An Etymological Dictionary of Astronomy and Astrophysics

To impart knowledge or skill to; give instruction to.

Etymology (EN): M.E. techen, O.E. tæcan; cf. O.H.G. zihan, Ger. zeihen “to accuse,” Goth. ga-teihan “to announce;” cognate with Pers. dis, → form.

Etymology (PE): Âmuxtan, âmuz- “to teach; learn;” Mid.Pers. hammoxtan, hammoz- “to teach; learn;” cf. Sogd. muck “teacher;” Choresmian mxs “to learn,” mwcy “to teach, instruct;” Proto-Iranian *mauc- “to learn; teach.”

To impart knowledge or skill to; give instruction to.

Etymology (EN): M.E. techen, O.E. tæcan; cf. O.H.G. zihan, Ger. zeihen “to accuse,” Goth. ga-teihan “to announce;” cognate with Pers. dis, → form.

Etymology (PE): Âmuxtan, âmuz- “to teach; learn;” Mid.Pers. hammoxtan, hammoz- “to teach; learn;” cf. Sogd. muck “teacher;” Choresmian mxs “to learn,” mwcy “to teach, instruct;” Proto-Iranian *mauc- “to learn; teach.”

A radioactive chemical element which does not exist naturally on Earth; symbol Tc. Atomic number 43; mass number of most stable isotope 98; melting point 2,200°C; boiling point 4,877°C. Technetium is synthesised via the → s-process in deep layers of
→ asymptotic giant branch stars.

See also: From the Gk. technetos “artificial,” initially called masurium.

A radioactive chemical element which does not exist naturally on Earth; symbol Tc. Atomic number 43; mass number of most stable isotope 98; melting point 2,200°C; boiling point 4,877°C. Technetium is synthesised via the → s-process in deep layers of
→ asymptotic giant branch stars.

See also: From the Gk. technetos “artificial,” initially called masurium.

The body of specialized procedures and methods used in any specific field, especially in an area of applied science.

Etymology (EN): From Fr. technique “formal practical details in artistic expression,” noun use of adj. technique “of art, technical,” from Gk. tekhnikos,
from tekhne “art, skill, craft, method, system;” cognate with Pers. tarâš- “to cut, hew; scape; shave,” tišé “axe,” as below.

Etymology (PE): Tašnik, related to Pers. tarâšidan “to cut, hew; scape; shave;” Mid.Pers. tâšitan “to cut, cleave; create by putting together different elements;” from Av. taš- “to cut off, fashion, shape, create,” taša- “axe” (Mod.Pers. taš, tišé “axe;” tarâšidan “to shave”), tašan- “creator;” cf. Skt. taks- “to fom by cutting, tool, hammer, form,” taksan- “wood-cutter, carpenter;” Gk. tekton “carpenter,”
tekhne “art, skill, craft, method, system;” L. textere “to weave;” PIE *teks- “to fashion.”
Fann or fan, from Pers. fan “way, manner, mode, art, science,” related to Mod/Mid.Pers. pand “path, advice, counsel;” Khotanese pande “road, path;” Ossetic fœndœg “path, road;” O.Pers. paθi- “path, way;” Av. paθ- “path, way,” variants paθi-, paθā-, pantay-;
cf. Skt. pánthā- “road, path, course;” Gk. patos “path, way,” pontos “sea;” L. pons “bridge, path;” P.Gmc. *finthanan “to find;” E. find; PIE base *pent- “to go, to tread.”

The body of specialized procedures and methods used in any specific field, especially in an area of applied science.

Etymology (EN): From Fr. technique “formal practical details in artistic expression,” noun use of adj. technique “of art, technical,” from Gk. tekhnikos,
from tekhne “art, skill, craft, method, system;” cognate with Pers. tarâš- “to cut, hew; scape; shave,” tišé “axe,” as below.

Etymology (PE): Tašnik, related to Pers. tarâšidan “to cut, hew; scape; shave;” Mid.Pers. tâšitan “to cut, cleave; create by putting together different elements;” from Av. taš- “to cut off, fashion, shape, create,” taša- “axe” (Mod.Pers. taš, tišé “axe;” tarâšidan “to shave”), tašan- “creator;” cf. Skt. taks- “to fom by cutting, tool, hammer, form,” taksan- “wood-cutter, carpenter;” Gk. tekton “carpenter,”
tekhne “art, skill, craft, method, system;” L. textere “to weave;” PIE *teks- “to fashion.”
Fann or fan, from Pers. fan “way, manner, mode, art, science,” related to Mod/Mid.Pers. pand “path, advice, counsel;” Khotanese pande “road, path;” Ossetic fœndœg “path, road;” O.Pers. paθi- “path, way;” Av. paθ- “path, way,” variants paθi-, paθā-, pantay-;
cf. Skt. pánthā- “road, path, course;” Gk. patos “path, way,” pontos “sea;” L. pons “bridge, path;” P.Gmc. *finthanan “to find;” E. find; PIE base *pent- “to go, to tread.”

The use of scientific knowledge for the creation and development of devices, machines, and techniques to achieve a commercial, industrial, or scientific objective.

See also: From Gk. tekhnologia “systematic treatment of an art, craft, or technique,” originally referring to grammar, from tekhno-, from tekhne,
→ technique, + → -logy.

The use of scientific knowledge for the creation and development of devices, machines, and techniques to achieve a commercial, industrial, or scientific objective.

See also: From Gk. tekhnologia “systematic treatment of an art, craft, or technique,” originally referring to grammar, from tekhno-, from tekhne,
→ technique, + → -logy.

The science or art of assembling, shaping, or ornamenting materials in construction; the constructive arts in general. → plate tectonics

Etymology (EN): L.L. tectonicus, from Gk. tektonikos “pertaining to building,” from tekton (genitive tektonos) “builder, carpenter,” → technique.

Etymology (PE): Sâzânik, from sâzân pr.p. of sâz-, sâxtan “to build, make, fashion; to adapt, adjust, be fit” (Mid.Pers. sâxtan, sâz-, Manichean Parthian s’c’dn “to prepare, to form;” Av. sak- “to understand, to mark,” sâcaya- (causative) “to teach”) + -ik, → -ics.

The science or art of assembling, shaping, or ornamenting materials in construction; the constructive arts in general. → plate tectonics

Etymology (EN): L.L. tectonicus, from Gk. tektonikos “pertaining to building,” from tekton (genitive tektonos) “builder, carpenter,” → technique.

Etymology (PE): Sâzânik, from sâzân pr.p. of sâz-, sâxtan “to build, make, fashion; to adapt, adjust, be fit” (Mid.Pers. sâxtan, sâz-, Manichean Parthian s’c’dn “to prepare, to form;” Av. sak- “to understand, to mark,” sâcaya- (causative) “to teach”) + -ik, → -ics.

The first genuine → brown dwarf, discovered in 1995. It is located in the → Pleiades open cluster at approximately 400 → light-years. Teide 1 is a faint object of apparent magnitude I = 19.03, with a late → M dwarf spectral type (M8), corresponding to 55±15 → Jupiter masses (Rebolo et al. 1995, Nature 377, 129).

See also: Named for Observatorio del Teide, Teide Observatory (Tenerife, Canary Islands, Spain), where this object was first detected.

The first genuine → brown dwarf, discovered in 1995. It is located in the → Pleiades open cluster at approximately 400 → light-years. Teide 1 is a faint object of apparent magnitude I = 19.03, with a late → M dwarf spectral type (M8), corresponding to 55±15 → Jupiter masses (Rebolo et al. 1995, Nature 377, 129).

See also: Named for Observatorio del Teide, Teide Observatory (Tenerife, Canary Islands, Spain), where this object was first detected.

Small glassy bodies whose chemical composition is unrelated to the geological formation in which they are found. They are found mostly in Australia, Java, Philippines and Indochina. Tektites are now thought to have been produced by the impact of meteorites on the earth’s surface.

See also: From Gk. tekt(os) “molten” + -ite a suffix used in the name of minerals and fossils.

Small glassy bodies whose chemical composition is unrelated to the geological formation in which they are found. They are found mostly in Australia, Java, Philippines and Indochina. Tektites are now thought to have been produced by the impact of meteorites on the earth’s surface.

See also: From Gk. tekt(os) “molten” + -ite a suffix used in the name of minerals and fossils.

A combining form meaning “distant.”

Etymology (EN): From Gk. tele-, combining form of tele “far off, afar, at or to a distance,” related to teleos “end, goal, result, perfection.”

Etymology (PE): Dur- “far,” from Mid.Pers. dūr “far, distant, remote;” O.Pers. dūra- “far (in time or space),” dūraiy “afar, far away, far and wide;” Av. dūra-, dūirē “far,” from dav- “to move away;” cf. Skt. dūrá- “far; distance (in space and time);” PIE base *deu- “to move forward, pass;” cf. Gk. den “for a long time,” deros “lasting long.”

A combining form meaning “distant.”

Etymology (EN): From Gk. tele-, combining form of tele “far off, afar, at or to a distance,” related to teleos “end, goal, result, perfection.”

Etymology (PE): Dur- “far,” from Mid.Pers. dūr “far, distant, remote;” O.Pers. dūra- “far (in time or space),” dūraiy “afar, far away, far and wide;” Av. dūra-, dūirē “far,” from dav- “to move away;” cf. Skt. dūrá- “far; distance (in space and time);” PIE base *deu- “to move forward, pass;” cf. Gk. den “for a long time,” deros “lasting long.”

The science and technology of measurement and transmission of data by optical, acoustical, or radioelectric means from remote sources, as from space vehicles, to receiving stations for recording and analysis.

See also: → tele- + → -metry.

The science and technology of measurement and transmission of data by optical, acoustical, or radioelectric means from remote sources, as from space vehicles, to receiving stations for recording and analysis.

See also: → tele- + → -metry.

An instrument used to collect and amplify light or other energy. → Refracting telescopes gather light by means of a lens, → reflecting telescopes by means of a mirror. → Radiotelescopes gather radio energy
by using an antenna. Telescopes have also been built that can gather X rays, gamma rays, and other forms of energy. → grazing incidence telescope.

Etymology (EN): From It. telescopio (used by Galileo, 1611), and Mod.L. telescopium (used by Kepler, 1613), both from Gk. teleskopos “far-seeing,” from → tele- “far” + -skopos “seeing,” from skopein “to watch, look, behold;” → -scope.

Etymology (PE): Durbin, from dur-, → tele-,

• -bin “to see; seer,” → -scope.

An instrument used to collect and amplify light or other energy. → Refracting telescopes gather light by means of a lens, → reflecting telescopes by means of a mirror. → Radiotelescopes gather radio energy
by using an antenna. Telescopes have also been built that can gather X rays, gamma rays, and other forms of energy. → grazing incidence telescope.

Etymology (EN): From It. telescopio (used by Galileo, 1611), and Mod.L. telescopium (used by Kepler, 1613), both from Gk. teleskopos “far-seeing,” from → tele- “far” + -skopos “seeing,” from skopein “to watch, look, behold;” → -scope.

Etymology (PE): Durbin, from dur-, → tele-,

• -bin “to see; seer,” → -scope.

A covering, usually hemispherical, that is rotatable about a central axis. There is a slit opening along one side wide enough to allow a telescope to be directed at any vertical angle up to 90°.

See also: → telescope; → dome.

A covering, usually hemispherical, that is rotatable about a central axis. There is a slit opening along one side wide enough to allow a telescope to be directed at any vertical angle up to 90°.

See also: → telescope; → dome.

The accuracy with which a telescope can be pointed to a particular coordinate in the sky.

See also: → telescope; → pointing; accuracy.

The accuracy with which a telescope can be pointed to a particular coordinate in the sky.

See also: → telescope; → pointing; accuracy.

The Telescope. An inconspicuous constellation situated in the southern hemisphere, at 19h right ascension, 50° south declination. Abbreviation: Tel; genitive: Telescopii.

See also: Telescopium was named by Abbé Nicolas Louis de Lacaille (1713-1762); → telescope.

The Telescope. An inconspicuous constellation situated in the southern hemisphere, at 19h right ascension, 50° south declination. Abbreviation: Tel; genitive: Telescopii.

See also: Telescopium was named by Abbé Nicolas Louis de Lacaille (1713-1762); → telescope.

The tenth of Saturn’s known satellites. It is irregularly-shaped and has a diameter of 29 x 22 x 20 km. Telesto orbits Saturn at a distance of 294,660 km. Telesto is co-orbital with Tethys, residing in Tethys’ leading Lagrangian point (L4). The images taken by the Cassini probe during its distant flyby on October 11, 2005 show that its surface is surprisingly smooth, devoid of small impact craters. Telesto was discovered by B. Smith, H. Reitsema, S. Larson, J. Fountain in 1980 from ground-based observations.

See also: In Gk. mythology Telesto was a daughter of Oceanus and Tethys.

The tenth of Saturn’s known satellites. It is irregularly-shaped and has a diameter of 29 x 22 x 20 km. Telesto orbits Saturn at a distance of 294,660 km. Telesto is co-orbital with Tethys, residing in Tethys’ leading Lagrangian point (L4). The images taken by the Cassini probe during its distant flyby on October 11, 2005 show that its surface is surprisingly smooth, devoid of small impact craters. Telesto was discovered by B. Smith, H. Reitsema, S. Larson, J. Fountain in 1980 from ground-based observations.

See also: In Gk. mythology Telesto was a daughter of Oceanus and Tethys.

1. Pertaining to the Earth, as a planet, or the earth or soil.
   
2. Derived from or containing → tellurium.

Etymology (EN): From L. tellur-, from tellus “earth” + → -ic.

Etymology (PE): Zamini, of or pertaining to zamin, → earth.

1. Pertaining to the Earth, as a planet, or the earth or soil.
   
2. Derived from or containing → tellurium.

Etymology (EN): From L. tellur-, from tellus “earth” + → -ic.

Etymology (PE): Zamini, of or pertaining to zamin, → earth.

A band seen in the spectra of celestial objects, which is due to absorption by gases such as oxygen, water vapor, and carbon dioxide in the Earth’s atmosphere

Etymology (EN): → telluric; → band.

A band seen in the spectra of celestial objects, which is due to absorption by gases such as oxygen, water vapor, and carbon dioxide in the Earth’s atmosphere

Etymology (EN): → telluric; → band.

A brittle metallic element usually found in combination with → gold and other → metals, used to → alloy stainless → steel and → lead, and, as bismuth telluride, in thermoelectric devices; symbol Te. → Atomic number 52;
→ atomic weight 127.60; → melting point 450°C; → boiling point 990°C; → specific gravity 6.24 at 20°C. It was discovered by the Roumanian mine director Franz Joseph Muller von Reichenstein in 1782 and overlooked for sixteen years until it was first isolated by German
chemist Martin-Heinrich Klaproth in 1798. The Hungarian chemist Paul Kitaibel independently discovered tellurium in 1789, prior to Klaproth’s work but after von Reichenstein.

See also: From L. tellur-, from tellus “earth” + -ium a L. suffix occurring in the name of some chemical elements.

A brittle metallic element usually found in combination with → gold and other → metals, used to → alloy stainless → steel and → lead, and, as bismuth telluride, in thermoelectric devices; symbol Te. → Atomic number 52;
→ atomic weight 127.60; → melting point 450°C; → boiling point 990°C; → specific gravity 6.24 at 20°C. It was discovered by the Roumanian mine director Franz Joseph Muller von Reichenstein in 1782 and overlooked for sixteen years until it was first isolated by German
chemist Martin-Heinrich Klaproth in 1798. The Hungarian chemist Paul Kitaibel independently discovered tellurium in 1789, prior to Klaproth’s work but after von Reichenstein.

See also: From L. tellur-, from tellus “earth” + -ium a L. suffix occurring in the name of some chemical elements.

A → periodic comet that is the progenitor of the
→ Leonids meteor shower. It has a period of 33 years, a → perihelion of 0.982 → astronomical units, an → eccentricity of 0.904, and an → inclination of 162.7°. It was first discovered in 1865 though its past appearances have been traced back to 1366.
Tempel-Tuttle is estimated to have a nucleus of radius 1.8 km and a mass of
1.2 × 10¹³ kg. Also designated 55P/Tempel-Tuttle.

See also: Named after the German astronomer Ernst Wilhelm Tempel (1821-1889) and the American astronomer Horace Parnell Tuttle (1837-1923), who independently discovered the comet on December 19, 1865 and January 6, 1866 respectively.

A → periodic comet that is the progenitor of the
→ Leonids meteor shower. It has a period of 33 years, a → perihelion of 0.982 → astronomical units, an → eccentricity of 0.904, and an → inclination of 162.7°. It was first discovered in 1865 though its past appearances have been traced back to 1366.
Tempel-Tuttle is estimated to have a nucleus of radius 1.8 km and a mass of
1.2 × 10¹³ kg. Also designated 55P/Tempel-Tuttle.

See also: Named after the German astronomer Ernst Wilhelm Tempel (1821-1889) and the American astronomer Horace Parnell Tuttle (1837-1923), who independently discovered the comet on December 19, 1865 and January 6, 1866 respectively.

A physical quantity characterizing the mean random motion of molecules in a physical body. In other words, a measure of the average kinetic energy of the particles of a system.

Etymology (EN): From L. temperatura “a tempering, moderation,” from temperatus, p.p. of temperare “to moderate, to mix.” Sense of “degree of heat or cold” first recorded 1670 (Boyle), from L. temperatura, used in this sense by Galileo.

Etymology (PE): Damâ, from dam “breath of an owen; bellows; smoke; air,” also “moment, time,” from Mid./Mod.Pers. damidan “to blow, breathe;” Av. dāδmainya- “blowing up;” cf.
Skt. dahm- “to blow,” dhámati “blows;” Gk. themeros “austere, dark-looking;” Lith. dumti “to blow;” PIE dhem-/dhemə- “to smoke, to blow.”

A physical quantity characterizing the mean random motion of molecules in a physical body. In other words, a measure of the average kinetic energy of the particles of a system.

Etymology (EN): From L. temperatura “a tempering, moderation,” from temperatus, p.p. of temperare “to moderate, to mix.” Sense of “degree of heat or cold” first recorded 1670 (Boyle), from L. temperatura, used in this sense by Galileo.

Etymology (PE): Damâ, from dam “breath of an owen; bellows; smoke; air,” also “moment, time,” from Mid./Mod.Pers. damidan “to blow, breathe;” Av. dāδmainya- “blowing up;” cf.
Skt. dahm- “to blow,” dhámati “blows;” Gk. themeros “austere, dark-looking;” Lith. dumti “to blow;” PIE dhem-/dhemə- “to smoke, to blow.”

Cosmology: Minute temperature variations of the cosmic microwave background radiation.

See also: → temperature; → anisotropy.

Cosmology: Minute temperature variations of the cosmic microwave background radiation.

See also: → temperature; → anisotropy.

A physical quantity that describes the rate of change of temperature with displacement in a given direction from a given reference point. Same as → thermal gradient.

See also: → temperature; → gradient.

A physical quantity that describes the rate of change of temperature with displacement in a given direction from a given reference point. Same as → thermal gradient.

See also: → temperature; → gradient.

Meteo.: A reversal in the normal temperature decrease, the temperature rising with increased elevation in the atmosphere instead of falling. A layer in which temperature increases with altitude.

See also: → temperature; → inversion.

Meteo.: A reversal in the normal temperature decrease, the temperature rising with increased elevation in the atmosphere instead of falling. A layer in which temperature increases with altitude.

See also: → temperature; → inversion.

An elementary unit of time defined as the duration which is necessary for light to travel a distance equal to the classical radius of an electron. Thus, one tempon (τ) is equal to (e²/mc²)(1/c)≅ 10^-23 seconds.

See also: From tamp, from L. tempus “time” + → -on.

An elementary unit of time defined as the duration which is necessary for light to travel a distance equal to the classical radius of an electron. Thus, one tempon (τ) is equal to (e²/mc²)(1/c)≅ 10^-23 seconds.

See also: From tamp, from L. tempus “time” + → -on.

1. Of or pertaining to time.
   

2. Pertaining to or concerned with the present life or this world; worldly.
   

3. Enduring for a time only; → temporary; transitory; → transient (opposed to eternal).
   

4. Secular, lay, or civil, as opposed to ecclesiastical.
   

5. Grammar: Of, pertaining to, or expressing time.

Etymology (EN): M.E., from O.Fr., from L. temporalis “of a time, but for a time, temporary,” from tempus (genitive temporis) “time, season, proper time or season,” of unknown origin.

Etymology (PE): Tâmeni, from tâmen, → time.

1. Of or pertaining to time.
   

2. Pertaining to or concerned with the present life or this world; worldly.
   

3. Enduring for a time only; → temporary; transitory; → transient (opposed to eternal).
   

4. Secular, lay, or civil, as opposed to ecclesiastical.
   

5. Grammar: Of, pertaining to, or expressing time.

Etymology (EN): M.E., from O.Fr., from L. temporalis “of a time, but for a time, temporary,” from tempus (genitive temporis) “time, season, proper time or season,” of unknown origin.

Etymology (PE): Tâmeni, from tâmen, → time.

A measure of the correlation between the phases of an → electromagnetic wave at different points along the direction of propagation. Temporal coherence indicates to what extent a source is monochromatic. Imagine a source emitting waves with wavelength λ ± Δλ. Waves with wavelength λ and λ + Δλ, which at some point in space constructively interfere, will no longer constructively interfere after some path length l_c = λ²/(2πΔλ); l_c is called the → coherence length.

See also: → temporal; → coherence.

A measure of the correlation between the phases of an → electromagnetic wave at different points along the direction of propagation. Temporal coherence indicates to what extent a source is monochromatic. Imagine a source emitting waves with wavelength λ ± Δλ. Waves with wavelength λ and λ + Δλ, which at some point in space constructively interfere, will no longer constructively interfere after some path length l_c = λ²/(2πΔλ); l_c is called the → coherence length.

See also: → temporal; → coherence.

A unit of time used in the Roman and Ottoman empires that divided the day from sunrise to sunset into 12 equal numbers of hours, resulting in long summer hours and short winter hours.

Etymology (EN): M.E., from O.Fr. temporal, from L. temporalis “of time, temporary,” from tempus (genitive temporis) “time, season, proper time or season,” → time; → hour.

Etymology (PE): Sâ’at→ hour; fasli, of or pertaining to fasl→ season.

A unit of time used in the Roman and Ottoman empires that divided the day from sunrise to sunset into 12 equal numbers of hours, resulting in long summer hours and short winter hours.

Etymology (EN): M.E., from O.Fr. temporal, from L. temporalis “of time, temporary,” from tempus (genitive temporis) “time, season, proper time or season,” → time; → hour.

Etymology (PE): Sâ’at→ hour; fasli, of or pertaining to fasl→ season.

The measure of the ability of an observing system to clearly separate events in time. In other words, the shortest time interval that can be determined between two different events.

See also: → temporal hour; → resolution.

The measure of the ability of an observing system to clearly separate events in time. In other words, the shortest time interval that can be determined between two different events.

See also: → temporal hour; → resolution.

Temporal character or nature.

See also: → temporal; → -ity.

Temporal character or nature.

See also: → temporal; → -ity.

Lasting, existing, serving, or effective for a time only; not permanent.

Etymology (EN): From L. temporarius “according to circumstances, of seasonal character, lasting a short time,” from tempus (genitive temporis) “time, season.”

Etymology (PE): Tâmenvâr, from tâmen “time”, → temporal, + -vâr suffix denoting suiting, befitting, resembling, in the manner of.

Lasting, existing, serving, or effective for a time only; not permanent.

Etymology (EN): From L. temporarius “according to circumstances, of seasonal character, lasting a short time,” from tempus (genitive temporis) “time, season.”

Etymology (PE): Tâmenvâr, from tâmen “time”, → temporal, + -vâr suffix denoting suiting, befitting, resembling, in the manner of.

To be indecisive or evasive to gain time or delay acting (Dictionary.com).

Etymology (EN): From M.Fr. temporiser “to pass one’s time, wait one’s time,” from M.L. temporizare “to pass time,” from L. tempus (genitive temporis), → temporal.

Etymology (PE): Tâmenidan from tâmen “time,” → temporal, + -idan, → -ize.

To be indecisive or evasive to gain time or delay acting (Dictionary.com).

Etymology (EN): From M.Fr. temporiser “to pass one’s time, wait one’s time,” from M.L. temporizare “to pass time,” from L. tempus (genitive temporis), → temporal.

Etymology (PE): Tâmenidan from tâmen “time,” → temporal, + -idan, → -ize.

A cardinal number, nine plus one.

Etymology (EN): M.E. ten(e), tenn(e), O.E. ten(e), tien(e); from P.Gmc. *tekhan (cf. O.S. tehan, O.N. tiu, Dan. ti, Du. tien, O.H.G. zehan, Ger. zehn “ten”), cognate with Pers. dah, as below.

Etymology (PE): Dah, from Mid.Pers. dah “ten;” Av. dasa “ten;” cf. Skt. dáśa- “ten;” Gk. deka “ten;” L. decem “ten;” O.Ir. deich; Lith. dešimtis “ten;” PIE base *dekm.

A cardinal number, nine plus one.

Etymology (EN): M.E. ten(e), tenn(e), O.E. ten(e), tien(e); from P.Gmc. *tekhan (cf. O.S. tehan, O.N. tiu, Dan. ti, Du. tien, O.H.G. zehan, Ger. zehn “ten”), cognate with Pers. dah, as below.

Etymology (PE): Dah, from Mid.Pers. dah “ten;” Av. dasa “ten;” cf. Skt. dáśa- “ten;” Gk. deka “ten;” L. decem “ten;” O.Ir. deich; Lith. dešimtis “ten;” PIE base *dekm.

Stretched tight, as a cord, fiber, etc.; drawn taut; rigid.

Etymology (EN): From L. tensus, p.p. of tendere “to stretch,” → tension.

Etymology (PE): Tanu “stretched, strained,” from tan + -u suffix of excess. The first element tan, from tanidan
“to spin, twist, weave” (Mid.Pers. tanitan; Av. tan- to stretch, extend;" cf. Skt. tan- to spin, stretch;" tanoti “stretches,” tantram “loom;” Gk. teinein “to stretch, pull tight;” L. tendere “to stretch;”
PIE base *ten- “to stretch”), Pers. târ “string,” tân “thread,” tur “fishing net, net, snare,” and tâl “thread” (Borujerdi dialect) belong to this family; variants tanta “cobweb,” tanadu, tafen, kartané, kârtané, kâtené,
Pashtu tanistah “cobweb;” cf. Skt. tantu- “cobweb, thread, string”).

Stretched tight, as a cord, fiber, etc.; drawn taut; rigid.

Etymology (EN): From L. tensus, p.p. of tendere “to stretch,” → tension.

Etymology (PE): Tanu “stretched, strained,” from tan + -u suffix of excess. The first element tan, from tanidan
“to spin, twist, weave” (Mid.Pers. tanitan; Av. tan- to stretch, extend;" cf. Skt. tan- to spin, stretch;" tanoti “stretches,” tantram “loom;” Gk. teinein “to stretch, pull tight;” L. tendere “to stretch;”
PIE base *ten- “to stretch”), Pers. târ “string,” tân “thread,” tur “fishing net, net, snare,” and tâl “thread” (Borujerdi dialect) belong to this family; variants tanta “cobweb,” tanadu, tafen, kartané, kârtané, kâtené,
Pashtu tanistah “cobweb;” cf. Skt. tantu- “cobweb, thread, string”).

Of or pertaining to → tension.

Etymology (EN): From M.L. tensilis “capable of being stretched,” from L. tensus, p.p. of tendere “to stretch,” → tension.

Etymology (PE): Taneši, related to taneš, → tension.

Of or pertaining to → tension.

Etymology (EN): From M.L. tensilis “capable of being stretched,” from L. tensus, p.p. of tendere “to stretch,” → tension.

Etymology (PE): Taneši, related to taneš, → tension.

The force tending to stretch (or produce tension in) an object

See also: → tensile; → force.

The force tending to stretch (or produce tension in) an object

See also: → tensile; → force.

General: The act of stretching or straining; the state of being stretched or strained.
Mechanics: The longitudinal deformation of an elastic body that results in its elongation.
Electricity: Voltage or potential; electromotive force.

Etymology (EN): M.E., from M.Fr. tension, from L. tensionem (nominative tensio) “a stretching,” from tensus, p.p. of tendere “to stretch,” cognate with Pers. taneš, as below.

Etymology (PE): Taneš, verbal noun from tanidan
“to spin, twist, weave;” Mid.Pers. tanitan; Av. tan- to stretch, extend;" cf. Skt. tan- to spin, stretch;" tanoti “stretches,” tantram “loom;” Gk. teinein “to stretch, pull tight;” L. tendere “to stretch;”
PIE base *ten- “to stretch”), Pers. târ “string,” tân “thread,” tur “fishing net, net, snare,” and tâl “thread” (Borujerdi dialect) belong to this family; variants tanta “cobweb,” tanadu, tafen, kartané, kârtané, kâtené,
Pashtu tanistah “cobweb;” cf. Skt. tantu- “cobweb, thread, string.”

General: The act of stretching or straining; the state of being stretched or strained.
Mechanics: The longitudinal deformation of an elastic body that results in its elongation.
Electricity: Voltage or potential; electromotive force.

Etymology (EN): M.E., from M.Fr. tension, from L. tensionem (nominative tensio) “a stretching,” from tensus, p.p. of tendere “to stretch,” cognate with Pers. taneš, as below.

Etymology (PE): Taneš, verbal noun from tanidan
“to spin, twist, weave;” Mid.Pers. tanitan; Av. tan- to stretch, extend;" cf. Skt. tan- to spin, stretch;" tanoti “stretches,” tantram “loom;” Gk. teinein “to stretch, pull tight;” L. tendere “to stretch;”
PIE base *ten- “to stretch”), Pers. târ “string,” tân “thread,” tur “fishing net, net, snare,” and tâl “thread” (Borujerdi dialect) belong to this family; variants tanta “cobweb,” tanadu, tafen, kartané, kârtané, kâtené,
Pashtu tanistah “cobweb;” cf. Skt. tantu- “cobweb, thread, string.”

A system of numbers or functions where components obey a certain law of transformation when the variables undergo a linear transformation. A tensor may consist of a single number, in which case it is referred to as a tensor of order zero, or simply a → scalar. The tensor of order one represents a → vector. Similarly there will be tensors of order two, three, and so on.

See also:
→ absolute tensor, → calculus of tensors, → contravariant tensor, → covariant tensor, → Einstein tensor, → energy-momentum tensor, → metric tensor, → order of a tensor, → relative tensor, → Ricci tensor, → Riemann curvature tensor, → scalar-tensor theory, → skew-symmetric tensor, → symmetric tensor, → tensor analysis, → tensor contraction, → tensor density, → tensor field, → tensor perturbation, → tensor rank, → tensor-vector-scalar (TeVeS) theory, → weight of a tensor.

See also: Agent noun of tense (v.) → tension.

A system of numbers or functions where components obey a certain law of transformation when the variables undergo a linear transformation. A tensor may consist of a single number, in which case it is referred to as a tensor of order zero, or simply a → scalar. The tensor of order one represents a → vector. Similarly there will be tensors of order two, three, and so on.

See also:
→ absolute tensor, → calculus of tensors, → contravariant tensor, → covariant tensor, → Einstein tensor, → energy-momentum tensor, → metric tensor, → order of a tensor, → relative tensor, → Ricci tensor, → Riemann curvature tensor, → scalar-tensor theory, → skew-symmetric tensor, → symmetric tensor, → tensor analysis, → tensor contraction, → tensor density, → tensor field, → tensor perturbation, → tensor rank, → tensor-vector-scalar (TeVeS) theory, → weight of a tensor.

See also: Agent noun of tense (v.) → tension.

A method of calculation in higher mathematics based on the properties of tensors.

See also: → tensor; → analysis.

A method of calculation in higher mathematics based on the properties of tensors.

See also: → tensor; → analysis.

An operation of tensor algebra that is obtained by setting unlike indices equal and summing according to a summation convention.

See also: → contraction; → tensor.

An operation of tensor algebra that is obtained by setting unlike indices equal and summing according to a summation convention.

See also: → contraction; → tensor.

A generalization of the tensor concept that like a tensor transforms, except for the appearance of an extra factor, which is the → Jacobian matrix of the transformation of the coordinates, raised to some power, in transformation law. The exponent, which is a positive or negative integer, is called the weight of the tensor density. → weight of a tensor density. Ordinary tensors are tensor densities of weight 0. Tensor density is also called → relative tensor.

See also: → tensor; → density.

A generalization of the tensor concept that like a tensor transforms, except for the appearance of an extra factor, which is the → Jacobian matrix of the transformation of the coordinates, raised to some power, in transformation law. The exponent, which is a positive or negative integer, is called the weight of the tensor density. → weight of a tensor density. Ordinary tensors are tensor densities of weight 0. Tensor density is also called → relative tensor.

See also: → tensor; → density.

A field of space and time each point of which has multiple directionality, and is describable by a tensor function.

See also: → tensor; → field.

A field of space and time each point of which has multiple directionality, and is describable by a tensor function.

See also: → tensor; → field.

The perturbation in the → primordial Universe plasma caused by → gravitational waves. These waves stretch and squeeze space in orthogonal directions and bring about → quadrupole anisotropy in incoming radiation temperature.

See also: → tensor; → perturbation.

The perturbation in the → primordial Universe plasma caused by → gravitational waves. These waves stretch and squeeze space in orthogonal directions and bring about → quadrupole anisotropy in incoming radiation temperature.

See also: → tensor; → perturbation.

The total number of → contravariant and → covariant indices (→ index) of a → tensor.

See also: → tensor; → rank.

The total number of → contravariant and → covariant indices (→ index) of a → tensor.

See also: → tensor; → rank.

A theory put forward to provide a basis for a relativistic generalization of the → MOdified Newtonian Dynamics (MOND) paradigm. TeVeS is based on three dynamical fields: a tensor field, a vector field, and a scalar field. In contrast to general relativity, it has two metrics, an Einstein metric and a physical metric. TeVeS has attracted considerable attention, since it can explain many galactic and cosmological observations without the need for → dark matter. Proposed by J. D. Bekenstein, 2004, “Relativistic gravitation theory for the modified Newtonian dynamics paradigm”, Phys. Rev. D, 70, 083509, arXiv:astro-ph/0403694.

See also: → tensor; → vector; → scalar; → theory.

A theory put forward to provide a basis for a relativistic generalization of the → MOdified Newtonian Dynamics (MOND) paradigm. TeVeS is based on three dynamical fields: a tensor field, a vector field, and a scalar field. In contrast to general relativity, it has two metrics, an Einstein metric and a physical metric. TeVeS has attracted considerable attention, since it can explain many galactic and cosmological observations without the need for → dark matter. Proposed by J. D. Bekenstein, 2004, “Relativistic gravitation theory for the modified Newtonian dynamics paradigm”, Phys. Rev. D, 70, 083509, arXiv:astro-ph/0403694.

See also: → tensor; → vector; → scalar; → theory.

A general term for materials of all types and sizes that are ejected by volcanic eruptions. It includes particles as tiny as volcanic ash and as large as bombs and blocks.

See also: From Gk. tephra “ashes.”

A general term for materials of all types and sizes that are ejected by volcanic eruptions. It includes particles as tiny as volcanic ash and as large as bombs and blocks.

See also: From Gk. tephra “ashes.”

Prefix denoting one million million (10¹²).

See also: From Gk. teras “monster.”

Prefix denoting one million million (10¹²).

See also: From Gk. teras “monster.”

A metallic chemical element; symbol Tb. Atomic number 65; atomic weight 158.9254; melting point 1,356°C; boiling point 3,123°C; specific gravity about 8.25. Terbium was discovered by the Swedish surgeon and chemist Carl-Gustav Mosander in 1843 in an yttrium salt, which he resolved into three elements. He called one yttrium, a rose colored salt he called terbium and a deep yellow peroxide he called erbium.

See also: From the “village of Ytterby” in Sweden, where the mineral ytterbite (the source of terbium) was first found.

A metallic chemical element; symbol Tb. Atomic number 65; atomic weight 158.9254; melting point 1,356°C; boiling point 3,123°C; specific gravity about 8.25. Terbium was discovered by the Swedish surgeon and chemist Carl-Gustav Mosander in 1843 in an yttrium salt, which he resolved into three elements. He called one yttrium, a rose colored salt he called terbium and a deep yellow peroxide he called erbium.

See also: From the “village of Ytterby” in Sweden, where the mineral ytterbite (the source of terbium) was first found.

1. A word or group of words that has a precise meaning and expresses a definite idea,
   used in a particular science, art, or profession. See also
   → terminology; → determine.
   

2. Math.: In an expression, a number or a letter standing alone; or a combination of such representing a unit, e.g.: a, b, 5, 4ab, 3a/b.
   

3. Physics: A set of atomic states having a definite → configuration and → spin and → orbital angular momentum  → quantum numbers. In the → LS coupling scheme, the entity ^2S+1L_J, in which 2S+1 is called the → multiplicity of the term.
   

4. Logic: The → subject or → predicate of a → categorical proposition. See also → syllogism.
   

5. In → first-order logic, an → individual constant, → individual variable, or → function.

Etymology (EN): M.E. terme, from O.Fr., from L. terminus “boundary, limit, end; boundary stone or marker,” variant termen “boundary, end;” cognate with Gk. termon “limit, boundary;” Skt. tarman “the top of the sacrificial (usually tripod) post; passage;”
Irish tearmann “a refuge, sanctuary, asylum;” this Irish word would point to the sacredness of the sacrificial post in primitive IE customs; Hittite tarma- “peg, plug, nail;” PIE base *ter- “to cross;” cf. Pers. tarm, târem, tarâ-, Av. tar- “to cross over,” as below.

Etymology (PE): Tarm, variant târem “boundary, limit,” more specifically “a wooden palisade to exclude people from a garden,” also “a wooden building of a circular form with an arched roof” (cf. Irish tearmann, as above), Tabari talm “pole, stick” (that marks a boundary),
Tâleši/Tâti talmi “pole, stick,” Garkâni taram “lever,” Lori, Laki tarm “poles fastened together in order to carry a corpse to the village cemetery;” O.Pers./Av. tar- “to cross over,” O.Pers.
vi-tar- “to go across,” Mid.Pers. vitartan “to pass,” Mod.Pers. gozar, gozaštan “to pass, cross;” cf. Skt. tarman “the top of the sacrificial post; passage,” tar- “to pass (through), overcome,” tárati “crosses, passes,” tirás “through, across, beyond;” see also → trans-.

1. A word or group of words that has a precise meaning and expresses a definite idea,
   used in a particular science, art, or profession. See also
   → terminology; → determine.
   

2. Math.: In an expression, a number or a letter standing alone; or a combination of such representing a unit, e.g.: a, b, 5, 4ab, 3a/b.
   

3. Physics: A set of atomic states having a definite → configuration and → spin and → orbital angular momentum  → quantum numbers. In the → LS coupling scheme, the entity ^2S+1L_J, in which 2S+1 is called the → multiplicity of the term.
   

4. Logic: The → subject or → predicate of a → categorical proposition. See also → syllogism.
   

5. In → first-order logic, an → individual constant, → individual variable, or → function.

Etymology (EN): M.E. terme, from O.Fr., from L. terminus “boundary, limit, end; boundary stone or marker,” variant termen “boundary, end;” cognate with Gk. termon “limit, boundary;” Skt. tarman “the top of the sacrificial (usually tripod) post; passage;”
Irish tearmann “a refuge, sanctuary, asylum;” this Irish word would point to the sacredness of the sacrificial post in primitive IE customs; Hittite tarma- “peg, plug, nail;” PIE base *ter- “to cross;” cf. Pers. tarm, târem, tarâ-, Av. tar- “to cross over,” as below.

Etymology (PE): Tarm, variant târem “boundary, limit,” more specifically “a wooden palisade to exclude people from a garden,” also “a wooden building of a circular form with an arched roof” (cf. Irish tearmann, as above), Tabari talm “pole, stick” (that marks a boundary),
Tâleši/Tâti talmi “pole, stick,” Garkâni taram “lever,” Lori, Laki tarm “poles fastened together in order to carry a corpse to the village cemetery;” O.Pers./Av. tar- “to cross over,” O.Pers.
vi-tar- “to go across,” Mid.Pers. vitartan “to pass,” Mod.Pers. gozar, gozaštan “to pass, cross;” cf. Skt. tarman “the top of the sacrificial post; passage,” tar- “to pass (through), overcome,” tárati “crosses, passes,” tirás “through, across, beyond;” see also → trans-.

1. Forming or found at the extreme point or limit of something, or relating to the very end of something.
   
2. Computers: An input/output device having a keyboard for communicating with a computer and usually a display.

Etymology (EN): M.E., from L. terminalis “pertaining to a boundary or end, final,” from terminus “end, boundary line,” → term.

Etymology (PE): Pâyâni, pâyâné, noun and adj. from pâyân “end, extremity; limit, boundary,” from pâ(y) “foot; step” (Mid.Pers. pâd, pây; Av. pad- “foot;” cf. Skt. pat; Gk. pos, genitive podos; L. pes, genitive pedis; P.Gmc. *fot; E. foot; Ger. Fuss; Fr. pied; PIE *pod-/*ped-).

1. Forming or found at the extreme point or limit of something, or relating to the very end of something.
   
2. Computers: An input/output device having a keyboard for communicating with a computer and usually a display.

Etymology (EN): M.E., from L. terminalis “pertaining to a boundary or end, final,” from terminus “end, boundary line,” → term.

Etymology (PE): Pâyâni, pâyâné, noun and adj. from pâyân “end, extremity; limit, boundary,” from pâ(y) “foot; step” (Mid.Pers. pâd, pây; Av. pad- “foot;” cf. Skt. pat; Gk. pos, genitive podos; L. pes, genitive pedis; P.Gmc. *fot; E. foot; Ger. Fuss; Fr. pied; PIE *pod-/*ped-).

The locus of stars on the → Hertzsprung-Russell diagram that are at the point of exhausting hydrogen in their cores. TAMS forms the upper luminosity boundary of the → main sequence strip. See also
→ zero age main sequence (ZAMS).

See also: → terminal; → age; → main; → sequence.

The locus of stars on the → Hertzsprung-Russell diagram that are at the point of exhausting hydrogen in their cores. TAMS forms the upper luminosity boundary of the → main sequence strip. See also
→ zero age main sequence (ZAMS).

See also: → terminal; → age; → main; → sequence.

1. The constant maximum velocity reached by a body falling under gravity through a liquid or gas, especially the atmosphere. The body ceases to accelerate downward because the force of gravity is equal
   to the opposing force of resistance by the medium.
   

2. The velocity acquired at the end of a body’s motion.
   

3. The velocity attained by → stellar wind at very large distance from the star. The material that escapes from the outer layers of the stars is accelerated outward from a small radial velocity at the → photosphere of the star, to some high velocity at large distance from the star.
   The theory of → radiation-driven winds predicts that the
   terminal velocity scales with the → escape velocity as: v_∞  ≅ 2-3 v_esc. The winds of hot → O stars experience fast acceleration and reach 80% of their terminal velocity near the star (some 3 R_*).
   The terminal velocity ranges from about 10 km s^-1 for a cool → supergiant star to 3000 km s^-1 for a luminous hot star. Terminal velocities are quite accurately measured from the violet trough of saturated → P Cygni line profiles in the ultraviolet (mainly N V λ1239, C IV λ1548, Si IV λ1394).

See also: → terminal; → velocity.

1. The constant maximum velocity reached by a body falling under gravity through a liquid or gas, especially the atmosphere. The body ceases to accelerate downward because the force of gravity is equal
   to the opposing force of resistance by the medium.
   

2. The velocity acquired at the end of a body’s motion.
   

3. The velocity attained by → stellar wind at very large distance from the star. The material that escapes from the outer layers of the stars is accelerated outward from a small radial velocity at the → photosphere of the star, to some high velocity at large distance from the star.
   The theory of → radiation-driven winds predicts that the
   terminal velocity scales with the → escape velocity as: v_∞  ≅ 2-3 v_esc. The winds of hot → O stars experience fast acceleration and reach 80% of their terminal velocity near the star (some 3 R_*).
   The terminal velocity ranges from about 10 km s^-1 for a cool → supergiant star to 3000 km s^-1 for a luminous hot star. Terminal velocities are quite accurately measured from the violet trough of saturated → P Cygni line profiles in the ultraviolet (mainly N V λ1239, C IV λ1548, Si IV λ1394).

See also: → terminal; → velocity.

A → shock wave inside the → heliopause where the → supersonic → solar wind abruptly slows from an average speed of 500 km s^-1 to → subsonic and becomes denser and hotter.

Etymology (EN): Termination, verbal noun from terminate, from → term; → shock.

Etymology (PE): Toš, šok, → shock; pâyâni, → terminal.

A → shock wave inside the → heliopause where the → supersonic → solar wind abruptly slows from an average speed of 500 km s^-1 to → subsonic and becomes denser and hotter.

Etymology (EN): Termination, verbal noun from terminate, from → term; → shock.

Etymology (PE): Toš, šok, → shock; pâyâni, → terminal.

The dividing line between the illuminated and the un-illuminated part of the Moon’s or a planet’s disk.

Etymology (EN): From L. terminator, from terminare, from terminus→ term.

Etymology (PE): Šid-marz, literally “light boundary,” from šid “light, sunlight” (Mid.Pers. šêt “shining, radiant, bright;” Av. xšaēta- “shining, brilliant, splendid, excellent”)

• marz “boundary, limit” (Mid.Pers. marz “boundary;” Av. marəza- “border, district,” marəz- “to rub, wipe;” Mod.Pers. parmâs “contact, touching” (→ contact), mâl-, mâlidan “to rub;” PIE base *merg- “boundary, border;” cf. L. margo “edge” (Fr. marge “margin”); P.Gmc. *marko;
  Ger. Mark; E. mark, margin).

The dividing line between the illuminated and the un-illuminated part of the Moon’s or a planet’s disk.

Etymology (EN): From L. terminator, from terminare, from terminus→ term.

Etymology (PE): Šid-marz, literally “light boundary,” from šid “light, sunlight” (Mid.Pers. šêt “shining, radiant, bright;” Av. xšaēta- “shining, brilliant, splendid, excellent”)

• marz “boundary, limit” (Mid.Pers. marz “boundary;” Av. marəza- “border, district,” marəz- “to rub, wipe;” Mod.Pers. parmâs “contact, touching” (→ contact), mâl-, mâlidan “to rub;” PIE base *merg- “boundary, border;” cf. L. margo “edge” (Fr. marge “margin”); P.Gmc. *marko;
  Ger. Mark; E. mark, margin).

1. The system of terms belonging to a particular science, art, specialized subject, or social group. Terminology is the way of naming concepts, which generally precede the corresponding terms. See also → lexicology.
   

2. The theory or science dealing with the relations between → terms and → concepts.

Etymology (EN): A hybrid word coined first in Fr., before 1764, by Yves Marie André (1675-1764), a Jesuit mathematician and philosopher, from termin, from L. terminus, → term, + epenthetic vowel -o- + Gk. -logia, → -logy. Recoined or borrowed in Ger. Terminologie in 1786, by C.G. Schütz of Jena; first appeared in E. in 1801.

Etymology (PE): From tarm, → term, + -šenâsi, → -logy.

1. The system of terms belonging to a particular science, art, specialized subject, or social group. Terminology is the way of naming concepts, which generally precede the corresponding terms. See also → lexicology.
   

2. The theory or science dealing with the relations between → terms and → concepts.

Etymology (EN): A hybrid word coined first in Fr., before 1764, by Yves Marie André (1675-1764), a Jesuit mathematician and philosopher, from termin, from L. terminus, → term, + epenthetic vowel -o- + Gk. -logia, → -logy. Recoined or borrowed in Ger. Terminologie in 1786, by C.G. Schütz of Jena; first appeared in E. in 1801.

Etymology (PE): From tarm, → term, + -šenâsi, → -logy.

To alter the environment of a planet or moon in a → terraforming process in order to make it habitable for life forms.

Etymology (EN): Probably taken from noun terraform,
from L. terra “earth,” → terrestrial; → form.

Etymology (PE): From zamin, → earth, + disidan “to → form.”

To alter the environment of a planet or moon in a → terraforming process in order to make it habitable for life forms.

Etymology (EN): Probably taken from noun terraform,
from L. terra “earth,” → terrestrial; → form.

Etymology (PE): From zamin, → earth, + disidan “to → form.”

The hypothetical process of altering the environment (atmosphere, temperature, surface topography, or ecology) of another planet or moon to improve the chances of survival of an indigenous biology or to allow habitation by terrestrial life forms. See also → ecopoiesis.

See also: Verbal noun of → terraform. The term first appeared in a science fiction novel, Seetee Shock (1949) by Jack Williamson, an American science fiction writer; but the actual concept pre-dates this work.

The hypothetical process of altering the environment (atmosphere, temperature, surface topography, or ecology) of another planet or moon to improve the chances of survival of an indigenous biology or to allow habitation by terrestrial life forms. See also → ecopoiesis.

See also: Verbal noun of → terraform. The term first appeared in a science fiction novel, Seetee Shock (1949) by Jack Williamson, an American science fiction writer; but the actual concept pre-dates this work.

Pertaining to, consisting of, or representing the Earth as distinct from other planets.

Etymology (EN): From L. terrestris “earthly,” from terra “earth,” literally “dry land” (as opposed to “sea”); 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,” L. torrere “to dry up, roast,” Goth. þaursus “dry, barren,” O.H.G. derren “to make dry,” durst “thirst;” Ger. dürr “arid;” O.E. þurstig “thirsty”).

Etymology (PE): Zamini adj. of zamin, variant zami “earth, floor, land;”
Mid.Pers. zamig; Av. zam- “the earth;” cf. Skt. ksam- “the ground, earth;” Gk. khthôn, khamai “on the ground;” L. homo “earthly being” (as in homo sapiens,
homicide, humble, humus, exhume), humus “the earth;” O.Russ. zemi “land, earth;” PIE root *dh(e)ghom “earth”.

Pertaining to, consisting of, or representing the Earth as distinct from other planets.

Etymology (EN): From L. terrestris “earthly,” from terra “earth,” literally “dry land” (as opposed to “sea”); 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,” L. torrere “to dry up, roast,” Goth. þaursus “dry, barren,” O.H.G. derren “to make dry,” durst “thirst;” Ger. dürr “arid;” O.E. þurstig “thirsty”).

Etymology (PE): Zamini adj. of zamin, variant zami “earth, floor, land;”
Mid.Pers. zamig; Av. zam- “the earth;” cf. Skt. ksam- “the ground, earth;” Gk. khthôn, khamai “on the ground;” L. homo “earthly being” (as in homo sapiens,
homicide, humble, humus, exhume), humus “the earth;” O.Russ. zemi “land, earth;” PIE root *dh(e)ghom “earth”.

A uniform atomic time scale for apparent geocentric ephemerides defined by a 1979 IAU resolution, which replaced Ephemeris Time. TDT is independent of the variable rotation of the Earth, and the length of the tropical year is defined in days of 86,400 seconds of international atomic time. In 1991 it was replaced by Terrestrial Time.

See also: → terrestrial; → dynamical; → time.

A uniform atomic time scale for apparent geocentric ephemerides defined by a 1979 IAU resolution, which replaced Ephemeris Time. TDT is independent of the variable rotation of the Earth, and the length of the tropical year is defined in days of 86,400 seconds of international atomic time. In 1991 it was replaced by Terrestrial Time.

See also: → terrestrial; → dynamical; → time.

A parameter representing the product of the → gravitational constant by the Earth’s mass. It is 3.987 x 10¹⁴ m³s^-2 or 3.987 x 10⁵ km³s^-2.

See also: → terrestrial; → gravitational; → constant.

A parameter representing the product of the → gravitational constant by the Earth’s mass. It is 3.987 x 10¹⁴ m³s^-2 or 3.987 x 10⁵ km³s^-2.

See also: → terrestrial; → gravitational; → constant.

The four innermost planets in the solar system, Mercury, Venus, Earth and Mars. They are called terrestrial because they have a compact, rocky surface like the Earth’s. The planets, Venus, Earth, and Mars have significant atmospheres while Mercury has almost none. These planets are approximately the same size, with the Earth the largest. They are considerably denser than the Jovian planets, ranging from a specific gravity of 4 for Mars to 5.5 for the Earth.

See also: → terrestrial; → planet.

The four innermost planets in the solar system, Mercury, Venus, Earth and Mars. They are called terrestrial because they have a compact, rocky surface like the Earth’s. The planets, Venus, Earth, and Mars have significant atmospheres while Mercury has almost none. These planets are approximately the same size, with the Earth the largest. They are considerably denser than the Jovian planets, ranging from a specific gravity of 4 for Mars to 5.5 for the Earth.

See also: → terrestrial; → planet.

The modern astronomical standard for the passage of time on the surface of the Earth. It is
the → coordinate time scale consistent with the theory of general relativity for an observer on the surface of the Earth. TT was renamed from Terrestrial Dynamical Time (TDT)
in 1991. The fundamental unit of TT is the day of 86,400 SI seconds. It is related to the International Atomic Time by the relation: TDT = TAI + 32.184 sec.

See also: → terrestrial; → time.

The modern astronomical standard for the passage of time on the surface of the Earth. It is
the → coordinate time scale consistent with the theory of general relativity for an observer on the surface of the Earth. TT was renamed from Terrestrial Dynamical Time (TDT)
in 1991. The fundamental unit of TT is the day of 86,400 SI seconds. It is related to the International Atomic Time by the relation: TDT = TAI + 32.184 sec.

See also: → terrestrial; → time.

1. Third in order, rank, level, stage, formation, etc.
   

2. Chem.: Being or containing a carbon atom having bonds to three other carbon atoms.
   

3. Geology: (usually with capital initial) A term formerly used to distinguish a major period of → geologic time, from the end of the → Cretaceous period about 65 million years ago to the start of the Quaternary period about 1.6 millions years ago. The International Commission on Stratigraphy no longer sustains this term as part of the formal stratigraphic nomenclature. Instead, the → Paleogene and → Neogene periods are recommended as the primary subdivisions of the Cenozoic era.

See also: From L. tertius, → third; → period.

1. Third in order, rank, level, stage, formation, etc.
   

2. Chem.: Being or containing a carbon atom having bonds to three other carbon atoms.
   

3. Geology: (usually with capital initial) A term formerly used to distinguish a major period of → geologic time, from the end of the → Cretaceous period about 65 million years ago to the start of the Quaternary period about 1.6 millions years ago. The International Commission on Stratigraphy no longer sustains this term as part of the formal stratigraphic nomenclature. Instead, the → Paleogene and → Neogene periods are recommended as the primary subdivisions of the Cenozoic era.

See also: From L. tertius, → third; → period.

The unit of → magnetic induction flux density in the SI system. It is the induction of a field in which each meter of conductor with a current of one → ampere and arranged perpendicular to the direction of the vector of induction is acted upon by a force of one → newton. 1 tesla = 1 → weber/m² = 10⁴→ gauss.

See also: Named after Nikola Tesla (1856-1943), American physicist, electrical engineer, and inventor, born in Smiljan, Lika, which was then part of the Austo-Hungarian Empire, region of Croatia.

The unit of → magnetic induction flux density in the SI system. It is the induction of a field in which each meter of conductor with a current of one → ampere and arranged perpendicular to the direction of the vector of induction is acted upon by a force of one → newton. 1 tesla = 1 → weber/m² = 10⁴→ gauss.

See also: Named after Nikola Tesla (1856-1943), American physicist, electrical engineer, and inventor, born in Smiljan, Lika, which was then part of the Austo-Hungarian Empire, region of Croatia.

A procedure by which the presence, quality, or genuineness of anything is determined.

Etymology (EN): M.E. test, originally “a small vessel for refining or assaying metals,” from O.Fr. test, from L. testum “earthen pot,” related to testa “piece of burned clay, earthen pot, shell,” related to texere “to weave;” → technique.

Etymology (PE): Âzmun, from âzmudan, âzmây- “to try, experiment, test;” Mid.Pers. uzmudan, ôzmutan “to test, try, prove;” from O.Pers./Av. *uz-mây-, from uz-, → ex-,

• mť(y)- “to measure;” from PIE *me- “measure;” cf. Skt. mati “measures,” matra “measure;” Gk. metra “lot, portion;” L. metri “to measure.”

A procedure by which the presence, quality, or genuineness of anything is determined.

Etymology (EN): M.E. test, originally “a small vessel for refining or assaying metals,” from O.Fr. test, from L. testum “earthen pot,” related to testa “piece of burned clay, earthen pot, shell,” related to texere “to weave;” → technique.

Etymology (PE): Âzmun, from âzmudan, âzmây- “to try, experiment, test;” Mid.Pers. uzmudan, ôzmutan “to test, try, prove;” from O.Pers./Av. *uz-mây-, from uz-, → ex-,

• mť(y)- “to measure;” from PIE *me- “measure;” cf. Skt. mati “measures,” matra “measure;” Gk. metra “lot, portion;” L. metri “to measure.”

Any of a pair of identical 1.96 kg gold-platinum cubes measuring 4.6 cm on a side that are planned to be used in the → eLISA experiment to detect → gravitational waves. The test masses will be released in → free fall in the the → LISA Pathfinder spacecraft. The aim is to test methods and techniques that will be used in the eLISA experiment to detect gravitational waves. Even in space there are forces capable of disturbing the cubes, including the radiation and wind from the Sun. Hence the test masses need be isolated from all of these non-gravitational influences. To do so, LISA Pathfinder continually measures their positions and manoeuvres around them with microthrusters to avoid ever touching them.

See also: → test; → mass

Any of a pair of identical 1.96 kg gold-platinum cubes measuring 4.6 cm on a side that are planned to be used in the → eLISA experiment to detect → gravitational waves. The test masses will be released in → free fall in the the → LISA Pathfinder spacecraft. The aim is to test methods and techniques that will be used in the eLISA experiment to detect gravitational waves. Even in space there are forces capable of disturbing the cubes, including the radiation and wind from the Sun. Hence the test masses need be isolated from all of these non-gravitational influences. To do so, LISA Pathfinder continually measures their positions and manoeuvres around them with microthrusters to avoid ever touching them.

See also: → test; → mass

Same as → significance testing and → rule of decision.

See also: → test; → significance.

Same as → significance testing and → rule of decision.

See also: → test; → significance.

In → plasma physics, → fluid dynamics, and → self-gravitating systems, a particle or ensemble of particles which are affected by the evolution of the rest of the system, but do not affect the rest of the system.
The test particle concept is used, e.g.,
for revealing a flow, describing the path of fluid elements, and so on.

See also: → test; → particle.

In → plasma physics, → fluid dynamics, and → self-gravitating systems, a particle or ensemble of particles which are affected by the evolution of the rest of the system, but do not affect the rest of the system.
The test particle concept is used, e.g.,
for revealing a flow, describing the path of fluid elements, and so on.

See also: → test; → particle.

That part of the working time of a telescope devoted to tests of coupled instruments or the telescope itself.

See also: → test; → time.

That part of the working time of a telescope devoted to tests of coupled instruments or the telescope itself.

See also: → test; → time.

The state or fact of being → testable. See also → falsifiability.

See also: → testable; → -ity.

The state or fact of being → testable. See also → falsifiability.

See also: → testable; → -ity.

The quality of a claim, hypothesis, or theory that can be verified by tests or experiments. See also → falsifiable.

See also: → test; → -able.

The quality of a claim, hypothesis, or theory that can be verified by tests or experiments. See also → falsifiable.

See also: → test; → -able.

The ninth of Saturn’s known satellites. It it 1060 km across and orbits at a mean distance of 294,660 km from Saturn. It has a rotational period of 1.89 days that equals its orbital period. Tethys is thought to be composed almost entirely of water-ice because of its low density (1.21 gm/cm³). The western hemisphere of Tethys is dominated by a huge impact crater called Odysseus, whose 400 km diameter is nearly 2/5 of that of Tethys itself. Tethys has two moons named Telesto and Calypso. It was discovered by J.-D. Cassini in 1684.

See also: In Gk. mythology Tethys was a Titaness and sea goddess who was both sister and wife of Oceanus.

The ninth of Saturn’s known satellites. It it 1060 km across and orbits at a mean distance of 294,660 km from Saturn. It has a rotational period of 1.89 days that equals its orbital period. Tethys is thought to be composed almost entirely of water-ice because of its low density (1.21 gm/cm³). The western hemisphere of Tethys is dominated by a huge impact crater called Odysseus, whose 400 km diameter is nearly 2/5 of that of Tethys itself. Tethys has two moons named Telesto and Calypso. It was discovered by J.-D. Cassini in 1684.

See also: In Gk. mythology Tethys was a Titaness and sea goddess who was both sister and wife of Oceanus.

Combining form meaning four.

Etymology (EN): From Gk. tetra-, combining form of tettares, tessares “four,” cognate with Pers. cahâr, → four.

Combining form meaning four.

Etymology (EN): From Gk. tetra-, combining form of tettares, tessares “four,” cognate with Pers. cahâr, → four.

1. A group of four.
   

2. A sequence of four → total lunar eclipses occurring at approximately six month intervals. Tetrads are relatively rare events. The first → total eclipse of a tetrad occurred on 15 April 2014, the next eclipse of the series will happen on 8 October 2014 and the next two eclipses on 4 April and 28 September 2015, respectively. The previous tetrad happened in 2003-2004 and the next one will be in 2032-2033.

Etymology (EN): From Gk. tetrad-, stem of tetras “group of four.”

Etymology (PE): Cahârgân, from cahâr, → four, + -gân suffix of plurality.

1. A group of four.
   

2. A sequence of four → total lunar eclipses occurring at approximately six month intervals. Tetrads are relatively rare events. The first → total eclipse of a tetrad occurred on 15 April 2014, the next eclipse of the series will happen on 8 October 2014 and the next two eclipses on 4 April and 28 September 2015, respectively. The previous tetrad happened in 2003-2004 and the next one will be in 2032-2033.

Etymology (EN): From Gk. tetrad-, stem of tetras “group of four.”

Etymology (PE): Cahârgân, from cahâr, → four, + -gân suffix of plurality.

Same as → quadrangle.

Etymology (EN): From Gk. tetragonon, from → tetra- + -gon “angled, angular,” from gonia “angle,”
related to gony “knee;” L. genu “knee;” Mod.Pers. zânu “knee;” Av. žnav-, žnu- “knee;” Skt. janu-; PIE base *g(e)neu-.

Etymology (PE): Cahârguš “four-cornered,” from cahâr, câr “four,” cognate with L. quattuor, → four,

• gušé, guš “corner, angle;” Mid.Pers. gôšak “corner.”

Same as → quadrangle.

Etymology (EN): From Gk. tetragonon, from → tetra- + -gon “angled, angular,” from gonia “angle,”
related to gony “knee;” L. genu “knee;” Mod.Pers. zânu “knee;” Av. žnav-, žnu- “knee;” Skt. janu-; PIE base *g(e)neu-.

Etymology (PE): Cahârguš “four-cornered,” from cahâr, câr “four,” cognate with L. quattuor, → four,

• gušé, guš “corner, angle;” Mid.Pers. gôšak “corner.”

A solid figure having four plane faces.

See also: → tetra-; → -hedron.

A solid figure having four plane faces.

See also: → tetra-; → -hedron.

1. The main body of matter in a manuscript, book, newspaper, etc., as distinguished from notes, appendixes, headings, illustrations, etc.
   

2. The actual wording of anything written or printed.
   

3. Any of the various forms in which a writing exists (Dictionary.com).

Etymology (EN): M.E., from L. textus “text, terms, structure,” originally, “pattern of weaving,”
→ texture, from texere “to weave.”

Etymology (PE): Bâfé, from bâftan “to weave,” → texture.

1. The main body of matter in a manuscript, book, newspaper, etc., as distinguished from notes, appendixes, headings, illustrations, etc.
   

2. The actual wording of anything written or printed.
   

3. Any of the various forms in which a writing exists (Dictionary.com).

Etymology (EN): M.E., from L. textus “text, terms, structure,” originally, “pattern of weaving,”
→ texture, from texere “to weave.”

Etymology (PE): Bâfé, from bâftan “to weave,” → texture.

A type of hypothetical → topological defect in the structure of → space-time that forms when large, complicated symmetry groups are completely broken.

Etymology (EN): M.E., from M.Fr., from L. textura “web, texture, structure,” from stem of textere “to weave;” PIE base *tek- “to make” → technique.

Etymology (PE): Bâft, verbal noun, past stem of bâftan “to weave;” Mid.Pers. waf- “to weave;” Av. ubdaēna- “consisting of woven texture,”
from *ubda- “woven,” p.p. from vaf- “to weave; to sing,” literally “to weave the songs;” cf. Skt. vabh- “to bind, fetter,” ubhnāti “he laces together;” Gk. hyphainein “to weave,”
hyphos “web;” P.Gmc. *webanan (cf. O.N. vefa, M.L.G., M.Du., Du. weven, O.H.G. weban, Ger. weben; O.E. wefan; E. weave), from PIE *webh-/*wobh- “to weave.”

A type of hypothetical → topological defect in the structure of → space-time that forms when large, complicated symmetry groups are completely broken.

Etymology (EN): M.E., from M.Fr., from L. textura “web, texture, structure,” from stem of textere “to weave;” PIE base *tek- “to make” → technique.

Etymology (PE): Bâft, verbal noun, past stem of bâftan “to weave;” Mid.Pers. waf- “to weave;” Av. ubdaēna- “consisting of woven texture,”
from *ubda- “woven,” p.p. from vaf- “to weave; to sing,” literally “to weave the songs;” cf. Skt. vabh- “to bind, fetter,” ubhnāti “he laces together;” Gk. hyphainein “to weave,”
hyphos “web;” P.Gmc. *webanan (cf. O.N. vefa, M.L.G., M.Du., Du. weven, O.H.G. weban, Ger. weben; O.E. wefan; E. weave), from PIE *webh-/*wobh- “to weave.”