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

1) To admit to be real or true; recognize the existence, truth, or fact of.
2) To recognize the authority, validity, or claims of.
3) To show or express appreciation or gratitude for (Dictionary.com).

A blend of M.E aknow "admit or show one's knowledge" (from O.E. oncnawan "understand") and M.E. knowlechen "to admit."

Âdânidan, from âdân, from prefix â- + dân present stem of dânestan, → know; cf. Sogd. âzân, azân "to acknowledge, to confess," from prefixed zân, variant of dân.

1) Recognition of the existence or truth of something.
2) An expression of appreciation (Dictionary.com).

→ acknowledge; → -ment.

Pertaining to the sense of hearing, or to → sound waves.

→ acoustics.

One of several peaks appearing in the → CMB angular power spectrum of the → cosmic microwave background radiation which are ripples left by acoustic oscillations of the plasma-radiation fluid in the early Universe (→ baryon acoustic oscillations). When the Universe was small and very hot, the free electron density was so high that photons could not propagate freely without being scattered by electrons. Ionized matter, electrons and radiation formed a single fluid, with the inertia provided by the baryons and the radiation pressure given by the photons.

→ acoustic; → peak.

Same as → sound pressure.

→ acoustic; → pressure.

A type of → longitudinal wave that consists of mechanical → vibrations of small → amplitude propagated in an → elastic medium. Acoustic waves exhibit phenomena like → diffraction, → reflection, and → interference, but not → polarization. Also called → sonic and → sound waves. See also → acoustic wave equation. The branch of physics concerned with the properties of sonic waves is called → acoustics.

→ acoustic; → wave.

A → differential equation that describes the time evolution of the → scalar potential of the field φ. It is expressed by: ∇²φ = (1/c²)∂²φ/∂t², where c is → velocity of → longitudinal waves and ∇² is the → Laplacian operator.

→ acoustic; → wave; → equation.

1) The study of sound, especially of its generation, propagation, and reception.
2) Those qualities of an enclosure that together determine its character with respect to distinct hearing.

From Fr. acoustique, from Gk. akoustikos "pertaining to hearing," from akoustos "heard, audible," from akouein "to hear," from copulative prefix a- + koein "to mark, perceive, hear," from PIE root *(s)keu- "to notice, observe."

Sedâyik from sedâ "sound" + Pers. suffix -ik, → -ics. Sedâ is most probably Persian, since it exists also in Indo-Aryan languages: Skt. (late Vedic): sabda "articulate sound, noise," Pali and Prakriti: sadda "sound, noise," Sindhi: sadu, sado "shout, call," Gujrâti sad "call, voice, echo," Marathi: sad "shouting to," Konkani sad "sound," Sinhali: sada "sound." Therefore, sadâ in Arabic "reverbrating noise, echo" may be borrowed from Persian, or a coincidence. Note that for the author of the classical Persian dictionary Borhân-e Qâte' (India, 1652 A.D.), the Arabic term is a loanword from Persian.

→ phone; →phonetics.

Relating to or occurring at sunset. → heliacal

Acronical, from Gk. akronukos, from akros "tip, end," cf. Av. aγra- "top, first," Skt. agra- "first, foremost, climax" + nuks, nuktos "night," → night.

Šâmgâhi, adj. of šâmgâh "evening," from šâm "evening, evening meal" + gâh "time." The first component, šâm, from Mid.Pers. šâm "evening meal, supper," from Av. xšāfnya- "evening meal," from Av. xšap-, xšapā-, xšapan-, xšafn- "night" (O.Pers. xšap- "night," Mid.Pers. šap, Mod.Pers. šab "night"); cf. Skt. ksap- "nigh, darkness;" Hittite ispant- "night." The second component gâh "time," Mid.Pers. gâh, gâs "time," O.Pers. gāθu-, Av. gātav-, gātu- "place, throne, spot;" cf. Skt. gâtu- "going, motion; free space for moving; place of abode;" PIE *gwem- "to go, come."

The rising of a star in the sky at or just after sunset. → heliacal rising.

→ acronical; → rising.

The setting of a star at nightfall. → heliacal setting.

→ acronical; → setting.

A southern hemisphere bright star (α Crucis) of magnitude 0.77 lying at a distance of 321 → light-years. It is apparently made up of three components. The primary component, Acrux A, is a blue subgiant of apparent magnitude 1.34 and spectral type B0.5 IV. The B component lies at about 4.1 arcsec away from the A component, which represents a distance of at least 400 AU, that is, more than 10 times the distance between the sun and planet Pluto. The C component lies about 90 arcsec away from A.

Acrux, from A, from Alpha, designating the brightest star of the constellation + crux, the constellation name. The name Acrux is probably a coinage of the American astronomer, Elijah H. Burritt, who published several editions of an astronomical atlas between 1833 and 1856.

1) The process of doing or performing something; something done or performed.
2) (v.intr.) To carry out an action; to produce an effect.

Act, from O.Fr. acte, from L. actus "a doing" and actum "a thing done," both from agere "to do, set in motion, drive, urge, chase, stir up," from PIE root *ag- "to drive, draw out or forth, move" (cf. Gk. agein "to lead, guide, drive, carry off," agon "assembly, contest in the games," agogos "leader;" Av. az- "to drive (away)," azaiti "drives," Mod.Pers. govâz "stick for driving cattle," from Av. gauuāza-, from gao- "cow, ox, cattle" (→ Bootes) + āza-, from az-, as above; Skt. aj- "to drive, sling," ájati "drives," ajirá- "agile, quick." The E. agile "characterized by quickness, lightness, and ease of movement; mentally quick or alert" is from this root.

In major European languages there are two fundamental and very close verbs which convey "work, action, activity". These are: 1) to do (in French faire, Spanish hacer, German machen) and 2) to act (French agir, Spanish actuar, German handeln). In Persian there is only one word for these two concepts: kardan; and this is obviously a big handicap. An ad hoc equivalent for action has therefore been koneš, from kardan "to do." The problem is that this solution, despite being widely used, confounds "to do" with "to act," and is incapable of forming all the related derivatives. Therefore, we propose žir, which derives from Av. žirā- "active, agile, clever;" Mid.Pers. žir, zir "active, busy" (loaned in Arm. žir "active, busy, clear"), Mod.Pers. zirak "clever, alert, intelligent;" Kurd. žir "agile," žiri "agility."

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.

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.

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.

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 t_i and a final instant t_f. 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 = ∫L_d 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 k^wer- "to do, to make."

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.

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

→ action; → variable.

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.