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

A representation of a real number between 0 and 1, as written a = d₁d₂d₃ ..., where each d_i is one of the digits 0, 1, 2, ..., 9. This means that a = d₁ x 10^-1 + d₂ x 10^-2 + d₃ x 10^-3+ ...

→ decimal; → representation.

The act or process of deciding. → rule of decision.

Verbal noun of → decide.

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

Verbal noun of → declare.

The → inflection of nouns, pronouns, or adjectives for case, number, and gender.

M.E. declenson, declynson (with suffix later assimilated to -sion), from O.Fr. declinaison, from L. declinatio, → declination

→ declination.

1) Angular distance (symbol δ) from the celestial equator. One of the coordinates, with → right ascension, that defines the position of a heavenly body in the equator system. Declination is measured positively (+) north or negatively (-) south of the celestial equator from 0° to 90°.
2) Angle between geographic North and magnetic North (symbol D).

Verbal noun of → decline; → -tion.

The axis to which the telescope tube is fastened in an → equatorial mounting.

→ declination; → axis.

For a telescope with an → equatorial mounting, a graduated circle attached to the → declination axis that shows the → declination to which the telescope is pointing.

→ declination; → circle.

The process or the state of breaking down a physical entity or an organic material.

From → de- + → composition.

1) A gradual decrease in surrounding → pressure, especially the controlled decrease in pressure that divers undergo after working in deep water or breathing compressed air.
2) Computers: The restoration of compressed electronic data to their full size.

→ de- + → compression.

A mathematical operation that allows to restore the original input signal, such as an astronomical image or spectrum, to its state before being affected by the → atmospheric turbulence and the → transfer function of the instrument. → convolution.

From → de- + → convolution.

An algorithm used to improve the resolution of an image particularly when the convolving function is well defined. Also called deconvolution code.

→ deconvolution; → algorithm.

A physical process that is contrary to accretion, referring to the outward direction of the mass flow from a star to its environment.

From → de- "reversal, removal," + -cretion, from L. accretionem (nom. accretio, gen. accretionis) "a growing larger," from stem of accrescere, → accretion.

A disk that would form around a star when the star injects matter into a close orbit. This is in contrast to an → accretion disk, which transfers matter from outside to the star. The mass gets injected into the decretion disk by a not yet well-known mechanism, most probably a combination of → non-radial pulsation, fast rotation, and possibly small-scale → magnetic fields. See also → viscous decretion disk.

→ decretion; → disk.

The process of restoring encrypted data back to the original information. See also → encryption and → decoding.

→ decrypt; → -tion.

1) The act or process of deducting; something that is or may be deduced.
2) A process of reasoning in which a conclusion is derived from the premises presented without a need for additional information. → deductive reasoning.

Verbal noun from → deduce.

1) The act or process of establishing some value or condition with precision.
2) The formal statement of the meaning or significance of a word, concept, etc.
3) Optics: The clarity, fidelity, sharpness, and brilliancy of an image formed by an optical system.

Verbal noun of → define.

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.

The act or state of deflecting or the state of being deflected. Amount of deviation.
Electronics: In a cathode-ray tube, the bending, by a magnetic field, of the beam of electrons after the focused beam leaves the electron gun.

Verbal noun of → deflect.

1) The angle by which a light ray is curved by the gravitational field of a massive body. Einstein's general relativity predicts that a light ray which tangentially grazes the surface of the Sun is deflected by 1''.7. This result was confirmed in 1919 when the apparent angular shift of stars close to the limb of the Sun was measured during a total solar eclipse.
2) In a cathode-ray tube, the angle through which the beam is bent, vertically, horizontally, or diagonally.

→ deflection; → angle.

The bending of a light ray under the gravitational effect of a massive body. → deflection angle.

→ deflection; → light.