An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



Number of Results: 20 Search : place
accurate to n decimal places
  رشمند با n رقم پس از جداگر یا ممیز   
rašmand bâ n raqam pas az jodâgar yâ momayez

Fr.: précis à n décimale, ~ avec n chiffres après la virgule, à n décimales près   

An expression specifying the number of meaningful digits to the right of the → decimal point. For example, e = 2.71828 ... = 2.718 is said to be accurate to three decimal places and 2.72 to two decimal places.

accurate; → decimal; → place.

apparent place
  جای ِ پدیدار   
jâ-ye padidâr

Fr.: position apparente   

Same as → apparent position.

apparent; → place.

catalog place
  جای ِ کاتالوگی   
jâ-ye kâtâlogi

Fr.: position catalogue   

Same as catalog position and → mean catalog place.

catalog; → place.

decimal place
  رقم پس از جداگر، ~ ~ ~ ممیز   
raqam pas az jodâgar, ~ ~ ~ momayez

Fr.: décimale, chiffre après la virgule   

The position of a digit to the right of a → decimal point written in decimal notation. In 0.032, for example, 0 is the first decimal place, 3 is the second decimal place, and 2 is the third decimal place.

decimal; → place.

Raqam, → digit; pas, → after; jodâgar, momayez, → decimal point.

jâ-be-jâyi (#)

Fr.: déplacement   

Physics: A vector quantity that specifies the change of position of a body or particle from the mean position or position of rest.
Geology: The offset of rocks caused by movement along a fault.

From displace, from → dis- + place + -ment.

Jâ bé jâyi, noun of jâ bé jâ literally "place to place," from "place," from Mid.Pers. giyag "place," O.Pers. ā-vahana- "place, village," Av. vah- "to dwell, stay," vanhaiti "he dwells, stays," Skt. vásati "he dwells," Gk. aesa (nukta) "to pass (the night)," Ossetic wat "room; bed; place," Tokharian B wäs- "to stay, wait;" PIE base ues- "to stay, live, spend the night."

displacement current
  جریان ِ جا-به-جایی   
jarayân-e jâ-be-jâyi (#)

Fr.: courant de déplacement   

In electromagnetism, a quantity which is not a real current (movement of charge), but has the units of current and has an associated magnetic field. The physical meaning of this displacement current is that a changing electric field makes a changing magnetic field.

displacement; → current.

Kant-Laplace hypothesis
  انگاره‌ی ِ کانت-لاپلاس   
engâre-ye Kant-Laplace

Fr.: hypothèse de Kant-Laplace   

The hypothesis of the origin of the solar system proposed first by Kant (1755) and later by Laplace (1796). According to this hypothesis, the solar system began as a nebula of tenuous gas. Particles collided and gradually, under the influence of gravitation, the condensing gas took the form of a disk. Larger bodies formed, moving in circular orbits around the central condensation (the Sun).

Named after the German prominent philosopher Immanuel Kant (1724-1804) and the French great mathematician, physicist, and astronomer Pierre-Simon Marquis de Laplace (1749-1827); → hypothesis.


Fr.: Laplace   

The French great mathematician, physicist, and astronomer Pierre-Simon Marquis de Laplace (1749-1827). → Laplace operator; → Laplace plane; → Laplace resonance; → Laplace transform; → Laplace's demon ; → Laplace's equation ; → Kant-Laplace hypothesis

Laplace operator
  آپارگر ِ لاپلاس   
âpârgar-e Laplace

Fr.: opérateur de Laplace   

Same as → Laplacian.

Laplace; → operator.

Laplace plane
  هامن ِ لاپلاس   
hâmon-e Laplace

Fr.: plan de Laplace   

The plane normal to the axis about which the pole of a satellite's orbit → precesses. In his study of Jupiter's satellites, Laplace (1805) recognized that the combined effects of the solar tide and the planet's oblateness induced a "proper" inclination in satellite orbits with respect to Jupiter's equator. He remarked that this proper inclination increases with the distance to the planet, and defined an orbital plane (currently called Laplace plane) for circular orbits that lies between the orbital plane of the planet's motion around the Sun and its equator plane (Tremaine et al., 2009, AJ, 137, 3706).

Laplace; → plane.

Laplace resonance
  باز‌آوایی ِ لاپلاس   
bâzâvâyi-ye Laplace

Fr.: résonance de Laplace   

An → orbital resonance that makes a 4:2:1 period ratio among three bodies in orbit. The → Galilean satellites → Io, → Europa, → Ganymede are in the Laplace resonance that keeps their orbits elliptical. This interaction prevents the orbits of the satellites from becoming perfectly circular (due to tidal interactions with Jupiter), and therefore permits → tidal heating of Io and Europa. For every four orbits of Io, Europa orbits twice and Ganymede orbits once. Io cannot keep one side exactly facing Jupiter and with the varying strengths of the tides because of its elliptical orbit, Io is stretched and twisted over short time periods.

This commensurability was first pointed out by Pierre-Simon Laplace, → Laplace; → resonance.

Laplace transform
  ترادیس ِ لاپلاس   
tarâdis-e Laplace (#)

Fr.: transformée de Laplace   

An integral transform of a function obtained by multiplying the given function f(t) by e-pt, where p is a new variable, and integrating with respect to t from t = 0 to t = ∞.

Laplace; → transform.

Laplace's demon
  پری ِ لاپلاس   
pari-ye Laplace

Fr.: démon de Laplace   

An imaginary super-intelligent being who knows all the laws of nature and all the parameters describing the state of the Universe at a given moment can predict all subsequent events by virtue of using physical laws. In the introduction to his 1814 Essai philosophique sur les probabilités, Pierre-Simon Laplace puts forward this concept to uphold → determinism, namely the belief that the past completely determines the future. The relevance of this statement, however, has been called into question by quantum physics laws and the discovery of → chaotic systems.

Laplace; → demon.

Laplace's equation
  هموگش ِ لاپلاس   
hamugeš-e Laplace

Fr.: équation de Laplace   

A → linear differential equation of the second order the solutions of which are important in many fields of science, mainly in electromagnetism, fluid dynamics, and is often used in astronomy. It is expressed by: ∂2V/ ∂x2 + ∂2V/ ∂y2 + ∂2V/ ∂z2 = 0. Laplace's equation can more concisely expressed by: ∇2V = 0. The function V may, for example, be the potential at any point in the electric field where there is no free charge. The general theory of solutions to Laplace's equation is known as potential theory.

Laplace; → equation.

mean catalog place
  جای ِ میانگین ِ کاتالوگی   
jâ-ye miyângin-e kâtâlogi

Fr.: position catalogue moyenne   

That point on the → celestial sphere at which an object would be seen from the solar system → barycenter affected by the → e-terms → aberration.

catalog; → mean; → place.

mean place
  جای ِ میانگین   
jâ-ye miyângin

Fr.: position moyenne   

An object's celestial position as determined for a given mean equator and equinox. → mean position.

mean; → place.

jâ (#)

Fr.: place, lieu   

An area, position, or portion of space. → mean place

O.E. from O.Fr. place, from M.L. placea "place, spot," from L. platea "courtyard, open space, broad street," from Gk. plateia (hodos) "broad (way)," feminine of platus "broad;" cognate with Av. pərəθu- "broad;" Skt. prthú- "broad, wide;" Lith. platus "broad;" Ger. Fladen "flat cake;" O.Ir. lethan "broad;" PIE base *plat- "to spread."

"place" (from Mid.Pers. giyag "place;" O.Pers. ā-vahana- "place, village;" Av. vah- "to dwell, stay," vanhaiti "he dwells, stays;" Skt. vásati "he dwells;" Gk. aesa (nukta) "to pass (the night);" Ossetic wat "room; bed; place;" Tokharian B wäs- "to stay, wait;" PIE base ues- "to stay, live, spend the night").

place-value notation
  نمادگان ِ جا-ارزشی   
nemâdgân-e jâ-arezeši

Fr.: notation positionnelle   

A mathematical notation system in which the → numerals get different values depending on their position relative to the other numerals. Same as → positional notation and → positional number system.

place; → value; → notation.

virtual displacement
  جابجایی ِ ویر‌آگین   
jâbejâyi-ye virâgin

Fr.: déplacement virtuel   

In → analytical mechanics, any infinitesimal change in the configuration of a material system, consistent with any constraints acting on the system at a given instant. If the constraints are stationary (→ scleronomous), then the actual displacement of the system, in an infinitesimal length of time dt, coincides with one of its virtual displacements. In the case of time-dependent (→ rheonomous) constraints, the actual displacement of the system does not coincide with any of the virtual ones, since the conditions imposed by the constraints vary during the time dt.

virtual; → displacement.

Wien's displacement law
  قانون ِ جا-به-جایی ِ وین   
qânun-e jâ-be-jâyi-ye Wien (#)

Fr.: loi du déplacement de Wien   

The wavelength corresponding to the maximum emissive power of a black body is inversely proportional to the absolute temperature of the body: λmax.T = 0.29 cm-deg. Wien's law explains why objects of different temperature emit spectra that peak at different wavelengths. Hotter objects emit most of their radiation at shorter wavelengths; hence they will appear to be bluer. Wien's law was an early attempt to describe the → blackbody radiation. The law closely approximated the true shape of the blackbody spectrum at short wavelengths, but ultimately failed because it relied solely on classical physics. It was superseded by → Planck's radiation law, which correctly describes the blackbody spectrum at all wavelengths.

After the German physicist Wilhelm Wien (1864-1928), who found the law in 1896. He was awarded the 1911 Nobel Prize in physics; → displacement; → law.