An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 1001
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.

plâž (#)

Fr.: plage   

A bright cloud-like feature that appears in the vicinity of a sunspot. Plages represent regions of higher temperature and density within the chromosphere. They are particularly visible when photographed through filters passing the spectral light of hydrogen or calcium.

From Fr., from It. piaggia, from L.L. plagia "shore;" noun use of the feminine of plagius "horizontal;" frpm Gk. plagios "slanting, sideways" from plag(os) "side" + -ios adj. suffix.

Plâž, loan from Fr., as above.

dašt (#)

Fr.: plaine   

An extent of flat land not noticeably diversified with mountains, hills, or valleys.

M.E. from O.Fr. plain, from L. planum "level ground, plain."

Dašt, from Mid.Pers. dašt "plain, open ground."

taxt- (#)

Fr.: plan-   

Variant of → plano-.



Fr.: Planck   

Short for Max Planck (1858-1947), German physicist, great authority on thermodynamics and creator of the quantum theory.

Planck curve
  خم ِ پلانک   
xam-e Planck

Fr.: courbe de Planck   

Same as → blackbody curve.

Planck; → curve.

Planck density
  چگالی ِ پلانک   
cagâli-ye Planck

Fr.: densité de Planck   

The density corresponding to a → Planck mass in a cubic region of edge length given by the → Planck length: ρP = c5/(ħG2) ≅ 5.16 x 1093 g cm-3, where c is the → speed of light, ħ is the → reduced Planck's constant, and G is the → gravitational constant.

Planck; → density.

Planck distribution
  واباژش ِ پلانک   
vâbâžeš-e Planck

Fr.: distribution de Planck   

The distribution of radiation with wavelength for a blackbody, given by → Planck's radiation law.

Planck; → distribution.

Planck energy
  کاروژ ِ پلانک   
kâruž-e Planck

Fr.: énergie de Planck   

The unit of energy in the system of Planck units. EP = √ (ħ c5/G) ≅ 1.22 x 1019 GeV. It can also be defined as EP = ħ / tP, where tP is the Planck time. This is an extraordinarily large amount of energy on the subatomic scale and particle accelerators have yet to produce a particle with this magnitude of energy. Understanding the properties of a subatomic particle that contains the Planck Energy is helpful in developing a Unified Field Theory which encompasses the realms of Quantum Theory and Relativity, although this too has evaded complete scientific understanding.

Planck; → energy.

Planck era
  دوران ِ پلانک   
dowrân-e Planck

Fr.: ère de Planck   

The first 10-43 seconds of the Universe's existence, when the size of the Universe was roughly the Planck length and during which quantum effects of gravity were significant. Also called Planck epoch. Our understanding of the Planck era is poor because theory which encompasses both quantum mechanics and general relativity is needed to be developed.

Planck; → era.

Planck function
  کریای ِ پلانک   
karyâ-ye Planck

Fr.: fonction de Planck   

Same as → Planck's blackbody formula.

Planck; → function.

Planck length
  درازای ِ پلانک   
derâzâ-ye Planck (#)

Fr.: longueur de Planck   

The size limit, lP = √ (ħ G/ c3), about 10-33 cm, at which Einstein's notions of space-time are supposed to break down, and space is predicted to become "foam like."

Planck; → length.

Planck mass
  جرم ِ پلانک   
jerm-e Planck

Fr.: masse de Planck   

The unit of mass in Planck's system of physical units, mP = √ (ħ c/ G) = 2.176 x 10-8 kg. It is also the mass of a black hole whose Compton wavelength is comparable to its Schwarzschild radius.

Planck; → mass.

Planck postulate
  فراوَس ِ پلانک   
farâvas-e Planck

Fr.: postulat de Planck   

The postulate that the energy of oscillators in a blackbody is quantized by E = nhν, where n = 1, 2, 3, ..., h is Planck's constant, and ν the frequency.

Planck; → postulate.

Planck Satellite
  ماهواره‌ی ِ پلانک   
mâhvâre-ye Planck

Fr.: Satellite Planck   

A European Space Agency (ESA) mission to map the full sky in the 30 GHz to 1 THz range and to measure the → anisotropies of the → cosmic microwave background (CMB) with a sensitivity set by fundamental limits, i.e. photon noise and contamination by foregrounds. It was launched on 14 May 2009, together with the → Herschel Satellite. Its observing position is a halo orbit around the L2 → Lagrangian point, some 1.5 million km from Earth. Its → Gregorian-like off-axis telescope has an effective aperture of 1.5 m and images the sky on two sets of feed-horns. The Low Frequency Instrument (LFI, at frequencies 30, 44, 70 GHz) amplifies with High Electron Mobility Transistors cooled at 20 K the radiation collected by 13 horns. The High Frequency Instrument (HFI, at 100, 143, 217, 353, 545, 857 GHz) detects the shorter waves with 52 bolometers cooled at only 0.1 degree above the → absolute zero. Both instruments can detect both the total intensity and polarization of photons. The Planck mission is intended to provide maps with a sensitivity of a few micro-Kelvin and an angular resolution down to 5 arcmin, which is considered as a major improvement with respect to the Wilkinson Microwave Anisotropy Probe (→ WMAP) launched by the NASA in 2002. Planck will provide a major source of information relevant to several cosmological and astrophysical issues, such as testing theories of the early Universe and the origin of cosmic structure. It will also provide to astronomers 9 complete maps of the full sky at wavelengths from 0.3 mm to 1 cm, that complement the 4 maps taken by the → IRAS satellite in the 2.5 to 100 micrometer range.

Planck; → satellite.

Planck scale
  مرپل ِ پلانک   
marple-e Planck

Fr.: échelle de Plancck   

1) A general term for anything roughly the size of the → Planck length.
2) Similarly, an energy on the order of the → Planck energy.

Planck; → scale.

Planck spectrum
  بیناب ِ پلانک   
binâb-e Planck

Fr.: spectrum de Planck   

Same as → blackbody spectrum.

Planck; → spectrum.

Planck time
  زمان ِ پلانک   
zamân-e Planck

Fr.: temps de Planck   

The time representing the → Planck length divided by the → speed of light. It is expressed by: tP = (Għ/c5)1/2≅ 5.4 x 10-44 s, where G is the → gravitational constant, ħ is the → reduced Planck's constant, and c is the → speed of light. At the Planck time, the mass density of the Universe is thought to approach the → Planck density.

Planck; → time.

Planck units
  یکاهای ِ پلانک   
yekâhâ-ye Planck (#)

Fr.: unités de Planck   

A set of → natural units in which the normalized units are: the gravitational constant, Planck's constant, the speed of light, the Coulomb constant, and Boltzmann's constant.

Planck; → unit.

Planck's blackbody formula
  دیسول ِ سیه‌جسم ِ پلانک   
disul-e siyah jesm-e Planck

Fr.: formule du corps noir de Planck   

A formula that determines the distribution of intensity of radiation that prevails under conditions of thermal equilibrium at a temperature T: Bv = (2hν3 / c2)[exp(hν / kT) - 1]-1 where h is Planck's constant and ν is the frequency.

Planck; → blackbody; → formula.

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