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

A variation of planetary orbital elements which is always in the same direction as time increases.

→ secular; → perturbation.

Same as → secular perturbation.

→ secular; → variation.

The process of organizing society or aspects of social life around non-religious values or principles.

Verbal noun of secularize "giyânidan" (گیانیدن); → secular

An optical instrument that follows the variation of → atmospheric turbulence by continuously measuring the → seeing conditions.

→ seeing; → monitor.

The act or practice of segregating. The state or condition of being segregated. → mass segregation.

Verbal noun of → segregate.

Any of a set of rules specifying the relationships between the → quantum numbers that characterize the initial and final states of a quantum-mechanical system in a → discrete transition. Transitions that do not agree with the selection rules are called → forbidden and have considerably lower probability. There are several types of selection rules (→ rigorous selection rule, → LS coupling, etc.) for → electric dipole transition (→ permitted), → magnetic dipole (forbidden), electric → quadrupole (forbidden), etc.

Selection, verbal noun of → select; → rule.

Absorption which varies with the wavelength of radiation incident upon an absorbing substance.

Selective, verbal noun of → select; → absorption.

Same as → horizontal eclipse.

From Gk. selene "Moon," related to sela "light, brightness, flame," + helion, → sun.

→ horizontal eclipse.

Same as → horizontal eclipse.

From Fr. selenelion, contraction of → selenehelion.

→ horizontal eclipse.

A parameter representing the product of the → gravitational constant by the → lunar mass. It is 49.03 x 10¹¹ m³ s^-2.

→ selenocentric; → gravitational; → constant.

The decrease in the radiation from a material caused by the absorption of a part of the radiation by the material itself.

→ self-; → absorption.

The generation of a voltage in a circuit due to self-inductance, the polarity of which tends to oppose the changing current in the circuit.

→ self-; → induction.

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.

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.

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.

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.

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

→ sensible; → horizon.

General: The act or process of separating. The place at which a division or parting occurs.
Astro.: The angular distance between the two components of a visual binary or optical double star.

M.E., from O.Fr. separation, from L. separationem, from separare "to pull apart," from se- "apart" + parare "make ready, prepare."

Jodâyi state noun of jodâ "separate," from Mid.Pers. yut "separate, different;" Av. yuta- "separate, apart."