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

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.

Verbal form of → deconvolution.

From → de- + → convolve.

1) To separate or detach; to cause to become disconnected or divergent.
2) Electronics: To reduce or eliminate the coupling of (one circuit or part to another).
3) Physics: To decrease or eliminate the shock waves of a nuclear explosion by having it take place underground.

→ de- + → couple.

Cosmology: In the early history of the Universe, separation of matter and radiation due to their non-interaction. At a redshift of 1000, that is about 400,000 years after the Big Bang, the temperature would have cooled to the point (4000 degrees Kelvin) where electrons and nuclei can recombine and form neutral hydrogen atoms. Since atoms do not scatter the radiation appreciably, free electrons were lacking, and the Universe became transparent to radiation. Same as → recombination. See also → decoupling era.

Verbal noun of decouple, from → de- + → couple + → -ing.

The era some 400,000 years after the → Big Bang, when the cosmic → blackbody radiation was last scattered by the matter. → decoupling. Same as → recombination era and → last scattering epoch.

→ decoupling; → era.

1) (v.tr.) To cause to diminish, to make less. (v.intr.) To diminish or lessen in extent, quantity, power, etc.
2) The act or process of decreasing; condition of being decreased. → Forbush decrease.

Decrease, from M.E. decres (n.), decresen, from O.Fr. descreistre, from L. decrescere, from → de- + crescere "to grow," → crescent.

Kâstan, kâh-, from Mid.Pers. kâhitan, kâstan, kâhênitan "to decrease, diminish, lessen," Av. kasu- "small, little" (Mod.Pers. keh), Proto-Iranian *kas- "to be small, diminish, lessen;" kâheš verbal noun from kâhidan.

1) The amount lost in the process of decreasing.
2) Math.: The quantity by which a variable is decreased. A negative → increment.
3) Physics: 1) The ratio of the amplitude of an oscillation to that of its succeeding oscillation in an underdamped vibrating system. 2) The intensity ratio of a series of spectral lines of the same nature, such as → Balmer decrement.

L decrementum, from decre(tus), → decrease + -mentum noun suffix -ment.

Kâheh, from kâh- present stem of kâhidan, → decrease + noun suffix -é.

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.

Make crypted data or information intelligible. See also → encrypt and → decode.

→ de- + crypt, → encrypt.

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

→ decrypt; → -tion.

To derive as a conclusion from facts or premises.

L. deducere "to lead down, derive," from → de- "down" + ducere "to lead."

Foruhâxtan, foruhâzidan, from foru- "down," → de- + Mid.Pers. hâxtan, hâzidan "to lead, guide, persuade," Av. hak-, hacaiti "to attach oneself to, to join," cf. Skt. sacate "accompanies, follows," Gk. hepesthai "to follow," L. sequi "to follow;" PIE *sekw- "to follow."

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.

Of or relating to → deduction.

From deduct, → deduce, + → -ive.

Reasoning from the → general to the → particular (or from → cause to → effect).

→ deductive; → reasoning.

1a) General: Extending well inward from an outer surface or back from an edge.
1b) Great in measure; intense. → deep exposure.
1c) Of colors, dark and vivid.
2) The deep part of a body of water, especially an area of the ocean floor having a depth greater than 5400 meters (Dictionary.com).

O.E. deop, from P.Gmc. *deupaz, from PIE *d(e)u- "deep, hollow."

Žarf "deep;" variants Gilaki jalf, julf, jal; Tabari jol, jal, jul; Baluci jahl, johl; Kermâni jarr "deep;" Mid.Pers. zufr; Av. jafra- "deep."
Gowd, probably ultimately from PIE root *g^wādh- "to sink, submerge;" cf. Av. vigāθô- "ravines, gorges;" Skt. gādha- "depth; shallow;" Gk. bessa "gorge, ravine."

An exposure in which the detector shutter remains open for a relatively long time in order to bring out the weaker features of the observed object. In practice a deep exposure with a CCD detector is usually obtained from co-addition of shorter exposures.

→ deep; → exposure.

An area on the sky whose image is obtained with a deep exposure, such as → Hubble Deep Field.

→ deep; → field.

An image obtained using a deep exposure to reveal the weak features of the object.

→ deep; → image.