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

A diverging lens having one surface convex and the opposite surface concave.

→ convex; → concave; → lens.

To move by argument or evidence to belief, agreement, consent, or a course of action (Dictionary.com).

From L. convincere "to overcome decisively," from the intensive prefix → com- + vincere "to conquer, overcome, defeat," from PIE root *weik- "to fight, conquer."

Paruxidan, from Parthian Mid.Pers. prywx- "to conquer, overcome," from prefix pari- + yux "yoke;" Av. yuj- "to harness, yoke," variants yuj, juh, jut, jot; Mid.Pers. jug, ayoxtan "to join, yoke;" Pers. (+*pari-) piruz, pêrôz "victorious," → yoke.

Capable of causing someone to believe that something is true or real (OxfordDictionaries.com).

→ convince; → -ing.

The act of convoking. The state of being convoked.

Verbal noun of → convoke.

To call together; summon to meet or assemble (Dictionary.com).

M.E., from M.Fr. convoquer, from L. convocare "to call together," from → con- "together," + vocare "to call," from vox, → voice.

Hamvacidan, from ham-, → com-, + vac "word," → voice, + -idan infinitive suffix.

1) A mathematical combination of two functions which involves multiplying the value of one function at a given point with the value of another function, the weighting function, for a displacement from that point and then integrating over all such displacements. The process is repeated for every point of the function. Convolution expresses how the shape of a function is altered by the other. In mathematical terms, the convolution of two functions f(x) and g(x) is defined by: f*g = ∫f(u)g(x - u) du, integral from -∞ to +∞.
2) Astro.: Convolution describes how an instrument, through its transfer function, affects an input signal. → deconvolution.

Verbal noun of → convolve.

A theorem stating that the → Fourier transform of the convolution of f(x) and g(x) is equal to the product of the Fourier transform of f(x) and g(x): F{f*g} = F{f}.F{g}.

→ convolution; → theorem.

1) To roll or wind together.
2) To bring about a → convolution.

From L. convolvere "to roll together," from → com- "together" + volvere "to roll, turn," PIE base *wel- "to turn, revolve;" cf. Skt. valati "he turns," ulba- "womb, vulva," Gk. eilyein "to roll, wrap, fold."

Hamâgiš, from ham- "together", → com-, + âgišidan "to entwine, to twist" (Dehxodâ), from Mid.Pers. gyš- "to bind, tie," hangyš- "to fasten to;" cf. Sogd. patigyš- "to imprison, confine;" Proto-Ir. *kaš- "to imprison" (Cheung 2007).

An identifier file that a website automatically places in the user's computer hard drive. The cookie is used by the website to identify that a user has been on the website previously. Users concerned about privacy may disable cookies in their browser's setting.

From Du. koekje "little cake," diminutive of koek "cake," from M.Du. koke, akin to cake, M.E., from O.N. kaka (O.H.G. kuocho "cake"), any relation with Pers. kâk "biscuit; dry bread"? (loaned in Ar. ka'k).

Moderately cold.

M.E., from O.E. col, PIE base *gel- "cold, to freeze."

Sard "cold, cool," from Mid.Pers. sart, Av. sarəta- "cold," Skt. śiśira- "cold," Ossetian sald "cold," L. calidus "warm," Lith. šaltas "cold," Welsh clyd "warm," PIE *keltos- "cool".

A highly unstable, → very massive star lying just below the empirical upper luminosity boundary in the → H-R diagram (→ Humphreys-Davidson limit) with spectral types ranging from late A to M. Cool hypergiants very likely represent a very short-lived evolutionary stage, and are distinguished by their high → mass loss rates. Many of them also show photometric and spectroscopic variability, and some have large → infrared excesses and extensive circumstellar ejecta. The evolutionary state of most of these stars is not known but they are all → post-main-sequence stars (Humphreys, 2008, IAUS 250).

→ cool; → hypergiant.

An agent of → cooling process.

→ cooling.

1) The process of losing heat; a falling temperature.
2) The participial adjective of to cool.

→ cool; → -ing.

A phenomenon observed in a → cluster of galaxies, whereby the cluster core loses energy via X-ray radiation because of the collisions between the gas particles. The radiation rate is proportional to the square of the density, and the → cooling time, which remains in the outer parts too large, becomes smaller than the → Hubble time in the core. As a result, the central regions of clusters of galaxies cool down; and since in the center of a cluster gas pressure and gravitational attraction are in equilibrium, the gas density has to rise to maintain the pressure necessary for supporting the outer layers of gas. To cause its density to rise, the cooled gas has to flow inward. As the densest gas, which cools quickest, is already concentrated in the center of the cluster, the inward flow will start at the center, soon followed by the outer layers. This flow of gas is called the cooling flow. Cooling flows are moderated through feedback due to the → supermassive black hole in the nucleus of the central galaxy. The gas inflow to the center fuels the → active galactic nucleus (AGN). The latter then heats again the gas through its → radio jets.

→ cooling; → flow.

The spectral → emission line through which the → colling process takes place.

→ cooling; → line.

The process of → radiative cooling in which the → temperature of an astrophysical system decreases due to the radiation of a major → emission line. For example, → molecular → emission at → millimeter wavelengths and → submillimeter wavelengths results in decreasing the temperature in molecular clouds. At temperatures less than 300 K, the main → coolant is the → carbon monoxide (CO) molecule which contains most of the carbon. Similarly, the → [C II] line is a major coolant in → photodissociation regions. See also → line cooling, → cooling time.

→ cooling; → process.

1) The time in which a → white dwarf cools to half its temperature. It depends on the composition, the mass, and the actual luminosity at some point in time. Cooling time is given by the relation: t = 8.8 × 10⁶ (12/A) (M)^5/7 (μ/2)^-2/7 (L)^-5/7 in years, where M and L are mass and luminosity in solar units, A the mean → atomic mass, and μ the → mean molecular weight (Iben & Tutukov, 1984, ApJ 282, 615). See also → Mestel theory; → white dwarf crystallization.
2) The time needed by a → plasma to radiate its thermal energy. The cooling time is directly proportional to the square root of the temperature and inversely proportional to the density. It turns out that for the → intercluster medium in a → cluster of galaxies this time is longer than the → age of the Universe. At the centers of some clusters, however, the cooling time is smaller than the age of the Universe due to the presence of a → cooling flow.

→ cooling; → time.

1) Any of a series of numbers which, in relation to a given → frame of reference, locate a point in space. See also: → astronomical coordinates→ canonical coordinates→ Cartesian coordinates→ celestial coordinates→ cylindrical coordinates→ equatorial coordinates→ Galactic coordinates→ generalized coordinates→ polar coordinates→ spherical coordinates→ precessed coordinates→ topocentric coordinates.
2) To place in the same order or rank; to organize in a concordant operation.

From L. co- "together," → com- + orinatus, p.p. of ordinare "to put in order, arrange," from ordo "order."

Hamârâ, from ham- "together," → com- + ârâ stem of ârâstan "to arrange, to set in order, adorn," Mid.Pers. ârây-, ârâstan "to arrange, adorn," O.Pers. râs- "to be right, straight, true," râsta- "straight, true" (Mod.Pers. râst "straight, true"), râd- "to prepare," Av. râz- "to direct, put in line, set," Av. razan- "order," Gk. oregein "to stretch out," L. regere "to lead straight, guide, rule," p.p. rectus "right, straight," Skt. rji- "to make straight or right, arrange, decorate," PIE base *reg- "move in a straight line."

Math: A system for locating each point in space by a set of numbers.
Astro: Values in a reference system used to relate the position of a body on the celestial sphere. Four main coordinate systems are utilized in astronomy: the equatorial, horizontal, ecliptic, and galactic coordinates systems.

→ coordinate; → system.

In relativity, the proper time in the specified reference frame. Because of time dilation, this may differ from the time experienced by any participant in the events being considered. It is the time basis (or coordinate) to be used in the theory of motions referred to this system.

→ coordinate; → time.