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.
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.
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.
nemudâr-e sotuni (#)
A type of graphical representation, used in statistics, in which frequency distributions are illustrated by rectangles.
Histogram, from Gk. histo-, a combining form meaning "tissue," from histos "mast, loom, beam, warp, web," literally "that which causes to stand," from histasthai "to stand," from PIE *sta- "to stand" (cf. Pers. ist-, istâdan "to stand;" O.Pers./Av. sta- "to stand, stand still; set;" Skt. sthâ- "to stand;" L. stare "to stand;" Lith. statau "place;" Goth. standan); → -gram.
Nemudâr, → diagram + sotuni "column-like," from sotun "column," from Mid.Pers. stun, from O.Pers. stênâ "column," Av. stuna-, Skt. sthuna- "column."
abar-now-axtar-e târixi (#)
Fr.: supernova historique
A supernova event recorded in the course of history before the invention of the telescope. The well recorded supernovae of this small group are SN 185, SN 1006, SN 1054 (→ Crab Nebula), SN 1181, SN 1572 (→ Tycho's star), and SN 1604 (→ Kepler's star).
1) The branch of knowledge dealing with past events.
History, from M.E. histoire, historie, from O.Fr. estoire, histoire, from L. historia "narrative, tale, story," from Gk. historia "a learning or knowing by inquiry, record, account," from historein "to inquire," from histor "one who knows or sees, wise man, " from PIE *wid-tor-, from base *weid- "to know; to see;" cf. Pers. bin- "to see" (present stem of didan); Mid.Pers. wyn-; O.Pers. vain- "to see;" Av. vaēn- "to see;" Skt. veda "I know." Related to Gk. idein "to see," and to eidenai "to know," → idea.
Târix, from Ar., itself, according to Abu Rayhân Biruni (973-1048, in Athar al-Baqqiya), loan from Mid.Pers. mâhrôz "date," first Arabicized as murux, from which the infinitive taurix, and then târix.
Fr.: givre, gelée
Another name for → frost.
Fr.: météorite d'Hoba
The world's largest meteorite found in 1920, near Grootfontein, Namibia. It was discovered by Jacobus H. Brits while ploughing one of his fields with an ox. The meteorite is tabular in shape and measures 2.95 x 2.84 m; it has an average thickness of about 1 m (1.22 m maximum and 0.75 m minimum). The Hoba meteorite weighs about 65-70 tons. Its chemical composition is 82.4 % iron, 16.4 % nickel, 0.8 % Cobalt, and traces of other metals. No crater is present around the site of the meteorite, probably because it fell at a lower rate of speed than expected. The flat shape of the object may be responsible for its low velocity at impact.
Named after Hoba West, the farm it was discovered; → meteorite.
Fr.: transfert de Hohmann
An → orbital maneuver using two timed engine impulses to move a spacecraft between two coplanar circular orbits. It is performed through an elliptic orbit which is tangent to both circles at their periapses (→ periapsis).
In honor of Walter Hohmann (1880-1945), German engineer who in his book, The Attainability of Celestial Bodies (1925), described the mathematical principles that govern space vehicle motion, in particular spacecraft transfer between two orbits.
surâx (#), câlé (#), câl (#)
1) General: An opening through something; an area where something is missing;
a serious discrepancy.
O.E. hol "orifice, hollow place," from P.Gmc. *khulaz (cf. O.H.G. hol, M.Du. hool, Ger. hohl "hollow"), from PIE base *kel- "to cover, conceal." → cell.
Surâx "hole," from Mid.Pers. sûlâk "whole, aperture,"
Av. sūra- "hole;" cf. Gk. koilos "hollow," L.
cava "cave," cavus "hollow;"
PIE base keuə- "to swell; vault, hole."
daršâneš-e surâx, ~ câlé
Fr.: injection de trou
The injection of holes in a semiconductor which can be produced by application of a sharp conducting point in contact with an n-type semiconductor.
1) sepantruz; 2) âsudruz; 3) âsudgân
Fr.: 1); 2) férié; 3) vacances
1) A day fixed by law or custom on which ordinary business is suspended in
commemoration of some event or in honor of some person.
1) Sepantruz, from sepant "holy,"
→ heiligenschein, + ruz, → day.
From M.E. holo-, from O.fr., from L. hol-, holo-, from Gk. holos "whole," akin to Pers. har- "every, all, each, any," as below.
Haru, from Mid.Pers. har(v) "all, each, every" (Mod.Pers. har "every, all, each, any"); O.Pers. haruva- "whole, all together;" Av. hauruua- "whole, at all, undamaged;" cf. Skt. sárva- "whole, all, every, undivided;" Gk. holos "whole, complete;" L. salvus "whole, safe, healthy," sollus "whole, entire, unbroken;" PIE base *sol- "whole."