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

A galaxy, usually young, which has a relatively important gas content.

→ gas; → rich; → galaxy.

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) Existing in the → state of a gas.
2) Pertaining to or having the characteristics of gas.

→ gas; → -eous.

An → isotope separation process using the different diffusion speeds of → atoms or → molecules for separation. This process is used to divide → uranium hexafluoride (UF₆) into two separate streams of U-235 and U-238. Before processing by gaseous diffusion, uranium is first converted from → uranium oxide (U₃O₈) to UF₆. The UF₆ is heated and converted from a solid to a gas. The gas is then forced through a series of compressors and converters that contain porous barriers. Because uranium-235 has a slightly lighter isotopic mass than uranium-238, UF₆ molecules made with uranium-235 diffuse through the barriers at a slightly higher rate than the molecules containing uranium-238. At the end of the process, there are two UF₆ streams, with one stream having a higher concentration of uranium-235 than the other (EVS, a Division of Argonne National Laboratory).

→ gaseous; → diffusion.

An → H II region, a → planetary nebula, or a → supernova remnant.

→ gaseous; → nebula.

1) (n.) A standard of measure or measurement, size, or quantity.
2) Any of a wide variety of devices or instruments used for measuring a parameter or characteristic of an object, such as its dimension, quantity, or mechanical accuracy.
3) Physics: One of the family of choices for a constant in the expression of → potential energy in a central force field. Force is connected with potential energy by the relation F = - ∂U/∂r, U = ∫F.dr. The upper limit in the integral can be chosen arbitrarily. The potential energy is usually considered zero at infinity.
4) (v.) To determine the exact dimensions, capacity, quantity, or force of; measure.

From Fr. jauge "gauging rod," perhaps from Frankish galga "rod, pole for measuring;" cf. O.N. gelgja "pole, perch;" O.H.G. galgo; Lith. zalga "pole, perch;" Arm. dzalk "pole;" E. gallows; see below.

Gaz "a yard for measuring cloth; a length of 24 finger-breadths, or six hands; the tamarisk-tree," from Mid.Pers. gaz "tamarisk," may be of the same origin as gauge. In verbal form with kardan "to do, to make" (Mid.Pers. kardan; O.Pers./Av. kar- "to do, make, build;" Av. kərənaoiti "he makes;" cf. Skt. kr- "to do, to make," krnoti "he makes, he does," karoti "he makes, he does," karma "act, deed;" PIE base k^wer- "to do, to make").

A class of elementary particles that includes the gluon, photon, W⁺, W^-, and Z⁰ particles, each having an integral spin.

→ gauge; → boson.

The mathematical group associated with a particular set of gauge transformations.

→ gauge; → group.

The invariance of any field theory under gauge transformation.

→ gauge; → invariance.

A principle underlying the quantum-mechanical description of the three non-gravitational forces. It allows a system to behave in the same way even though it has undergone various transformations. The earliest physical theory which had a gauge symmetry was Maxwell's electrodynamics.

→ gauge; → symmetry.

A field theory in which it is possible to perform a transformation without altering any measurable physical quantity.

→ gauge; → theory.

A change of the fields of a gauge theory that does not change the value of any measurable quantity.

→ gauge; → transformation.

A technique in which the thickness, density, or quantity of a material is determined by the amount of radiation it absorbs.

Gauging, from → gauge + → -ing, suffix of nouns formed from verbs, expressing the action of the verb or its result.

Gazkard, from gaz, → gauge, + kard past stem of kardan "to do, make," → gauge.

In the atomic theory of spectral line formation, a quantum mechanical correction factor applied to the absorption coefficient in the transition of an electron from a bound or free state to a free state.

Gaunt, after John Arthur Gaunt (1904-1944), English physicist born in China, who significantly contributed to the calculation of continuous absorption using quantum mechanics; → factor

The c.s.g. unit of magnetic flux density (or magnetic induction), equal to 1 maxwell per square centimeter, or 10^-4 tesla.

Named after the German mathematician and physicist Carl Friedrich Gauss (1777-1855).

The total electric flux ψ out of an arbitrary closed surface in free space is equal to the net charge within the surface divided by the → permittivity. In differential form: ∇ . E = ρ/ε₀, where ρ is the → charge density and ε₀ the permittivity. The integral form of the law: ∫E . dS = Q/ε₀ (closed surface integral). This is one of the four → Maxwell's equations.

→ gauss; → law; → electricity.

The → magnetic flux through an arbitrary closed surface equals zero. Mathematically, in differential form: ∇ . B = 0 and in integral form: Φ_B = ∫B.dS = 0 (closed surface integral). This is one of the four → Maxwell's equations. This law expresses the fact that there are no free magnetic poles (→ monopoles) in nature and that all the lines of force of a magnetic field are closed curves.

→ gauss; → law; → magnetism.

If a → polynomial with → integer coefficients can be → factorized into polynomials with → rational number coefficients, it can be factorized using only integers.

→ Gaussian; → lemma.

The total normal induction over any closed surface drawn in an electric field is equal to 4π times the total charge of electricity inside the closed surface. Gauss's theorem applies also to other vector fields such as magnetic, gravitational, and fluid velocity fields. The theorem can more generally be stated as: the total flux of a vector field through a closed surface is equal to the volume → integral of the vector taken over the enclosed volume. Also known as → divergence theorem, Ostrogradsky's theorem, and Gauss-Ostrogradsky theorem.

→ gauss; → theorem.

Of or relating to Carl Friedrich Gauss or his mathematical theories of magnetism, electricity, astronomy, or probability. → Gaussian distribution; → Gaussian profile.

→ gauss.