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

A spectrum of absorption lines or bands, produced when light from a hot source, itself producing a continuous spectrum, passes through a cooler gas.

→ absorption; → spectrum.

Of the → cosmic microwave background radiation, a plot of how much the temperature varies from point to point on the sky versus the angular frequency. This spectrum answers fundamental questions about the nature of the Universe. → cosmic microwave background anisotropy; → dipole anisotropy.

→ angular; → power; → spectrum.

The spectrum produced by an atom or mixture of atoms as a result of vaporization within an electric arc generated between two electrodes.

→ arc; → spectrum.

A spectrum which consists of a number of bands each having one sharp edge. Each band is composed of a large number of closely spaced emission or absorption lines. Band spectra are typical of molecules. Bands produced by titanium oxide, zirconium oxide, and carbon compounds are characteristic of low temperature stars.

Band spectrum, from → band + → spectrum.

Binâb-e bândi, from binâb, → spectrum + bândi, relating to bând, → band.

A curve displaying → blackbody radiation intensity versus the wavelength for a given temperature, according to → Planck's blackbody formula. It is an asymmetrical curve with a sharp rise on the short wavelength side and a much more gradually sloping long-wavelength tale. Same as → Planck spectrum.

→ blackbody; → spectrum.

A plot displaying the amplitude of → cosmic microwave background anisotropy as a function of angular size or → multipole index. Same as → angular fluctuation spectrum. The plot, based the on WMAP and other data, shows a plateau at large angular or length scales (→ Sachs-Wolfe plateau), then a series of peaks at progressively smaller scales. These features arise from the gravity-driven acoustic oscillations of the coupled photon-baryon fluid in the early Universe (→ baryon acoustic oscillation). In particular, a strong peak is seen on an angular scale (at l ~220), corresponding to the physical length of the → sound horizon at the → recombination era. It depends on the curvature of space. If space is positively curved, then this sound horizon scale will appear larger on the sky than in a flat Universe (the first peak will move to the left). The second peak (l ~ 550), which is the first harmonic of the main peak, relates to the baryon/photon ratio. The third peak can be used to help constrain the total matter density.

→ angular; → fluctuation; → spectrum.

A spectrum of known substances used as a standard of comparison for investigating spectra of celestial objects.

→ comparison; → spectrum.

A stellar spectrum displaying lines characterising two stars of different types.

→ composite; → spectrum.

An electromagnetic spectrum in which emitted or absorbed radiation is present continuously over all wavelengths in a given range.

→ continuous; → spectrum.

Binâb, → spectrum; peyvasté→ continuous.

A spectrum in which the component wavelengths (and wave numbers and frequencies) constitute a discrete sequence of values (finite or infinite in number) rather than a continuum of values.

→ discrete; → spectrum.

The range of frequencies over which electromagnetic waves are propagated. → electromagnetic radiation.

→ electromagnetic; → spectrum.

A spectrum consisting of emission lines, produced when the light does not undergo absorption between the source and the spectrograph.

→ emission; → spectrum.

Of cosmic rays, the plot representing the number of particles as a function of their energy.

→ energy; → spectrum.

An optical spectrum, produced by a diffraction grating, in which the difference in path length of light from adjacent slits is one wavelength.

→ first; → order; → spectrum.

The spectrum of the solar → chromosphere obtained during a → solar eclipse in the instant before or after → totality. In the flash spectrum the usual solar → absorption lines are replaced with bright → emission lines. This is because in that very short interval only the → photosphere is eclipsed by the Moon, and not the chromosphere. The American astronomer Charles A. Young was the first to observe it during the the solar eclipse of 1870 (December 22) in Spain.

The flash designation comes from the fact that the change from dark-line to bright-line spectrum is very rapid; → flash; → spectrum.

A graphical display of the intensity of radiation or energy versus frequency.

→ frequency; → spectrum.

The distribution of energy over different scales in a → turbulent flow where → energy cascade occurs. Let E be the energy per unit → wave number (k) and ε the energy → dissipation parameter, E = E(k,ε). → Dimensional analysis yields: E = Cε^2/3k^-5/3, where C is the → Kolmogorov constant.

A. N. Kolmogorov, 1941, Local structure of turbulence in an incompressible fluid for very large Reynolds numbers, Doklady Acad Sci. USSR 31, 301; → spectrum.

Spectrum consisting of discrete lines (emission or absorption), each corresponding to a particular wavelength, as opposed to a continuous spectrum.

→ line, → spectrum.

A spectrum of charged particles, arranged in order of mass or mass-to-charge ratios. → mass spectrometry.

→ mass; → spectrum.

A plot of the mass-to-charge ratio of elementary particles, sorted by their isotopic mass.

→ mean; → spectrum.