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

That part of → annual aberration proportional to the → eccentricity of the Earth's orbit.

→ elliptic; → aberration.

An act or instance of emigrating; a body of emigrants; emigrants collectively.

Verbal noun of → emigrate.

Of a stellar → nuclear fusion, the equation describing the → energy generation rate as a function of → density and → temperature.

→ energy; → generation; → equation.

Of a stellar → nuclear fusion, the energy produced per unit mass per unit time, usually denoted ε (erg g^-1s^-1). The general form of the energy generation equation is: ε = ε₀ρ^λT^ν, where ε₀, ρ, and λ are constants over some efficiently restricted range of → temperature T, → density ρ, and → chemical composition. The temperature exponent ν is about 4, 15, and 40 for → proton-proton chain, → CNO cycle, and → triple alpha process, respectively.

→ energy; → generation; → rate.

The physical process by which a liquid is transformed to the gaseous state, usually by means of heat; the opposite of → condensation. Also called vaporization.

From L. evaporationem (nom. evaporatio), from evaporare "to disperse in vapor," from → ex- "out" + → vapor "steam."

Boxârš, verbal noun of boxâridan "to evaporate," from boxâr, → vapor.

1) An act or instance of exploring or investigating; examination.
2. The investigation of unknown regions.
3) The process of searching for minerals by means of geological studies.
4) Medicine: An examination or investigation for diagnostic purposes, usually involving endoscopy or a surgical procedure.

Verbal noun of → explore.

A compact stellar remnant (e.g., a → white dwarf, → neutron star, or → black hole) that undergoes → inspiral into a much more massive object (→ supermassive black hole found → galactic centers). EMRIs are potential sources of low-frequency → gravitational waves. Predictions of the EMRI event rates span a wide range, from ~ 10^-9 to 10^-6 yr^-1 per galaxy (Merritt et al. 2011, Physical Review D 84, 044024). See also → resonant relaxation.

→ extreme; → mass; → ratio; → inspiral.

1) The act of federating or uniting in a league.
2) A political unit formed from smaller units on a → federal basis.

Verbal noun of → federate.

The → calibration of the flux received by a detector in terms of absolute units.

→ flux; → calibration.

The ratio of the → focal length of a reflecting surface or lens to its effective diameter, i.e. to its → aperture. The smaller the focal ratio, the smaller the image scale and the more luminous the image for a given aperture.

→ focal; → ratio.

The mass ratio of gas to dust. It amounts to approximately 100 in the → interstellar medium, but may vary in → molecular clouds and → circumstellar disks due to dust → grain evaporation, → dust settling, → condensation of gas, etc. The gas-to-dust ratio depends on the → metallicity. It is larger in galaxies with lower metallicity.

→ gas; → dust; → ratio.

1) A coming into being.
2) The → production of → energy (→ heat or → electricity).

Verbal noun of → generate.

Libration resulting from changes in the location of the observer with respect to body. More specifically, a lunar libration motion that results from the Earth based observer seeing the Moon from different directions at different times. There are three types of geometrical libration: → libration in longitude, → libration in latitude, and → diurnal libration. See also → physical libration.

→ geometric; → libration.

If a line segment is divided into a larger subsegment (a) and a smaller subsegment (b), when the larger subsegment is related to the smaller exactly as the whole segment is related to the larger segment, i.e. a/b = (a + b)/a. The golden ratio, a/b is usually represented by the Greek letter φ. It is also known as the divine ratio, the golden mean, the → golden number, and the golden section. It was believed by Greek mathematicians that a rectangle whose sides were in this proportion was the most pleasing to the eye. Similarly, the ratio of the radius to the side of a regular → decagon has this proportion. The numerical value of the golden ratio, given by the positive solution of the equation φ² - φ - 1 = 0, is φ = (1/2)(1 + √5), approximately 1.618033989. The golden ratio is an → irrational number. It is closely related to the → Fibonacci sequence.

→ golden; → ratio.

Conversion of dust grains into smaller grains due to high environmental temperatures.

→ grain; → evaporation.

The acceleration caused by the force of gravity. At the Earth's surface it is determined by the distance of the object form the center of the Earth: g = GM/R², where G is the → gravitational constant, and M and R are the Earth's mass and radius respectively. It is approximately equal to 9.8 m s^-2. The value varies slightly with latitude and elevation. Also known as the → acceleration of gravity.

→ gravitational; → acceleration.

A wavelength calibration of astronomical spectra using a helium-argon light source.

→ helium; → argon; → calibration.

→ High Energy Stereoscopic System (H.E.S.S.).

→ H.E.S.S.; → collaboration.

The process of combining with → water.

Verbal noun of → hydrate.

The process by virtue of which the original image can be created by removing the blurring and the noise that occur during image formation.

→ image; → restoration.