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

1) To give or provide the meaning of. To ascribe a particular meaning or significance to something. To try to make understandable something that is dense, complicated, or ambiguous. Related concept: → explain.
2) Physics: To relate a mathematical → formalism to physical → observables. → interpretation.

From M.E. interpreten, from L. interpretari "explain, expound, understand," from interpres "agent, translator," from → inter- + pres of uncertain origin.

Âzand, from â- nuance/intensive prefix + Mid.Pers. zand "interpretation, commentary; knowledge" (zandik "gnostic; heretic"); Av. zan- "to know, recognize;" O.Pers. dan- "to know" (Mid./Mod.Pers. dân-, dânestan "to know"); variant O.Pers./Av. xšnā- "to know, learn, come to know, recognize" (Mid./Mod.Pers. šenâxtan, šenâs- "to recognize, to know" ); cf. Skt. jñā- "to recognize, know," jānāti "he knows;" Gk. gignoskein "to know, think, judge," cognate with L. gnoscere, noscere "to come to know" (Fr. connaître; Sp. conocer); O.E. cnawan, E. know; Rus. znat "to know;" PIE base *gno- "to know" + -idan infinitive suffix; kardan verb of compound infinitives, → -ize.

1) The act of interpreting; elucidation; explication.
2) Physics: Providing relations between the mathematical symbols of a → formalism and physical → observables. → Copenhagen Interpretation.

Verbal noun of → interpret.

The dimming of light during its travel in the → interstellar medium due to absorption by → intervening → dust grains. Since shorter wavelengths are particularly affected, the spectrum of the light is increasingly dominated by the long wavelength end of the spectrum. As a result, the light is "reddened" as it travels through space. Robert J. Trumpler (1886-1956), a Swiss-American astronomer, was the first to produce a definite evidence of the existence of → interstellar extinction and to estimate its magnitude (1930).

→ interstellar; → reddening.

A graph showing the relation between → interstellar absorption (in magnitudes) and wavelength.

→ interstellar; → reddening; → curve.

The absorption of a photon by an electron in a strong electric field. → bremsstrahlung.

→ inverse; → bremsstrahlung.

A force law that applies to the → gravitational and → electromagnetic forces in which the magnitude of the force decreases in proportion to the inverse of the square of the → distance.

→ inverse; → square; → law.

A quantity used in studies of → emission nebulae to convert the → ionic abundance of a given chemical element to its total → elemental abundance. The elemental abundance of an element relative to hydrogen is given by the sum of abundances of all its ions. In practice, not all the ionization stages are observed. One must therefore correct for unobserved stages using ICFs. A common way to do this was to rely on → ionization potential considerations. However, → photoionization models show that such simple relations do not necessarily hold. Hence, ICFs based on grids of photoionization models are more reliable. Nevertheless here also care should be taken for several reasons: the atomic physics is not well known yet, the ionization structure of a nebula depends on the spectral energy distribution of the stellar radiation field, which differs from one model to another, and the density structure of real nebulae is more complicated than that of idealized models (see, e.g., Stasińska, 2002, astro-ph/0207500, and references therein).

→ ionization; → correction; → factor.

An H II region whose → exciting star(s) do not have enough → Lyman continuum photons to ionize the whole region. → density-bounded H II region.

→ ionization; → bounded; → H II region.

Same as → H II region.

→ ionized; → hydrogen; → region.

The region of the Earth's upper atmosphere containing a small percentage of free electrons and ions produced by photoionization of the constituents of the atmosphere by solar ultraviolet radiation.

→ ion + → sphere.

1) Electromagnetism: A bar of → soft iron that passes through a coil and serves to increase the → inductance of the coil.
2) The innermost part of some planets, such as Mercury, Venus, and Earth, which have a molten iron-rich core.
3) The end point in the evolution of stars with a mass above ~ 10 → solar masses. Such a star evolves in several stages over millions of years during which various → thermonuclear reactions take place in the star core. Each stage results in a core composed of heavier elements. The process ends when → silicon burning produces a core of iron-nickel. Since iron has the maximum → binding energy per → nucleon, the → nuclear fusion cannot proceed further. The iron core shrinks and heats up. It is maintained against → gravitational collapse by → electron degeneracy pressure, but it continues to grow as Si burning adds more iron. When the core reaches its → Chandrasekhar limit, it becomes unstable and undergoes the → core collapse.

→ iron; → core.

1) Lacking symmetry, even shape, formal arrangement, etc. → irregular galaxy; → irregular variable.
2) Not according to rule, or to the accepted principle, method, course, order, etc.

From O.Fr. irregulier, from M.L. irregularis, from → in- "not" + L. regularis from regula "rule," from PIE *reg- "move in a straight line," hence, "to direct, rule" (cf. Pers. râst "right, straight;" O.Pers. rāsta- "straight, true," rās- "to be right, straight, true;" Av. rāz- "to direct, put in line, set," razan- "order;" Skt. raj- "to direct, stretch," rjuyant- "walking straight;" Gk. orektos "stretched out;" L. regere "to lead straight, guide, rule," p.p. rectus "right, straight;" Ger. recht; E. right).

Bisâmân, from bi- "not, without" + sâmân "order, arrangement, disposition; boundary, limit," Lârestâni sâmon "sign or mark separating one field from another," Gilaki, Tabari šalmân "a straight peace of wood or beam, post;" Mid.Pers. sâmânak, sahmân "limit;" loaned into Arm. sahmân; cf. Skt. sīmān-, sīmā- "boundary, border, limit."

A galaxy with no spiral structure and no symmetric shape. Irregular galaxies are usually filamentary or very clumpy in shape and tend to smaller than others. Two types of irregular galaxies are defined, → Irr I galaxy and → Irr II galaxy.

→ irregular; → galaxy.

A satellite whose orbit around its planet is eccentric, inclined with respect to the equatorial plane, and relatively far from the planet. Strong solar perturbations cause the orbit to precess. → regular satellite.

→ irregular; → satellite.

A type of variable star in which variations in brightness show no regular periodicity. There are two main types, irregular eruptive variables and irregular pulsating variables.

→ irregular; → variable.

Not relevant to or connected with what is considered.

→ in- "not;" → relevant.

Not capable of returning to an original condition. → irreversible process.

Irreversible, from ir- "not," variant of → in- + → reversible.

A physical process in which the combined → entropy of the → system and the → environment increases. During an irreversible process the system is not in equilibrium at all instances of time. Most of the processes in nature are irreversible. → reversible process.

→ irreversible; → process.

Meteo.: An area of relatively strong winds that are concentrated in a narrow band in the upper troposphere of the middle latitudes and subtropical regions of the Northern and Southern Hemispheres.

→ jet; → stream.

An interplanetary mission currently in development by the → European Space Agency planned for launch in 2020. It is aimed mainly at in-depth studies of three potentially ocean-bearing satellites, → Ganymede, → Europa, and → Callisto. JUICE will complete a unique tour of the Jupiter system including several flybys of each planet-sized world, culminating with orbit insertion around Ganymede, the largest moon in the Solar System, followed by nine months of operations in its orbit. JUICE will carry the most powerful scientific payload ever flown to the outer Solar System. It consists of 10 state-of-the-art instruments plus one experiment that uses the spacecraft telecommunication system with ground-based instruments.

→ Jupiter; → icy; → explorer; → moon.