An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

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).

→ 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).

→ 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.

Termination, verbal noun from terminate, from → term; → shock.

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.

From L. terminator, from terminare, from terminus→ term.

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.

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.

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.

Probably taken from noun terraform, from L. terra "earth," → terrestrial; → form.

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.

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.

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").

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.

→ 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.

→ 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.

→ 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.

→ 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.

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.

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.

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.

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.

→ test; → mass

Same as → significance testing and → rule of decision.

→ 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.

→ test; → particle.

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

→ test; → time.

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

→ testable; → -ity.