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

The inward spiraling of an orbiting → black hole toward a central → supermassive black hole (SMBH) as it radiates → gravitational wave. As a result, the orbit decays, and the orbital period decreases, leading to the → merging of both black holes as they get close enough. Once merged, the single hole goes through a stage called → ringdown.

→ in; → spiral.

The condition of a system when it is disturbed by internal or external forces. The system continues to depart from the original condition, in contrast to a stable system, which will return to its previous condition when disturbed.

From → in- "not" + → stability

A narrow, almost vertical, band on the right hand side of the → main sequence in the → H-R diagram occupied by many different types of → pulsating stars (→ RR Lyrae, → Cepheids, → W Virginis, → ZZ Ceti). Stars traverse this region at least once after they leave the main sequence. The narrow temperature range of the instability strip corresponds to the stellar → effective temperature that can sustain → partial ionization zones, capable of maintaining stellar oscillations. The blue (hot) edge of the instability strip pertains to stars with surface temperatures hotter than ~ 7500 K. Because these stars have partial ionization zones too close to their surface, the pulsation mechanism is not active. The red (cooler) edge of the instability strip is determined by stars with a temperature lower than ~ 5500 K. In these stars convection prevents the build-up of heat pressure necessary to drive pulsations.

→ instability; → strip.

1) To place in position or connect for service or use.
2) To establish in an office, position, or place (Dictionary.com).

From M.L. installare, from L. → in- + M.L. stallum "stall," from a Germanic source (compare O.H.G. stal "standing place, stand, place, stable, stall," Ger. Stall "stable," Stelle "place"), from PIE root *stel- "to put, stand;" cf. Gk. stele "standing block, slab," stellein "to set in order, arrange, array, equip, make ready."

Darhidan, literally "to place in," from dar "in, into," → in-, + -hidan present stem of (ne)hâdan "to put, place, establish" → position.

1) Something installed, as machinery or apparatus placed in position or connected for use.
2) The act of installing.
3) The fact of being installed (Dictionary.com).

→ install; → -tion.

1) A case or occurrence of anything.
2) An example put forth in proof or illustration (Dictionary.com).

M.E., from O.Fr. instance, from L. instantia "presence; earnestness, urgency," literally "a standing near," from instans, → instant.

Seté, from set, present stem of setâdan, variant of istâdan "to stand," → standard, + -é noun suffix.

1a) An → infinitesimal or very short space of time;  a → moment.
1b) The point of time now present or present with reference to some action or even.
2a) Succeeding without any interval of time; prompt;  → immediate.
2b) Occurring, done, or prepared with a minimal amount of time and effort; produced  rapidly and with little preparation (Dictionary.com).

M.E., from O.Fr. instant (adj.) "assiduous, at hand," from M.L. instans-, in classical L. "present, pressing, urgent," literally "standing near," pr.p. of instare "to urge, to stand near, be present," → insist.

1) Lahzé, from Ar. laHZat, laHZa "glance; moment."
2) Setand (variant of istandé), from setâdan, variant of istâdan "to stand," → instance.

1) Occurring, done, or completed in an instant.
2) Existing at or pertaining to a particular instant (Dictionary.com).

→ instant; → -an; → -eous.

The → acceleration of a particle at time t defined by a = lim Δv/Δt = dv/dt. It is the limiting value of Δv/Δt at time t as both Δv and Δt approach zero.

→ instantaneous; → acceleration.

The velocity of a particle at some one instant of time, or at some one point of its path. It can be defined as the limiting value of the average velocity when the second point is taken closer and closer to the first point.

→ instantaneous; → velocity.

The arched upper surface of the human foot between the toes and the ankle (Dictionary.com).

→ in-; → step.

Ruyé, → surface; pâ, → foot.

To provoke, urge, or incite.

From L. instigatus, p.p. of instigare "to urge on, incite," from → in- "in" + *stigare "to prick," from PIE root *steig- "to prick, stick, pierce," cognate with Pers. tig, tiz, → sharp.

Âqâlidan "to excite, rouse."

The act of instigating; incitement.

Verbal noun of → instigate.

1) An object used for producing music.
2) A measuring device designed to record the present value of a quantity under observation.

From O.Fr. instrument, from L. instrumentem "a tool, apparatus, furniture," from instruere "to arrange, furnish," from → in- + struc- (var. s. of struere "to put together") + -tus p.p. suffix.

1) Sâz "(musical) instrument; apparatus; harness; furniture," from sâzidan, sâxtan "to build, make, fashion; to adapt, adjust, be fit" (from Mid.Pers. sâxtan, sâz-, Manichean Parthian s'c'dn "to prepare, to form;" Av. sak- "to understand, to mark," sâcaya- (causative) "to teach").
2) Sâzâl, from sâz + -âl, → -al.

The correctable part of the inaccuracy of a measuring instrument.

→ instrument; → error.

Of, relating to, or performed by or with one or more instruments.
See also:
→ instrumental broadening, → instrumental flexure, → instrumental magnitude, → instrumental profile, → instrumental response function, → instrumentalism, → instrumentalist.

Adj. of → instrument.

The broadening of a point source caused by the response functions of the telescope and the instrument used.

→ instrumental; → broadening.

An image defect caused by the mechanical flexure of materials; for example the curved-shape image of a long slit in a spectrograph.

→ instrumental; → flexure.

The magnitude derived directly using → Pogson's relation. The instrumental magnitude depends on → detector→ sensitivity, telescope → aperture, exact filter → bandpass, etc. It must be → calibrated to some standard → photometric system.

→ instrumental; → magnitude.

The shape of instrument's response to the input signal. The Fourier transform of the source function by the instrument function.

→ instrumental; → profile.