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

A collaborative project between → NASA and → ESA to develop and operate a space-based gravitational wave detector sensitive at frequencies between 0.03 mHz and 0.1 Hz. LISA detects gravitational-wave induced strains in → space-time by measuring changes of the separation between fiducial masses in three spacecraft 5 million km apart. Ultimately, NASA and ESA decided in 2011 not to proceed with the mission. LISA was not the highest ranked mission in the 2010 Decadal Survey and funding constraints prevented NASA from proceeding with multiple large missions (http://lisa.nasa.gov). → LISA pathfinder.

→ laser; → interferometer; → space; → antenna.

Present but not visible, apparent, or actualized; existing as potential (Dictionary.com). → latent heat.

From L. latentem (nominative latens), pr.p. of latere "to lie hidden."

Nahân "concealed, hid; clandestine;" Mid.Pers. nihân "secrecy, a secret place, a hiding place," nihânik "concealed;" Av. niδāti- "deposing, deposit."

The amount of → thermal energy that is absorbed or released by a unit amount of a substance in the process of a phase change under conditions of constant pressure and temperature.

→ latent; → heat.

An important quantity in the characterization of → gravitational lensing. The lensing potential is obtained by projecting the three-dimensional Newtonian potential on the lens plane and by properly re-scaling it. It is a two-dimensional analog to the → gravitational potential.

→ lensing; → potential.

An observed increase in the intensity of radio, extreme ultraviolet, or X-radiation from the Sun from its center to its limb.

→ limb; → brightening.

A measure of the total effect of an absorption or emission line. The line intensity is equal to the integration of the absorption coefficient over the entire shape of the absorption line.

→ line; → intensity.

A measure of the amount of light that a point source radiates in a given direction. It is expressed by the luminous flux per unit leaving the source in the direction per unit of solid angle.

→ luminous; → intensity.

Strength of a magnetic field at a point, denoted H. The force which could be exerted on unit north magnetic pole situated at that point. Measured in oersteds. Same as → magnetic field strength.

→ magnetic; → intensity.

In → magnetohydrodynamic (MHD) treatment of → plasmas, that component of the → Lorentz force which is directed toward the centre of curvature of the → magnetic field lines and thus acts to straighten out the field lines. The Lorentz force can be decomposed into two components orthogonal to the magnetic field: j× B = (B . ∇) B / μ₀ - ∇ (B² / 2μ₀), where j is the → current density, μ₀ is the → magnetic permeability of free space, and B is the → magnetic flux density. The left side term is the Lorentz force, the first term on the right side is the magnetic tension and the second term the → magnetic pressure.

→ magnetic; → tension.

A vector field A defined so that the → magnetic field  B is given by its → curl: B = ∇ x A.

→ magnetic; → vector; → potential.

The abstract tensor operation which is computed in a particular → reference frame using the → metric components. The metric tensor defines magnitude and direction of vectors about a point.

→ metric; → tensor.

A hand covering enclosing the four fingers together and the thumb separately (Dictionary.com). → glove, → mitt.

M.E. miteyn, from M.Fr., O.Fr. mitaine, from from O.Fr. mite "mitten," and from M.L. mitta.

Dasmtuž, literally "hand-shoe" (Ger. Handschuh, "glove," literally "hand-shoe"), from dast, → hand, + Muž, variant of Pers. muzé "shoe," Mid.Pers. môg "shoe, boot;" cf. Pers. paymôz- / paymôxtan "to dress;" Av. (+ pati-paitišmaoc- "to shoe;" Proto-Ir. *(h)mauc-? "to dress, clothe" (Cheung 2007).

A potential in a field of force obeying the inverse-square law such as → gravitational potential.

→ Newtonian; → potential.

Math.: The fact that no → solution exists for a given → problem. In mathematics, nonexistence usually is a matter of impossibility.

→ non-; → existence.

The property possessed by a round body that is flattened at the poles.

Noun from → oblate.

Many times; frequently; in many cases.

M.E. oftin, from O.E. oft "often, frequently," akin to cognates: O.Frisian ofta, Danish ofte, O.H.G. ofto, Ger. oft, of unknown origin.

Basvân, from bas "many, much," → frequency, + -vân on the model of farâvân, → abundance.

Having very great or unlimited power or authority.

→ omni-; → power.

(polar flattening) The ratio of the difference between equatorial and polar diameters to the equatorial diameter. A sphere has an oblateness of 0; an infinitely thin disk has an oblateness of 1 (Ellis et al., 2007, Planetary Ring Systems, Springer).

→ optical; → oblateness.

The maximum number of the indices (→ index) of a tensor.

→ order; → tensor.

An antenna comprising a parabolic reflector with a receiving and/or transmitting element positioned at or near its focal point.

→ parabolic; → antenna.