high-excitation blob (HEB)
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.
setâre-ye meh-jerm (#), ~ por-jerm (#)
Fr.: étoile massive
high-mass X-ray binary (HMXB)
dorin-e partow-e iks-e por-jerm
Fr.: binaire X de forte masse
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.
leyzer-e por-tavân (#)
Fr.: laser de puissance
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.
Fr.: observation à haute résolution
An observation that provides a particularly narrow, peaked image of a point source. → point spread function.
high-velocity clouds (HVCs)
Fr.: nuages à grande vitesse
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 (vLSR> 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.
Fr.: région montagneuse, hauts plateaux
A mountainous or elevated region; → plateau.
highly siderophile element (HSE)
bonpâr-e besyâr âhandust
Fr.: élément hautement sidérophile
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.
1) vaniž 2) vanižidan
Fr.: 1) randonnée; 2) marcher à pied
1) A long walk or march for recreational activity, military training,
or the like.
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."
fazâ-ye Hilbert (#)
Fr.: espace de Hilbert, espace hilbertien
A generalization of Euclidean space in a way that extends methods of
vector algebra from the two- and three-dimensional spaces to
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.
sayyârakhâ-ye Hilda (#)
Fr.: astéroides Hida
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").
Fr.: sphère de 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.
Fr.: stabilité de Hill
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.
Himalia (Jupiter VI)
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).
Hindu-Arabic numeral system
râžmân-e adadhâ-ye Hendi-Arabi
Fr.: numération indo-arabe
Same as → Indian numeral system.
O.E. hype "hip," akin to Du. heup, O.H.G. huf, Ger. Hüfte, Swed. höft, Goth. hups "hip," of uncertain origin.
Šanj (Dehxodâ) "hip, buttock, thigh, haunch," of unknown origin.
A → European Space Agency satellite, which was launched in August 1989 and operated until March 1993. It was the first space mission devoted to → astrometry with an unprecedented degree of accuracy. The telescope on Hipparcos had a main mirror of diameter 29 cm. Calculations from observations by the main instrument generated the Hipparcos Catalogue of 118,218 stars charted with the highest precision (published in 1997) containing positions, distances, → parallaxes, and → proper motions. An auxiliary star mapper pinpointed many more stars with lesser but still unprecedented accuracy, in the Tycho Catalogue of 1,058,332 stars. The Tycho 2 Catalogue, completed in 2000, brings the total to 2,539,913 stars, and includes 99% of all stars down to magnitude 11. → Gaia.
Hipparcos, acronym for → High → Precision → Parallax → Collecting → Satellite, chosen for its similarity to the name of the Greek astronomer Hipparchus of Nicaea (c. 190-125 BC), one of the most influential astronomers of antiquity, who compiled an extensive star catalogue in which he gave the positions of over 1,000 stars and also classified them according to their magnitude (on a scale of 1 to 6, brightest to faintest). Ptolemy later incorporated this information into his → Almagest. In addition, he discovered the → precession of the equinoxes.
The smallest known moon orbiting the planet → Neptune, discovered in 2013. Hippocamp has an estimated diameter of only about 34 km and orbits close to → Proteus, the outer and the second largest of Neptune's moons. The orbital → semi-major axes of the two moons differ by only 10%. Hippocamp is probably an ancient fragment of Proteus. Billions of years ago a comet collision would have chipped off a chunk of Proteus. Images from the Voyager 2 space probe from 1989 show a large → impact crater on Proteus, whose size compares with Hippocamp's (Showalter et al., 2019, Nature 566, 350).
Formerly known as S/2004 N 1, Hippocamp is named after the sea creatures in Greek and Roman mythology. The mythological Hippocampus possesses the upper body of a horse and the lower body of a fish. The Roman god Neptune would drive a sea-chariot pulled by Hippocampi.
A curve described by the → polar equation r2 = 4b (a - b sin2θ), where a and b are positive constants. For appropriate values of a and b, the curve looks like the infinity symbol, ∞. See also → spheres of Eudoxus.