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

A tensor whose components are distinguished by → superscript indices.

→ contra-; + variant; → variance; → tensor.

1) To give or supply (help, money, etc.) for a common purpose.
2) To provide (ideas, suggestions, work, etc.) for a common goal, such as an article, a book.

From L. contributus, p.p. of contribuere "to bring together, unite, collect," from → com- + tribuere "to pay, assign, allot," from tribus "tribe."

Hambâžidan, from ham- "together," → com-, + bâž "tribute, toll, impost," → distribute.

1) The act of contributing.
2) Something contributed.

Verbal noun of → contribute.

In general, mass motions within a → fluid resulting in transport and mixing of the properties of that fluid when the temperature gradient exceeds some critical value. Convection, along with → conduction and → radiation, is a principal means of → energy transfer. → Schwarzschild's criterion.

From L. convectionem "the act of carrying," from p.p. stem of convehere "to carry together," from → com- "together" + vehere "to carry," 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"

Hambaz, from ham- "together" + baz "to carry, move," → evection.
Hambord, from ham- "together," → com- + bord, from bordan "to carry," Mid.Pers. burdan, O.Pers./Av. bar- "to bear, carry," barəθre "to bear (infinitive)," Skt. bharati "he carries," Gk. pherein, L. fero "to carry," PIE base *bher- "to carry."

Same as → convective zone.

Of or relating to → convection.

A body of → fluid which transports energy through the → convection process.

→ convective; → cell.

Meteorology: A cloud that owes its vertical development, and possibly its origin, to convection.

→ convective; → cloud.

The central region of a → massive star where → convection prevails due to steep gradient of temperature relative to pressure.

→ convective; → core.

1) A → convective zone situated beneath the surface of solar type stars.
2) Stellar models show that → massive stars also possess an outer convective envelope encompassing several percent of the stellar radius. Fast rotation amplifies the size of the convective envelope in → OB stars and developes anisotropic convective envelops (Maeder et al. 2008, A&A 479, L37).

→ convective; → envelope

In a → massive star, penetration of the upper layers of the → convective core into the → radiative zone due to → turbulence effects. The enlargement of the convective core results in more luminous stars in theoretical models.

→ convective; → overshooting.

A common feature of the atmosphere that ranges from small-scale → vortices such as → dust devils, to large-scale systems such as → cyclones.

→ convective; → vortex.

A zone inside a star in which → convection takes place; the central → core in → massive stars and the zone underneath → photosphere in low mass stars like the Sun. Recent works predict the presence of a thin convection zone in sufficiently massive main sequence stars which originates from the iron opacity and partial helium ionization. See also → iron convection zone.

→ convective; → zone.

1) General: To tend to meet in a point; incline toward each other.
2) Math: (of an infinite series) to have a finite sum. (of an improper integral) to have a finite value.

From L.L. convergere "to incline together" from → com- "together" + vergere "to bend."

Hamgerâyidan, from ham- "together," → com- + gerâyidan "to incline toward, verge on; to intend," Mid.Pers. grayidan "to lean, incline; to intend, desire," → diverge.

1) General: Act or state of converging.
2) Math: The property of a → sequence or → series which ensures that it will approach a definite → finite limit. See also: → divergence.

From converg-, from → convergent + -ence, equivalent to → -ance.

Hamgerâyi, verbal noun from hamgerâyidan, → converge.

Coming together, as a light beam after passing through a convex lens which brings the beam into the focus.

Verbal ddj. from → converge.

A concave mirror that reflects a parallel beam into a convergent beam.

From → converge + → -ing; → mirror.

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.