An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 902
aktinide (#)

Fr.: actinide   

Any member of the group of → chemical elements with → atomic numbers from 89 (→ actinium) to 103 (→ lawrencium), analogous to the → lanthanides.

From the chemical element → actinium.

aktiniom (#)

Fr.: actinium   

A silver-white radioactive → chemical element; symbol Ac. The first member of the → actinide series of the → periodic table. → Atomic number 89; → atomic weight 227.0278; → melting point about 1,050°C; → boiling point 3,200°C ± 300°C; → specific gravity 10.07; → valence +3. It is found with uranium minerals in pitchblende. Its longest lived → isotope is 227Ac with a → half-life of 21.77 years.

From actin-, variant of actino-, from Gk. aktinos "ray, beam" + → -ium. The discovery of actinium is shared between two chemists who independently found the element. The earlier discovery was made by the French chemist André Debierne (1874-1949) in 1899 in pitchblende residues left after Pierre and Marie Curie had extracted → radium. The element was rediscovered in 1902 by the German chemist Friedrich Otto Giesel (1852-1927), who called it emanium.


Fr.: actinomètre   

Any instrument for measuring the intensity of radiation, especially that of the Sun, in its thermal, chemical, and luminous aspects.

Actinometer, from actino- combining form with the meaning "ray, beam," from Gk. aktis, aktin "ray," + → -meter.

Partow, → ray; + -sanj, → -meter.

  ژیرش، کنش   
žireš, koneš (#)

Fr.: action   

1) The process or state of acting or of being active.
2) According to → Newton's third law of motion, an external force that is applied to a body and that is counteracted by an equal force in the opposite direction ( → reaction).
3) A quantity whose → dimension (ML2T-1) coincides with that of → angular momentum, the → impulse of a force, or → energy x → time. The action plays an important part in → analytical mechanics, → quantum mechanics, and in a number of other fields of physics. Initially introduced in analytical mechanics, the concept of action has become a basic ingredient of modern physics, due to the role it has played in the generalization of → variational principle.
4) A scalar quantity computed as a function of the path followed by a system during its evolution between an initial instant ti and a final instant tf. It is defined by the → integral of the → Lagrangian between the two instants:
S = ∫L dt
In the framework of the → field theory, the action is expressed by the integral of the → Lagrangian density over the corresponding space-time volume:
S = ∫Ld d4x.
In classical physics, the path actually followed by the system is the one for which S is stationary (→ least action problem).
5) → quantum of action.
6) Math.: The action is a → functional, a mathematical relationship which takes an entire path and produces a single number.

Action, from O.Fr. action, from L. actionem, from agere "to do," → act.

Žireš, verbal noun from žir stem of žiridan "to act;" → act. Koneš, noun from kardan "to do, to make," Mid.Pers. kardan, O.Pers./Av. kar- "to do, make, build," Av. kərənaoiti "makes," cf. Skt. kr- "to do, to make," krnoti "makes," karma "act, deed;" PIE base kwer- "to do, to make."

action at a distance
  ژیرش از دور   
žireš az dur

Fr.: action à distance   

The instantaneous action of a body on another body independently of the distance separating them. The description of → gravity by → Newton's law and → electrostatics by → Coulomb's law are examples of action at a distance. According to Newton, → gravitation acts directly and instantaneously between two objects. For example, if the Sun should suddenly break apart, the Earth's orbit would be affected instantaneously. However, action at a distance violates the → principle of relativistic causality. According to → general relativity, gravitational effects travel at the → speed of light. For modern physics there is no instantaneous action at a distance.

action; → distance.

action variable
  ورتنده‌ی ِ ژیرش   
vartande-ye žireš

Fr.: variable d'action   

The time integral associated with the evolution of a physical system in the phase space.

action; → variable.


Fr.: activer   

1) To induce activity in a system that is static, as in neutron activation of radioactivity.
2) To start the operation of an electrical device.

Activate, verb from → active.

Žirândan, transitive verb from žir, → act.


Fr.: activation   

1) The process of inducing or creating a state of → activity.
2) The process of producing a → radioactive isotope by bombarding a → stable → nuclide with → nuclear particles (such as → protons, → neutrons, → alpha particles, heavy ions, etc.).

Verbal noun of → activate; → -tion.

activation energy
  کاروژ ِ ژیرانش   
kâruž-e žirâneš

Fr.: énergie d'activation   

Chemistry: The minimum amount of energy that is required to activate → atoms or → molecules to a condition in which they can undergo a → chemical reaction. Most reactions involving neutral molecules cannot take place at all until they have acquired the energy needed to stretch, bend, or otherwise distort one or more → bonds. In most cases, the activation energy is supplied by → thermal energy.

activation; → energy.


Fr.: actif   

1) Being in a state of action; not quiescent.
2) Functioning or capable of functioning.
3) Marked by vigorous activity.

M.Fr. actif, from L. activus, from actus, p.p. of agere, → act.

Žirâ, adj. from stem žir, → act + suffix .

active galactic nucleus (AGN)
  هسته‌ی ِ کهکشان ِ ژیرا   
haste-ye kahkašân-e žirâ

Fr.: noyau actif de galaxie   

A central region of an → active galaxy, which is a → light-year or less in diameter and has an abnormally high luminosity. The nucleus emits high energy radiation (→ gamma rays, → X-rays, → ultraviolet) and shows → variability over various time-scales, sometimes very short (hours to weeks). Emission line spectra reveal high velocity motions up to 104 km s-1. AGNs are divided into two main types. Type I refers to an AGN whose nucleus is visible (the spectra has both narrow and broad emission lines), while in type II AGN, the broad line region (BLR) is obscured and the lines are very narrow. This may be due either to the viewing angle or some intrinsic difference in structure. See also → broad-line region, → narrow-line region, → quasar.

active; → galactic; → nucleus.

active galaxy
  کهکشان ِ ژیرا   
kahkašân-e žirâ

Fr.: galaxie active   

A galaxy that produces huge amounts of energy at its center, which cannot be attributed to normal processes from stars, interstellar medium, and their interactions. There are several types of active galaxies: → Seyfert galaxies, → quasars, and → blazars. All of these objects show brightness variations, some as short as 3 hours. These fluctuations indicate a relatively very small size for the central object, because an object cannot vary in brightness faster than light can travel across it. For example, an object that is one → light-year in diameter cannot vary significantly in brightness over a period of less than one year.

active; → galaxy.

active optics
  نوریک ِ ژیرا   
nurik-e žirâ

Fr.: optique active   

A technique for improving the → resolving power of a telescope by controlling the shape of the main mirror at a relatively slow rate. The → image quality is optimized automatically through constant adjustments by in-built corrective → actuators operating at fairly low temporal frequency ~0.05 Hz or less. → adaptive optics.

active; → optics.

active prominence
  زبانه‌ی ِ ژیرا   
zabâne-ye žirâ

Fr.: protubérance active   

A solar → prominence with very rapid motion (up to 2,000 km s-1), moving and changing in appearance over a few minutes of time, in contrast to a → quiescent prominence.

active; → prominence.

active region
  ناحیه‌ی ِ ژیرا   
nâhiye-ye žirâ

Fr.: région active   

An area of the Sun exhibiting → solar activity with the presence of → sunspots, → flares, → faculae, → prominences, and other phenomena associated with intense magnetic fields.

active; → region.

active sun
  خورشید ِ ژیرا   
xoršid-e žirâ

Fr.: soleil actif   

The Sun during its 11-year cycle of activity when spots, flares, prominences, and variations in radiofrequency radiation are at a maximum.

active; → sun.

  ژیرش‌باوری، ژیرش‌کاری   
žireš-bâvari, žireš-kâri

Fr.: activisme   

1) The doctrine or practice of vigorous action or involvement as a means of achieving political or other goals, sometimes by demonstrations, protests, etc. ( See also → activist.
2) Philosophy: a) A theory that the essence of reality is pure activity, especially spiritual activity, or process. b) A theory that the relationship between the mind and the objects of perception depends upon the action of the mind (

active; → action; → -ism.

  ژیرش‌باور، ژیرش‌کار   
žireš-bâvar, žireš-kâr

Fr.: activiste   

An especially active, vigorous advocate of a cause, especially a political cause (

Agent noun from → activism.

  ژیرایی، ژیرندگی   
žirâyi, žirandegi

Fr.: activité   

For a radioactive substance, the average number of atoms disintegrating per unit time.

Activity, from → active + -ity.

Žirandegi, noun from žirandé, → active.


Fr.: acteur   

1) One who takes part; a participant.
2) A theatrical performer.

From → act + → -or.

Žirandé adj./noun from žir, → act + suffix -andé. Žirmand, from žir + mand.

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