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

A criterion for the instability of a basic swirling flow with an arbitrary dependence of angular velocity Ω(r) on the distance r from the axis of rotation. This states that in → inviscid fluids: Ω(r) < 0 for instability, where Ω = (1/r³) (d/dr)(r⁴Ω⁴).

→ Rayleigh; → criterion.

1) General: Action in response to some influence, event, stimulus.
2) An equal and opposite force exerted by a body against a force acting upon it. → principle of action and reaction.
3) A → nuclear reaction; → chain reaction.
4) → chemical reaction.

Verbal noun of → react.

The speed with which a → chemical reaction takes place. In other words, the change in → concentration of a → substance divided by the → time interval during which the change is observed.

→ reaction; → rate.

The operation of a computer during the actual time that the related physical processes take place so that the results can be used to guide the physical processes.

→ real; → time; → operation.

1) The act of receding, going back, or withdrawing.
2) Economics: A period of an economic contraction, sometimes limited in scope or duration (Dictionary.com).

From Fr. récession "a going backward, a withdrawing," from L. recessionem "a going back," noun of action from p.p. stem of recedere "to go back, fall back; withdraw, retire," from → re- "back" + cedere "to go," → process.

Duršod, from dur, → remote, + šod "going," past stem of šodan "to go, to become," → change. Vâraveš, from vâ-, → re-, + raveš verbal noun of raftan "to go," → method.

The velocity with which an object moves away from another object or a reference point.

→ recession; → velocity.

An act of recognizing or the state of being recognized.

Verbal noun of → recognize.

1) The process or result of combining again.
2) The capture of an electron by a positive ion. It is the inverse process to → ionization.

Verbal noun of → recombine.

A measure of the specific rate at which oppositely charged ions join to form neutral particles. It is given by the rate at which those ions recombine, divided by the product of the densities of the two species involved.

→ recombination; → coefficient.

A recombination radiation that is continuous over a range of frequencies. Same as → continuum emission.

→ recombination; → continuum.

Same as → recombination era.

→ recombination; → epoch.

The era some 380,000 years after the → Big Bang (at a → redshift of about 1,100), when the Universe had cooled sufficiently so that protons and electrons combined to form → neutral hydrogen in a process called → recombination. The temperature was about 3,000 K and the ionization fraction low enough for Universe to become transparent to light. Consequently matter and radiation decouple from one another because no further → scattering of the radiation occurs. The observation of the → cosmic microwave background radiation provides a means of studying the Universe at the recombination era. Also called recombination epoch and → decoupling era.

→ recombination; → era.

An → emission line in a spectrum produced in an → H II region when a free electron combines with an ionized atom to form a neutral atom or an ion of lower → ionization stage. Same as → free-bound emission.

→ recombination; → line.

Radiation produced when a free electron in a plasma is captured by an ionized atom.

→ recombination; → radiation.

In → H II regions the rate at which free electrons recombine with → ionized hydrogen atoms (protons).

→ recombination; → rate.

The time period necessary for a cloud of atomic hydrogen to be → ionized by the ultraviolet photons of a central → massive stars.

→ recombination; → time.

1) An act of reconciling, as when former enemies agree to an amicable truce.
2) The state of being reconciled, as when someone becomes resigned to something not desired.
3) The process of making consistent or compatible (Dictionary.com).

From O.Fr. reconciliacion and directly from L. reconciliationem noun of action from p.p. stem of reconciliare. "to bring together again; regain," from → re- "again" + concilare "make friendly"

šti, from Mid.Pers. âštêh "peace;" Av. āšti- "peace, treaty of peace; agreement," āxšta-- "pacified, appeased."

1) Math.: The process of determining the length of a curve.
2) Physics: Conversion of an alternating into a direct current.
3) Astro.: The process of rectifying a spectrum.

Verbal noun of → rectify.

The motion of light in the first approximation, as evidenced from the formation of shadows and other every day experience. However, → diffraction

→ rectilinear; → propagation; → light.

A → sequence based on a → rule that gives the next → term as a → function of the previous term(s). For example, the sequence 3, 9, 21, 45,... can be represented by the recurrence relation u_n+1 = 2u_n + 3, where u₁ = 3 and n ≥ 1.

→ recurrence; → relation.