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

A process that is invariant in distribution under scaling of time. Schematically, images taken of such a process at different time scales will look similar.

→ self-; → similar; → process.

The property of being → self-similar.

→ self-; → similarity.

An empirical relation between the → refractive index of a medium and the wavelength of light passing through the medium: n² - 1 = Σ (A_iλ²/(λ² - λ_i²)), where n is the refractive index at wavelength λ, and A_i and λ_i are constants.

Named after Wolfgang Sellmeier who derived the equation in 1871; → equation.

1) Of, pertaining to, or arising from the different meanings of words or other signs and symbols.
2) Of or pertaining to → semantics.

From Fr. sémantique, from Gk. semantikos "significant," from semainein "to show, signify, indicate by a sign," from sema "sign."

Cemârik, from cemâr, → meaning, + -ik, → -ic.

The study of the → meaning of signs or symbols, as opposed to their formal relations (→ syntactics).

→ semantic; → -ics.

Biology: The male reproductive fluid, containing spermatozoa in suspension. → inseminate, → insemination; → fecundate, → fecundation.

M.E., from L. semen "seed;" akin to serere "to sow;" cf. O.C.S. seme, O.H.G. samo; E. sow.

From Mid.Pers. šusar "semen; liquid, fluid;" Av. xšudra- "semen; liquid, fluid;" related to Pers. šostan/šuy- "to → wash."

A combining form meaning "half," freely prefixed to English words of any origin.

From L. semi- "half," from PIE *semi-; cf. Skt. sāmi "half," sāmi-krita- "half-done;" Gk. hemi- "half;" O.E. sam-; Goth. sami- "half."

Nim, nimé "half," from Mid.Pers. nêm, nêmag "half;" Av. naēma- "half;" cf. Skt. néma- "half."

A → spectral line for which the upper and lower → energy levels have different values of S, the total → spin angular momentum. These lines violate the quantum mechanical → selection rule under → LS coupling, ΔS = 0. For example, the Ca I λ6573 line results from transition between the upper → triplet state (³P₁) with a total spin angular momentum S = 1 and the → ground state, a → singlet state (¹S₀, total spin angular momentum S = 0). A semi-forbidden line is marked by a right bracket following the atom name, i.e. Ca I], in the above-mentioned case. Same as → interconnection line and → intersystem line.

→ semi-; → forbidden; → line.

An → atomic transition whose probability is reduced by a factor of the order of 10⁶ because of → selection rules. Same as → interconnection line.

→ semi-; → forbidden; → transition.

Half the length of the major axis of an ellipse; a standard element used to describe an elliptical orbit. see orbital elements

→ semi-; → major; → axis.

Any of various solid crystalline substances, such as germanium or silicon, which has conducting properties intermediate between metals and insulators.

→ semi-; → conductor.

In a semiconductor device, a region of transition between semiconducting regions of different electrical properties.

→ semiconductor; → junction.

An instability occurring in the region just outside the → convective core of a → massive star. The instability occurs when a → superadiabatic layer is stabilized by a chemical gradient. In fact, semiconvection takes place if → Schwarzschild's criterion for convection is fulfilled but at the same time → Ledoux's criterion is not fulfilled. The time-scale of semiconvection is the thermal time-scale, which is short compared to the nuclear time-scale in → main sequence stars but long compared to the time-scale of convection. However, semiconvection has a profound influence on the → post-main sequence star evolution. It affects the convective mixing above the hydrogen shell source, determines the appearance and extent of → blue loops in the → Hertzsprung-Russell diagram during core → helium burning, and is essential for defining the extent of the convective cores during core helium burning (See, e.g., N. Langer, 2012, Ann. Rev. Astron. Astrophys. 50, 107).

→ semi-; → convection.

A binary system whose secondary member fills its Roche lobe but whose primary member does not.

→ semi-; detached, p.p. of detach, from O.Fr. destachier (Fr. détacher), from des- "apart," + -tachier (as in atachier "to attach"); → binary.

Dorin, → binary; nim-jodâ, from nim-→ semi- + jodâ "separate," from Mid.Pers. yut "separate, different;" Av. yuta- "separate, apart."

Same as → semidetached binary.

→ semi-; detached, p.p. of detach, from O.Fr. destachier (Fr. détacher), from des- "apart," + -tachier (as in atachier "to attach"); → system.

Râžmân, → system; nim-jodâ, from nim-→ semi- + jodâ "separate," from Mid.Pers. yut "separate, different;" Av. yuta- "separate, apart."

The angle at the observer subtended by the equatorial radius of the Sun, Moon, or a planet.

→ semi-; → diameter.

Describing an → equation or → formula that results from a → combination of → experiment and → theory.

→ semi-; → empirical.

Same as → Weizsacker formula.

→ semiempirical; → binding; → energy; → formula.

Half the → latus rectum. For an ellipse, semilatus rectum has the expression l = b²/a, where a and b are semi-major and minor axes of the ellipse. It can also be expressed in terms of → eccentricity, e, as: l = a(1 - e²).

→ semi-; → latus rectum.

1) Of or pertaining to → signs.
2) Of or pertaining to → semiotics.

From Gk. semeiotikos "significant," also "observant of signs," adj. form of semeiosis "indication," from semeion "to signal, interpret a sign," from sema "sign."