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

A mixing process in a → fluid caused by the → random relative motions due to → Brownian motion of the individual particles. See also → eddy diffusion.

→ molecular; → diffusion.

An → electromagnetic radiation emitted by → interstellar molecules through → transitions between → energy states of → molecules.

→ molecular; → emission.

The formula of a chemical compound, showing the kind and arrangement of atoms.

→ molecular; → formula.

A molecule consisting of two hydrogen atoms (H₂) which is the most abundant molecule in the Universe. Molecular hydrogen plays a fundamental role in many astrophysical contexts. It is found in all regions where → self-shielding against the ultraviolet photons, responsible for its → photodissociation, is sufficiently large. Containing two identical hydrogen atoms, H₂ is highly symmetric. Due to this property, the molecule has no → dipole moment and all → rotation-vibrational transitions within the electronic → ground state are → quadrupolar with low → spontaneous emission  → Einstein coefficient values. The molecule exists in two almost independent states, namely → orthohydrogen and → parahydrogen. H₂ may be excited through several mechanisms, including: 1) → far ultraviolet (FUV) induced → optical pumping and → collisional excitation in → photodissociation regions (PDRs) associated with → star formation; 2) → hard X-rays penetrating and heating regions within → molecular clouds, which in turn excite H₂ via collisions with electrons or hydrogen atoms; and 3) collisional excitation of H₂ due to acceleration produced by interstellar → shock waves. H₂ is thought to be chiefly produced via surface reactions on → interstellar grains, but the exact formation mechanism is not fully understood.

→ molecular; → hydrogen.

An outflow of molecular material, often → bipolar, observed in the regions of → star formation. Molecular outflows are thought to be driven by → bipolar jets from → protostars. They are probably → bow shocks which have had time to cool and be observable in molecular lines. Molecular outflows are poorly → collimated compared to the jets and tend to be slow moving (velocities 10-20 km s^-1). Some bipolar outflows may be driven by → stellar winds.

→ molecular; → outflow.

The ability of a molecular entity to be distorted from its normal shape by an external → electric field. When a molecule is subjected to an electric field there is a small displacement of electrical centers which induces a dipole in the molecule. More specifically, the molecular polarizability α is defined as the ratio of the induced → dipole moment (p) to the local electric field (E) that produces this dipole moment: α = p/E (in cgse units).

→ molecular; → polaizable; → -ity.

In → propositional logic, a → sentence containing at least one → connectives. See also → atomic proposition.

→ atomic; → proposition.

The dynamical motion of chemically bound atoms which constantly change their position with each other. The vibration of molecules is treated within → quantum theory. Therefore, the energy of molecular vibration can only take → discrete values. To a first approximation, molecular vibrations can be approximated as → simple harmonic oscillator assigned to each mode.

→ molecular; → vibration.

The sum of the atomic weights of all the atoms in a molecule.

→ molecular; → weight.

The smallest unit of a chemical compound. A molecule consist of two or more atoms held together by covalent bonds.

From Fr. moléclue, from Mod.L.molecula, diminutive of L. moles "mass, massive structure, barrier;" → -ula

A hypothetical, large molecular sphere, as a component of the → stellar atmosphere, suggested to encompass → red giant and → supergiant stars. This suggestion has offered satisfactory explanations to the spectrum of → Mu Cephei (Tsuji 2003), but it is not clear whether MOLspheres are common features of the atmospheres of all such stars.

MOL, from → molecular; → sphere.

1) Physics: An expression involving the → product a → quantity, such as → force or → mass, and its perpendicular → distance from a reference point, such as → moment of force (or → torque), → moment of inertia, → moment of momentum.
2) Statistics: For a → random variable X, its nth moment about the mean is the expected value of the nth power of X, where n is a positive integer. The nth moment of the deviation of X from the mean is called the nth central moment. The first moment is the → mean, the second central moment is the → variance.
3) A short indefinite period of time.

From O.Fr. moment, from L. momentum "movement, moving power," also "instant, importance," contraction of *movimentum, from movere, → move.

Gaštâvar literally "that which makes turn, turning agent," from gašt "turning," past stem of gaštan, gardidan "to turn, to change" (Mid.Pers. vartitan; Av. varət- "to turn, revolve;" 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") + âvar agent noun of âvardan "to bring; to cause, produce" (Mid.Pers. âwurtan, âvaritan; Av. ābar- "to bring; to possess," from prefix ā- + Av./O.Pers. bar- "to bear, carry," bareθre "to bear (infinitive)," bareθri "a female that bears (children), a mother;" Mod.Pers. bordan "to carry;" Skt. bharati "he carries;" Gk. pherein; L. fero "to carry").
Dam, "breath; moment; time," from Mod./Mid.Pers. damidan "to breathe, blow;" Av. dāδmainya- "blowing up," Skt. dahm- "to blow," dhámati "blows," Gk. themeros "austere, dark-looking," Lith. dumti "to blow," PIE dhem-/dhemə- "to smoke, to blow".

A measure of a force's tendency to cause a body to → rotate about a specified → axis. It is given by the force times the perpendicular → distance of the → line of action from the axis. Same as → torque

→ moment; → force.

A quantity which is a measure of the inertness of a body in rotatory motion about an axis. It is equal to the sum of the products of the masses of all particles of the body by the squares of their distances from this axis: I = Σm_ir_i², where r_i is the distance of the particle of mass m_i from the axis. Moment of inertia depends only upon the shape of the body and the arrangement of its mass with respect to the axis. For a solid sphere it is (2/5)MR². Moment of inertia is used in place of mass in problems involving rotation. Thus, the → angular momentum is Iω and → angular kinetic energy is (1/2)Iω², where ω is → angular velocity.

→ moment; → inertia.

Same as → angular momentum.

→ moment; → momentum.

In → Newtonian mechanics, the momentum p of a body with → mass m and → velocity v is the product of these two quantities: p = mv. Momentum usually means → linear momentum as opposed to → angular momentum.

From L. momentum "movement, moving power," from movere "to move," → move.

Jonbâk, from jonb present stem of jonbidan "to move" (Mid.Pers. jumbidan, jumb- "to move," Lori, Laki jem "motion," related to gâm "step, pace;" O.Pers. gam- "to come; to go," Av. gam- "to come; to go," jamaiti "goes," gāman- "step, pac;" Mod.Pers. âmadan "to come;" Skt. gamati "goes;" Gk. bainein "to go, walk, step," L. venire "to come;" Tocharian A käm- "to come;" O.H.G. queman "to come;" E. come; PIE root *gwem- "to go, come") + -âk noun suffix.

1) Philo.: The doctrine that reality consists of an unchanging whole in which change is mere illusion. → pluralism.
2) Philo.: The doctrine that the person consists of only a single substance, or that there is no crucial difference between mental and physical events or properties.
3) The attempt to explain anything in terms of one principle only. → dualism, → materalism, → idealism (Dictionary.com).

→ mono-; → -ism.

1) (v.) To watch closely or evaluate something on a constant or regular basis.
To oversee, supervise, or regulate.
2) (n.) A video device that displays data or images generated by a computer or terminal.

From L. monitor "one who reminds, admonishes, or checks," from monere "to remind, warn, advise," related to memini "I remember, I am mindful of," mens "mind," from PIE base *men- "to think;" Pers. cognates under → idea.

Pahregar "watch, guard," agent noun from pahré (Dehxodâ) "watch, guarding," from Mid.Pers. pahr, pahrag "guard;" Av. pāθra.vant "guard, watchman," from *pāθra-, from Av. pā- "to protect," pāti "guards," nipā(y)- (with → ni-) "to watch, observe, guard," nipātar- "protector, watcher," nipāθri- "protectress;" cf. Skt. pā- "to protect, keep," tanû.pā- "protecting the body," paś.pā- "shepherd;" Gk. poma "lid, cover," poimen "shepherd;" L. pascere "to put out to graze," pastor "shepherd;" Lith. piemuo "shepherd;" PIE base *pā- "to protect, feed."
Pahridan verb from pahr, as above.

1) A combining form meaning "alone, single, one," as in monochromatic, Monoceros, monotonic.
2) In chemistry applied to compounds containing one atom of a particular element (monohydrate).

From Gk. mono-, from monos "single, alone," from PIE base *men- "small, isolated," also represented by Gk. manos "rare, sparse."

Tak "single, alone", from Mid.Pers. tak "single, alone," maybe related to tâk, tâi "unit, piece."
Yek "one, alone," from Mid.Pers. êwak (Proto-Iranian *aiua-ka-); O.Pers. aiva- "one, alone;" Av. aēuua- "one, alone;" cf. Skt. éka- "one, alone, single; " Gk. oios "alone, lonely;" L. unus "one;" Ger. ein; E. one.
Yektâ-, from yek, as above, + tâ "fold, plait, ply; piece, part," also a multiplicative suffix; Mid.Pers. tâg "piece, part."
Mono-, loan from Gk., as above.

The Unicorn. An extensive but faint constellation across the celestial equator , at 7h right ascension, 4° south declination. Abbreviation: Mon; genitive: Monocerotis.

Monoceros "the unicorn," from O.Fr., from L., from Gk. monokeros, from → mono- "single" + keras "horn," kara "head," karena "head, top;" cf. Pers. soru "horn," sar "head;" L. cornu "horn," cerebrum "brain;" Skt. śiras- "head, chief;" O.E. horn "horn of an animal," also "wind instrument" (originally made from animal horns), from P.Gmc. *khurnaz (Ger. Horn, Du. horen), from PIE *ker- "head, horn, top, summit."

Takšâx, from tak "single" → mono- + šâx "horn, branch" (Mid.Pers šâk; cf. Skt. sakha- "a branch, a limb;" Arm. cax; Lith. šaka; O.S. soxa; PIE *kakhâ "branch").