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

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."

The study of linguistic and non-linguistic signs and symbols used in natural and artificially constructed languages. Semiotics is usually divided into three branches: 1) → pragmatics, 2) → semantics, and 3) → syntax.

→ semiotic; → -ics.

A type of giant or supergiant pulsating variable star, with intermediate or late spectra, showing noticeable periodicity in its light changes, accompanied or sometimes interrupted by various irregularities. Periods lie in the range from 20 to more than 2000 days, while the shapes of the light curve may be rather different and variable with each cycle. The amplitudes may be from several hundredths to several magnitudes (usually 1-2 magnitudes in the V filter). Examples are Betelgeuse, Antares, and Rasalgethi. Semiregular variables are classified in several subtypes: SRA, SRB, SRC, and SRD.

→ semi-; → regular; → variable.

1) Older or elder (designating the older of two men bearing the same name, as a father whose son is named after him, often written as Sr. or sr. Compare → junior.
2a) Of higher or the highest rank or standing.
2b) (in American schools, colleges, and universities) Of or relating to students in their final year or to their class (Dictionary.com).

M.E., from L. senior "older," comparative of senex (genitive senis) "old," from PIE root *sen- "old;" cf. Av. hana- "old;" O.Pers. hanata- "old age, lapse of time;" Skt. sanah "old;" Armenian hin "old;" Gk. enos "old, of last year;" Lith. senas "old," senis "an old man;" Goth. sineigs "old," O.Irish sen, O.Welsh hen "old." sjunio

Mehtar "greater, elder, governor," from meh "great, large, principla," cognate with L. mas, → Big Bang, + comparative suffix -tar.

The perception or awareness of stimuli through the senses.

From M.L. sensationem (nominative sensatio), from L.L. sensatus "endowed with sense, sensible," from L. sensus "feeling," → sense.

Hess-kard, hesseš, verbal nouns of hess kardin, hessidan, → sense.

1) Any of the faculties, as sight, hearing, smell, taste, by which a person or animal obtains information about the physical world.
2) To perceive by the senses; become aware of.

M.E., from O.Fr. sens, from L. sensus "perception, feeling, undertaking," from sentire "perceive, feel, know."

Hess, loan from Ar. Hess kardan, hessidan infinitives from hess.

1) Capacity for sensation or feeling; responsiveness to sensory stimuli.
2) Physics: The realignment of a magnetic compass pointer along a magnetic field line after the pointer has been deflected.

→ sensible; → -ity.

That can be perceived by the senses.

M.E., from O.Fr. from L. sensibilis "having feeling, perceptible by the senses," from sensus, p.p. of sentire "perceive, feel," → sense.

Hess-pazir, from hess, → sense + pazir, → -able; hessidani, from hessidan (v.) + -i, → -able.

The great circle of the celestial sphere whose poles are the nadir and zenith. Same as astronomical horizon.

→ sensible; → horizon.