model is the confirmation that the disks rotate in a Keplerian way (→ Keplerian orbit), allowing for the identification of viscosity as the mechanism that makes the disk grow (see, e.g., Klement et al., 2015, A&A 584, A85).

See also: → viscous; → decretion; → disk.

A model for explaining several observational features of → circumstellar disks around → Be stars. According to this model, the central star provides → angular momentum to the disk at the innermost radius, and then it is redistributed over the whole disk via → viscosity. Thus, in isolated Be stars, the equatorial disk can spread out to a large distance as long as the star can give angular momentum to the disk.

The VDD model, first introduced by Lee et al. (1991, MNRAS, 250, 432) and further developed by several other researchers, is now widely accepted as the best physical model for describing the circumstellar disks of Be stars. Among the growing evidence supporting the VDD model is the confirmation that the disks rotate in a Keplerian way (→ Keplerian orbit), allowing for the identification of viscosity as the mechanism that makes the disk grow (see, e.g., Klement et al., 2015, A&A 584, A85).

See also: → viscous; → decretion; → disk.

A degradation of → mechanical energy that is irreversibly converted to → thermal energy due to → viscous forces in the → fluid. Viscous dissipation occurs in → turbulent flows.

See also: → viscous; → dissipation.

A degradation of → mechanical energy that is irreversibly converted to → thermal energy due to → viscous forces in the → fluid. Viscous dissipation occurs in → turbulent flows.

See also: → viscous; → dissipation.

A fluid whose viscosity is sufficiently large to make the viscous forces a significant part of the total force field in the fluid.

See also: → viscous; → fluid.

A fluid whose viscosity is sufficiently large to make the viscous forces a significant part of the total force field in the fluid.

See also: → viscous; → fluid.

The force per unit volume or per unit mass arising from the action of tangential stresses in a moving → viscous fluid.

See also: → viscous; → force.

The force per unit volume or per unit mass arising from the action of tangential stresses in a moving → viscous fluid.

See also: → viscous; → force.

1. General: The state or fact of being visible. → crescent Moon visibility, → Venus visibility.
   

2. Optics: → fringe visibility. See also: → visibility function, → visibility plane.
   

3. Meteo.: A measure of transparency of the atmosphere. The maximum horizontal distance at which objects can be identified. → turbidity.

See also: → visible + → -ity.

1. General: The state or fact of being visible. → crescent Moon visibility, → Venus visibility.
   

2. Optics: → fringe visibility. See also: → visibility function, → visibility plane.
   

3. Meteo.: A measure of transparency of the atmosphere. The maximum horizontal distance at which objects can be identified. → turbidity.

See also: → visible + → -ity.

The → Fourier transform of a source’s → brightness distribution, weighted by the characteristics of the → interferometer’s antennas.

See also: → visibility; → function.

The → Fourier transform of a source’s → brightness distribution, weighted by the characteristics of the → interferometer’s antennas.

See also: → visibility; → function.

In → interferometry, the projection of a → baseline onto the plane normal to the source direction defining a vector in (u,v) space, measured in wavelength units.

See also: → visibility; → plane.

In → interferometry, the projection of a → baseline onto the plane normal to the source direction defining a vector in (u,v) space, measured in wavelength units.

See also: → visibility; → plane.

1. Capable of being seen by, or perceptible to, the human eye.
   

2. → visible light.

Etymology (EN): M.E., from O.Fr. visible, from L. visibilis “that may be seen,” from visus, p.p. of videre “to see;” cognate with Pers.
bin, present stem of didan “to see”
(Mid.Pers. wyn-; O.Pers. vain- “to see;” Av. vaēn- “to see;”
cf. Skt. veda “I know;” Gk. oida “I know,” idein “to see;” PIE base *weid- “to know, to see”).

Etymology (PE): Diyâr “visible” in several dialects, e.g. štiyâni, Malâyeri, Širâzi, Tabari, related to didan “to see;” Mid.Pers. ditan “to see, regard, catch sight of, contemplate, experience;” O.Pers. dī- “to see;” Av. dā(y)- “to see,” didāti “sees;” cf. Skt. dhī- “to perceive, think, ponder; thought, reflection, meditation,” dādhye; Gk. dedorka “have seen.”
Padidâr (→ phenomenon) and peydâ are both also related to dā(y)-
(with prefixes).

1. Capable of being seen by, or perceptible to, the human eye.
   

2. → visible light.

Etymology (EN): M.E., from O.Fr. visible, from L. visibilis “that may be seen,” from visus, p.p. of videre “to see;” cognate with Pers.
bin, present stem of didan “to see”
(Mid.Pers. wyn-; O.Pers. vain- “to see;” Av. vaēn- “to see;”
cf. Skt. veda “I know;” Gk. oida “I know,” idein “to see;” PIE base *weid- “to know, to see”).

Etymology (PE): Diyâr “visible” in several dialects, e.g. štiyâni, Malâyeri, Širâzi, Tabari, related to didan “to see;” Mid.Pers. ditan “to see, regard, catch sight of, contemplate, experience;” O.Pers. dī- “to see;” Av. dā(y)- “to see,” didāti “sees;” cf. Skt. dhī- “to perceive, think, ponder; thought, reflection, meditation,” dādhye; Gk. dedorka “have seen.”
Padidâr (→ phenomenon) and peydâ are both also related to dā(y)-
(with prefixes).

That line where Earth and sky appear to meet, and the projection of this line upon the celestial sphere. Also known as the apparent horizon.

See also: → visible; → horizon.

That line where Earth and sky appear to meet, and the projection of this line upon the celestial sphere. Also known as the apparent horizon.

See also: → visible; → horizon.

The portion of the → electromagnetic radiation
that can be seen by the human → eye. The → wavelengths extend from about 400 nm (violet) to 750 nm (red). The wavelengths of various colors of the visible spectrum are as follows: → violet: 390-455 nm; → blue: 455-492 nm; → green: 492-577; → yellow: 577-597; → orange: 597-622; → red: 622-780 nm.

See also: → visible; → light.

The portion of the → electromagnetic radiation
that can be seen by the human → eye. The → wavelengths extend from about 400 nm (violet) to 750 nm (red). The wavelengths of various colors of the visible spectrum are as follows: → violet: 390-455 nm; → blue: 455-492 nm; → green: 492-577; → yellow: 577-597; → orange: 597-622; → red: 622-780 nm.

See also: → visible; → light.

The portion of → electromagnetic spectrum corresponding to → visible light.

See also: → visible; → spectrum.

The portion of → electromagnetic spectrum corresponding to → visible light.

See also: → visible; → spectrum.

The act or power of sensing with the eyes. → averted vision; → acuity of vision.

Etymology (EN): M.E., from O.Fr. vision, from L. visionem (nominative visio) “act of seeing, sight, thing seen,” from p.p. stem of videre “to see,” cognate with Pers. bin, present stem of didan “to see”
(Mid.Pers. wyn-; O.Pers. vain- “to see;” Av. vaēn- “to see;”
cf. Skt. veda “I know;” Gk. oida “I know,” idein “to see;” PIE base *weid- “to know, to see”).

Etymology (PE): Negâh, “look,” from Mid.Pers. nikâh “look, glance, observation;” Proto-Iranian *ni-kas- “to look down,” from ni- “down, below,” → ni- (PIE),

• *kas- “to look, appear;” cf. Av. nikā-, nikāta- (in the name of the 15-th nask) “that which is observed,” ākas- “to look;” Mid.Pers. âkâh, Mod.Pers. âgâh “aware, knowing;” Skt. kāś- “to become visible, appear;” Ossetic kast/kaesyn “to look;” did, from didan “to see” (Mid.Pers. ditan “to see, regard, catch sight of, contemplate, experience;” O.Pers. dī- “to see;” Av. dā(y)- “to see,” didāti “sees;” cf. Skt. dhī- “to perceive, think, ponder; thought, reflection, meditation,” dādhye; Gk. dedorka “have seen”).

The act or power of sensing with the eyes. → averted vision; → acuity of vision.

Etymology (EN): M.E., from O.Fr. vision, from L. visionem (nominative visio) “act of seeing, sight, thing seen,” from p.p. stem of videre “to see,” cognate with Pers. bin, present stem of didan “to see”
(Mid.Pers. wyn-; O.Pers. vain- “to see;” Av. vaēn- “to see;”
cf. Skt. veda “I know;” Gk. oida “I know,” idein “to see;” PIE base *weid- “to know, to see”).

Etymology (PE): Negâh, “look,” from Mid.Pers. nikâh “look, glance, observation;” Proto-Iranian *ni-kas- “to look down,” from ni- “down, below,” → ni- (PIE),

• *kas- “to look, appear;” cf. Av. nikā-, nikāta- (in the name of the 15-th nask) “that which is observed,” ākas- “to look;” Mid.Pers. âkâh, Mod.Pers. âgâh “aware, knowing;” Skt. kāś- “to become visible, appear;” Ossetic kast/kaesyn “to look;” did, from didan “to see” (Mid.Pers. ditan “to see, regard, catch sight of, contemplate, experience;” O.Pers. dī- “to see;” Av. dā(y)- “to see,” didāti “sees;” cf. Skt. dhī- “to perceive, think, ponder; thought, reflection, meditation,” dādhye; Gk. dedorka “have seen”).

1. Of or pertaining to seeing or sight.
   

2. → optical.

Etymology (EN): M.E., from L.L. visualis “of sight,” from L. visus “sight,” from visus, .pp. of videre “to see;” cognate with Pers.
bin, present stem of didan “to see”
(Mid.Pers. wyn-; O.Pers. vain- “to see;” Av. vaēn- “to see;”
cf. Skt. veda “I know;” Gk. oida “I know,” idein “to see;” PIE base *weid- “to know, to see”).

Etymology (PE): Didi, of or pertaining to did, from didan “to see” (Mid.Pers. ditan “to see, regard, catch sight of, contemplate, experience;” O.Pers. dī- “to see;” Av. dā(y)- “to see,” didāti “sees;” cf. Skt. dhī- “to perceive, think, ponder; thought, reflection, meditation,” dādhye; Gk. dedorka “have seen”); didgâni, adj. of didgân, plural of didé, did “sight, eye; seen;” didâri, from didâr, from didan.

1. Of or pertaining to seeing or sight.
   

2. → optical.

Etymology (EN): M.E., from L.L. visualis “of sight,” from L. visus “sight,” from visus, .pp. of videre “to see;” cognate with Pers.
bin, present stem of didan “to see”
(Mid.Pers. wyn-; O.Pers. vain- “to see;” Av. vaēn- “to see;”
cf. Skt. veda “I know;” Gk. oida “I know,” idein “to see;” PIE base *weid- “to know, to see”).

Etymology (PE): Didi, of or pertaining to did, from didan “to see” (Mid.Pers. ditan “to see, regard, catch sight of, contemplate, experience;” O.Pers. dī- “to see;” Av. dā(y)- “to see,” didāti “sees;” cf. Skt. dhī- “to perceive, think, ponder; thought, reflection, meditation,” dādhye; Gk. dedorka “have seen”); didgâni, adj. of didgân, plural of didé, did “sight, eye; seen;” didâri, from didâr, from didan.

Same as → acuity of vision.

See also: → visual; → acuity.

Same as → acuity of vision.

See also: → visual; → acuity.

A → binary system of stars whose components can be resolved telescopically and which have detectable orbital motion.

See also: → visual; → binary.

A → binary system of stars whose components can be resolved telescopically and which have detectable orbital motion.

See also: → visual; → binary.

The → extinction in the visual range of the electromagnetic radiation.

See also: → visual; → extinction

The → extinction in the visual range of the electromagnetic radiation.

See also: → visual; → extinction

The → apparent magnitude of a celestial body in the color sensitivity region of the human eye at a wavelength of 5600 Å. Visual magnitude is now essentially synonymous with V magnitude, which is determined photometrically.

See also: → visual; → magnitude.

The → apparent magnitude of a celestial body in the color sensitivity region of the human eye at a wavelength of 5600 Å. Visual magnitude is now essentially synonymous with V magnitude, which is determined photometrically.

See also: → visual; → magnitude.

1. The act of visualizing (→ visualize).
   

2. The presentation of → information on a → screen.

Etymology (EN): Verbal noun of → visualize.

Etymology (PE): Cašm-did, Mid.Pers. cašm-did “visible,” Mod.Pers. cašm-didâr by Tusi, in Pers. translation of Sufi’s “Book of Fixed Stars,” from cašm “eye” (Mid.Pers. cašm, Av. cašman- “eye,” ākas- “to look,” from prefix ā- + Proto-Iranian *kas- “to look, appear,” cf. Skt. cáksus- “seeing”) + did past stem of didan “to see” (Mid.Pers. ditan “to see, regard, catch sight of, contemplate, experience;” O.Pers. dī- “to see;” Av. dā(y)- “to see,” didāti “sees;” cf. Skt. dhī- “to perceive, think, ponder; thought, reflection, meditation,” dādhye; Gk. dedorka “have seen”).

1. The act of visualizing (→ visualize).
   

2. The presentation of → information on a → screen.

Etymology (EN): Verbal noun of → visualize.

Etymology (PE): Cašm-did, Mid.Pers. cašm-did “visible,” Mod.Pers. cašm-didâr by Tusi, in Pers. translation of Sufi’s “Book of Fixed Stars,” from cašm “eye” (Mid.Pers. cašm, Av. cašman- “eye,” ākas- “to look,” from prefix ā- + Proto-Iranian *kas- “to look, appear,” cf. Skt. cáksus- “seeing”) + did past stem of didan “to see” (Mid.Pers. ditan “to see, regard, catch sight of, contemplate, experience;” O.Pers. dī- “to see;” Av. dā(y)- “to see,” didāti “sees;” cf. Skt. dhī- “to perceive, think, ponder; thought, reflection, meditation,” dādhye; Gk. dedorka “have seen”).

1. To make → visual or → visible.
   

2. To present → image or → information on a → screen, usually a → computer  → display.

See also: From → visual + → -ize; → visualization.

1. To make → visual or → visible.
   

2. To present → image or → information on a → screen, usually a → computer  → display.

See also: From → visual + → -ize; → visualization.

The science, production, and study of → grapes.

Etymology (EN): From L. viti(s) “vine” + → culture.

Etymology (PE): Mowkâri, from mow→ vine + kâri noun from kâštan “to cultivate,” → culture.

The science, production, and study of → grapes.

Etymology (EN): From L. viti(s) “vine” + → culture.

Etymology (PE): Mowkâri, from mow→ vine + kâri noun from kâštan “to cultivate,” → culture.