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

The act or process of converting; state of being converted. → convert.

Verbal noun of → convert.

Hâgard, from hâ- prefix denoting "reversal; to," sometimes creating nuance [Dehxodâ], + gard present stem of gardidan, gaštan "to change; to turn;" Mid.Pers. vartitan; Av. varət- "to turn, revolve;" cf. Skt. vrt- "to turn, roll," vartate "it turns round, rolls;" L. vertere "to turn;" O.H.G. werden "to become;" PIE base *wer- "to turn, bend."

1) A numerical factor that, by multiplication or division, translates one unit or value into another.
2) In → molecular cloud studies, a factor used to convert the → carbon monoxide (CO) line intensity to → molecular hydrogen (H₂) → column density; usually denoted X_CO = I(CO) / N(H₂). This useful factor relates the observed CO intensity to the cloud mass. A general method to derive X_CO is to compare the → virial mass and the ¹²CO (J = 1-0) luminosity of a cloud. The basic assumptions are that the CO and H₂ clouds are co-extensive, and molecular clouds obey the → virial theorem. However, if the molecular cloud is subject to ultraviolet radiation, selective → photodissociation may take place, which will change the situation. Moreover, molecular clouds may not be in → virial equilibrium. To be in virial equilibrium molecular clouds must have enough mass, greater than about 10⁵ solar masses. The way → metallicity affects X_CO is a matter of debate, and there is no clear correlation between X_CO and metallicity. Although lower metallicity brings about higher ultraviolet fields than in the solar vicinity, other factors appear to be as important as metallicity for the determination of X_CO. In the case of the → Magellanic Clouds, X_CO(SMC) = 14 ± 3 × 10²⁰ cm^-2 (K km s^-1)^-1, which is larger than X_CO (LMC) = 7 ± 2 × 10²⁰ cm^-2 (K km s^-1)^-1. An independent method to derive X_CO is to make use of the gamma ray emission from a cloud. The flow of → cosmic ray protons interacts with interstellar low-energy hydrogen nuclei in clouds creating neutral → pions. These pions quickly decay into two gamma rays. It is therefore possible to estimate the number of hydrogen nuclei and hence the cloud mass from the gamma ray counts. Such a gamma-ray based conversion factor is estimated to be 2.0 × 10²⁰ cm^-2 (K km s^-1)^-1 for Galactic clouds, in good agreement with the result obtained from the virial method. However, the gamma ray flux is not well known in general, so this method is uncertain as well. See, e.g., Fukui & Kawamura, 2010 (ARAA 48, 547).

→ conversion; → factor.

1) To change units of one measuring or calculating system into units of another.
2) To transform from one material or state to another.

M.E. converten, O.Fr. convertir, from L. convertere "to turn around, transform," from → com- "together" + vertere "to turn;" cognate with Mod.Pers. gardidan "to change, to turn," → conversion.

Compound verb from hâgard, → conversion, + kardan "to do, to make," → -ize.

A device that receives data in one form and converts it to another. → analog-to-digital converter.

→ convert; → -er.

Having a surface that is curved or rounded outward.

From M.Fr. convexe, from L. convexus "vaulted, arched," p.p. of convehere "to bring together," from → com- "together" + vehere "to bring" (cf. Skt. vah- "to carry, lead," vahitra "vehicle," Av. vazaiti "to lead," Mid.Pers. waz-, wazidan "to carry away," Gk. oxos "chariot," PIE base *wegh- "to go, carry, drive").

Kuž "humped," Mid.Pers. kôf "hill, mountain; hump" (Mod.Pers. kuh, "mountain"), kôfik "humpbacked," O.Pers. kaufa-, Av. kaofa- "mountain."

A lens that converges an incident beam of light to a focus.

→ convex; → lens.

A → spherical mirror with a reflecting surface curved outward, that is toward the object.

→ convex; → mirror.

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.