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

A model in which a system of self-gravitating particles will gradually aggregate into larger and larger gravitationally bound groups and clusters.

→ hierarchical; → clustering.

A cosmology characterized by clustering of galaxy clusters in increasingly larger systems.

→ hierarchical; → cosmology.

A → multiple star system in which the stars can be divided into two groups, each of which traverses a larger orbit around the system's center of mass. Each of these smaller groups must also be hierarchical, which means that they must be divided into smaller subgroups which themselves are hierarchical, and so on. Hierarchical multiple systems have long-term dynamical stability.

→ hierarchical; → multiple; → system.

A cosmological → structure formation model in which the smallest gravitationally bound structures (→ quasars and galaxies) form first, followed by → groups, → galaxy clusters, and → superclusters of galaxies.

→ hierarchical; → structure; → formation.

A triple star system in which the (inner) binary is orbited by a third body in a much wider orbit. → hierarchical multiple system.

→ hierarchical; → stellar; → system.

A system in which the components are organized in increasingly larger structures.

From O.Fr. ierarchie, from M.L. hierarchia "ranked division of angels," from Gk. hierarchia "rule of a high priest," from hierarches "high priest, leader of sacred rites," from ta hiera "the sacred rites" (neut. pl. of hieros "sacred") + archein "to lead, rule."

Pâygân, from pâyé "step, rank, degree," from pây, pâ "foot, step," from Mid.Pers. pâd, pây; Av. pad- "foot" (cf. Skt. pat; Gk. pos, gen. podos; L. pes, gen. pedis; P.Gmc. *fot; E. foot; Ger. Fuss; Fr. pied; PIE *pod-/*ped-) + -gân suffix forming plural entities, from Mid.Pers. -gânag, -gâna, from Proto-Iranian *kāna-ka-.

Same as → Indian numeral system.

→ numeral; → system.

An operator which takes a real number to the same real number.

→ identity; → operator.

The minimum temperature to which a fuel must be heated in order to initiate self sustained combustion independent of another heat source.

→ ignition; → temperature.

Latin verb meaning "to command, rule, reign."

L. imperare "to command, give orders, exercise authority," from → in- "into, in" + parare "to make ready, supply, order," related to parire "produce, give birth to," from PIE root *pere- "to produce, procure;" cf. Skt. prthukah "child, calf, young of an animal;" Gk. poris "calf, bull;" Czech spratek "brat, premature calf;" Lith. periu, pereti "to brood;" O.H.G. farro, Ger. Farre, Du. varre "bull," O.E. fearr "bull;" see below for possible Iranian cognates.

Parmâtidan, from BMP plm'(d)y "to command, order," Sogd. framat- "to command," variants of farmudan, farmâyidan "to command, to order," ultimately from prefixed Proto-Ir. *fra-maH-, from *maH- "to measure," → experiment.

1a) A command or order.
1b) → imperative case.
2a) Absolutely necessary or required; extremely important.
2b) Of the nature of or expressing a command; commanding.

From L.L. imperativus "pertaining to a command," from imperat-, p.p. stem of → imperare "to command."

Parmât, noun from present stem of parmâtidan, → imperare; parmâtii, adj. from parmât.

The grammatical mood of a verb that expresses a command or a request, as in close the door!.

→ imperative; → case.

In an imperative manner.

Adverb from → imperative; → -ly.

The → numeral system consisting of the numerals 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9 which evolved into the system we use today. The Indian numerals was a place-value or positional system. The Indians were the first to develop a base 10 positional system. Same as → Hindu-Arabic numeral system.

Indian, from India, → Indus; → numeral; → system.

An optical camera equipped with a → detector which is sensitive to → infrared radiation.

→ infrared; → camera.

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.

Math.: An operator whose inverse is a differential operator.

→ integral; → operator.

To act upon one another; have a mutual or reciprocal action.

Interact, from → inter- + → act.

A binary star system in which mass transfer between the components takes place. → contact binary; → Roche lobe.

Interacting, adj. of → interact; → binary.

Galaxies that are close enough for their mutual gravitational attraction to produce perturbed shapes or extruded filaments of stellar material, called → tidal tails. Most galaxies are in clusters, and gravitational interactions between them are common.

Interacting, adj. of → interact; → galaxy.