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

→ supergalactic coordinate system.

→ supergalactic; → longitude.

The symmetry plane of the → Local Supercluster, where density of galaxies in our environment is the largest. The plane passes through the → Virgo cluster of galaxies, about which many of the brightest galaxies in the sky are concentrated. The supergalactic plane was recognized by Gérard de Vaucouleurs (1918-1995) in 1953 from the  → Shapley-Ames catalogue.

→ supergalactic; → plane.

A star with maximum intrinsic brightness and low density. The radius of a supergiant can be as large as 1000 times that of the Sun. See also → blue supergiant; → red supergiant; → yellow supergiant.

→ super-; → giant

A highly luminous → B[e] star with a luminosity greater than 10⁴L_sun. A number of such objects exist in the → Magellanic Clouds, e.g. LMC R126, R66, SMC R4, and R50. A likely example in our Galaxy is MWC 300.

→ supergiant; → B[e] star.

One of a number of large convective cells (about 15,000-30,000 km in diameter) in the solar photosphere, distributed fairly uniformly over the solar disk, that last longer than a day.

→ super-; → granulation; → cell.

The total amount of energy liberated by a → supernova. A typical supernova radiates between 10⁵¹ and 10⁵²  → erg, or 10^44-45 J (→ joules).

→ supernova; → energy.

The working together or simultaneous action of separate elements or agencies when the result is greater than the sum of the individual effects or capabilities.

From Mod.L. synergia, from Gk. synergia "joint work, help," from synergos "working together," related to synergein "to work together, help another," from → syn- "together" + → ergon, → work, → erg.

Hamkâruži, from ham- "together," → syn-, + kâruž, → energy, + -i noun suffix.

1) The energy in the form of heat emitted by an object by virtue of its temperature.
2) The total potential and kinetic energies associated with the random motions of the particles of a material. The quantity of thermal energy possessed by a body determines its temperature. The thermal energy which is absorbed, given up, or transferred from one material to another is heat.
3) The characteristic energy of → thermal neutrons at room temperature, about 0.025 eV.

→ thermal; → energy.

The minimum energy necessary for the occurrence of some chemical/physical effect.

→ threshold; → energy.

The sum of all forms of energy involved in a system.

→ total; → energy.

A particle belonging to the most energetic population of → cosmic rays with an energy above ~ 10²⁰ → electron-volts. The UHECRs constitute a real challenge for theoretical models, because their acceleration requires extreme conditions hardly fulfilled by known astrophysical objects. See also → UHECR puzzle, → Greisen-Zatsepin-Kuzmin cutoff.

→ ultra- + → high-energy cosmic ray.

A neutrino particle accelerated to energies above 10¹⁸ → electron-volts. They are produced by the interaction of → ultra-high-energy cosmic ray (UHECR)s with the → cosmic microwave background radiation. Also called → cosmogenic neutrinos. See also → Greisen-Zatsepin-Kuzmin limit.

→ ultra-; → high; → energy; → neutrino.

In particle physics the lowest energy allowed by field quantization when all fields are in their → ground states. Vacuum energy is predicted to arise from → virtual particles that fluctuate in and out of existence, as manifested by the → Casimir effect. The cosmological → dark energy is postulated to be related to vacuum fluctuations. There is however an enormous discrepancy with the predictions of quantum field theory. In this theory the value of vacuum energy density is expected to be roughly of the order ρ_v≅ E_max⁴, where E_max is the maximum energy at which the field theory is valid. At energies of the order of the → Planck energy, E_Pl≅ 10¹⁹ GeV, vacuum energy might be roughly: ρ_v≅ E_Pl⁴≅ 10⁷⁶ GeV⁴. On the other hand, the vacuum energy density in standard cosmological model is given by: ρ_Λ = Ω_Λ.ρ_crit, where Ω_Λ is the → density parameter for the → cosmological constant and ρ_crit is the → critical density. More explicitly, ρ_Λ = Ω_Λ . 3 H²/(8πG). Using present-day values of Ω_Λ (0.7) and H (70) leads to ρ_Λ = 10^-46 GeV⁴. Therefore, the discrepancy between the prediction and the observed value is 122 orders of magnitude.

→ vacuum; → energy.

A catalog of → reflection nebulae containing 158 objects. The catalog gives information for all BD and CD stars north of δ = -33 deg which are surrounded by reflection nebulosity visible on both the blue and red prints of the → Palomar Observatory Sky Survey .

van den Bergh, S., 1966, AJ, 71, 990; → catalog

Optics: A measure of the convergence or divergence of a pair of light rays, defined as the reciprocal of the distance between the point of focus and a reference plane.
Ophthalmology: The turning motion of the eyeballs toward or away from each other.

back formation from → convergence and → divergence, ultimately from L. vergere "to turn, bend, be inclined;" cognate with Pers. gardidan "to turn, to change," → version.

Gerâyi, from gerâyidan "to incline toward; to intend; to make for." Gerâ may be a variant of Mod.Pers. kil "bent, inclined" (k/g and l/r interchanges), from PIE base *klei- "to lean, incline," cognate with L. clinare "to bend" (E. declination, inclination, etc.), Gk. klinein "to cause to slope, slant, incline," Skt. sri- "to lean," O.Pers. θray-, Av. sray- "to lean," P.Gmc. *khlinen (Ger. lehnen, E. lean).

The energy due to the vibration of the molecules making up atoms (→ molecular vibration). A molecule in space can have energies in various forms: → rotational energy, vibrational energy, or electronic energy. These energies of molecules are → quantized and a particular molecule can exist in different rotational and vibrational → energy levels. The molecules can move from one level to another level only by a jump involving a finite amount of energy. → Quantum mechanics predicts that any molecule can never have zero vibrational energy, that is atoms can never be completely at rest relative to each other. The harmonically oscillating molecules can undergo vibrational changes determined by simple selection rules obtained from → Schrödinger equation.

→ vibrational; → energy.

The space containing a cluster of galaxies filled with a tenuous gas of temperature 10⁵ to 10⁷ K and density 10^-6 to 10^-4 cm^-3. WHIM has been continuously shock-heated during the process of structure formation. It is so highly ionized that it can only absorb or emit far-ultraviolet and soft X-ray photons, primarily at spectral lines of highly ionized C, O, Ne, and Fe. WHIM is thought to be the main reservoir of missing baryons.

→ warm; → hot; → intergalactic medium.

A merger between → gas-rich galaxies. Wet mergers may lead to enhanced star formation, trigger → active galactic nuclei, and transform a → disk galaxy into an → elliptical galaxy. The larger the → redshift, the wetter mergers should be.

→ wet; → merger.

The → work of the resultant force exerted on a particle equals the change in kinetic energy of the particle.

→ work; → energy; → principle.

An evolved, → very massive star of spectral type F or G with a very high luminosity (~10⁵ times solar) lying near the empirical upper luminosity boundary in the → H-R diagram (→ Humphreys-Davidson limit). Yellow hypergiants have high → mass loss rates (10^-5-10^-3 solar masses per year) and are in a short, transitional evolutionary stage. Their evolutionary state is thought to correspond to post-red supergiants rapidly evolving in blueward loops in the H-R diagram. In their post-RSG blueward evolution these stars enter a temperature range (6000-9000 K), called → yellow void, with increased dynamical instability. Their link to other advanced evolutionary phases of massive stars such as → Luminous Blue Variables and → Wolf-Rayet stars is still an open issue in stellar evolution theory. The most famous yellow hypergiant is → Rho Cassiopeiae.

→ yellow; → hypergiant.