An Etymological Dictionary of Astronomy and Astrophysics
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A supergiant star with spectral type K or M. Red supergiants are the largest stars in the Universe, but not necessarily the most massive. Betelgeuse and Antares are the best known examples of a red supergiant.

→ red; → supergiant.

The energy which a particle has when it is at rest. According to Einstein's → mass-energy relation, it is equal to the → rest mass times the square of the → speed of light: E = mc².

→ rest; → energy.

Same as → rest energy.

→ rest; → mass; → energy.

The → kinetic energy of rotational motion of an object. It is expressed by E_R = (1/2)Iω², where I is the → moment of inertia and ω → angular velocity (2π/P).

→ rotation; → energy.

The → kinetic energy due to the → rotation of and object. Rotational energy is part of the total kinetic energy of the body. It is given by: (1/2)Iω², where I is the → moment of inertia and ω is the → angular velocity. Same as → angular kinetic energy.

→ rotational; → energy.

A unit of energy used in atomic physics, equal to about 13.6 electron-volts, the ionization potential of hydrogen.

In honor of the Swedish physicist Johannes Robert Rydberg (1854-1919), who did important contributions on spectroscopy, and in particular found a relatively simple expression relating the various lines in the spectra of chemical elements (1890).

A fundamental constant of atomic physics appearing in the → Rydberg formula. The Rydberg constant for hydrogen is 109,739 cm^-1.

→ rydberg; → constant.

A term inserted into a formula for the energy of a single electron in the outermost shell of an atom to take into account the failure of the inner electron shells to screen the nuclear charge completely.

→ rydberg; → correction.

A formula, used in atomic physics, which describes the wavelengths or frequencies of light in various series of related spectral lines, such as those emitted by hydrogen atoms.

→ rydberg; → formula.

During the → main sequence stage, a star burns the hydrogen in its core and transforms it into helium. When the helium mass amounts to about 10% of the initial stellar mass, the star can no longer maintain the → hydrostatic equilibrium in its core; the star increases its volume and leaves the main sequence in order to become a → red giant.

Named after the Brazilian astrophysicist Mario Schönberg (1914-1990) and Subramahmanyan Chandrasekhar, → Chandrasekhar limit, who were the first to point out this limit and derive it (1942, ApJ 96, 161).

Same as → Weizsacker formula.

→ semiempirical; → binding; → energy; → formula.

The energy required to remove a particle (a proton or a neutron) from a particular atomic nucleus.

→ separation; → energy.

A criterion for → convective stability in → massive stars. The Solberg-Høiland stability criterion corresponds to the inclusion of the effect of → rotation (variation of → centrifugal force) in the convective stability criterion. It is a combination of → Ledoux's criterion (or possibly → Schwarzschild's criterion) and → Rayleigh's criterion. Both the dynamical shear and Solberg-Høiland instabilities occur in the case of a very large → angular velocity decrease outwards. Therefore, in a → rotating star the Ledoux or Schwarzschild criteria for convective instability should be replaced by the Solberg-Høiland criterion. More specifically, this criterion accounts for the difference of the centrifugal force for an adiabatically displaced fluid element. It is also known as the axisymmetric baroclinic instability. It arises when the net force (gravity + buoyancy + centrifugal force) applied to a fluid parcel in an adiabatical displacement has components only in the direction of the displacement (A. Maeder, Physics, Formation and Evolution of Rotating Stars, 2009, Springer).

E. Høiland, 1939, On the Interpretation and Application of the Circulation Theorems of V. Bjerknes. Archiv for mathematik og naturvidenskab. B. XLII. Nr. 5. Oslo.
H. Solberg, 1936 (reprint), Le mouvement d'inertie de l'atmosphere stable et son rôle dans la théorie des cyclones.
H. Solberg, 1941, On the Stability of the Circular Vortex. Avhandl. utg. av Det Norske Videnskaps-Akademi i Oslo. I. Mat-Naturv. Klasse. No. 11.
Wasiutynski, J. 1946, Astrophysica Norvegica, 4, 1.

The energy which → sound waves impart to a medium. Same as acoustic energy.

→ sound; → energy.

A plot showing the energy emitted by a source as a function of the radiation wavelength or frequency. It is used in many branches of astronomy to characterize astronomical sources, in particular mainly in → near infrared and → middle infrared to study → protostars or → young stellar objects. The SED of these objects is divided in four classes.
Class 0 in which the SED represents a very embedded protostar, where the mass of the central core is small in comparison to the mass of the → accreting envelope. The SED is characterized by the → blackbody radiation of the envelope and peaks at → submillimeter wavelengths.
Class I objects possess a SED that peaks in the → far infrared and is characterized by a weak contribution of the blackbody of the central protostar (detected in near infrared) and the emission of a thick disk and dense envelope. These objects have less mass in the envelope and more massive central cores with respect to Class 0.
Class II objects are the → classical T Tauri stars with a SED due to the emission of a thin disk and the central star. They have accumulated most of their final mass and have dispersed almost completely their circumstellar envelope.
Finally, Class III objects have pure photospheric spectra. Their SED is peaked in the optical and is well approximated by a blackbody emission with a faint → infrared excess due to the presence of a residual optically thin disk that may be the origin of → planetesimals.
This classification scheme can be made more quantitative by defining a → spectral index.

→ spectral; → energy; → distribution.

The splitting of a single atomic level into a group of closely spaced levels when the substance producing the single line is subjected to a uniform magnetic field. → Zeeman effect; → Stark effect.

→ spliting; → energy level.

1) To sink or plunge under water or beneath the surface of any enveloping medium.
2) To cover or overflow with water; immerse (Dictionary.com).

From L. submergere, from → sub- + mergere "to dip, immerse;" probably by rhotacism from PIE *mezg- "to dip, plunge;" cf. Skt. majj- "to sink in water;" Lith. mazgoju "to wash."

Marcidan, from Av. mraoc- "to float, submerge;" cf. Skt. mroc/mloc "to go down, set (of the Sun), to disappear, to hide;" Kurd., Laki, Nahâvandi, Bovir-Ahmadi mala- "swim," Kurd. melâna "ship, boat," melaq "wave" may be related to this Av. form.

Of or pertaining to a system composed of nearby groups and clusters of galaxies in the → local Universe. Se also → galaxy cluster.

→ super-; → galactic.

A spherical → coordinate system in which the → equator is the → supergalactic plane. Supergalactic longitude, SGL, is measured → counterclockwise from direction l = 137.37 deg, b = 0 deg (between 0 and 360 deg). The zero point for supergalactic longitude is defined by the intersection of this plane with the → Galactic plane. In the → equatorial coordinate system (J2000) this is approximately 2.82 h, +59.5 deg. Supergalactic latitude, SGB, is measured from the supergalactic plane, positive northward and negative southward. The North Supergalactic Pole (SGB=90 deg) lies at galactic coordinates l = 47.37 deg, b = +6.32 degrees, corresponding to the equatorial coordinate system (J2000) 18.9 h, +15.7 deg.

→ supergalactic; → coordinate; → system.

→ supergalactic coordinate system.

→ supergalactic; → latitude.