An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 688
Ekman number
  عدد ِ اکمن   
adad-e Ekman

Fr.: nombre d'Ekman   

A → dimensionless quantity that measures the strength of → viscous forces relative to the → Coriolis force in a rotating fluid. It is given by Ek = ν/(ΩH2), where ν is the → kinematic viscosity of the fluid, Ω is the → angular velocity, and H is the depth scale of the motion. The Ekman number is usually used in describing geophysical phenomena in the oceans and atmosphere. Typical geophysical flows, as well as laboratory experiments, yield very small Ekman numbers. For example, in the ocean at mid-latitudes, motions with a viscosity of 10-2 m2/s are characterized by an Ekman number of about 10-4.

Ekman layer; → number.

ekpyrotic Universe
  گیتی ِ آتشزاد   
giti-ye âtašzâd

Fr.: Univers ekpyrotique   

A cosmological model in which the → Big Bang is not the beginning of the → Universe, but a transitory phase in a more global scenario. The ekpyrotic Universe model is fundamentally different from the → standard cosmology and offers radically different explanations for the cosmological problems (→ homogeneity, → isotropy, → flatness, → magnetic monopoles, etc.). In this highly speculative model → space-time has five dimensions, four spatial and one temporal. Two three-dimensional → branes, one visible and one hidden, collide following the contraction of the extra dimension. The contraction produces a blue shift effect that converts gravitational energy into brane kinetic energy. Some fraction of this kinetic energy is converted into matter and radiation that can fuel the Big Bang. The resulting temperature is finite, so the hot Big Bang phase begins without a → singularity. Apart from being speculative, this model suffers from several fine tunings (J. Khoury et al. 2001, Phys. Rev. D64, 123522 (hep-th/0103239); P. J. Steinhardt & N. Turok, 2002, Phys. Rev. D65, 126003 (hep-th/0111098), and references therein).

Ekpyrotic is inspired by the ancient Stoic doctrine according to which the world ends in a supreme conflagration, called ekpyrosis, and then reborns from the fire (palingenesis), only to be destroyed again at the end of the new cycle; ekpyrosis, from Gk. ek- "out of," → ex-, + → pyro- combining form of pyr, → fire, + -sis a suffix used to form nouns of action, process, state, condition, such as thesis, analysis, catharsis; → Universe.

Giti, → Universe; âtašzâd, literally "born out of fire," from âtaš, → fire, + zâd "born," from zâdan "to bring forth," → generate.

El Nino
  ال نی‌نیو   
El Ninyo (#)

Fr.: El Niño   

El Niño. A significant warming of the ocean surface over the eastern and central equatorial Pacific that occurs at irregular intervals, generally ranging between two and seven years. El Niño conditions, which are often characterized by "warm events," most often develop after late December during the early months of the year and decay during the following year. → La Nina.

From Sp. El Niño "the child," i.e. "the Christ Child," alluding to the appearance of the current near Christmas. The term was originally applied by fishermen of northern Peru.

Elara (Jupiter VII)

Fr.: Elara   

The thirteenth known moon of Jupiter, discovered in 1905 by Charles Perrine.

In Gk. mythology, Elara was the mother by Zeus of the giant Tityus.

kešâyand (#)

Fr.: élastique   

Of, pertaining to, or noting a body having the property of → elasticity. See also → elastic collision, → elastic deformation, → elastic limit, → elastic scattering.

From Fr., from Gk. elastos "ductile, flexible," related to elaunein "to strike, beat out."

Kešâyand, from keš stem of kešidan/kašidan "to pull, drag, draw" (Av. karš- "to draw, to plough," karša- "furrow;" cf. Skt. kars-, kársati "to pull, drag, plough," Gk. pelo, pelomai "to be busy, to bustle") + âyand agent form of âmadan "to come; to become," from Mid.Pers. âmatan (O.Pers. gam- "to come; to go," Av. gam- "to come; to go," jamaiti "goes;" O.Iranian *āgmatani; Skt. gamati "goes;" Gk. bainein "to go, walk, step;" L. venire "to come;" Tocharian A käm- "to come;" O.H.G. queman "to come;" E. come; PIE root *gwem- "to go, come").

elastic collision
  همکوبش ِ کشایند   
hamkubš-e kešâyand

Fr.: collision élastique   

A collision between two particles which conserves the total kinetic energy and momentum of the system.

elastic; → collision.

elastic deformation
  وادیسش ِ کشایند   
vâdiseš-e kešâyand

Fr.: déformation élastique   

A deformation of a → solid body in which the change (→ strain) in the relative position of points in the body disappears when the deforming stress is removed. See also → elastic limit.

elastic; → deformation.

elastic limit
  حد ِ کشایند   
hadd-e kešâyand

Fr.: limite d'élasticité, ~ élastique   

The smallest → stress beyond which a → solid body can no longer return to its original shape. The material ceases to obey → Hooke's law. Also called → yield point.

elastic; → limit.

elastic scattering
  پراکنش ِ کشایند   
parâkaneš-e kešâyand

Fr.: diffusion élastique   

In a → collision between two → particles, the reaction in which the total → kinetic energy of the system, projectile plus target, is the same before the collision as after.
In the interaction of → electromagnetic waves with particles, the scattering when the → wavelength (→ frequency) of the → scattered light is the same as the → incident light (→ Rayleigh scattering, → Mie scattering).

elastic; → scattering.

elastic wave
  موج ِ کشایند   
mowj-e kešâyand (#)

Fr.: onde élatique   

A wave that propagates by → elastic deformation of the medium. The → propagation takes place by a change in shape that disappears when the forces are removed. In other words, the displaced particles transfer momentum to adjoining particles, and are themselves restored to their original position. A → seismic wave is a type of elastic wave.

elastic; → wave.

kešâyandi (#)

Fr.: élasticité   

The ability of a body which has been → deformed by an applied → force to return to its original shape when the force is removed. Up to a certain point the material obeys → Hooke's law. See also → ductility, → plasticity.

elastic + → -ity.

ârenj (#)

Fr.: coude   

The joint of the human → arm between the → upper arm and the → forearm.

M.E. elbowe, from O.E. elboga, elnboga, from ell + bow. Cognate with Scots elbuck, Du. elleboog, Ger. Ellbogen, Ellenbogen, Dan. albue, Icelandic olbogi, olnbogi "elbow."

Ârenj "elbow," variants âranj, âran "elbow," araš "forearm;" Mid.Pers. âranj, O.Pers. arašan- "cubit," Av. arəθnâ- "elbow," Skt. aratni- "elbow," Iranian stem aratan-, araθn-, borrowed from Iranian into General Slavic as aršin "ell."

barqi (#)

Fr.: électrique   

Pertaining to, derived from, produced by, or associated with electricity.

Term coined in by the English physicist William Gilbert (1540-1603) in treatise De Magnete (1600), from L. electrum "amber," from Gk. elektron "amber."

Barqi, adj. of barq, → electricity.

electric arc
  کمان ِ برقی   
kamân-e barqi

Fr.: arc électrique   

A luminous and extremely hot electrical → discharge between two → electrodes when an ionized → plasma is created in the air or gas across the electrodes.

electric; → arc.

electric charge
  بار ِ برقی   
bâr-e barqi (#)

Fr.: charge électrique   

The intrinsic property of matter responsible for all electric phenomena, occurring in two forms arbitrarily designated → negative and → positive.

electric; → charge.

electric circuit
barqrâh (#)

Fr.: circuit électrique   

Physics: A closed path followed by an → electric current; a number of → conductors interconnected for the purpose of carrying an electric current.

electric; → circuit.

electric current
  جریان ِ برق   
jarayân-e barq (#)

Fr.: courant électrique   

The → rate at which → electric charge → flows past a given point through a → conductor, measured in → amperes.

electric; → current.

electric dipole
  دیپل ِ برقی، دی‌قطبه ِ ~   
dipol-e barqi, diqotbe-ye ~

Fr.: dipôle électrique   

1) A type of → charge distribution consisting of two charges, a positive and a negative charge of the same magnitude separated by a distance s, which is small compared to the distance r to the point P at which the → electric potential is V and the → electric field intensity is E.The potential falls as the square of the distance (1/r2) and the electric field intensity decreases as the cube of the distance (1/r3).
2) A simple → antenna consisting of a pair of oppositely charged → conductors capable of radiating an → electromagnetic wave in response to the movement of an electric charge from one conductor to the other.

electric; → dipole.

electric discharge
  وابار ِ برقی   
vâbâr-e barqi

Fr.: décharge électrique   

The flow of electricity through a gas, resulting in the emission of radiation that is characteristic of the gas and of the intensity of the current.

electric; → discharge.

electric field
  میدان ِ برقی   
meydân-e barqi (#)

Fr.: champ électrique   

The effect produced by the existence of an → electric charge in the volume of space that surrounds it. The direction of the field is taken to be the direction of the force it would exert on a positive test charge. The electric field is radially outward from a positive charge and radially in toward a negative point charge.

electric; → field.

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