Bohr's third postulate farâvas-e sevom-e Bohr Fr.: troisième postulat de Bohr One of the postulates used in the → Bohr model, whereby the atom emits (absorbs) a quantum of electromagnetic energy (→ photon) when the electron passes from an orbit with a greater (lesser) n value to one with a lesser (greater) value. The energy of the quantum is equal to the difference between the energies of the electron on its orbits before and after the transition or "jump": hν = ε_{1} - ε_{2}, where h is the → Planck's constant and ν the frequency of the transition. |
Kepler's third law qânun-e sevom-e Kepler (#) Fr.: troisième loi de Kepler The ratio between the square of a planet's → orbital period (P) to the cube of the mean distance from the Sun (a) is the same for all planets: P^{2}∝ a^{3} (year 1618). More accurately, P^{2} = (4π^{2}a^{3}) / [G(M_{1} + M_{2})], where M_{1} and M_{2} are the masses of the two orbiting objects in → solar masses and G is the → gravitational constant. In our solar system M_{1} = 1. The → semi-major axis size (a is expressed in → astronomical units and the period (P) is measured in years. |
Newton's third law of motion sevomin qânun-e Newtoni-ye jonbeš (#) Fr.: troisième loi newtonienne de mouvement In a system where no external forces are present, every action force is always opposed by an equal and opposite reaction. |
principle of excluded third parvaz-e sevomi sokalândé Fr.: principe du tiers exclu Same as → principle of excluded middle. |
third sevom (#) Fr.: troisième Next after the second; the ordinal number for three. → Newton's third law of motion; → third contact; → third dredge-up; → third law of thermodynamics. 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. |
third contact parmâs-e sevom 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. |
third dredge-up borunkešid-e sevom 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. → third; → law; → thermodynamics. |
third quarter cârak-e sevom 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. |