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

A model of the Solar System proposed by Copernicus in which the Sun lies at the center with the planets orbiting around it. In this model, the Earth is a planet, and the Moon is in orbit around the Earth, not the Sun. The stars are distant objects that do not revolve around the Sun. Instead, the Earth is assumed to rotate once in 24 hours, causing the stars to appear to revolve around the Earth in the opposite direction. This model readily explained both the varying brightness of the planets and the → retrograde motion. In the Copernican model the planets executed uniform circular motion about the Sun. As a consequence, the model could not explain all the details of planetary motions on the celestial sphere without → epicycles of the → Ptolemaic system. However, the Copernican system required many fewer epicycles than its predecessor because it moved the Sun to the center. Hence, Copernicus borrowed elements from variants of the Ptolemaic system developed by Middle Eastern astronomers, mainly the Iranian Nasireddin Tusi (1201-1274) and the Damascene Ibn al-Shatir (1304-1375), which Copernicus apparently knew about.

Nicolaus Copernicus (1473-1543), the L. rendition of the Polish original name Mikołaj Kopernik, author of the epoch making work De revolutionibus orbium coelestium (On the Revolutions of the Celestial Spheres), published in 1543, in which he exposed his heliocentric system; → model.

1) Physics: A basic statement that there should be no "special" observers to explain the phenomena. The principle is based on the discovery by Copernicus that the motion of the heavens can be explained without the Earth being in the geometric center of the system, so the Aristotelian/Ptolemaic assumption that we are observing from a special position can be given up.
2) Exobiology: By extension, human beings and the Earth are not at the centre of the → Universe and therefore are not "special". Life would therefore be commonplace. Compare → anthropic principle.

→ Copernican model; → principle.

A malleable, ductile, reddish metal with a bright luster that is known from antiquity, and has been mined for some 5000 years; symbol Cu. → Atomic number 29; → atomic weight 63.546; → melting point 1,083.4°C; → boiling point 2,567°C; → specific gravity 8.96 at 20°C. Copper is an excellent conductor of heat and electricity and is widely used for various purposes, either pure or in numerous alloys such as bronze and brass in combination with → tin and → zinc. Its → radioactive isotopes have half-lives from 5.10 min (⁶⁶Cu) to 61.0 hr (⁶⁷Cu). Copper is mostly created inside → massive stars, via the → s-process, after they leave the → main sequence.

M.E. coper; O.E. coper, copor; cf. O.N. koparr, Ger. Kupfer, the original Germaic word from L.L. cuprum, contraction of L. Cyprium (æs) "Cyprian (metal)," referriing to the island which was the primary source of copper for the Romans, after Gk. Kyprios "Cypress," literally "land of cypress trees."

Mes "copper," of unknown origin; maybe related to Skt. māsaka- "a weight of gold;" Pali māsa- "a small coin, of copper, of very low value;" Prakrit māsa-.

A supernova arising from the → core collapse of a → massive star. Same as → Type Ib, → Type Ic, or → Type II supernova.

→ core; → collapse; → supernova.

An operator that acts on the → eigenstate describing the → harmonic oscillator to raise its → energy level by one step. The creation operator is the → Hermitian conjugate operator of the → annihilation operator.

→ creation; → operator.

A device producing cross dispersion.

→ cross; → disperser.

Dispersion of a light beam by using two dispersing elements (grating, grism), one for separating spectral orders, the other for resolving spectral features within an order.

→ cross; → dispersion.

A spectrograph that utilizes cross dispersion.

→ cross; → dispersion; → spectrograph.

The highest temperature for a given → ferromagnetic substance above which the → magnetization is lost and the substance becomes merely → paramagnetic. The Curie temperature of iron is about 1043 K and that of nickel 631 K.

Named after the French physicist Pierre Curie (1859-1906), a pioneer in magnetism, crystallography, and radioactivity. In 1903 he received the Nobel Prize in Physics with his wife Marie Curie (1867-1934, née Maria Skłodowska), and Henri Becquerel (1852-1908); → temperature.

A second order, → partial differential operator in space-time, defined as: ▫² = ∂²/∂x² + ∂²/∂y² + ∂²/∂z² - (1/c²)∂²/∂t², or ▫² = ∇² - (1/c²)(∂²/∂t²), where ∇² is the → Laplacian and c is the → speed of light. This operator is the square of the → four-dimensional operator  ▫, which is Lorentz invariant.

→ d'Alembert's principle; → operator.

The experiment carried out in 1927 that confirmed the → de Broglie hypothesis as to the → wave nature of the → electron. It showed that electrons scattering off crystals form a → diffraction pattern. The experimental setup consisted of a → nickle chloride → crystal as → target, an electron gun, and a → detector placed on a graduated circular scale. The intensity of the reflected electrons was measured as a function of angle and electron energy. The observations showed a strong intensity peak at a certain angle. The nickel crystal acted as a → diffraction grating. → Constructive interference occurred at a particular angle, where the peak intensity was observed in accord with → Bragg's law. Interestingly, the intent of the initial experiment was was not to confirm the de Broglie hypothesis. In fact, the discovery was made by accident.

Carried out by American physicists Clinton Davisson (1881-1958) and Lester Germer (1896-1971); → experiment.

The characteristic → temperature of the → crystal as given by the → Debye model of → specific heats.

→ debye; → temperature.

In → vector calculus, a vector → partial derivative represented by the symbol → nabla and defined in three dimensions to be:
∇ = (∂/∂x)i + (∂/∂y)j + (∂/∂z)k.
It appears in the operations → gradient: ∇f, → divergence: ∇ . E, → curl: ∇ x E, and → Laplacian: ∇ . ∇f = ∇²f.

From Gk. alphabet letter delta.

A mechanism predicted by theoretical models of → supernova explosion that operates after the → supernova shock fails to deliver a → prompt supernova explosion. The delayed supernova explosion mechanism assumes that a few tenth of a second after the → iron core collapse, the supernova shock is stalled due to energy dissipation. The material between the → protoneutron star and the stalled shock is mainly disintegrated into neutrons and protons due to the high temperatures (a few MeV) in this region. As the → neutrinos coming from the protoneutron star run through this material, a fraction of the neutrinos are captured by the → nucleons, and their energy is deposited in the material. As a result, the material behind the shock is heated by the neutrinos. If this neutrino heating is efficient enough, the stalled shock can be reinvigorated to bring about a supernova explosion.

→ delay; → supernova; → explosion.

1) To spread or distribute from a fixed or constant source.
2) To become dispersed.

M.E., from M.Fr. disperser "scatter," from L. dispersus, p.p. of dispergere "to scatter," from → dis- "apart" + spargere "to scatter," from PIE base *(s)pregh- "to scatter;" cf. Av. spareg- "to germinate, shoot, sprout," fra-sparəγa- "shoot, sprout," Skt. parjanya- "rain, rain god," Lith. spurgas "sprout."

Pâšidan "to scatter, sprinkle," az ham pâšidan "to scatter on all sides;" cf. Gazi pâšn-/pâšnâ "to scatter, spread," Lor. perxa "sprinkling;" Av. paršat.gauu- "having a speckled cow;" Skt. prs- "to sprinkle," parsati "sprinkles;" Toch. pärs- "to sprinkle;" Lith. purškiu "I spray;" PIE roor *pers- "to spray, sprinkle."

1) The resolution of white light into its component wavelengths, either by → refraction or by → diffraction. Dispersion is actually an effect in which radiations having → different wavelengths travel at different speeds in the medium. Since the → angle of refraction of each radiation vary as a function of its → wavelength, the component waves deviate from each other.
2) The rate of change of → refractive index with wavelength: dn/dλ. → Cauchy's equation shows that dispersion varies approximately as the inverse cube of the wavelength.
3) The selective → retardation of → radio waves when they propagate through a → plasma. As a result, higher → frequency waves from a → pulsar will arrive at the Earth before the lower frequencies due to the presence of → intervening → ionized gas in the → interstellar medium. → dispersion measure.
4) Statistics: The spread of values of a → variable around the → mean or → median of a → distribution.

Verbal noun of → disperse.

A graph displaying the variation of the → refractive index of a substance against the wavelength of the electromagnetic wave passing through the substance.

→ dispersion; → curve.

An equation representing the variation of → refractive index as a function of → wavelength; for example → Cauchy's equation and → Sellmeier's equation.

→ dispersion; → equation.

A parameter used in radio astronomy which describes the amount of dispersion in a radio signal due to its passage through an intervening plasma. It is proportional to the product of the interstellar electron density and the distance to the source.

→ dispersion; → measure.

An equation that describes how the → angular frequency, ω, of a wave depends on its → wave number, k. For the simplest of waves, where the speed of propagation, c, is a constant, ω(k) = ck. If the → phase velocity depends on k, that is for a dispersive medium, the function ω(k) is nonlinear.

→ dispersion; → relation.