An Etymological Dictionary of Astronomy and Astrophysics

Any physical quantity which requires a direction to be stated in order to define it completely, for example velocity. Compare with → scalar.

Etymology (EN): From L. vector “one who carries or conveys, carrier,” from p.p. stem of vehere “carry, convey;” cognate with Pers. vâz (in parvâz “flight”); Av. vaz- “to draw, guide; bring; possess; fly; float,” vazaiti “guides, leads”
(cf. Skt. vah- “to carry, drive, convey,” vahati “carries,”
pravaha- “bearing along, carrying,” pravāha- “running water, stream, river;” O.E. wegan “to carry;” O.N. vegr; O.H.G. weg “way,” wegan “to move,” wagan “cart;” M.Du. wagen “wagon;” PIE base *wegh- “to drive”).

Etymology (PE): Bordâr “carrier,” agent noun from bordan “to carry, transport” (Mid.Pers. burdan;
O.Pers./Av. bar- “to bear, carry,” barəθre “to bear (infinitive);” Skt. bharati “he carries;” Gk. pherein “to carry;” L. ferre “to carry;” PIE base *bher- “to carry”).

The study of → vectors and → vector spaces.

See also: → vector; → analysis.

Of a rotating body, a vector of magnitude ω (→ angular velocity) pointing in the direction of advance of a right-hand screw which is turned in the direction of rotation.

See also: → vector; → angular; → velocity.

In nuclear physics, a → boson with the spin quantum number equal to 1.

See also: → vector; → boson.

The study of vector functions between vector spaces by means of → differential and integral calculus.

See also: → vector; → calculus.

A → tensor density of → order 1.

See also: → vector; → density.

A vector each of whose → components is a → scalar field. For example, the → gradient of the scalar field F, expressed by:
∇F = (∂F/∂x)i + (∂F/∂y)j + (∂F/∂z)k.

See also: → vector; → field.

A function whose value at each point is n-dimensional,
as compared to a scalar function, whose value is one-dimensional.

See also: → vector; → function.

Any particle of unit spin, such as the W boson, the photon, or the rho meson.

See also: → vector; → meson.

The perturbation in the → primordial Universe plasma caused by → vorticity. These perturbations cause → Doppler shifts that result in → quadrupole anisotropy.

See also: → vector; → perturbation.

Of two vectors, a vector whose direction is perpendicular to the plane containing the two initial vectors and whose magnitude is the product of the magnitudes of these vectors and the sine of the angle between them: A x B = C, C = |AB sin α|. The direction of C is given by the → right-hand screw rule. Same as → cross product. See also → scalar product.

See also: → vector; → product.

A system of mathematical objects consisting of a set of (muultidimensional) vectors associated with a set of (one-dimensional) scalars, such that vectors can be added together and vectors can be multiplied by scalars while preserving the ordinary arithmetic properties (associativity, commutativity, distributivity, and so forth).

See also: → vector; → space.

The brightest star in the constellation → Lyra and the 5th brightest star in the sky. It is an A type → main sequence star of visual magnitude 0.03. Vega
is also one of the closer stars to the Earth, lying just 25.0 light-years away. Vega’s axis of rotation is nearly pointing at the Earth, therefore it is viewed pole-on. Fast rotation has flattened Vega at its poles, turning it from a sphere into an oblate spheroid. The polar diameter of Vega is 2.26 times that of the Sun, and its equatorial diameter 2.75 solar. The poles are therefore hotter (10,150 K) than the equator (7,950 K).

See also: Vega, from Ar. al-Waqi’ contraction of an-Nasr al-Waqi’ (النسر‌الواقع) “swooping eagle,” from an-Nasr “eagle, vulture” + al-Waqi’ “falling, swooping.”

1. Any of various herbaceous plants having parts that are used as food, such as peas, beans, cabbage, potatoes, cauliflower, and onions.
   

   2. Botany: Of, relating to, characteristic of, derived from, or consisting of plants or plant material (e.g. vegetable oils) (TheFreeDictionary.com).

Etymology (EN): → vegetate; → -able.

Etymology (PE): 1) Sabzijât “class or category of greens,” from sabzi, → green, + -jât a suffix denoting class, group, or division of things.

2. Giyâhi, related to giyâh, → plant.

Of, relating to, or characteristic of plants.

See also: → vegetate; → -al.

1. To grow or sprout as a plant by nutriment imbibed through roots and leaves.
   

   2. To lead a passive life without much physical, mental, or social activity.

Etymology (EN): Ultimately from L. vegetatus, p.p. of vegetare “to enliven, to animate,” from vegetus “vigorous, enlivened, active,” from vegere “to be alive, active;” akin to Skt. vaja- “force, strength;” PIE root *weg- “to be strong, be lively.”

Etymology (PE): Giyâhidan, infinitive forum giyâh, → plant.

1. All the plants or plant life of a place.
   

   2. (Botany) Plant life as a whole, especially the plant life of a particular region.
      

   3. The act or process of vegetating.

See also: Verbal noun from → vegetate.

1. Of, relating to, or characteristic of plants or their growth.
   

   2. Noting the parts of a plant not specialized for reproduction (TheFreeDictionary.com).

Etymology (EN): → vegetate; → -ive.

Etymology (PE): Giyâhvâr, from giyâh, → plant,

• -vâr suffix denoting “resembling, like,” → -oid.

1. A piece of opaque or transparent cloth worn by women as a covering for the head and shoulders.
   

2. Something that covers, screens, or conceals.

Etymology (EN): M.E. veile; O.Fr. voile “a head-covering” (also “sail”),
from L. vela, plural of velum “curtain, covering; sail.”

Etymology (PE): Vâšâmé “veil,” variants vâšâm, bâšâmé, bâšâm, from Mid.Pers. *varšâmak (loaned in Arm. varšamak “veil, scarf”); cf. Sogd. wâršâmé “veil;” from Proto-Ir. *varšāmaka-, from *varšām-, from *varš-, from var- “to cover;” cf. Av. var- “to cover, conceal;” Skt. var- “to cover;” Mid.Pers. warr “garment,” prefixed uzvâr-, uzvârdan “to uncover, show, apprehend, interprete;” Mod.Pers. šalvâr “trousers” (literally “thigh cover;” the first component šal “thigh,” šelang “thigh; step, distance between feet when walking,” cognate with Gk. skelos “leg”); Kurd. (Soriani) barg “cover; clothes,” da barg girtin “to wrap in a cover.”

A part of the → Cygnus loop, an old → supernova remnant.

See also: → veil; → nebula.

1. General: An act of covering with or as if with a veil.
   

2. A weakening of the → spectral lines of a star that occurs when the spectral lines are filled in by → continuum emission or light from a → companion star.

See also: Verbal noun from veil (v.).

Any of the tubes forming part of the blood circulation system of the body, carrying mainly oxygen-depleted blood towards the heart (OxfordDictionaries.com).

Etymology (EN): M.E. veine, from O.Fr. veine “vein, artery, pulse,” from L. vena “a blood vessel,” also “a water course, a vein of metal,” of unknown origin.

Etymology (PE): Siyâhrag, literally “black vessel,” from siyâh, → black, + rag, → vessel.

The Sail. A part of the constellation Argo in the Southern hemisphere, which was later divided into three parts, the others being Carina and Puppis. Vela is situated at about 10h right ascension, -50° declination. Abbreviation: Vel; Genitive: Velorum.

Etymology (EN): From L. vela, plural of velum “sail, curtain, covering,” velare “to cover, veil.”

Etymology (PE): Bâdbân “sail,” literally “wind keeper,” from bâd→ wind + -bân a suffix denoting “keeper, guard,” sometimes forming agent nouns or indicating relation, → host.

A pulsar with a short period (89 milliseconds) associated with the → Vela supernova remnant. It is approximately 1500 light-years distant. The Vela pulsar is one of the few pulsars detectable optically. Its optical flashes, of visual magnitude 26, were detected in 1977. Also named PSR 0833-45.

See also: → Vela; → pulsar.

A → supernova remnant located in the southern Milky Way in the constellation → Vela. It has a large angular diameter of about 8° and lies 250 ± 30 pc away (Cha et al. 1999, ApJ 515, L25). Its overall emission is dominated by the interaction of the → supernova blast wave with the → interstellar medium. This SNR is also notable for a number of protrusions extending well beyond its rim, which were suggested to be fragments of ejecta from the supernova explosion. X-ray spectroscopy has since confirmed several of these protrusions to indeed be strongly enriched with ejecta. The age of the SNR is estimated to be ~11,000 years, based on the spin-down rate of the associated → Vela pulsar, but ages as large as 20,000-30,000 years have also been argued.

See also: → Vela; → supernova remnant.

A compact radio source about 1500 light-years distant associated with the
Vela supernova remnant. It has a nonthermal radio spectrum and is
about 20 percent polarized. It is associated with the Gum Nebula, the
Vela pulsar, and the X-ray source 2U 0832-45.

See also: → Vela; X for → X ray.

The time rate of change of position in a given direction, measured as length per unit time. → speed.

Etymology (EN): L. velocitatem (nominative velocitas) “swiftness, speed,” from velox (genitive velocis) “swift.”

Etymology (PE): Tondâ, from tond “swift, rapid, brisk; fierce, severe” (Mid.Pers. tund “sharp, violent;” Sogdian tund “violent;” cf. Skt. tod- “to thrust, give a push,” tudáti “he thrusts;” L. tundere “to thrust, to hit” (Fr. percer, E. pierce, ultimately from L. pertusus, from p.p. of pertundere “to thrust or bore through;”
PIE base *(s)teud- “to thrust, to beat”) + noun suffix -â.

A plot of the radial velocity of an object against time, derived from the Doppler shift of spectral lines.

See also: → velocity; → curve.

The → standard deviation of a velocity → distribution. It indicates how objects of
the sample move relative to one another. Objects with similar velocities have a small velocity dispersion, whereas objects with very different velocities have a large velocity dispersion.

See also: → velocity; → dispersion.

Fluid Mechanics: The rate at which the velocity changes with the distance across the flow. When a fluid flows past a stationary wall, the fluid right close to the wall does not move. However, away from the wall the flow speed is not zero. Therefore a velocity gradient exists, which is due to adhesive, cohesive, and frictional forces. The amount of the velocity gradient is characteristic of the fluid.

See also: → velocity; → gradient.

In the theory of → radiation-driven winds, an equation that describes the behavior of the → wind velocity of → hot stars as a function of distance from the star. This velocity β-law is given by the expression:

v(r) = v_∞(1 - R/r)^β, where v_∞ is the → terminal velocity, R is the stellar radius, and r the distance from the center. For → O-type stars, the exponent is estimated to be β = 0.8.

See also: → velocity; → law.

A → physical constant which represents the ultimate speed limit for anything moving through space, according to the theory of → special relativity. It is the speed of propagation of → electromagnetic waves in a vacuum, equal to 299,792.458 km/s (nearly 3 x 10⁸ m/s). The velocity of light appears as the connecting link between mass and energy in the → mass-energy relation. Usually denoted by c, from L. celeritas “swiftness,” from celer “swift,” → acceleration.

See also: → velocity; → speed;
→ light.

→ dynamic pressure.

See also: → velocity; → pressure.

A plot of the fluid velocity as a function of position.

See also: → velocity; → profile.

Of a dynamical system, a three-dimensional space which consists of the set of values that the velocity can take (v_x, v_y, v_z). → phase space.

See also: → velocity; → space.

The linear relation wherein all galaxies are moving away from one another,
with velocities that are greater with increasing distance of the galaxy. Same as → Hubble’s law.

See also: → velocity; → distance; → relation.

The location in a → fluid stream where the
→ cross section of the → stream is at a minimum, and fluid velocity is the highest, such as in the case of a → jet issuing out of a → nozzle.

Etymology (EN): L. vena “channel;” contracta, “contracted,” → contract.

Etymology (PE): Šâre-gozar “fluid passage,” → fluid; → passage, terengidé, → contracted.

A schematic diagram using circles to represent sets and the relationships between them. Each circle represents one set. Two or more may be overlapped. The areas of overlap indicate subsets.

See also: Named after John Venn (1834-1923), a British logician and philosopher, who introduced the diagram; → diagram.

The subterranean conduit from the underlying → magma chamber through which a volcano ejects igneous material. Same as volcanic vent.

Etymology (EN): M.E. venten “to furnish (a vessel) with a vent,” from O.Fr. esventer “to air,” from es-, → ex-,

• venter, from vent, from L. ventus “wind.”

Etymology (PE): Dudkaš “chimney,” literally “smoke extractor,” from dud, → smoke,

• kaš “to extract, to draw,” present stem of kešidan/kašidan “to carry, draw, protract,
  trail, drag” (Mid.Pers. kešidan “to draw, pull;” Av. karš- “to draw; to plow,” karša- “furrow;” cf. Skt. kars-, kársati “to pull, drag, plow;”
  Gk. pelo, pelomai “to move, to bustle;” PIE base k^wels- “to plow”).

A → device used to → measure the → quantity of → fluid  → flowing through a → pipe.

See also: Named after Italian physicist Giovanni Battista Venturi (1746-1822); → tube

The second → planet from the → Sun, at a mean distance of roughly 108.21 × 10⁶ km (0.72 → astronomical units). The → greatest elongation of Venus is about 47°, making it visible at most about 3 hours after sunset or before sunrise. Venus has the most circular orbit of any planet in the solar system. Venus is only slightly smaller than Earth (95% of Earth’s diameter, 80% of Earth’s mass). Its chemical composition and density are comparable to those of the Earth. It takes Venus just under 224.401 days to orbit the Sun, compared to the 365 day → orbital period of the Earth. Venus’ rotation is → retrograde, that is it actually rotates from east to west, as opposed to west to east (→ prograde) which is the common rotating direction of most other planets. Seen from Venus, the sun would rise in the west and set in the east. Moreover, it takes about 244 Earth days for Venus to rotate once (→ sidereal rotation). This is longer than its orbital period. The length of its → solar day is about 117 Earth days. → Venus rotation. Its axial tilt is only three degrees, so there are no seasons on Venus. The → atmosphere on the surface of Venus consists mostly of → carbon dioxide, with a small trace of → nitrogen. Venus has a surface pressure about 90 times that of the Earth. See also: → Venus visibility, → transit of Venus.

Etymology (EN): O.E., from L. Venus, the goddess of beauty and love in ancient Roman mythology, from venus “love, sexual desire, beauty, charm;” PIE base *wen- “to desire, love, wish;” cf. Av. vāunuš “lovingly,” vantā- “beloved one, wife;” Skt. van- “to love, desire,” vanánā- “desire,” vanitā- “beloved one, wife;” O.H.G. wunsc(h) “wish,” wunsken “to wish.”

Etymology (PE): Nâhid, planet Venus, Mid.Pers. Anahid; O.Pers. anāhita-
“immaculate, unstained,” goddess of pure waters and fertility, from Av. arədvī-sūra-anāhita “valient and unsustained lord of waters,” from arədvī- (Skt. Saravastī) probably “she who possesses water,” + sūra- “strong, powerful” (Skt. śūra- “valiant, courageous”) + anāhita- “unstained,” from an- negation prefix + āhita “spotted.”

The → sidereal rotation period of Venus, or its → sidereal day, is 243.025 Earth days (retrograde). The length of a → solar day on Venus (that is one entire day-night period) is 116.75 Earth days, that is significantly shorter than the sidereal day because of the retrograde rotation. One Venusian year is about 1.92 Venusian solar days.

See also: → Venus; → rotation.

The conditions under which Venus can be seen from Earth as
it travels in its orbit around the Sun.

The → synodic period of Venus, that is the time Venus takes to be seen again from the Earth in the same position with respect to the Sun, is 583,92 days
or just over 19 months. When Venus is between Earth and Sun (→ inferior conjunction) or on the far side of the sun (→ superior conjunction), it is invisible in the Sun’s glare. Since its → greatest elongation from the Sun is never more than 47°, Venus appears only as “the morning star” and “the evening star.” So at its greatest → western elongation Venus will rise about three hours ahead of the Sun and at its greatest → eastern elongation it will set about three hours after sunset. Its entire cycle is as follows:

Day 0: Superior conjunction, “full Venus.”
Day 35: Venus appears in evening sky.
Day 221: Greatest → eastern elongation, “last quarter.”
Day 271: Retrogression of Venus begins.
Day 286: Disappearance from the evening sky.
Day 292: Inferior conjunction, “new Venus.”
Day 298: Venus appears in morning sky.
Day 313: Retrogression ends.
Day 362: Greatest → western elongation, “first quarter.”
Day 549: Disappearance from morning sky.
Day 584: Superior conjunction, “full venus.”

Therefore, Venus is visible as an evening star for 286 Earth days,
as a morning star for 251 days, and is invisible for 47 days.

In addition, the orbital periods of Earth and Venus are closely correlated. After 8 Earth years or 13 Venus orbits, the two planets assume almost the same relative positions – just 0.032 percent away from a perfect orbital resonance of 8:13. After this period of about 2920 Earth days, Venus appears just 1.5° (about 22 hours) in advance of its former position.

Moreover, Venus exhibit → phases because its orbit lies within the Earth’s. When Venus situated on the far side of the Sun from Earth, the planet is fully illuminated from our point of view. But its disk is small, just 10’’ across, because it is nearly 300 million km away. When Venus is almost closest to Earth, on the near side of the Sun, it’s about 60 million km away. Then it appears as a slender but much brighter crescent with a disk nearly 50’’ across. See also → transit of Venus.

See also: → Venus; → visibility.

A new kind of optical telescope with a 8.4-m diameter → primary mirror currently under construction in Chile and scheduled to begin operations in October 2023. Initially named Large Synoptic Survey Telescope (LSST), it will use a 3200 megapixel camera and an automated data processing system.

It will have a large → field of view almost 10 square degrees of sky, or 40 times the size of the full moon. The LSST will move quickly between images
to rapidly → survey the sky.

From its mountain top site in the Andes (Cerro Pachon, a 2,682-m high mountain in Coquimbo Region), the LSST will take more than 800 panoramic images each night with its 3.2 billion-pixel camera, recording the entire visible sky twice each week. Each patch of sky it images will be visited 1000 times during the survey, each of its 30-second observations will be able to detect objects 10 million times fainter than visible with the human eye.

The LSST’s combination of telescope, mirror, camera, → data processing, and survey will capture changes in billions of faint objects. Hence, the data it provides will be used to create an animated, three-dimensional cosmic map with unprecedented depth and detail. This map will serve many purposes, from locating the → dark matter and characterizing the properties of the → dark energy, to tracking transient objects, to studying our own Milky Way Galaxy in depth. It will even be used to detect and track → potentially hazardous asteroids that might impact the Earth.

See also: Named after Vera C. Rubin (1928-2016) whose work on galaxy rotation rates supported the existence of dark matter in galactic halos.

A member of a major category of words that refers to an action or a state. Verbs present a complex system of forms in Indo-European languages. The set of → inflectional forms of a verb is called a → conjugation. Verbs are usually distinguished for person and number along with tense and mood (if applicable).

Etymology (EN): M.E., from O.Fr. verbe from L. verbum “verb,” originally “a word,” from PIE root *wer- “to speak;” cf. Av. urvāta- “command;” Skt. vrata-
“command, vow;” Gk. rhetor “public speaker,”
eirein “to speak, say;” Lith. vardas “name;” Goth. waurd, O.E. “word.”

Etymology (PE): Karvâz, literally “action word,” from kar- present stem of kardan “to do, make” (Mid.Pers. kardan;
O.Pers./Av. kar- “to do, make, build,” Av. kərənaoiti “he makes;” cf. Skt. kr- “to do, to make,” krnoti “he makes, he does,” karoti “he makes, he does,” karma “act, deed;” PIE base k^wer- “to do, to make”) + vâz “word,” variants vâ&#382, âvâz, vâj, vât, vâ, → voice.

In exactly the same words; word for word.

Etymology (EN): From M.L. verbatim “word for word,” from L. verbum “word,” → verb.

Etymology (PE): Vâž-be-vâž, literally “word for word,” from vâž, → word.

Optics: A measure of the convergence or divergence of a pair of light rays, defined as the reciprocal of the distance between the point of focus and a reference plane.
Ophthalmology: The turning motion of the eyeballs toward or away from each other.

Etymology (EN): back formation from → convergence and → divergence, ultimately from L. vergere “to turn, bend, be inclined;” cognate with Pers. gardidan “to turn, to change,” → version.

Etymology (PE): Gerâyi, from gerâyidan “to incline toward; to intend; to make for.”
Gerâ may be a variant of Mod.Pers. kil “bent, inclined” (k/g and l/r interchanges),
from PIE base *klei- “to lean, incline,” cognate with L. clinare “to bend” (E. declination, inclination, etc.), Gk. klinein “to cause to slope, slant, incline,” Skt. sri- “to lean,” O.Pers. θray-, Av. sray- “to lean,” P.Gmc. *khlinen (Ger. lehnen, E. lean).

In logical positivism philosophy, the claim that a statement is literally meaningful (it expresses a proposition) if and only if it either actually has been verified or could at least in principle be verified.

See also: Quality noun from → verifiable; → principle.

That can be verified. → verify; → verification; → verifiability principle.

See also: → verify; → -able.

The act of verifying. The state of being verified.
The process of research and examination required to establish correctness, authenticity, or validity.

See also: Verbal noun of → verify.

To ascertain the truth or correctness of, as by examination, research, or comparison.

Etymology (EN): M.E. verifien, from M.Fr. verifier, from M.L. verificare “to make true,” from L. verus “true;” → -fy.

Etymology (PE): Râst-jostan, literally “to seek the truth, to seek the right,” from râst “right, true; just, upright, straight” (Mid.Pers. râst “true, straight, direct;” Soghdian rəšt “right;” O.Pers. rāsta- “straight, true,” rās- “to be right, straight, true;” Av. rāz- “to direct, put in line, set,” razan- “order;”
cf. Skt. raj- “to direct, stretch,” rjuyant- “walking straight;” Gk. orektos “stretched out;” L. regere “to lead straight, guide, rule,” p.p. rectus “right, straight;” PIE base *reg- “move in a straight line,” hence, “to direct, rule”)

• jostan/juyidan “to seek, strive for” (Proto-Iranian *iud- “to struggle for something, to fight;” Av. yūδ- “to fight, struggle;” Mod.Pers. justan, juy- “to search, seek, ask for;” cf. Mid.Pers. vijuyihitan “to search, seek”).

Of or pertaining to spring. → vernal equinox.

Etymology (EN): From L. vernalis “of the spring,” from vernus “of spring,” from uēr “spring,” cognate with Pers. bahâr, as below.

Etymology (PE): Bahâri of or pertaining to bahâr “spring;” Mid.Pers. wahâr “spring;” O.Pers. vāhara- “spring time,” θūra-vāhara- “name of a spring month;” Av. vaηhar “spring;” cf. Skt. vasara- “relating or appearing in the morning;”
Gk. ear “spring;” L. uēr “spring,” vernus “of spring;” O.N. vār “spring;” Lith. vasara “summer;” O.C.S. vesna “spring.”

The point of intersection between the ecliptic and the celestial equator at which the Sun passes from south to north of the celestial equator during its apparent annual motion. The instant of this event. It occurs on March 20, 21 or rarely 19. At the vernal equinox, as with the → autumnal equinox, night and day are equal in length world over. Several thousands years ago the vernal equinox was in Aries, but because of precession it has now slid west into Pisces. Right ascension and celestial longitude are measured from the vernal equinox. Also known as spring equinox.
→ First Point of Aries.

See also: → vernal; → equinox.

The intersection point between the → celestial equator and the → ecliptic from where the Sun apparently enters into the northern celestial hemisphere.

See also: → vernal; → point.

The time interval between two successive passages of the Sun, when the true longitude of the Sun is considered.
In other words, the interval during which the Sun’s true longitude increases by 360 degrees. Its mean length for the epoch J2000.0 is 365.24236460 real solar days (approximately 365.2424 days). The vernal-equinox year, on which the Iranian calender is based, should not be confused with → tropical year. See also: A concise review of the Iranian calendar. → Iranian calendar

See also: → vernal; → equinox; → year.

A small movable scale running parallel to the main graduated scale in certain measuring instruments, such as the → sextant, used to obtain a fractional reading of one of the divisions on the main scale. Also known as Vernier scale.

See also: After the French mathematician Pierre Vernier (1580-1637), who invented the scale in 1631.

A particular form or variant of something.
An account of something, given from a specific point of view.

Etymology (EN): M.E., from M.Fr. version, from M.L. versionem (nominative versio) “a turning,” from p.p. stem of L. vertere “to turn;” cognate with Pers. gardidan “to change,” as below.

Etymology (PE): Gardâk, present stem of gardidan “to change, to turn” (Mid.Pers. vartitan “to change, to turn;” Av. varət- “to turn, revolve;” cf. Skt. vrt- “to turn, roll,” vartate “it turns round, rolls;” L. vertere “to turn;”
O.H.G. werden “to become;” PIE base *wer- “to turn, bend”) + -âk noun suffix.

Plural form: vertices.

1. Astro.: A point in the → celestial sphere toward which or from which the common motion of a group of stars is directed.
   

2. Math.: The → point where two → sides of a → plane figure or an → angle  → intersect.
   

3. In → graph theory, any of the points of which graphs are formed. Same as → node.

Etymology (EN): From L. vertex “highest point,” literally “the turning point,” originally “whirlpool,” from vertere “to turn,” cognate with Pers. vartidan, gardidan, → version.

Etymology (PE): Târak, variant târ “top, vertex, head, the middle of the head;” cf. Sogd. târ “summit, forehead;” Yaghnobi tôr(k) “the back of the head;” Yazghulami tur “summit, head;” Proto-Ir. *starH- “to spread,” → expand; PIE *ster- “spread, extend.”

1. The apparent → direction of → gravity at the point of observation.
   

2. Being in a position or direction → perpendicular to the → plane of the → horizon. See also → normal.

Etymology (EN): Vertical, literally “of or at the vertex, directly overhead,” from M.Fr. vertical, from L.L. verticalis “overhead,” from L. vertex (genitive verticis) “highest point”

Etymology (PE): Hajin, from haj, variant hac “anything held vertical, erected in the manner of a spear” (Dehxodâ), may be from Proto-Ir. *hac- “to follow;” cf. Av. (+ *ā-) hac- “to stick to;” Mid.Pers. hâz- “to lead, guide;”
→ associate.

The greater circle on the celestial sphere which passes through → zenith, → nadir,
and the star and whose plane is perpendicular to the plane of horizon. Same as → azimuth circle.

See also: → vertical; → circle.

In computer science, a scaling in which the processing power of the same node/system is increased by increasing/decreasing its resources (CPU, memory, etc.). See also → horizontal scaling.

See also: → vertical; → scaling.

Plural of → vertex.

See also: → vertex.

In a high degree. → Very Large Telescope (VLT); → very massive star; → very high frequencies (VHF).

Etymology (EN): M.E.; O.Fr verai “true;” L. verax (genitive veracis) “truthful,” from verus “true.”

Etymology (PE): Besyâr, from bas “many, much” (Mid.Pers. vas “many, much;” O.Pers. vasiy “at will, greatly, utterly;” Av. varəmi “I wish,” vasô, vasə “at one’s pleasure or will,” from vas- “to will, desire, wish”).

Radio frequencies in the range 30 to 300 mega Hz.

See also: → very; → high; → frequency.

A radio interferometer consisting of 27 antennas, each 25 m in diameter, in a Y-shaped configuration. It is located about 100 km west of Socorro, New Mexico, and is operated by the United States National Radio Astronomy Observatory. The VLA has the resolution of a single antenna 36 km wide and the sensitivity of a dish 130 m across.

See also: → very; → large; → array.

A network of ten 25-m radio telescopes for
→ very-long-baseline interferometry (VLBI), operated by the U.S. National Radio Astronomy Observatory. Eight of the VLBA telescopes are distributed
across the continental United States, while the other two are in Hawaii and the Virgin Islands, giving a maximum baseline of about 8,000 km and a resolution better than a milliarcsecond at its shortest wavelength.

See also: → very; → large; → baseline; → array.

An observing facility consisting of four 8.2 m telescopes, with the combined collecting area of a 16 m mirror, owned and operated by the European Southern Observatory at an altitude of 2635 m at the Paranal Observatory in Chile. The four reflecting unit telescopes are called Antu “Sun” in the language of Chile’s indigenous Mapuche people, Kueyen “Moon,” Melipal “Southern Cross,” and Yepun “Venus.” Each unit is equipped with several sophisticated instruments. The light of the individual telescopes can be combined using interferometric techniques to achieve superior resolution. → VLT Interferometer (VLTI). The wavelength range covered by the VLT is extremely wide, ranging from deep ultraviolet to mid-infrared.

See also: → very; → large; → telescope.

In evolutionary models of → post-asymptotic giant branch stars,
the occurrence of the helium shell burning when the star has reached the → white dwarf cooling track.
This leads to the possibility of a violent → helium shell flash and expansion on a time-scale of ≤ 10 years. The rapid expansion and prompt change in surface composition observed in → Sakurai’s Object are thought to be due to such a very late thermal pulse.

See also: → very; → late; → thermal; → pulse.

A star with a typical mass of one-hundredth of the mass of the Sun (→ solar mass) and a luminosity of about one-millionth that of the Sun (→ solar luminosity). Same as
→ brown dwarf.

See also: → very; → low; → mass; → star.

A star of mass around 100 → solar masses. See also:
→ supermassive star, → massive star, → canonical upper limit.

See also: → very; → massive; → star.

A special type of carbonaceous → interstellar dust grains
with a size ranging from 10 to 150 Å and consisting of tens to hundreds of atoms. In contrast to → big grains, VSGs are not in → thermal equilibrium. They can be heated to very high temperatures (~ 1000 K) by the absorption of a single photon. It is thought that VSGs are clusters of → PAH.

See also: → very; → small; → grain.

A technique in radio interferometry in which the individual telescopes are not directly
connected together, but instead make their observations separately with very accurate timings. The data are later sent to a central correlator to be combined. With this technique the individual telescopes can be arbitrarily far apart, and so the technique provides the highest resolution images in astronomy, typically down to a few milliarcseconds.

See also: → very; → large; → baseline; → interferometry.

1. A tube or duct, as an artery or vein, containing or conveying blood or some other body fluid.
   

   2. Botany: A duct formed in the xylem, composed of connected cells that have lost their intervening partitions, that conducts water and mineral nutrients (Dictionary.com).

Etymology (EN): M.E., from O.Fr. vessel “container, receptacle; ship,” from L.L. vascellum “small vase or urn,” also “a ship,” alteration of L. vasculum, diminutive of vas “vessel.”

Etymology (PE): 1) Rag “blood vessel, vein; lineage, race, stock,” from Mid.Pers. rag, from Proto-Iranian *raha-ka-, from *raha- “liquid, essence,” + suffix -ka-; cf. Av. ranhā- “name of a mythical stream;” Skt. rása- “juice (of plants), liquid, essence,” rásavant-, rasin- “juicy;” L. ros “dew;” Lith. ràsa “dew;” O.C.S. rosa “dew.”

2. Âvand “vessel,” contraction of âbvand, literally “water utensil,” from âb, → water, + vand “vessel, vase, cup,” from bastan “to bind, shut,” → shutter.