gerder-ye nâzok, disk-e ~
Fr.: disque mince
A disk component of a → spiral galaxy containing → stars, → gas, and → dust which are confined to the galaxy's → plane of rotation. In contrast to → thick disks, thin disks contain the bulk of the → baryonic matter in spiral galaxies. For example, on the order of 60-90% of the baryonic matter in the → Milky Way is located in the thin disk. The scale height of the thin disk in the Milky Way is about 400 → light-years, whereas its scale length is about 10,000 light-years. Moreover, the outer regions of thin disks appear to be bent by the → warp phenomenon. The thin disks of spiral galaxies are active sites of → star formation, especially in the spiral arms. For this reason, stars in the thin disk tend to be relatively young. Thin disk stars also tend to be → metal-rich compared with thick disk and → halo stars, and typically have a → metallicity similar to that of the Sun.
adasi-ye nâzok (#)
Fr.: lentille mince
A lens whose thickness is considered small in comparison with the distances generally associated with its optical properties. Such distances are, for example, radii of curvature of the two spherical surfaces, primary and secondary focal lengths, and object and image distances. → thick lens.
1) A material object without life or consciousness; an inanimate object.
M.E. thing; O.E. þing "meeting, assembly, discussion;" cf. O.Norse þing "assembly, meeting, council;" O.Frisian thing "assembly, action, matter, thing;" O.Saxon thing; O.Du. dinc "law suit, matter, thing;" M.Du. ding; Du. ding; O.Ger. ding, dinc "assembly;" M.H.G. dinc "assembly;" Ger. ding "matter, affairs, thing." Hence, the word originally meant "assembly, meeting," then came to mean a specific issue discussed at such an assembly, and finally came to indicate "an object."
Ciz, from Mid.Pers. ciš, tis "thing, affair;" O.Pers. cišciy "anything."
Fr.: penser, réfléchir
To employ one's mind rationally and objectively in evaluating or dealing with a given situation.
M.E. thinken, variant of thenken, O.E. thencan; P.Gmc. *thankjan (cf. O.Fris. thinka, O.S. thenkian, O.H.G. denchen, Ger. denken, Goth. thagkjan).
Andišidan, infinitive from andiš-; Mid.Pers. handeš-, handešidan "to think, consider, reflect," ultimately from Proto-Iranian *ham-dis-, from *ham- "together, with, same," → syn- + *dis- "form, appearance," cf. Av. daēs- "to show," daēsa- "sign, omen;" Mod.Pers. dis, disé "form, appearance," variants -diz, -diš; Mid.Pers. dêsag "form, appearance," dêsidan "to form, build;" Sogd. andiš "to seem," andêš "to show," andêšik "appearing;" cf. Skt. deś- "to show, point out;" PIE *deik- "to show" (cf. Gk. deiknumi "to show," dike "manner, custom;" L. dicere "to utter, say;" O.H.G. zeigon, Ger. zeigen "to show;" O.E. teon "to accuse," tæcan "to teach").
M.E. thirde, O.E. (north) thirda, variant of ridda, from P.Gmc. *thridjas (cf. O.Fris. thredda, O.S. thriddio, M.L.G. drudde, Du. derde, O.H.G. dritto, Ger. dritte, Goth. thridja).
Sevom, ordinal number for sé, → three.
Fr.: troisième contact
The end of the total phase of a solar eclipse marked by the trailing edge of the Moon first revealing the Sun.
Fr.: troisième dragage
A → dredge-up process that occurs in the stellar interior during He shell burning, as in → asymptotic giant branch (AGB) stars. These stars consist of a degenerate carbon-oxygen core, surrounded by a helium-rich region, above which lies a hydrogen-rich convective envelope. Following thermal pulses of the helium-burning shell, the convective envelope moves inward in mass, penetrating the hydrogen-exhausted regions. This is known as third dredge-up. As convection moves inward, nuclear processed materials are carried to the surface.
third law of thermodynamics
qânun-e sevom-e garmâtavânik
Fr.: troisième loi de la thermodynamique
The → entropy of an idealized state of maximum order is zero at the temperature of → absolute zero. Another version of this law: As a system approaches absolute zero, all processes cease and the entropy of the system approaches a minimum value.
Fr.: troisième quartier
The phase of the Moon when half the visible disk of the waning Moon is illuminated. This quarter occurs when the celestial longitude of the Moon is 270° greater than the Sun's.
A cardinal number, 10 times 3.
M.E. thritty, O.E. thritig, from thri, threo "three" + -tig "group of ten, -ty."
Si, from Mid.Pers. sih; O.Pers. *ciθas nominative singular of *ciθant-; Av. θrisant- "thirty;" cf. Skt. trimśát- "thirty."
Fr.: classification de Tholen
A fundamental system for the classification of → asteroids based on → albedo and → spectral characteristics. The Tholen scheme includes 14 types with the majority of asteroids falling into one of three broad categories, and several smaller types. → C-type asteroid, → M-type asteroid, → S-type asteroid.
David J. Tholen (1984) Ph.D. thesis, University of Arizona; → classification.
The British physicist Sir Joseph John Thomson (1856-1940), discoverer of the electron (1897), Nobel Prize in Physics (1906). → Thomson atom, → Thomson cross section, → Thomson effect, → Thomson scattering, → Joule-Thomson effect.
atom-e Thomson (#)
Fr.: atome de Thomson
The earliest theoretical description of the inner structure of atoms whereby an atom consists of a sphere of positive electricity of uniform density, throughout which is distributed an equal and opposite charge in the form of electrons. The diameter of the sphere was supposed to be of the order of 10-8 cm, the magnitude found for the size of the atom. → Rutherford atom.
Thomson cross section
Fr.: section efficace de Thomson
The → cross section involved the → Thomson scattering of electromagnetic waves by a free electron. It is defined by: σT = 8πre2/3, where re is the classical → electron radius. Its value is 0.665 245 x 10-28 m2.
Fr.: effet de Thomson
The absorption or emission of heat when current is passed through a single conductor whose ends are kept at different temperatures. If current is passed from hotter end to colder end of a copper wire, then heat is evolved along the length of the wire. When current is passed from colder end to the hotter end, then heat is absorbed.
parâkaneš-e Thomson (#)
Fr.: diffusion de Thomson
The classical, → non-relativistic scattering of photons by free charged particles. When an electromagnetic wave is incident on a charged particle, the electric and magnetic components of the wave exert a force on the particle, setting it into motion. As it accelerates, it in turn radiates in all directions. Such scattering is independent of wavelength and equal numbers of photons are scattered forward and backward. Thomson scattering occurs in stellar atmospheres and in any non-relativistic → plasma. Thomson scattering is normally taken as the minimum → opacity.
A soft, ductile, lustrous, silver-white, → radioactive
metal; symbol Th. → Atomic number 90;
→ atomic weight 232.0381;
→ melting point about 1,750 °C;
→ boiling point about 4,790 °C;
→ specific gravity 11.7 at 20 °C.
It was discovered in the mineral thorite (ThSiO4) by the
Swedish chemist Jons Jacob Berzelius in 1828.
It was first isolated by the chemists D. Lely Jr. and L. Hamburger in 1914.
From Thor, the "Scandinavian god of thunder."
Thorne-Zytkow object (TŻO)
Fr.: objet Thorne-Żytkow
A theoretical class of → stellar objects in which a → neutron star core is surrounded by a large and diffuse envelope. TŻOs are expected to form as a result of the evolution of two → massive stars in a → close binary, with the neutron star forming when the more massive star explodes as a → supernova. During subsequent evolution of the system, the expanding envelope of the companion may lead to a common envelope state and the spiral-in of the neutron star into the core of its companion. Alternately, a TŻO may be produced when a newly-formed neutron star receives a supernova "kick" velocity in the direction of its companion and becomes embedded. Supergiant TŻOs are predicted to be almost identical in appearance to → red supergiants (RSGs). The best features that can be used at present to distinguish TŻOs from the general RSG population are the unusually strong → heavy element and → lithium lines present in their spectra, products of the star's fully → convective envelope linking the → photosphere with the extraordinarily hot burning region in the vicinity of the neutron star core. These objects are thought to be extremely rare, with as few as 20-200 of them predicted to exist in the Galaxy at present, though some authors have doubted whether such an object could survive the merger with the envelope intact. A candidate is HV 2112 (Levesque et al., 2014, MNRAS, arXiv:1406.0001; Beasor et al., 2018, MNRAS, arXiv:1806.07399).
Thorne K. S., Żytkow A., 1975, ApJ 199, L19.
Fr.: pensée, réflexion
The product of mental activity; that which one thinks; the act or process of thinking.
M.E. thoght; O.E. (ge)thoht, from stem thencan "to think;" cf. O.Fris. thinka, O.S. thenkian, O.H.G. denchen, Ger. denken "to think."
Andišé, noun from andišidan, → think.
andiš-âzmâyeš, âzmâyeš-e andišeyi
Fr.: expérience de pensée
A demonstration which is carried out in the realm of the imagination, rather than in a laboratory. Thought experiments are designed to test ideas, theories, and hypotheses which cannot physically be tested, at least with current scientific equipment. Some examples: → Maxwell's demon; → Einstein's elevator; Heisenberg's gamma-ray microscope; → Schrodinger's cat. Also called Gedanken experiment.