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

The → theory of relativity.

→ theory; → relativity.

1) The state or quality of being reliable.
2) A statement of the error or precision.

→ reliable; → -ity.

In → general relativity, the gravity resulting from a → negative pressure. See also → cosmological constant.

→ repulsive; → gravity.

A property of a → conductor which is defined as the ratio of the → electric intensity (E) to the → current density (J): ρ = E/J. The greater the resistivity, the greater the intensity needed to establish a given current density, or the smaller the current density for a given intensity. A "perfect" conductor would have zero resistivity, and a "perfect" → insulator an infinite resistivity.

From → resistive + → -ity.

1) The state or fact of being responsible, answerable, or accountable for something within one's power, control, or management.
2) An instance of being responsible.
3) A person or thing for which one is responsible (Dictionary.com).

→ responsible; → -ity.

A performance criterion for an electronic detector, the ratio of the detector's electrical output to its optical input.

→ responsive; → -ity.

1) The quality or state of being → rigid. See also → modulus of rigidity.
2) → magnetic rigidity.

→ rigid + → -ity.

The → opacity of a gas of given composition, temperature, and density averaged over the various wavelengths of the radiation being absorbed and scattered. The radiation is assumed to be in → thermal equilibrium with the gas, and hence have a → blackbody spectrum. Since → monochromatic opacity in stellar plasma has a complex frequency dependence, the Rosseland mean opacity facilitates the analysis. Denoted κ_R, it is defined by: 1/κ_R = (π/4σT³) ∫(1/k_ν) (∂B/∂T)_νdν, summed from 0 to ∞, where σ is the → Stefan-Boltzmann constant, T temperature, B(T,ν) the → Planck function, and k_ν monochromatic opacity (See Rogers, F.J., Iglesias, C. A. Radiative atomic Rosseland mean opacity tables, 1992, ApJS 79, 507).

Named after Svein Rosseland (1894-1985), a Norwegian astrophysicist, who obtained the expression in 1924; → mean; → opacity.

The velocity of a → rotational motion; same as → angular velocity.

→ rotational; → velocity.

The ability of something, especially a computer system, to adapt to increased demands.

→ scalable; → -ity.

A → tensor density of → order 0.

→ scalar; → density.

A region of infinite → space-time curvature postulated to lie within a → black hole.

→ Schwarzschild black hole; → singularity.

The quality of the practices and theories that aim at establishing reproducible regularities in phenomena by using experimental method and providing a clearly formulated description.

→ scientific + → -ity.

Instability caused by a slow dissipation of energy.

→ secular; → instability.

1) The condition in which the equilibrium configuration of a system is stable over long periods of time.
2) The condition of a star when it is stable against arbitrary adiabatic perturbations.

→ secular; → stability.

1) Freedom from care, anxiety, or doubt; well-founded confidence.
2) Something that secures or makes safe; protection; defense.
3) A department or organization responsible for protection or safety (Dictionary.com).

→ secure; → -ity.

The → gravitational attraction of a system of masses, such of a planet, that allows the system to be held together by their mutual gravity. Self-gravity between atoms allows a → star to hold together, despite tremendous temperature and pressure. Similarly, to be considered a → planet, a body must have enough mass so that its self-gravity pulls it into a near-spherical shape.

→ self-; → gravity.

The property of being → self-similar.

→ self-; → similarity.

1) Capacity for sensation or feeling; responsiveness to sensory stimuli.
2) Physics: The realignment of a magnetic compass pointer along a magnetic field line after the pointer has been deflected.

→ sensible; → -ity.

1) The required brightness for an object in order to be detected by an observing instrument. A highly sensitive telescope can detect dim objects, while a telescope with low sensitivity can detect only bright ones.
2) Of a radio receiver or similar device, the minimum input signal required to produce a specified output signal having a specified signal-to-noise ratio.

State noun from → sensitive.