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

For a given component in a → gas mixture, the change in → Gibbs free energy (G) with respect to change in amount of the component (n), when pressure, temperature, and amounts of other components remain constant: ∂G/∂n. Components are in equilibrium if their chemical potentials are equal.

→ chemical; → potential.

1) The state of being complete and entire.
2) Logic: The condition of a → formal system if every → valid  → inference is → provable by means of the rules of the system.

From → complete + → -ness.

In photometric studies of a → population of astronomical objects (usually stars or galaxies), the magnitude that represents the faintest members of the population.

→ completeness; → magnitude.

1) Agreement or accordance with facts, form, or characteristics previously shown or stated.
2) Agreement or harmony between parts of something complex; compatibility.
3) Physics: Degree of → viscosity or firmness.
4) The state or quality of holding or sticking together and retaining shape.
5) Conformity with previous attitudes, behaviour, practice, etc. (TheFreeDictionary.com).

→ consist; → -ency.

1) Showing consistency; not self-contradictory.
2) In agreement or harmony (with); accordant.
3a) Maths.: The quality of an equation if it has a solution.
3b) Maths.: (of a set of equations) Satisfied by at least one solution.
4) Logic: (of a formal system) Not permitting the deduction of a contradiction from the axioms (TheFreeDictionary.com).

→ consist; → -ent.

Hânesgâr, from hânes- present stem of hânesidan, → consist, + -gâr agect noun suffix (on the model of sâzgâr), → -or.

1) Something that is contained.
2) The topics or matter treated in a written work.

M.E., from L. contentum from p.p. of continere, → contain.

A tensor whose components are distinguished by → superscript indices.

→ contra-; + variant; → variance; → tensor.

A tensor whose components are distinguished by → subscript indices.

→ covariant; → tensor.

One of the simplest kinds of antenna which is connected at the center to a radio-frequency feed line for transmitting or receiving radio frequency energy. It differs from the dish antenna in that it consists of many separate antennas that collect energy by feeding all their weak individual signals into one common receiving set.

→ dipole; → antenna.

A measure of the extent to which mass has been shifted from the polar regions of a (spinning) body toward its equator (Ellis et al., 2007, Planetary Ring Systems, Springer).

→ dynamic; → oblateness.

A mathematical entity describing the → curvature of → space-time in → Einstein's field equations, according to the theory of → general relativity. It is expressed by G_μν = R_μν - (1/2) g_μνR, where R_μν is the Ricci tensor, g_μν is the → metric tensor, and R the scalar curvature. This tensor is both symmetric and divergence free.

Named after Albert Einstein (1879-1955); → tensor.

The strength of an electric field at any point as measured by the force exerted upon a unit positive charge placed at that point.

→ electric; → intensity.

The amount of → work required to move a unit → electric charge from → infinity to a specific point against an → electric field. The → SI unit of electric potential is → joules per → coulomb, otherwise known as → volt.

→ electric; → potential.

A potential φ defined so that the → electric field  E is expressed by a combination of its → gradient and the variation of the → magnetic vector potential over time: E = -∇φ -∂A/∂t.

→ electric; → scalar; → potential.

The combination of both → electric scalar potential and → magnetic vector potential.

→ electromagnetic; → potential.

A tensor (T_μν) related to the → Einstein tensor through → Einstein's field equations. The energy-momentum tensor depends upon the distribution of the → energy and → matter in the space.

→ energy; → momentum; → tensor.

An intellectual movement in Europe during the 17th and 18th centuries celebrating human reason and scientific thought as the instruments of progress and subjecting conventional ways of thinking to rigorous critique. The Enlightenment culminated with the writings of Jean-Jacques Rousseau (1712-1778) and the Encyclopédistes, the philosophy of Immanuel Kant (1724-1804), and the political ideals of the French and American Revolutions, while the precursor in science and philosophy included Francis Bacon (1561-1626), René Descartes (1596-1650), Isaac Newton (1643-1727), John Locke (1632-1704), and Thomas Hobbes (1588-1679).

From enlighten, from en- + → light + -en + → -ment.

Asr, → age; rowšangari, noun from rowšangar "enlightener," from rowšan "light, bright, luminous, splendid," cognate with L. lux, → bright, + -gar a suffix of agent nouns, → -or.

An imaginary surface surrounding a body, or group of bodies, over which the gravitational field is of constant strength and, at all points, is directed perpendicular to the surface. For a single star the surface is spherical. In a close binary system the equipotential surface of the components interact to become hourglass-shaped. → Roche lobe; → Lagrangian points.

From → equi-; → potential; → surface.

A space project, initially → LISA, consisting of a configuration of three satellites, aimed to detect low frequency → gravitational waves that cannot be measured by ground-based detectors. The detection range will be from about 0.1 milliHz to 1 Hz. One "mother" and two "daughter" spacecrafts will be brought into an orbit around the Sun, which is similar to the Earth's orbit. The satellites will fly in a near-equilateral triangle formation, with a constant distance of one million km between, following the Earth along its orbit at a distance of around 50 million km. The mother spacecrafts carries two and each of the daughter spacecraft carry one free-flying → test masses that will be kept as far as possible free of external disturbances. The mutual distances of the test masses from satellite to satellite will be measured by means of high-precision, → Michelson-like laser → interferometry. In this way, the extremely small distance variations between the test masses of two satellites can be detected which are caused by the passages of a gravitational waves. The required measurement accuracy of the distances amounts to typically 1/100 of the diameter of a hydrogen atom (10^-12 m) at a distance of two million km.

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

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.