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

A branch of astrophysics that deals with objects emitting highly energetic radiation, such as X-ray astronomy, gamma-ray astronomy, and extreme ultraviolet astronomy, as well as neutrinos and cosmic rays.

→ high; → energy; → astrophysics.

Cosmic rays which typically have energies in the range 10¹⁵ to 10²⁰ electron volts. For the most part, they are protons and other atomic nuclei, and come from distant cosmos, perhaps even from outside our own Galaxy.

→ high; → energy; → cosmic; → ray.

A neutrino produced in high-energy particle collisions, such as those occurring when → cosmic rays strike atoms in the Earth's → atmosphere. Their energy range expands from a few → MeVs up to tenths of a → peta- (P) → electron-volts.

→ high; → energy; → neutrino.

A rare class of → H II regions in the → Magellanic Clouds. In contrast to the typical H II regions of the Magellanic Clouds, which are extended structures (sizes of several arc minutes corresponding to more than 50 pc, powered by a large number of exciting stars), HEBs are very dense and small regions (~ 4" to 10" in diameter corresponding to ~ 1-3 pc). They have a higher degree of → excitation ([O III] 5007Å /Hβ) with respect to the typical H II regions, and are, in general, heavily affected by local → dust. They are powered by a relatively smaller number of → massive stars.

→ high; → excitation; → blob.

A star whose mass exceeds 8 solar masses. Same as → massive star. → intermediate-mass star; → low-mass star.

→ high; → mass; → star.

A member of one of the two main classes of → X-ray binary systems where one of the components is a neutron star or a black hole and the other one a → massive star. HMXBs emit relatively → hard X-rays and usually show regular pulsations, no X-ray bursts, and often X-ray eclipses. Their X-ray luminosity is much larger than their optical luminosity. In our Galaxy HMXBs are found predominantly in the → spiral arms and within the → Galactic disk in young → stellar populations less than 10⁷ years old. One of the most famous HMXB is Cygnus X-1 which was the first stellar-mass black hole discovered. See also: → low-mass X-ray binary.

→ high; → mass; → X-ray; → binary.

A laser beam with the output power in the range 10¹²-10¹⁵ watts/cm², capable of depositing kilo-joule order energies during nano-second time intervals in small volumes (about 1 mm³). High power lasers, which can produce temperatures of 10-50 million degrees and pressures of 10-100 million bars, are used to simulate astrophysical conditions in laboratories.

→ high; → power;, → laser.

leyzer, → laser; por "much, many, full," → full; tavân, → power.

An observation that provides a particularly narrow, peaked image of a point source. → point spread function.

→ high; → resolution; → observation.

A population of neutral or partly ionized gas clouds in the → Galactic halo which are seen as high-altitude structures in the → atomic hydrogen  → 21 cm emission at high radial velocities (v_LSR > 100 km/sec). They have substantial neutral → column densities (> 10¹⁹ cm^-2) and their → metallicities range from 0.1 to about 1.0 times solar. The distances to the majority of them remain unknown. They may represent the continuing infall of matter onto the → Local Group. See also → compact high-velocity clouds.

→ high; → velocity; → cloud.

A mountainous or elevated region; → plateau.

→ high; → land.

Kuhsâr "mountainous, hilly area," from kuh, → mountain, + -sâr suffix denoting profusion, abundance, variant -zâr, → catastrophe.

A → chemical element that is → geochemically characterized as having a strong → affinity to partition into → metals relative to → silicates. The highly siderophile elements, → ruthenium (Ru), → rhodium (Rh), → palladium (Pd), → rhenium (Re), → osmium (Os), → iridium (Ir), → platinum (Pt), and → gold (Au), are of interest to planetary scientists because they give insights into the early history of → accretion and → differentiation. HSEs prefer to reside in the metal of planetary cores. Therefore, the HSEs found in planetary → mantles are considered to be overabundant relative to their known preferences for metal over silicate. Therefore, it has been inferred that processes other than → equilibrium partitioning have been responsible for establishing the abundances of → mantle siderophiles. A detailed understanding of the absolute → concentrations and relative abundances of the HSEs may therefore give important insights into the earliest history of a planet (Jones et al., 2003, Chemical Geology 196, 21).

From Gk. sidero-, from sideros "iron" + → -phile.

Âhandust, from âhan, → iron, + -dust, → -phile.

1) A long walk or march for recreational activity, military training, or the like.
2) To walk or march a great distance, especially through rural areas, for pleasure, exercise, military training, or the like (Dictionary.com).

From E. dialectal hyke "to walk vigorously," maybe a Northern form of hitch "to move or draw (something) with a jerk," of unknown origin.

Vaniž, from Sangesari wəniž-/wəništ "to walk about, go round;" cf. Shughni näγ-, Roshani niγ-, naγên- "to turn round;" Book Pahlavi/Zoroastrian Mid.Pers. nâz-, nâž- "to roll, turn;" Mid.Pers. nâys- "be proud, delicate."

A generalization of Euclidean space in a way that extends methods of vector algebra from the two- and three-dimensional spaces to infinite-dimensional spaces.
Multi-dimensional space in which the eigenfunctions of quantum mechanics are represented by orthogonal unit vectors.

Named after the German mathematician David Hilbert (1862-1943), recognized as one of the most influential mathematicians of the 19th and early 20th centuries for his numerous contributions to various areas of mathematics; → space.

The asteroids found on the outer edge of the main asteroid belt in a 2:3 orbital resonance with Jupiter. The group is not an asteroid family since the members are not physically related. The group consists of asteroids with semi-major axes between 3.70 AU and 4.20 AU, eccentricities less than 0.30, and inclinations less than 20°. It is dominated by D- and P-type asteroids.

Named for the prototype 153 Hilda, discovered by Johann Palisa (1848-1925) on November 2, 1875, and named Hilda after a daughter of his teacher, the astronomer Theodor von Oppolzer (1841-1886); → asteroid.

A natural elevation of the earth's surface, smaller than a mountain.

M.E.; O.E. hyll, from P.Gmc. *khulnis (cf. M.Du. hille, Low Ger. hull "hill," O.N. hallr "stone," Goth. hallus "rock," O.E. holm "rising land, island"), from PIE base *kel- "to rise, to be prominent" (cf. Skt. kuta- "summit, peak;" Mod.Pers. kutal, kotal high hill, the skirts of a hill;" Tabari dialect keti "hill; top of the head; L. collis "hill," culmen "top, summit," cellere "raise," celsus "high;" Gk. kolonos "hill," kolophon "summit;" Lith. kalnas "mountain," kalnelis "hill").

Tappé "hill."

The spherical region around a → secondary in which the secondary's gravity is more important for the motion of a particle about the secondary than the tidal influence of the → primary. The radius is described by the formula: r = a (m/3M)^1/3, where, in the case of the Earth, a is the semi-major axis of the orbit around the Sun, m is the mass of Earth, and M is the mass of the Sun. The Hill sphere for the Earth has a radius of 0.01 → astronomical units (AU). Therefore the Moon, lying at a distance of 0.0025 AU, is well within the Hill sphere of the Earth.

Named for George William Hill (1838-1914), an American astronomer who described this sphere of influence; → sphere.

The condition for the stability of a → three-body system. Three-body systems exist widely in the → solar system and → extrasolar systems, including Sun-planet-moon systems, planets-star systems, and → triple star systems. This concept of stability was introduced by Hill (1878). He used the → Jacobi integral to construct bounds of motion for → conservative systems with time-independent → potentials, which was introduced to study the stability of the Moon in the Sun-Earth → restricted three-body problem. The stability is defined by the → zero-velocity surface based on the Jacobi integral. The concept of the Hill stability has been used by many researchers to study the stability of three-body systems. The studies include the Hill stability in the full → three-body problems, the hierarchical three body problems, and the restricted three body problems (See, e.g., S. Gong & J. Li, 2015, Astrophys Space Sci. 358,37).

Hill, G.W.: Researches in the lunar theory. Am. J. Math. 1(2), 129-147 (1878); → stability.

A process in which a → close encounter between a → tightly bound binary star system and a → supermassive black hole causes one binary component to become bound to the black hole and the other to be ejected at very high velocities, up to 4,000 km s^-1. → hypervelocity star.

Hills, J. G, "Hyper-velocity and tidal stars from binaries disrupted by a massive Galactic black hole," Nature 331, 687; → mechanism.

The tenth of Jupiter's known satellites, 186 km in diameter revolving at a mean distance of 11,480,000 km from Jupiter. Discovered in 1904 by the Argentine-American astronomer Charles Dillon Perrine (1867-1951).

Himalia was a nymph of the island of Rhodes. She was seduced by the god Zeus (Jupiter).

Same as → Indian numeral system.

→ numeral; → system.