An Etymological Dictionary of Astronomy and Astrophysics

A tailless amphibian with a short stout body and related to → frogs. In contrast to frogs, it has short legs and dry warty skin that can secrete a toxic, milky substance.

Etymology (EN): M.E. tode, toode, tade, tadde, from O.E. tadige, tadie, of unknown origin, cognate with Scots tade, taid, taed, ted “toad;” Dan. tudse, Swed. tassa, tossa, O.E. taxe, tosca “toad.”

Etymology (PE): Vazaq “toad,” variants Tabari, Aftari vak, Tabari vag, (prefixed) qurbâqé, Lori, Laki qorvâ, korvâx, Kurd. baq, Zâzâ baqa; Mid.Pers. vazak, vak; Av. vazaγa- “frog.”

A tailless amphibian with a short stout body and related to → frogs. In contrast to frogs, it has short legs and dry warty skin that can secrete a toxic, milky substance.

Etymology (EN): M.E. tode, toode, tade, tadde, from O.E. tadige, tadie, of unknown origin, cognate with Scots tade, taid, taed, ted “toad;” Dan. tudse, Swed. tassa, tossa, O.E. taxe, tosca “toad.”

Etymology (PE): Vazaq “toad,” variants Tabari, Aftari vak, Tabari vag, (prefixed) qurbâqé, Lori, Laki qorvâ, korvâx, Kurd. baq, Zâzâ baqa; Mid.Pers. vazak, vak; Av. vazaγa- “frog.”

1. The present day, time, or age.
   

   2. The present epoch in the cosmic evolution since the → Big Bang characterizd by the → redshift  z = 0.

Etymology (EN): M.E. today, from O.E. todæge, to dæge “on (this) day,” from to “at, on” + dæge, dative of dæg “→ day.”

Etymology (PE): Emruz “today,” from Mid.Pers. imrôc, imrôz, from im “this; here” + rôz, ruz, → day.

1. The present day, time, or age.
   

   2. The present epoch in the cosmic evolution since the → Big Bang characterizd by the → redshift  z = 0.

Etymology (EN): M.E. today, from O.E. todæge, to dæge “on (this) day,” from to “at, on” + dæge, dative of dæg “→ day.”

Etymology (PE): Emruz “today,” from Mid.Pers. imrôc, imrôz, from im “this; here” + rôz, ruz, → day.

Each of the five digits on the end of the foot.

Etymology (EN): M.E. to, from O.E. tā akin to Ger. Zehe “toe,” Du. teen.

Etymology (PE): Pângol, literally “foot finger,” from pâ, → foot, + ângol (Dehxodâ) “finger,” variant of angošt, → finger.

Each of the five digits on the end of the foot.

Etymology (EN): M.E. to, from O.E. tā akin to Ger. Zehe “toe,” Du. teen.

Etymology (PE): Pângol, literally “foot finger,” from pâ, → foot, + ângol (Dehxodâ) “finger,” variant of angošt, → finger.

A machine producing a → toroidal magnetic field for confining a → plasma in
→ nuclear fusion research.

See also: From Rus. Tokamak, acronym from toroidal’naya kamera s magnitnymi katushkami “toroidal chamber with magnetic coils.”
It was invented in the 1950s by Soviet physicists Igor Yevgenyevich Tamm and Andrei Sakharov (who had been inspired by an original idea of Oleg Lavrentyev).

A machine producing a → toroidal magnetic field for confining a → plasma in
→ nuclear fusion research.

See also: From Rus. Tokamak, acronym from toroidal’naya kamera s magnitnymi katushkami “toroidal chamber with magnetic coils.”
It was invented in the 1950s by Soviet physicists Igor Yevgenyevich Tamm and Andrei Sakharov (who had been inspired by an original idea of Oleg Lavrentyev).

A set of astronomical tables drawn up by a group of astronomers in Toledo, Spain, mainly Zarqâli, and compiled after 1068. This work, which represents the first original development of Andalusian astronomy, was extremely influential in Europe for three centuries until the advent of the → Alfonsine Tables. The main sources for the bulk of the table collections were those of the Persian astronomer Khwârizmi (mainly planetary latitudes), Battâni (planetary equations), and Ptolemy. In fact the oldest version of the Toledan Tables was mainly modeled on Khwârizmi’s Sindhind, but had admixture from Battâni. In addition, the oldest versions of the Toledan Tables preserve some tables of Khwârizmi that are rare or absent elsewhere. The Toledan Tables also incorporated the theory of → trepidation. The original Arabic version of the Toledan Tables has been lost, but two Latin versions have survived, one by Gerard of Cremona (12th century) and one by an unknown author.

See also: Toledo, a city in central Spain, 70 km south of Madrid; → table.

A set of astronomical tables drawn up by a group of astronomers in Toledo, Spain, mainly Zarqâli, and compiled after 1068. This work, which represents the first original development of Andalusian astronomy, was extremely influential in Europe for three centuries until the advent of the → Alfonsine Tables. The main sources for the bulk of the table collections were those of the Persian astronomer Khwârizmi (mainly planetary latitudes), Battâni (planetary equations), and Ptolemy. In fact the oldest version of the Toledan Tables was mainly modeled on Khwârizmi’s Sindhind, but had admixture from Battâni. In addition, the oldest versions of the Toledan Tables preserve some tables of Khwârizmi that are rare or absent elsewhere. The Toledan Tables also incorporated the theory of → trepidation. The original Arabic version of the Toledan Tables has been lost, but two Latin versions have survived, one by Gerard of Cremona (12th century) and one by an unknown author.

See also: Toledo, a city in central Spain, 70 km south of Madrid; → table.

The maximum permissible error or variation in a dimension of an object.

Etymology (EN): M.E., from O.Fr. tolerance, from L. tolerantia “endurance,” from tolerans, pr.p. of tolerare “to bear, endure, tolerate.”

Etymology (PE): Ravâdâri, noun from ravâdâr “consenter; judging right; lawful,” from ravâ “admissible; allowable; tolerated” (from raftan “to go, walk; to flow;” Mid.Pers. raftan, raw-, Proto-Iranian *rab/f- “to go; to attack” + -dâr “having, possessor” (from dâštan “to have, to possess,” Mid.Pers. dâštan, O.Pers./Av. root dar- “to hold, keep back, maitain, keep in mind,” Skt. dhr-, dharma- “law,”
Gk. thronos “elevated seat, throne,” L. firmus “firm, stable,” Lith. daryti “to make,” PIE *dher- “to hold, support”).

The maximum permissible error or variation in a dimension of an object.

Etymology (EN): M.E., from O.Fr. tolerance, from L. tolerantia “endurance,” from tolerans, pr.p. of tolerare “to bear, endure, tolerate.”

Etymology (PE): Ravâdâri, noun from ravâdâr “consenter; judging right; lawful,” from ravâ “admissible; allowable; tolerated” (from raftan “to go, walk; to flow;” Mid.Pers. raftan, raw-, Proto-Iranian *rab/f- “to go; to attack” + -dâr “having, possessor” (from dâštan “to have, to possess,” Mid.Pers. dâštan, O.Pers./Av. root dar- “to hold, keep back, maitain, keep in mind,” Skt. dhr-, dharma- “law,”
Gk. thronos “elevated seat, throne,” L. firmus “firm, stable,” Lith. daryti “to make,” PIE *dher- “to hold, support”).

A colorless, flammable liquid, insoluble in water and soluble in alcohol and ether, used as a solvent and in the manufacture of other organic chemicals and explosives. Chemical formula C₆H₅CH₃. Same as methylbenzene and phenylmethane. See also → trinitrotoluene.

See also: From tolu, from the older name toluol, which refers to tolu balsam, an aromatic extract from the tropical Colombian tree Myroxylon balsamum, from which it was first isolated, + -ene suffix used to form names of unsaturated hydrocarbons, from Gk. -ene denoting origin or source.

A colorless, flammable liquid, insoluble in water and soluble in alcohol and ether, used as a solvent and in the manufacture of other organic chemicals and explosives. Chemical formula C₆H₅CH₃. Same as methylbenzene and phenylmethane. See also → trinitrotoluene.

See also: From tolu, from the older name toluol, which refers to tolu balsam, an aromatic extract from the tropical Colombian tree Myroxylon balsamum, from which it was first isolated, + -ene suffix used to form names of unsaturated hydrocarbons, from Gk. -ene denoting origin or source.

Any of several techniques, such as → Doppler tomography, for constructing a spatial distribution of physical quantity given measurements that are essentially line-integrals (“projections”) through the distribution. Most famously, in medical tomography, the absorption of X-rays by a specimen is directly related to the line integral to make detailed images of a predetermined plane section of a solid object while blurring out the images of other planes.

Etymology (EN): From Gk. tomo- combining form of tomos “a cut, section, slice” tome “cutting” + → -graphy.

Etymology (PE): Borešnegâri, from boreš “section, slice, cutting,” from boridan “to cut”
(Mid.Pers. britan, brinitan “to cut off;” Av. brī- “to shave, shear,” brin-; cf. Skt. bhrī- “to hurt, injure,” bhrinanti “they hurt”) + -negâri, → -graphy.

Any of several techniques, such as → Doppler tomography, for constructing a spatial distribution of physical quantity given measurements that are essentially line-integrals (“projections”) through the distribution. Most famously, in medical tomography, the absorption of X-rays by a specimen is directly related to the line integral to make detailed images of a predetermined plane section of a solid object while blurring out the images of other planes.

Etymology (EN): From Gk. tomo- combining form of tomos “a cut, section, slice” tome “cutting” + → -graphy.

Etymology (PE): Borešnegâri, from boreš “section, slice, cutting,” from boridan “to cut”
(Mid.Pers. britan, brinitan “to cut off;” Av. brī- “to shave, shear,” brin-; cf. Skt. bhrī- “to hurt, injure,” bhrinanti “they hurt”) + -negâri, → -graphy.

A → metric unit of → mass, equal to 1000 → kilograms.

See also: M.E. tunne unit of weight or capacity (cf. O.Fris. tunne, M.Du. tonne, O.H.G. tunna, Ger. tonne), also found in M.L. tunna and O.Fr. tonne, perhaps from a Celtic source.

A → metric unit of → mass, equal to 1000 → kilograms.

See also: M.E. tunne unit of weight or capacity (cf. O.Fris. tunne, M.Du. tonne, O.H.G. tunna, Ger. tonne), also found in M.L. tunna and O.Fr. tonne, perhaps from a Celtic source.

A musical sound of definite pitch, consisting of several relatively simple constituents called partial tones, the lowest of which is called the fundamental tone and the others harmonics or overtones.

Etymology (EN): M.E., from O.Fr. ton, from L. tonus “a sound, tone, accent,” literally “stretching,” from Gk. tonos “vocal pitch, raising of voice,” related to teinein “to stretch,” cognate with Pers. tanidan “to spin, weave,” → tension.

Etymology (PE): Ton, loan from Fr., as above.

A musical sound of definite pitch, consisting of several relatively simple constituents called partial tones, the lowest of which is called the fundamental tone and the others harmonics or overtones.

Etymology (EN): M.E., from O.Fr. ton, from L. tonus “a sound, tone, accent,” literally “stretching,” from Gk. tonos “vocal pitch, raising of voice,” related to teinein “to stretch,” cognate with Pers. tanidan “to spin, weave,” → tension.

Etymology (PE): Ton, loan from Fr., as above.

A criterion for the stability of the disk of a → spiral galaxy. It is expressed by the → Toomre parameter.

See also: → Toomre criterion; → criterion.

A criterion for the stability of the disk of a → spiral galaxy. It is expressed by the → Toomre parameter.

See also: → Toomre criterion; → criterion.

The scale beyond which for a thin, rotating disk, rotation stabilizes self-gravitational contraction. The Toomre length is given by: λ_T = 4π²GΣ / κ², where G is the → gravitational constant, Σ is the mass → surface density, and κ is the → epicyclic frequency (Toomre 1964, ApJ 139, 1217).

See also: → Toomre parameter; → length.

The scale beyond which for a thin, rotating disk, rotation stabilizes self-gravitational contraction. The Toomre length is given by: λ_T = 4π²GΣ / κ², where G is the → gravitational constant, Σ is the mass → surface density, and κ is the → epicyclic frequency (Toomre 1964, ApJ 139, 1217).

See also: → Toomre parameter; → length.

A quantity that measures the stability of a differentially rotating disk of matter against → gravitational collapse. It is expressed by the relation: Q = c_sκ / πGΣ, where c_s is the → sound speed, κ the → epicyclic frequency, G the → gravitational constant, and Σ the → surface density. The disk is linearly stable for Q > 1 and linearly unstable for Q < 1.

See also: After Alar Toomre (1936-), an American astrophysicist of Estonian origin, professor of mathematics at the Massachusetts Institute of Technology; → parameter.

A quantity that measures the stability of a differentially rotating disk of matter against → gravitational collapse. It is expressed by the relation: Q = c_sκ / πGΣ, where c_s is the → sound speed, κ the → epicyclic frequency, G the → gravitational constant, and Σ the → surface density. The disk is linearly stable for Q > 1 and linearly unstable for Q < 1.

See also: After Alar Toomre (1936-), an American astrophysicist of Estonian origin, professor of mathematics at the Massachusetts Institute of Technology; → parameter.

The experiment which provided the first accurate measurement of the speed of light. The experiment, conducted by the French physicist Armand H. L. Fizeau (1819-1896) in 1849,
used a rotating wheel containing 720 teeth. The function of the wheel was to cut a light beam into short pulses and to measure the time required for these pulses to travel to a distant mirror and back (17.34 km). The round-trip time for each pulse could be calculated to be about 1/18,000 sec, which yielded the value of 315,300 km/sec for the speed of light. Leon Foucault (1819-1868) improved on Fizeau’s method by replacing the cogwheel with a rotating mirror. Foucault’s estimate, published in 1862, was 298,000 km/s.

Etymology (EN): From tooth; M.E.; O.E. toth (cf. O.S., Dan., Swed., Du. tand, O.N. tönn, O.Fris. toth, O.H.G. zand, Ger. Zahn, Goth. tunthus), cognate with Pers. dandân, as below;
→ wheel; → experiment.

Etymology (PE): Âzmâyeš, → experiment; carx→ wheel; dandâne-dâr “toothed,” from dandân “tooth,” Mid.Pers. dandân; Av. dantan-; cf. Skt. dánta-; Gk. odontos; L. dens (Fr. dent); Lith. dantis, O.Ir. det, Welsh dent; PIE base *dont-/*dent- “tooth.”

The experiment which provided the first accurate measurement of the speed of light. The experiment, conducted by the French physicist Armand H. L. Fizeau (1819-1896) in 1849,
used a rotating wheel containing 720 teeth. The function of the wheel was to cut a light beam into short pulses and to measure the time required for these pulses to travel to a distant mirror and back (17.34 km). The round-trip time for each pulse could be calculated to be about 1/18,000 sec, which yielded the value of 315,300 km/sec for the speed of light. Leon Foucault (1819-1868) improved on Fizeau’s method by replacing the cogwheel with a rotating mirror. Foucault’s estimate, published in 1862, was 298,000 km/s.

Etymology (EN): From tooth; M.E.; O.E. toth (cf. O.S., Dan., Swed., Du. tand, O.N. tönn, O.Fris. toth, O.H.G. zand, Ger. Zahn, Goth. tunthus), cognate with Pers. dandân, as below;
→ wheel; → experiment.

Etymology (PE): Âzmâyeš, → experiment; carx→ wheel; dandâne-dâr “toothed,” from dandân “tooth,” Mid.Pers. dandân; Av. dantan-; cf. Skt. dánta-; Gk. odontos; L. dens (Fr. dent); Lith. dantis, O.Ir. det, Welsh dent; PIE base *dont-/*dent- “tooth.”

The highest point or part. The higher end of anything on a slope.

Etymology (EN): M.E., O.E. top “summit, crest, tuft;” cf. O.N. toppr “tuft of hair,” O.Fris. top “tuft,” O.Du. topp, Du. top, O.H.G. zopf “end, tip, tuft of hair,” Ger. Zopf “tuft of hair.”

Etymology (PE): Bâlâ “up, above, high, elevated, height” (variants boland “high, tall, elevated, sublime,” borz “height, magnitude” (it occurs also in the name of the mountain chain Alborz),
Laki dialect berg “hill, mountain;”
Mid.Pers. buland “high;” O.Pers. baršan- “height;” Av. barəz- “high, mount,” barezan- “height;” cf. Skt. bhrant- “high;” L. fortis “strong” (Fr. and E. force); O.E. burg, burh “castle, fortified place,” from P.Gmc. *burgs “fortress;” Ger. Burg “castle,” Goth. baurgs “city,” E. burg, borough, Fr. bourgeois, bourgeoisie, faubourg; PIE base *bhergh- “high.”

The highest point or part. The higher end of anything on a slope.

Etymology (EN): M.E., O.E. top “summit, crest, tuft;” cf. O.N. toppr “tuft of hair,” O.Fris. top “tuft,” O.Du. topp, Du. top, O.H.G. zopf “end, tip, tuft of hair,” Ger. Zopf “tuft of hair.”

Etymology (PE): Bâlâ “up, above, high, elevated, height” (variants boland “high, tall, elevated, sublime,” borz “height, magnitude” (it occurs also in the name of the mountain chain Alborz),
Laki dialect berg “hill, mountain;”
Mid.Pers. buland “high;” O.Pers. baršan- “height;” Av. barəz- “high, mount,” barezan- “height;” cf. Skt. bhrant- “high;” L. fortis “strong” (Fr. and E. force); O.E. burg, burh “castle, fortified place,” from P.Gmc. *burgs “fortress;” Ger. Burg “castle,” Goth. baurgs “city,” E. burg, borough, Fr. bourgeois, bourgeoisie, faubourg; PIE base *bhergh- “high.”

A cosmological model of → structure formation in which larger structures, such as galaxy → superclusters or perhaps even the vast → filaments and → voids, form earlier and then they fragment into smaller structures such as individual galaxies. Opposite of → bottom-up structure formation.

See also: → top; → down; → structure; → formation.

A cosmological model of → structure formation in which larger structures, such as galaxy → superclusters or perhaps even the vast → filaments and → voids, form earlier and then they fragment into smaller structures such as individual galaxies. Opposite of → bottom-up structure formation.

See also: → top; → down; → structure; → formation.

A star formation process in which → massive stars form more abundantly than that predicted by standard models, whereby the top end of the → initial mass function is significantly flatter than the canonical → Salpeter slope.

See also: → top; → heavy; → initial mass function.

A star formation process in which → massive stars form more abundantly than that predicted by standard models, whereby the top end of the → initial mass function is significantly flatter than the canonical → Salpeter slope.

See also: → top; → heavy; → initial mass function.

1. The subject of a discourse or of one of its parts.
   

   2. The main and explicit subject matter of a literary work, often composed of several themes.

Etymology (EN): From L. topica, from Gk. topikos “pertaining to a common place, of a place,” from topos “a place.”

Etymology (PE): Bârak, from bâre “subject, matter, meaning,” as in dar bare-ye “in the matter of; about,” + nuance suffix -ak.

1. The subject of a discourse or of one of its parts.
   

   2. The main and explicit subject matter of a literary work, often composed of several themes.

Etymology (EN): From L. topica, from Gk. topikos “pertaining to a common place, of a place,” from topos “a place.”

Etymology (PE): Bârak, from bâre “subject, matter, meaning,” as in dar bare-ye “in the matter of; about,” + nuance suffix -ak.

A coordinate system that uses the observer’s location as its central reference point. Usually, the difference in the position of an object in the sky measured using topocentric and geocentric coordinates is very small because most celestial objects are so far away. However, for nearby objects this is not true. The Sun, for example, may appear displaced as much as eight arcseconds from its geocentric position, and the Moon by as much as one degree.

Etymology (EN): Topocentric, from topo- combining form of Gk. topos “place” + centric, from → center; → coordinate.

Etymology (PE): Hamârâhâ, → coordinate; jâ-markazi “topocentric,” from jâ “place” (from Mid.Pers. giyâg “place;” O.Pers. ā-vahana- “place, village;” Av. vah- “to dwell, stay,” vanhaiti “he dwells, stays;” Skt. vásati “he dwells;” Gk. aesa (nukta) “to pass (the night);”
Ossetic wat “room; bed; place;” Tokharian B wäs- “to stay, wait;” PIE base ues- “to stay, live, spend the night”) + markazi, of, pertaining to markaz, → center.

A coordinate system that uses the observer’s location as its central reference point. Usually, the difference in the position of an object in the sky measured using topocentric and geocentric coordinates is very small because most celestial objects are so far away. However, for nearby objects this is not true. The Sun, for example, may appear displaced as much as eight arcseconds from its geocentric position, and the Moon by as much as one degree.

Etymology (EN): Topocentric, from topo- combining form of Gk. topos “place” + centric, from → center; → coordinate.

Etymology (PE): Hamârâhâ, → coordinate; jâ-markazi “topocentric,” from jâ “place” (from Mid.Pers. giyâg “place;” O.Pers. ā-vahana- “place, village;” Av. vah- “to dwell, stay,” vanhaiti “he dwells, stays;” Skt. vásati “he dwells;” Gk. aesa (nukta) “to pass (the night);”
Ossetic wat “room; bed; place;” Tokharian B wäs- “to stay, wait;” PIE base ues- “to stay, live, spend the night”) + markazi, of, pertaining to markaz, → center.

Of or relating to → topology.

See also: → topology; → -ic; → -al

Of or relating to → topology.

See also: → topology; → -ic; → -al

In → cosmological models, a stable configuration of → matter formed when the → early Universe underwent → phase transitions during which fundamental symmetries were broken. There are a number of possible types of defects,
such as domain walls, → cosmic strings, → magnetic monopoles, and → texture s.
Same as → cosmic defect.

See also: → topological; → defect.

In → cosmological models, a stable configuration of → matter formed when the → early Universe underwent → phase transitions during which fundamental symmetries were broken. There are a number of possible types of defects,
such as domain walls, → cosmic strings, → magnetic monopoles, and → texture s.
Same as → cosmic defect.

See also: → topological; → defect.

A set X together with a collection of open subsets T that satisfies the three following conditions: 1) The empty set Ø and X are in T. 2) The intersection of a finite number of sets in T is also in T.
3) The union of an arbitrary number of sets in T is also in T.

See also: → topological; → space.

A set X together with a collection of open subsets T that satisfies the three following conditions: 1) The empty set Ø and X are in T. 2) The intersection of a finite number of sets in T is also in T.
3) The union of an arbitrary number of sets in T is also in T.

See also: → topological; → space.

The study of the properties of geometric figures that remain invariant under certain transformations, as bending or stretching. A circle is topologically equivalent to an ellipse (into which it can be deformed by stretching) and a sphere is equivalent to an ellipsoid.

Etymology (EN): From topo- combining form of Gk. topos “place”

• → -logy.

Etymology (PE): Topošenâsi, from topo-, loan from Gk., as above, + šenâsi→ -logy.

The study of the properties of geometric figures that remain invariant under certain transformations, as bending or stretching. A circle is topologically equivalent to an ellipse (into which it can be deformed by stretching) and a sphere is equivalent to an ellipsoid.

Etymology (EN): From topo- combining form of Gk. topos “place”

• → -logy.

Etymology (PE): Topošenâsi, from topo-, loan from Gk., as above, + šenâsi→ -logy.

A light to be carried in the hand, consisting of some combustible substance, as resinous wood, or of twisted flax or the like soaked with tallow or other flammable substance, ignited at the upper end (Dictionary.com).

Etymology (EN): M.E. torche, from O.Fr. torche “torch,” originally “twisted thing,” then “torch formed of twisted tow dipped in wax,” probably from V.L. *torca, alteration of L.L. torqua, from torquere “to twist,” → torque.

Etymology (PE): Âhir, from Kurd. âhir “torch,” variant of âzar, → fire.

A light to be carried in the hand, consisting of some combustible substance, as resinous wood, or of twisted flax or the like soaked with tallow or other flammable substance, ignited at the upper end (Dictionary.com).

Etymology (EN): M.E. torche, from O.Fr. torche “torch,” originally “twisted thing,” then “torch formed of twisted tow dipped in wax,” probably from V.L. *torca, alteration of L.L. torqua, from torquere “to twist,” → torque.

Etymology (PE): Âhir, from Kurd. âhir “torch,” variant of âzar, → fire.

A scale used to assess the threat posed by the → impact of a → near-Earth object (NEO). It considers the impact energy as well as the probability of impact. It is designed to communicate to the public the risk associated with a NEO in more qualitative form than the → Palermo scale. The → impact hazard is expressed by a number between 0 and 10 depending on the probability that an impact will occur and the kinetic energy of the potential → impactor. The extent of damage ranges from inconsequential (0) to catastrophic (10). The scale is color-coded such that white = no consequence; green = meriting careful monitoring; yellow = meriting concern; orange = threatening events; red = impact is certain.

See also: Named for Torino, because the scale was adopted by that city in Italy in 1999;
→ scale.

A scale used to assess the threat posed by the → impact of a → near-Earth object (NEO). It considers the impact energy as well as the probability of impact. It is designed to communicate to the public the risk associated with a NEO in more qualitative form than the → Palermo scale. The → impact hazard is expressed by a number between 0 and 10 depending on the probability that an impact will occur and the kinetic energy of the potential → impactor. The extent of damage ranges from inconsequential (0) to catastrophic (10). The scale is color-coded such that white = no consequence; green = meriting careful monitoring; yellow = meriting concern; orange = threatening events; red = impact is certain.

See also: Named for Torino, because the scale was adopted by that city in Italy in 1999;
→ scale.

A mass of rotating air with high wind speeds at its center. It is produced in a very severe thunderstorm and appears as a funnel cloud extending from the base of a Cumulonimbus to the ground.

Etymology (EN): Tornado, metathesis from Sp tronada “thunderstorm,” from tronar “to thunder,” from L. tonare “to thunder,” → thunder.

Etymology (PE): Pic-tuf, from pic present stem of picidan “to twist, entwine, coil” (Mid.Pers. pecidan “to twist, entwine”) + tuf short for tufân, → storm.
Tufân-e picandé, from tufân→ storm + picandé agant noun/adj. of picidan</i “to twist, roll.”

A mass of rotating air with high wind speeds at its center. It is produced in a very severe thunderstorm and appears as a funnel cloud extending from the base of a Cumulonimbus to the ground.

Etymology (EN): Tornado, metathesis from Sp tronada “thunderstorm,” from tronar “to thunder,” from L. tonare “to thunder,” → thunder.

Etymology (PE): Pic-tuf, from pic present stem of picidan “to twist, entwine, coil” (Mid.Pers. pecidan “to twist, entwine”) + tuf short for tufân, → storm.
Tufân-e picandé, from tufân→ storm + picandé agant noun/adj. of picidan</i “to twist, roll.”

A surface of revolution obtained by rotating a closed plane curve about an axis parallel to the plane which does not intersect the curve. The simplest toroid is the → torus. The solid enclosed by such a surface.

See also: From tor-, from → torus + → -oid.

A surface of revolution obtained by rotating a closed plane curve about an axis parallel to the plane which does not intersect the curve. The simplest toroid is the → torus. The solid enclosed by such a surface.

See also: From tor-, from → torus + → -oid.

A magnetic field which is generated in a → plasma inside a → toroid, as in a → tokamak, by the electric current which spirals around the toroid. Toroidal field has no radial component. → poloidal magnetic field.

See also: → toroid; → magnetic field.

A magnetic field which is generated in a → plasma inside a → toroid, as in a → tokamak, by the electric current which spirals around the toroid. Toroidal field has no radial component. → poloidal magnetic field.

See also: → toroid; → magnetic field.

The tendency of a → force applied to an object to cause the object to → rotate about a given → axis or → point. Torque is the rotational analogue of or the turning effect of a force. It is equal to the product of the force and its distance from the reference axis.

More specifically, if a force F acts on a single particle at a point P whose position with respect to the origin O of the inertial reference is given by the distance vector r, the torque T acting on the particle with respect to the origin O is defined as: T = r × F. Torque is a → vector quantity. Its magnitude is given by: rF sin θ, where θ is the angle between r and F; its direction is normal to the plane formed by r and F. The sense is given by the → right-hand screw rule for the → vector product of two vectors. Torque has the same dimensions as work, but work is a scalar.

Etymology (EN): From L. torquere “to twist;” cf. Skt. tarku- “spindle;” maybe Mod.Pers. duk “spindle;” Mid.Pers. dôk “spindle;” O.C.S. traku “band, girdle,” O.H.G. drahsil “turner,” Ger. drechseln “to turn on a lathe;” O.E. thweorh “transverse, perverse, angry, cross;” E. thwart; PIE base *twork-/*twerk- “twist”

Etymology (PE): Gaštâvar literally “that which makes turn, turning agent,” from gašt “turning,” past stem of gaštan, gardidan “to turn, to change” (Mid.Pers. vartitan; Av. varət- “to turn, revolve;” 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”) + âvar
agent noun of âvardan “to bring; to cause, produce” (Mid.Pers. âwurtan, âvaritan; Av. ābar- “to bring; to possess,” from prefix ā- + Av./O.Pers. bar- “to bear, carry,” bareθre “to bear (infinitive),” bareθri “a female that bears (children), a mother;” Mod.Pers. bordan “to carry;” Skt. bharati “he carries;” Gk. pherein; L. fero “to carry”).

The tendency of a → force applied to an object to cause the object to → rotate about a given → axis or → point. Torque is the rotational analogue of or the turning effect of a force. It is equal to the product of the force and its distance from the reference axis.

More specifically, if a force F acts on a single particle at a point P whose position with respect to the origin O of the inertial reference is given by the distance vector r, the torque T acting on the particle with respect to the origin O is defined as: T = r × F. Torque is a → vector quantity. Its magnitude is given by: rF sin θ, where θ is the angle between r and F; its direction is normal to the plane formed by r and F. The sense is given by the → right-hand screw rule for the → vector product of two vectors. Torque has the same dimensions as work, but work is a scalar.

Etymology (EN): From L. torquere “to twist;” cf. Skt. tarku- “spindle;” maybe Mod.Pers. duk “spindle;” Mid.Pers. dôk “spindle;” O.C.S. traku “band, girdle,” O.H.G. drahsil “turner,” Ger. drechseln “to turn on a lathe;” O.E. thweorh “transverse, perverse, angry, cross;” E. thwart; PIE base *twork-/*twerk- “twist”

Etymology (PE): Gaštâvar literally “that which makes turn, turning agent,” from gašt “turning,” past stem of gaštan, gardidan “to turn, to change” (Mid.Pers. vartitan; Av. varət- “to turn, revolve;” 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”) + âvar
agent noun of âvardan “to bring; to cause, produce” (Mid.Pers. âwurtan, âvaritan; Av. ābar- “to bring; to possess,” from prefix ā- + Av./O.Pers. bar- “to bear, carry,” bareθre “to bear (infinitive),” bareθri “a female that bears (children), a mother;” Mod.Pers. bordan “to carry;” Skt. bharati “he carries;” Gk. pherein; L. fero “to carry”).

A unit of pressure used in the field of high vacuum, equivalent to 1 mm of mercury

See also: After the Italian scientist Evangelista Torricelli (1608-1647), who invented the first barometer.

A unit of pressure used in the field of high vacuum, equivalent to 1 mm of mercury

See also: After the Italian scientist Evangelista Torricelli (1608-1647), who invented the first barometer.

A stream of water flowing with great rapidity and violence. See also → rapids.

Etymology (EN): M.E., from M.Fr. torrent, from L. torrentem (nominative torrens) “a rushing (stream),” from torrere, “to parch, dry up, roast,” → torrid.

Etymology (PE): Lâhez, from Tabari lahez “an overwhelming flow,” Baxtiyâri lâhiz “flood.” The first component lâh, lah maybe related to lur, Lori, Kordi laf, Tabari lé “flood,” → cataclysm.

A stream of water flowing with great rapidity and violence. See also → rapids.

Etymology (EN): M.E., from M.Fr. torrent, from L. torrentem (nominative torrens) “a rushing (stream),” from torrere, “to parch, dry up, roast,” → torrid.

Etymology (PE): Lâhez, from Tabari lahez “an overwhelming flow,” Baxtiyâri lâhiz “flood.” The first component lâh, lah maybe related to lur, Lori, Kordi laf, Tabari lé “flood,” → cataclysm.

In fluid dynamics, a theorem that relates the speed of fluid flowing out of an opening to the height of fluid above the opening: v = (2gh)^1/2, where v is the exit velocity of the water, h is the height of the water column, and g is the acceleration due to gravity (9.81 m/s²). It was later shown to be a particular case of → Bernoulli’s theorem.

See also: After the Italian scientist Evangelista Torricelli (1608-1647), who found this relationship in 1643.

In fluid dynamics, a theorem that relates the speed of fluid flowing out of an opening to the height of fluid above the opening: v = (2gh)^1/2, where v is the exit velocity of the water, h is the height of the water column, and g is the acceleration due to gravity (9.81 m/s²). It was later shown to be a particular case of → Bernoulli’s theorem.

See also: After the Italian scientist Evangelista Torricelli (1608-1647), who found this relationship in 1643.

Subject to the weather that is hot and dry enough to scorch land.

Etymology (EN): From L. torridus “dried with heat, scorching hot,” from torrere “to dry up, roast,” related to terra “earth,” literally “dry land;” from PIE base *ters- “to dry” (cf. Pers. tešné “thirsty;” Mid.Pers. tašnak “thirsty;” Av. taršu- “dry,” taršna- “thirst;” Skt. trsta- “dry,” tars- “to be thirsty;”
Gk. teresesthai “to become or be dry;” Goth. þaursus “dry, barren,” O.H.G. derren “to make dry,” durst “thirst;” Ger. dürr “arid;” O.E. þurstig “thirsty”).

Etymology (PE): Tafsân, tafsâ, from tafsidan “to become hot,” variants tâftan, tâbidan “to shine;”
Mid.Pers. tâftan “to heat, burn, shine;” taftan “to become hot;” Parthian t’b “to shine;”
Av. tāp-, taf- “to warm up, heat,” tafsat “became hot,” tāpaiieiti “to create warmth;” cf. Skt. tap- “; to heat, be/become hot; to spoil, injure, damage; to suffer,” tapati “burns;” L. tepere “to be warm,” tepidus “warm;” PIE base *tep- “to be warm.”

Subject to the weather that is hot and dry enough to scorch land.

Etymology (EN): From L. torridus “dried with heat, scorching hot,” from torrere “to dry up, roast,” related to terra “earth,” literally “dry land;” from PIE base *ters- “to dry” (cf. Pers. tešné “thirsty;” Mid.Pers. tašnak “thirsty;” Av. taršu- “dry,” taršna- “thirst;” Skt. trsta- “dry,” tars- “to be thirsty;”
Gk. teresesthai “to become or be dry;” Goth. þaursus “dry, barren,” O.H.G. derren “to make dry,” durst “thirst;” Ger. dürr “arid;” O.E. þurstig “thirsty”).

Etymology (PE): Tafsân, tafsâ, from tafsidan “to become hot,” variants tâftan, tâbidan “to shine;”
Mid.Pers. tâftan “to heat, burn, shine;” taftan “to become hot;” Parthian t’b “to shine;”
Av. tāp-, taf- “to warm up, heat,” tafsat “became hot,” tāpaiieiti “to create warmth;” cf. Skt. tap- “; to heat, be/become hot; to spoil, injure, damage; to suffer,” tapati “burns;” L. tepere “to be warm,” tepidus “warm;” PIE base *tep- “to be warm.”

The part of the Earth’s surface between the tropics of Cancer and Capricorn

See also: → torrid; → zone.

The part of the Earth’s surface between the tropics of Cancer and Capricorn

See also: → torrid; → zone.

A surface produced by the revolution of a conic section (such as a circle) around a line lying in its plane, but not cutting the conic. The solid enclosed by such a surface.

Etymology (EN): From L. torus “a round, swelling protuberance.”

Etymology (PE): Cambar “torus,” originally “hoop, circle,” from Mid.Pers. cambar “hoop; a ring-shaped headdress,” cambar vâcik “playing tambourine.”

A surface produced by the revolution of a conic section (such as a circle) around a line lying in its plane, but not cutting the conic. The solid enclosed by such a surface.

Etymology (EN): From L. torus “a round, swelling protuberance.”

Etymology (PE): Cambar “torus,” originally “hoop, circle,” from Mid.Pers. cambar “hoop; a ring-shaped headdress,” cambar vâcik “playing tambourine.”

Constituting or comprising the whole; entire; complete in extent or degree. Related term → general = harvin (هروین).

Etymology (EN): M.E., from O.Fr. total, from M.L. totalis “entire, total,” from L. totus “all, whole, entire,” of unknown origin.

Etymology (PE): Mid.Pers. hamâk, hamâg “total, all,” hamâkih “totality,” related to Mod.Pers. hamé- “all,” variant hami “all the time, always;” Mid.Pers. hamê “all the time, always;” Av. hama- “any” (cf. Skt. sama-“any, every, whichever;” Gk. amo-then “whichever;”
Goth. sums “any;” O.N. sumr “any;” O.E. sum “some;” E. some) + suffix -âk.

Constituting or comprising the whole; entire; complete in extent or degree. Related term → general = harvin (هروین).

Etymology (EN): M.E., from O.Fr. total, from M.L. totalis “entire, total,” from L. totus “all, whole, entire,” of unknown origin.

Etymology (PE): Mid.Pers. hamâk, hamâg “total, all,” hamâkih “totality,” related to Mod.Pers. hamé- “all,” variant hami “all the time, always;” Mid.Pers. hamê “all the time, always;” Av. hama- “any” (cf. Skt. sama-“any, every, whichever;” Gk. amo-then “whichever;”
Goth. sums “any;” O.N. sumr “any;” O.E. sum “some;” E. some) + suffix -âk.

Same as → elemental abundance.

See also: → total; → abundance.

Same as → elemental abundance.

See also: → total; → abundance.

An → eclipse in which the whole of the disk of the Sun or Moon is obscured. See also
→ annular eclipse, → partial eclipse, → totality, → totality path.

See also: → total; → eclipse.

An → eclipse in which the whole of the disk of the Sun or Moon is obscured. See also
→ annular eclipse, → partial eclipse, → totality, → totality path.

See also: → total; → eclipse.

The sum of all forms of energy involved in a system.

See also: → total; → energy.

The sum of all forms of energy involved in a system.

See also: → total; → energy.

A function whose value is defined for all possible input values.

See also: → total; → function.

A function whose value is defined for all possible input values.

See also: → total; → function.

In a → rotating star, the sum of the → gravitational, → centrifugal, and → radiative accelerations. See also → effective gravity.

See also: → total; → gravity.

In a → rotating star, the sum of the → gravitational, → centrifugal, and → radiative accelerations. See also → effective gravity.

See also: → total; → gravity.

A phenomenon occurring when a light ray traveling cross
an → interface from a higher → refractive index medium to a lower refractive index medium hits the interface at an angle larger than the → critical angle. In these conditions the light will not pass through to the second → medium at all. Instead, all of it will be reflected back into the first medium.

See also: → total; → internal; → reflection.

A phenomenon occurring when a light ray traveling cross
an → interface from a higher → refractive index medium to a lower refractive index medium hits the interface at an angle larger than the → critical angle. In these conditions the light will not pass through to the second → medium at all. Instead, all of it will be reflected back into the first medium.

See also: → total; → internal; → reflection.

A → lunar eclipse when the entire → Moon passes through the Earth’s → umbra. The maximum duration of a total lunar eclipse is 1h 47m. It happens when the Moon crosses the umbra at its → apogee, where it moves the most slowly, and the Earth is at its → aphelion. The longest total lunar eclipse of the 21st century, lasting 1h 42m 59s, occurred on the night of 27 to 28 July 2018 (Europe, Africa, Asia, Australia, and New Zealand). See also → tetrad.

See also: → total; → lunar; → eclipse.

A → lunar eclipse when the entire → Moon passes through the Earth’s → umbra. The maximum duration of a total lunar eclipse is 1h 47m. It happens when the Moon crosses the umbra at its → apogee, where it moves the most slowly, and the Earth is at its → aphelion. The longest total lunar eclipse of the 21st century, lasting 1h 42m 59s, occurred on the night of 27 to 28 July 2018 (Europe, Africa, Asia, Australia, and New Zealand). See also → tetrad.

See also: → total; → lunar; → eclipse.

The sum of → static pressure, → dynamic pressure, and → hydrostatic pressure in the → Bernoulli equation.

See also: → total, → pressure.

The sum of → static pressure, → dynamic pressure, and → hydrostatic pressure in the → Bernoulli equation.

See also: → total, → pressure.

1. Of or relating to a centralized government that does not tolerate parties of differing opinion and that exercises dictatorial control over many aspects of life.
   

   2. Exercising control over the freedom, will, or thought of others; authoritarian; autocratic.
      

   3. An adherent of totalitarianism (Dictionary.com).

Etymology (EN): From totali-, from → totality + -arian, a suffix forming adjectives or nouns ending in → -ary.

Etymology (PE): Hamâkigerâyi, from hamâki, → totality, + -gerâ, → ist.

1. Of or relating to a centralized government that does not tolerate parties of differing opinion and that exercises dictatorial control over many aspects of life.
   

   2. Exercising control over the freedom, will, or thought of others; authoritarian; autocratic.
      

   3. An adherent of totalitarianism (Dictionary.com).

Etymology (EN): From totali-, from → totality + -arian, a suffix forming adjectives or nouns ending in → -ary.

Etymology (PE): Hamâkigerâyi, from hamâki, → totality, + -gerâ, → ist.

1. The practices and principles of a totalitarian regime.
   

   2. Absolute control by the state or a governing branch of a highly centralized institution (Dictionary.com).

See also: → totalitarian; → -ism.

1. The practices and principles of a totalitarian regime.
   

   2. Absolute control by the state or a governing branch of a highly centralized institution (Dictionary.com).

See also: → totalitarian; → -ism.

The period during a → solar eclipse when the → Sun is completely blocked by the → Moon. Totality for a → lunar eclipse is the period when the Moon is in the complete → shadow of the → Earth. For a solar eclipse totality can last from only several fractions of a second to a theoretical maximum of 7m 31s, depending on the → distance from the Moon to the Earth. For a lunar eclipse totality can last up to 1h 47m, also depending on the distance from the Moon to the Earth and on its → passage through the shadow. See also → totality path.

See also: → total; → -ity.

The period during a → solar eclipse when the → Sun is completely blocked by the → Moon. Totality for a → lunar eclipse is the period when the Moon is in the complete → shadow of the → Earth. For a solar eclipse totality can last from only several fractions of a second to a theoretical maximum of 7m 31s, depending on the → distance from the Moon to the Earth. For a lunar eclipse totality can last up to 1h 47m, also depending on the distance from the Moon to the Earth and on its → passage through the shadow. See also → totality path.

See also: → total; → -ity.

Of a → solar eclipse, the path of the → umbra across the → Earth. The totality path is usually about 100 km across, but under the most favorable conditions, when the → Moon is at its nearest → distance to Earth and the Earth is at its farthest distance from the Sun, the umbra can have a diameter of about 270 km.

See also: → totality; → path.

Of a → solar eclipse, the path of the → umbra across the → Earth. The totality path is usually about 100 km across, but under the most favorable conditions, when the → Moon is at its nearest → distance to Earth and the Earth is at its farthest distance from the Sun, the umbra can have a diameter of about 270 km.

See also: → totality; → path.

1a) To put the hand, finger, etc., on or into contact with (something) to feel it.

1b) To come into contact with and perceive (something), as the hand or the like does.

2. The act or fact of touching (Dictionary.com)

Etymology (EN): M.E. to(u)chen, from O.Fr. tochier “to touch, hit; deal with” from V.L. *toccare “to knock, strike” as a bell.

Etymology (PE): Basâvidan, ultimately from Proto-Ir. *apa-sau-, from *sau- “to rub;” cf. Sogdian ps’w- “to touch;” Pers.

• sâyidan, variants sâbidan, sudan “to bruise, file, touch” pasâvidan “to touch” (Khotanese sauy- “to rub.”

1a) To put the hand, finger, etc., on or into contact with (something) to feel it.

1b) To come into contact with and perceive (something), as the hand or the like does.

2. The act or fact of touching (Dictionary.com)

Etymology (EN): M.E. to(u)chen, from O.Fr. tochier “to touch, hit; deal with” from V.L. *toccare “to knock, strike” as a bell.

Etymology (PE): Basâvidan, ultimately from Proto-Ir. *apa-sau-, from *sau- “to rub;” cf. Sogdian ps’w- “to touch;” Pers.

• sâyidan, variants sâbidan, sudan “to bruise, file, touch” pasâvidan “to touch” (Khotanese sauy- “to rub.”

A building or structure taller than its diameter and high relative to its surroundings, either separated or forming part of a building.

Etymology (EN): From M.E. tour, earlier tur, tor, from O.Fr., from L. turris, from Gk. tyrris “tower.”

Etymology (PE): Borj “tower,” related to Pers. borz “height, magnitude, greatness,” boland “high,” bâlâ “up, above, high, elevated, height,”
Laki dialect berg “hill, mountain;” Mid.Pers. burz “height,” buland “high;” O.Pers. baršan- “height;” Av. barəz- “high, mount,” barezan- “height;” cf. Skt. bhrant- “high;” L. fortis “strong” (Fr. and E. force); O.E. burg, burh “castle, fortified place,” from P.Gmc. *burgs “fortress;” Ger. Burg “castle,” Goth. baurgs “city,” E. burg, borough, Fr. bourgeois, bourgeoisie, faubourg; PIE base *bhergh- “high;” borj loaned into Ar. from Mid.Pers. as burj.

A building or structure taller than its diameter and high relative to its surroundings, either separated or forming part of a building.

Etymology (EN): From M.E. tour, earlier tur, tor, from O.Fr., from L. turris, from Gk. tyrris “tower.”

Etymology (PE): Borj “tower,” related to Pers. borz “height, magnitude, greatness,” boland “high,” bâlâ “up, above, high, elevated, height,”
Laki dialect berg “hill, mountain;” Mid.Pers. burz “height,” buland “high;” O.Pers. baršan- “height;” Av. barəz- “high, mount,” barezan- “height;” cf. Skt. bhrant- “high;” L. fortis “strong” (Fr. and E. force); O.E. burg, burh “castle, fortified place,” from P.Gmc. *burgs “fortress;” Ger. Burg “castle,” Goth. baurgs “city,” E. burg, borough, Fr. bourgeois, bourgeoisie, faubourg; PIE base *bhergh- “high;” borj loaned into Ar. from Mid.Pers. as burj.

A telescope, usually of long → focal length, that is situated underneath a tower. Tower telescopes are mainly used for observation of the Sun. See also → solar telescope; → solar tower.

See also: → tower; → telescope.

A telescope, usually of long → focal length, that is situated underneath a tower. Tower telescopes are mainly used for observation of the Sun. See also → solar telescope; → solar tower.

See also: → tower; → telescope.

An object, often a representation of something, that a child can play with

Etymology (EN): M.E. toye, of unknown origin.

Etymology (PE): Bâzicé, from bâzi “game, play;” Mid.Pers. wâzig “play, game;” related to bâzidan “to play,” bâxtan “to loose;” cf. Skt. vāja- “contest, war, prize, booty;” + -cé suffix of relation.

An object, often a representation of something, that a child can play with

Etymology (EN): M.E. toye, of unknown origin.

Etymology (PE): Bâzicé, from bâzi “game, play;” Mid.Pers. wâzig “play, game;” related to bâzidan “to play,” bâxtan “to loose;” cf. Skt. vāja- “contest, war, prize, booty;” + -cé suffix of relation.

A simplified model that succeeds in capturing and furthering our understanding of one particular aspect of a physical situation, but which does not manage to describe all important aspects of that situation (Carl H. Brans).

See also: → toy; → model.

A simplified model that succeeds in capturing and furthering our understanding of one particular aspect of a physical situation, but which does not manage to describe all important aspects of that situation (Carl H. Brans).

See also: → toy; → model.