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

A positively charged particle emitted from the nuclei of certain atoms during radioactive disintegration. The alpha particle has an atomic weight of 4 and a positive charge equal in magnitude to 2 electronic charges; hence it is essentially a helium nucleus.

→ alpha; → particle.

Any → elementary particle with a → charge of opposite sign to the same particle in normal matter.

→ anti- "opposite, opposing, against" + → particle.

The area of science which deals with → elementary particle and → high-energy phenomena in → astrophysics and → cosmology.

→ astro-; → particle; → physics.

A narrow unidirectional flow of particles

→ beam; → particle.

An → electron or a → positron emitted from an unstable nucleus during a → radioactive process known as → beta decay.

The term "beta particle" relates to the early history of the → radioactivity studies when the nature of the emergent particles was not elucidated; → particle.

Any particle containing either a → positive or → negative → electric charge.

→ charged; → particle.

A particle which cannot be divided into other constituents. More specifically, a particle whose field appears in the fundamental field equations of the unified field theory of elementary particles, in particular in the Lagrangian. For example, the → electron, the → photon, and the → quark are elementary particles, whereas the proton and neutron are not. The elementary nature of a particle can be revised depending on new observations or theories. Also called → fundamental particle.

Elementary, M.E. elementare, from M.F. élémentaire, from L. elementarius, from → element + adj. suffix -arius; → particle.

Bonyâdin, from bonyâd "basis, foundation," variant of bonlâd, from bon "basis; root; foundation; bottom" → element + lâd "root; foundation; reason, cause; wall" + adj. suffix -in.

Electrons and atomic nuclei ejected by solar flares, travelling with velocities amounting to a fraction of the velocity of light, and energies mostly in the range 1-100 million → electronvolts (eV), but occasionally as high as 15 billion eVs. Also known as solar → cosmic rays.

Energetic, from Gk. energetikos, from energe-, → energy, + -tikos a suffix, equivalent in meaning to → -ic, occurring in adjectives; → solar; → particle.

Zarrehâ plural of zarré, → particle; xoršidi, → solar; kâružmand from kâruž, → energy, + -mand possession suffix.

In quantum field theory, a particle that transfers momentum and energy between interacting objects, and is said to mediate the interaction. All four of the fundamental forces involve the exchange of one or more particles. For example, photon is the exchange particle of the electromagnetic force.

→ exchange, → particle.

Same as → elementary particle.

→ fundamental; → particle.

Fluid mechanics: In the → Lagrangian method, a particle that moves as though it is an element of fluid. The particle concept is an approach to solving complicated fluid dynamics problems by tracking a large number of particles representing the fluid. The particle may be thought of as the location of the center of mass of the fluid element with one or more property values.

→ Lagrangian; → particle.

A solid particle of → nanoscale size; e.g. a → nanodust grain.

→ nano-; → particle.

1) A unit of → matter smaller than the → atom or its main components. The term particle also includes any (currently hypothetical) new particles that might be discovered, such as the supersymmetric partners of the → quarks and → leptons and → bosons.
2) Mechanics: A material body (a body possessing mass) the size of which can be neglected in investigating its motion.
3) Grammar: In some languages, a word that has a grammatical function but does not fit into the main parts of speech (i.e. → noun, → verb, → adverb, → preposition). For example, in English, off, on, out, and up in call off, pass on, rule out, and grow up, respectively.
See also:
→ alpha particle, → antiparticle, → astroparticle physics, → beta particle, → charged particle, → elementary particle, → energetic solar particle, → exchange particle, → Lagrangian particle, → nanoparticle, → particle horizon, → particle nature, → particle physics, → relativistic particle, → resonance particle, → sink particle, → Smoothed Particle Hydrodynamics, → strange particle, → subatomic particle, → test particle, → virtual particle, → wave-particle duality.

From L. particula "little bit or part," diminutive of pars (genitive partis), from PIE base *per- "to assign, allot;" cf. Mid.Pers. pârag "gift, offering, bribe;" Mod.Pers. pâreh "gift" (→ partial); Gk. porein "to provide, give, grant," peprotai "it has been granted;" Skt. purtá- "gift, pay, reward."

Zarré, from Ar. dharrat "particle." Pârul, from pâr, → part, + -ul, → -ule.

For an observer at a given epoch t₀, the boundary between the observable and the unobservable regions of the → Universe. Therefore, the distance to the particle horizon at t₀ defines the size of the → observable Universe. Same as → cosmic horizon.

→ particle; → horizon.

A general term to describe → light involving the following phenomena: → reflection, → refraction, and → photoelectric effect. Compare → wave nature.

→ particle; → nature.

The branch of physics that deals with the smallest known structures of matter and energy in order to understand the fundamental particles and forces of nature.

→ particle; → physics.

A particle which has a speed comparable to the velocity of light.

→ relativistic; → particle.

A hadronic particle which exists for only a very brief time (10^-23 seconds) before decaying into hadrons; also called resonance. The existence of a resonance cannot be observed directly; it can only be inferred from studying the longer-lived products of its decay.

→ resonance; → particle.

In hydrodynamics codes, a way of treating a collapsing or accreting region, such as a star, as a simple → point mass. Indeed, in many situations, the scale of interest is much larger than the scale of the → accreting object itself and it would be impossible to perform the calculation otherwise. → Sinks are generally modeled as → Lagrangian particles (see, e.g., Bates et al. 1995, MNRAS 277, 362; Krumholz et al. 2004, ApJ 611, 399; Federrath et al. 2010, ApJ 713, 269).

→ sink; → particle.

A numerical method for modeling → compressible hydrodynamic flows, which uses particles to simulate a continuous fluid flow. Because the system of hydrodynamical basic equations can be analytically solved only for few exceptional cases, the SPH method provides a numerical algorithm to solve systems of coupled → partial differential equations for continuous field quantities. The main advantage of the method is that it does not require a computational grid to calculate spatial → derivatives and that it is a Lagrangian method, which automatically focuses attention on fluid elements. The equations of motion and continuity are expressed in terms of ordinary differential equations where the body forces become classical forces between particles. This method was first independently developed by Lucy (1977, AJ 82, 1013) and Gingold & Monaghan (1977, MNRAS 181, 375).

Smoothed Particle Hydrodynamics, first used by Gingold & Monaghan (1977); → smooth; → particle; → hydrodynamics.