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

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 699
dimensional
  وامونی   
vâmuni

Fr.: dimensionnel   

Of or pertaining to → dimension.

dimension; → -al.

dimensional analysis
  آنالس ِ وامونی، آناکاوی ِ ~   
ânâlas-e vâmuni, ânâkâvi-ye ~

Fr.: analyse dimensionnelle   

A technique used in physics based on the fact that the various terms in a physical equation must have identical → dimensional formulae if the equation is to be true for all consistent systems of unit. Its main uses are:
a) To test the probable correctness of an equation between physical quantities.
b) To provide a safe method of changing the units in a physical quantity.
c) To solve partially a physical probable whose direct solution cannot be achieved by normal methods.

dimensional; → analysis.

dimensional formula
  دیسول ِ وامونی   
disul-e vâmuni

Fr.: formule dimensionnelle   

Symbolic representation of the definition of a physical quantity obtained from its units of measurement. For example, with M = mass, L = length, T = time, area = L2, velocity = LT-1, energy = ML2T-2. → dimensional analysis.

dimensional; → formula.

dimensionless quantity
  چندی ِ بی‌وامون   
candi-ye bivâmun

Fr.: quantité sans dimension   

A quantity without an associated → physical dimension. Dimensionless quantities are defined as the ratio of two quantities with the same dimension. The magnitude of such quantities is independent of the system of units used. A dimensionless quantity is not always a ratio; for instance, the number of people in a room is a dimensionless quantity. Examples include the → Alfven Mach number, → Ekman number, → Froude number, → Mach number, → Prandtl number, → Rayleigh number, → Reynolds number, → Richardson number, → Rossby number, → Toomre parameter. See also → large number.

dimension + -less M.E. from O.E. læs (adv.), læssa (adj.), akin to O.Fr. les "less."

Bi- "without," → a-, + vâmun, → dimension.

dimer
  دی‌مر   
dimer

Fr.: dimère   

A molecule resulting from combination of two identical molecules.

From → di- "two, twice, double," + -mer a combining form denoting member of a particular group, → isomer.

diode
  دیود   
diod (#)

Fr.: diode   

An electronic component with two active terminals, an → anode and a → cathode, through which current passes in one direction (from anode to cathode) and is blocked in the opposite direction. Diodes have many uses, including conversion of → alternating current to → direct current, regulation of votage, and the decoding of audio-frequency signals from radio signals.

di- "two, twice, double," + hodos "way."

Dione (Saturn IV)
  دیونه   
Dioné

Fr.: Dioné   

The fourth largest moon of Saturn and the second densest after Titan. Its diameter is 1,120 km and its orbit 377,400 km from Saturn. It is composed primarily of water ice but must have a considerable fraction of denser material like silicate rock.

Discovered in 1684 by Jean-Dominique Cassini, Italian born French astronomer (1625-1712). In Gk. mythology Dione was the mother of Aphrodite (Venus) by Zeus (Jupiter).

diopter
  دیوپتر   
dioptr (#)

Fr.: dioptre   

A unit of optical measurement that expresses the refractive power of a lens or prism. In a lens or lens system, it is the reciprocal of the focal length in meters.

L. dioptra, from Gk. di-, variant of dia- "passing through, thoroughly, completely" + op- (for opsesthai "to see") + -tra noun suffix of means.

Dioptr loanword from Fr.

dioptra
  دیوپترا   
dioptrâ

Fr.: dioptra   

An instrument used in antiquity to measure the apparent diameter of the Sun and the Moon. It was a rod with a scale, a sighting hole at one end, and a disk that could be moved along the rod to exactly obscure the Sun or Moon. The Sun was observed directly with the naked eye at sunrise or sunset in order to prevent eye damage. Aristarchus (c.310-230 B.C.), Archimedes (c. 290-212 B.C.), Hipparchus (died after 127 B.C.), and Ptolemy (c.100-170 A.D.) used the dioptra. The instrument could also serve for measurement of angles, land levelling, surveying, and construction of aqueducts and tunnels.

diopter.

dioxide
  دی‌اکسید   
dioksid

Fr.: dioxyde   

Any → oxide containing two → atoms of → oxygen the → molecule.

di-; → oxide.

dip
  نشیب   
našib (#)

Fr.: inclinaison   

1) Navigation: The angular difference between the visible horizon and the true horizon. Same as → dip of the horizon.
2) Geodesy: The angle between the horizontal and the lines of force of the Earth's magnetic field at any point. → magnetic dip.
3) Aviation: The angle between the true and apparent horizon, which depends on flight height, the Earth's curvature, and refraction.

O.E. dyppan "to immerse," cognate with Ger. taufen "to baptize," and with → deep.

Našib, → depression.

dip angle
  زاویه‌ی ِ نشیب   
zâviye-ye našib

Fr.: angle d'inclinaison   

The angular difference between the → visible horizon and the → true horizon. Same as → dip of the horizon.

dip; → angle.

dip of the horizon
  نشیب ِ افق   
našib-e ofoq

Fr.: inclinaison de l'horizon   

The angle created by the observer's line of sight to the → apparent horizon and the → true horizon. Neglecting the → atmospheric refraction, dip of the horizon can be expressed by θ (radians) = (2h/R)1/2, where h is the observer's height and R the Earth's radius. An an example, for a height of 1.5m above the sea, and R = 6.4 x 106 m, the dip angle is about 0.00068 radians, or 0.039 degrees, about 2.3 minutes of arc, quite appreciable by the eye. See also → distance to the horizon. Same as → dip angle.

dip; → horizon.

Diphda (β Ceti)
  وزغ   
Vazaq

Fr.: Diphda   

The brightest star in the constellation → Cetus; a → red supergiant (K0 III) of visual magnitude 2.04.

Diphda, from Ar. zafda' (ضفدع) "frog." It is also designated as Deneb Kaitos, from zanab al-qaytusذنب القیطس "tail of Cetus."

Mid.Pers. wazaγ, vak; Av. vazaγa- "frog," → tadpole orbit.

diphthong
  دوواکه   
dovâké

Fr.: diphthongue   

Phonetics: A → vowel sound produced by a blended sequence of two separate vowels in a single syllable, where the sound begins as one vowel and moves toward another (as in loud, light, and lair).

From M.Fr. diphthongue, from L.L. diphthongus, from Gk. diphthongos "having two sounds," from → di- "double" + phthongos "sound, voice."

Dovâké, from do "two, → di-" + vâké, vâkvoice.

diplopia
  دوبینی   
dobini (#)

Fr.: diplopie   

A pathological condition of vision in which a single object appears double because the eyes are not focusing properly. Same as → double vision.

From L. diplo- "double, in pairs," from Gk., combining form of diplos "twofold" + -opia, from Gk. -opia, from ops "eye."

Dobini, from dotwo + bini "vision, seeing," from bin "to see; seer" (present stem of didan; Mid.Pers. wyn-; O.Pers. vain- "to see;" Av. vaēn- "to see;" Skt. veda "I know;" Gk. oida "I know," idein "to see;" L. videre "to see;" PIE base *weid- "to know, to see").

dipole
  دوقطبه   
doqotbé (#)

Fr.: dipole   

1) A combination of two electrically or magnetically charged particles of opposite signs, which are separated by a very small distance.
2) Chemistry: A molecule containing both positively and negatively charged groups.

di- "two, twice, double," + → pole.

dipole anisotropy
  ناهمسانگردی ِ دوقطبه   
nâhamsângardi-ye doqotbé

Fr.: anisotropie dipolaire   

A form of anistropy in the temperature of the → cosmic microwave background radiation, appearing as one hot pole and one cold pole, caused by our motion with respect to the cosmic background radiation. The temperature variations, amounting to 1 part in 1000, yield a velocity of about 600 km/sec for our Galaxy with respect to the background. → cosmic microwave background anisotropy.

dipole; → anisotropy.

dipole antenna
  آنتن ِ دوقطبه   
ânten-e doqotbé (#)

Fr.: antenne dipôle   

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.

dipole moment
  گشتاور ِ دوقطبه   
gaštâvar-e doqotbé (#)

Fr.: moment dipolaire   

1) The product of the strength of either of the charges in an → electric dipole and the distance separating the two charges. It is expressed in → coulomb meters. Dipole moment is a → vector quantity. Its direction is defined as toward the positive charge. In chemistry dipole moment is a quantitative measure of polarity in a molecule; the unit is the → debye.
2) The product of the strength of either of the poles in a → magnetic dipole and the distance separating the two poles. Dipole moment is a vector quantity. Its direction is defined as toward the magnetic north pole.

dipole; → moment.

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