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

The act or an instance of considering.

→ consider; → -tion.

The maximum amount of the apparent yearly displacement of a star, resulting from the → aberration of starlight. The value of the constant of aberration, κ, at J2000.0 is 20".49552. κ = (v/c) csc 1", where v is the average speed of the Earth about the Sun and c is the → speed of light in vacuum. The Earth's speed is given by: v = 2πa / [P(1 - e²)^1/2], where a is the → semi-major axis of the Earth's orbit, e is the → eccentricity of the Earth's orbit, and P is the → sidereal period of the Earth. Same as → constant of annual aberration. See also → constant of diurnal aberration.

→ constant; → aberration.

Same as → constant of aberration.

→ constant; → annual; → aberration.

The quantity 0''.3200 ρ cos φ', where ρ is the geocentric distance of the observer measured in units of → equatorial radius the Earth and φ' is the observer's → geocentric latitude. The numerical part is equal to 2πa csc1'' / (cP), where a is the equatorial radius of the Earth, P is its → sidereal period of rotation, and c is the → speed of light in vacuum.

→ constant; → diurnal; → aberration.

The apparent acceleration corresponding to the → Coriolis force. It is the acceleration which, when added to the acceleration of an object relative to a rotating → reference frame and to its → centrifugal acceleration, gives the acceleration of the object relative to a fixed reference frame. Coriolis acceleration equals 2ω x v, where ω is the → angular velocity of the rotating reference frame and v is the radial velocity of a particle relative to the center of the rotating reference frame.

→ Coriolis effect; → force.

→ accelerating Universe.

→ cosmic; → acceleration.

The act or process of moving, or of causing to move, with decreasing speed. Sometimes called negative acceleration.

Verbal noun of decelerate.

A parameter designating the rate at which the expansion of the Universe would slow down owing to the braking gravitational effect of the matter content of the Universe. It is expressed by: q(t) = -R(t)R ^..(t)/R ^.2(t), where R(t) represents the size of the Universe at time t. See also → expansion parameter; compare with → acceleration parameter.

→ deceleration; → parameter.

The act of declaring; announcement.
2) Something that is announced or proclaimed.

Verbal noun of → declare.

A rapid → chemical reaction in which the → output of → heat is enough to enable the reaction to proceed and be accelerated without input of heat from another source. The effect of a true deflagration under confinement is an → explosion. See also: → detonation; → explosion.

Verbal noun of → deflagrate.

1) The → act or → circumstance of proving or being → proved conclusively, as by → reasoning or a show of → evidence.
2) Something serving as → proof or supporting evidence.
3) An exhibition, as of feeling; display; → manifestation (Dictionary.com).

Verbal noun of → demonstrate.

The process of introducing → deuterium into a → chemical compound.

Verbal noun of → deuterate.

The breaking up of a body into fragments. For example, that of an unstable nuclei either spontaneously or as a result of bombardment by fast-moving particles, or the breaking up of a comet.

Disintegration, verbal noun of disintegrate, from → dis- + → integration.

Vâpâši, forupâši, from vâ-, frou-→ de- + pâši, noun of pâšidan→ disperse.

The aberration of a star's position due to the rotation of the Earth. Its value depends on the latitude of the observer, and is only 0''.32 in the case of an observer at the equator, where the rotational velocity is greatest.

→ diurnal; → aberration.

Daily geometrical libration of the Moon arising from the fact that observers at different points on the Earth see the Moon from slightly different angles. As the Moon rises in the east, you are positioned on one side of our planet, and by the time it sets in the west. Earth's rotation has carried you to the other side. This change in position produces a slight → parallax effect that adds about another 1° of libration in longitude. Two other geometrical libration are → libration in longitude and → libration in latitude. See also → physical libration.

→ diurnal; → libration.

Continuance in time; a period of existence or persistence; length of time during which anything continues.

Noun of action from L. durare "to harden," → during.

Pâyeš, noun of action from pâyidan, → last (v.).

The → absorption of → electromagnetic radiation from an astrophysical object by → dust grains associated with that object.

→ dust; → obscuration.

Tiregi, → obscuration, pat, → by; qobâr, → dust.

The same as → elliptic aberration.

e, → elliptic; → term; → aberration.

The fraction of the Sun's area occulted by the Moon. It should not be confused with → eclipse magnitude, which is the fraction of the Sun's diameter occulted by the Moon. Eclipse obscuration may be expressed as either a percentage or a decimal fraction (e.g., 50% or 0.50) (F. Espenak, NASA).

→ eclipse; obscuration, verbal noun from → obscure.

Of an atom, a form of notation which shows how the electrons are distributed among the various atomic orbital and energy levels. The format consists of a series of numbers, letters and superscripts. For example, 1s² 2s² 2p³ means: 2 electrons in the 1s subshell, 2 electrons in the 2s subshell, and 3 electrons in the 2p subshell.

→ electron; → configuration.