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

In a theoretical → Hertzsprung-Russell diagram, the path taken by an evolving star.

→ evolutionary; → track.

A → differential equation composed of → continuous  → differentiable functions for which certain conditions are fulfilled. The equation M(x,y)dx + N(x,y)dy = 0 is called exact if M(x,y) and N(x,y) are continuous differentiable functions for which the following relationship is fulfilled: ∂M/∂y = ∂N/∂x, and ∂M/∂y and ∂N/∂x are continuous in some region.

→ exact; → differential; → equation.

1) The act of examining; inspection; inquiry; investigation.
2) The state of being examined.
3) The act or process of testing pupils, candidates, etc., as by questions (Dictionary.com).

Noun from → examine.

1) The act of excepting or the fact of being excepted.
2) Something excepted. 

Verbal noun of → except.

Forming an exception; not ordinary.

→ exception; → -al.

The act of removal; an excising. The surgical removal of a foreign body or of tissue.

Verbal noun of → excise.

1) The addition of → energy to an → atomic or → molecular system, → transferring it from its → ground state to an → excited state.
2) A property of an → emission nebula usually expressed by the ratio [O III] 5007Å/Hβ.

Verbal noun of → excite; → -tion.

Amount of energy (usually measured in → electron-volts) required to bring an electron from its → ground state to a given → excited state.

→ excitation; → energy.

In quantum mechanics, the energy that is necessary to change a system from a → ground state to a given → excited state; also called excitation energy.

→ excitation; → potential.

Of a gas or plasma, the temperature deduced from the → populations of atomic → excited states, as expressed by the Boltzmann formula: N_u/N_l = (g_u/g_l) exp (-ΔE/kT_ex), where N_u and N_l are the upper level and lower level populations respectively, g_u and g_l the statistical weights, ΔE = hν the energy difference between the states, k is → Boltzmann's constant, and h→ Planck's constant. The higher the energy of the occupied states, the higher the excitation temperature.

→ excitation; → temperature.

An act or instance of excluding; the state of being excluded.

Verbal noun of → exclude.

In → quantum mechanics, the principle according to which no → two → fermions of the same kind may simultaneously → occupy the same → quantum state. Also known as → Pauli exclusion principle.

→ exclusion; → principle.

A process in which an astronomical body loses mass mainly in the direction of its → equatorial regions, as opposed to → accretion.

From L. → ex- + crescere "to grow," → accretion.

An expanding → equatorial → disk or → torus of material ejected by a star. The phenomenon may result from a stellar → merger or an increase in its rate of → rotation or → stellar winds. Contrasted with → accretion disk.

→ excretion; → disk.

1) A short trip or outing to some place, usually for a special purpose and with the intention of a prompt return.
2) Physics: The displacement of a body or a point from a mean position or neutral value, as in an oscillation (Dictionary.com). → geomagnetic excursion.

From L. excursion- "a running forth, expedition," figuratively "an outset, opening," from excurrere "to run out," from → ex- "out" + currere "to run," → current.

Zocâr, literally "wander out, " from zo- "out," → ex-, + câr "to come and go, wander," related to car-, caridan "to psature, graze;" (Karingân) cârumé "excursion, walking around," (Sorxé) câqâle, (Sangesar, Semnân) ceqala "excursion;" Av. car- "to come and go, wander;" cf. Skt. car- "to move, walk, go;" Gk. pelomai "I move;" L. colere "to till, cultivate;" PIE root *k^welH- "to move, turn, wander."

The act of executing something; the state of being executed.

Verbal noun of → execute; → -tion.

1) Vigorous action; physical or mental effort.
2) The application or exercise of force, power, or faculties.

→ exert; → -tion.

1) The act or process of exhausting.
2) The state of being exhausted.
3) Extreme weakness or fatigue.
4) The total consumption of something (Dictionary.com).

→ exhaust; → -tion.

1) General: The act or process of expanding; the state or quality of being expanded. → expansion of the Universe.
2) Math.: The process of expressing a quantity, or a quantity expressed, as a sum of a series of terms. For example the expression (2x - 1)(x + 3) can be expanded to: 2x² + 5x - 3. See also → binomial expansion.

Noun from → expand.

The receding of galaxies from one another at a speed proportional to their separation, as inferred by Edwin Hubble from the observed Doppler shift of distant galaxies. → Hubble constant describes the local rate of the expansion.

→ expansion; → universe.