An Etymological Dictionary of Astronomy and Astrophysics

A young, nearby cluster of stars (spectral types A1-K) visible to the naked eye in the constellation → Taurus about 150 light-years away. Its individual stars (more than 200) appear to spread out in space. → Aldebaran is a foreground star in that region of the sky.

Etymology (EN): In Gk. mythology, a group of nymphs and sisters of Hyas, or else his daughters, and when Hyas died while hunting, killed by a lion or a boar, they grieved his death exceedingly, and turned into the stars called Hyades.

Etymology (PE): Huâdes, from Gk., as above.

A young, nearby cluster of stars (spectral types A1-K) visible to the naked eye in the constellation → Taurus about 150 light-years away. Its individual stars (more than 200) appear to spread out in space. → Aldebaran is a foreground star in that region of the sky.

Etymology (EN): In Gk. mythology, a group of nymphs and sisters of Hyas, or else his daughters, and when Hyas died while hunting, killed by a lion or a boar, they grieved his death exceedingly, and turned into the stars called Hyades.

Etymology (PE): Huâdes, from Gk., as above.

Composed of two distinct races, breeds, varieties, species, or heterogeneous elements.

Etymology (EN): Hybrid, from L. hybrida, from ibrida “a crossbred animal,” of unknown origin.

Etymology (PE): Doragé, literally “of two veins, races,” from do, → two, + ragé, from rag “vein; lineage; race,” → vessel.

Composed of two distinct races, breeds, varieties, species, or heterogeneous elements.

Etymology (EN): Hybrid, from L. hybrida, from ibrida “a crossbred animal,” of unknown origin.

Etymology (PE): Doragé, literally “of two veins, races,” from do, → two, + ragé, from rag “vein; lineage; race,” → vessel.

A rare type of solar eclipse where at some places the eclipse is annular while at other places it appears total. This duality comes about when the vertex of the Moon’s umbral shadow pierces Earth’s surface at some points, but falls short of the planet along other portions of the eclipse path. Hybrid eclipses are also known as → annular-total eclipses. In most cases, hybrid eclipses begin as annular, transform into total, and then revert back to annular before the end of their track. In rare instances, a hybrid eclipse may begin annular and end total, or vice versa (F. Espenak, NASA).

See also: → hybrid; → eclipse.

A rare type of solar eclipse where at some places the eclipse is annular while at other places it appears total. This duality comes about when the vertex of the Moon’s umbral shadow pierces Earth’s surface at some points, but falls short of the planet along other portions of the eclipse path. Hybrid eclipses are also known as → annular-total eclipses. In most cases, hybrid eclipses begin as annular, transform into total, and then revert back to annular before the end of their track. In rare instances, a hybrid eclipse may begin annular and end total, or vice versa (F. Espenak, NASA).

See also: → hybrid; → eclipse.

A star on the upper → main sequence which simultaneously exhibits low-order pressure mode (→ p mode) and high-order gravity mode (→ g mode) characteristic of β Cephei and → slowly pulsating B stars, respectively. Examples include: γ Pegasi, HD 43317, and HD 50230.

See also: → hybrid; → pulsator.

A star on the upper → main sequence which simultaneously exhibits low-order pressure mode (→ p mode) and high-order gravity mode (→ g mode) characteristic of β Cephei and → slowly pulsating B stars, respectively. Examples include: γ Pegasi, HD 43317, and HD 50230.

See also: → hybrid; → pulsator.

A hypothetical object composed of a → quark matter in the central regions, enveloped by ordinary → hadronic matter.

See also: → hybrid; → star.

A hypothetical object composed of a → quark matter in the central regions, enveloped by ordinary → hadronic matter.

See also: → hybrid; → star.

→ hydro-.

→ hydro-.

1. The Water Serpent. The longest and largest constellation in the sky, stretching almost 7 hours of right ascension, and covering over 1300 square degrees, from → Canis Minor to → Libra. It lies south of → Cancer, → Leo, and → Virgo, and is best seen in the northern hemisphere during the months of February through May. Its brightest star is → Alphard. Abbreviation: Hya; Genitive: Hydrae.
   

2. The third satellite of → Pluto discovered in 2005 by astronomers using the → Hubble Space Telescope images. Also called Pluto III (P3). It has an estimated diameter of between 60 and 170 km and an → orbital period of 38.2 days. It orbits the → barycenter of the → Pluto-→ Charon system at a distance of about 65,000 km.

Etymology (EN): Hydra, from L. hydrus, from Gk. hydra “water-snake;” cf. Av. udra- “otter;” Skt. udrá- “otter;” O.H.G. ottar “otter;” O.E. otor, ottor; Ger. Otter; E. otter; Lith. udras, udra “otter;” akin to → water. In Gk. mythology, this constellation represents the gigantic nine-head water-snake which haunted the swamps of Lerna. Herakles was sent to destroy her as one of his twelve labours, but for each of her heads that he decapitated, two more sprang forth. So with the help of Iolaos, Herakles applied burning brands to the severed stumps, cauterizing the wounds and preventing regeneration. In the battle he also crushed a giant crab (→ Cancer)
beneath his heel which had come to assist Hydra.

Etymology (PE): Hudrâ, from Gk. hydra, as above. → Hydrus (آبمار)

1. The Water Serpent. The longest and largest constellation in the sky, stretching almost 7 hours of right ascension, and covering over 1300 square degrees, from → Canis Minor to → Libra. It lies south of → Cancer, → Leo, and → Virgo, and is best seen in the northern hemisphere during the months of February through May. Its brightest star is → Alphard. Abbreviation: Hya; Genitive: Hydrae.
   

2. The third satellite of → Pluto discovered in 2005 by astronomers using the → Hubble Space Telescope images. Also called Pluto III (P3). It has an estimated diameter of between 60 and 170 km and an → orbital period of 38.2 days. It orbits the → barycenter of the → Pluto-→ Charon system at a distance of about 65,000 km.

Etymology (EN): Hydra, from L. hydrus, from Gk. hydra “water-snake;” cf. Av. udra- “otter;” Skt. udrá- “otter;” O.H.G. ottar “otter;” O.E. otor, ottor; Ger. Otter; E. otter; Lith. udras, udra “otter;” akin to → water. In Gk. mythology, this constellation represents the gigantic nine-head water-snake which haunted the swamps of Lerna. Herakles was sent to destroy her as one of his twelve labours, but for each of her heads that he decapitated, two more sprang forth. So with the help of Iolaos, Herakles applied burning brands to the severed stumps, cauterizing the wounds and preventing regeneration. In the battle he also crushed a giant crab (→ Cancer)
beneath his heel which had come to assist Hydra.

Etymology (PE): Hudrâ, from Gk. hydra, as above. → Hydrus (آبمار)

A relatively poor → galaxy cluster at about 50 Mpc containing a pair of bright galaxies near its centre: NGC 3309 and NGC 3311. Also known as Abell 1060 (→ Abell catalog), Hydra I is the prototype of an evolved and dynamically relaxed cluster, being dominated by early-type galaxies and having a regular core shape.

See also: → Hydra; → cluster.

A relatively poor → galaxy cluster at about 50 Mpc containing a pair of bright galaxies near its centre: NGC 3309 and NGC 3311. Also known as Abell 1060 (→ Abell catalog), Hydra I is the prototype of an evolved and dynamically relaxed cluster, being dominated by early-type galaxies and having a regular core shape.

See also: → Hydra; → cluster.

To combine chemically with → water.

Etymology (EN): From → hydr-, → hydro-

• -ate a verbal suffix.

Etymology (PE): Hidridan, from Gk. → hydr-, âbidan, from âb, → water,

• -idan infinitive suffix.

To combine chemically with → water.

Etymology (EN): From → hydr-, → hydro-

• -ate a verbal suffix.

Etymology (PE): Hidridan, from Gk. → hydr-, âbidan, from âb, → water,

• -idan infinitive suffix.

Combined with → water molecules.

See also: P.p./adj. of → hydrate.

Combined with → water molecules.

See also: P.p./adj. of → hydrate.

The process of combining with → water.

See also: Verbal noun of → hydrate.

The process of combining with → water.

See also: Verbal noun of → hydrate.

Operated, moved, or employing water or other liquids in motion.

See also: From Gk. hydraulikos organon “water organ,” from → hydro- “water” + aulos “musical instrument, hollow tube.”

Operated, moved, or employing water or other liquids in motion.

See also: From Gk. hydraulikos organon “water organ,” from → hydro- “water” + aulos “musical instrument, hollow tube.”

A device, which uses the energy of water flowing by gravity intermittently through a pipe to force a small portion of the water to a height greater than that of the source.

See also: → hydraulic; → ram.

A device, which uses the energy of water flowing by gravity intermittently through a pipe to force a small portion of the water to a height greater than that of the source.

See also: → hydraulic; → ram.

A binary compound containing hydrogen and another element, such as CH, OH, and HCl.

Etymology (EN): → hydr- + -ide.

Etymology (PE): Hidrur, loan from Fr.

A binary compound containing hydrogen and another element, such as CH, OH, and HCl.

Etymology (EN): → hydr- + -ide.

Etymology (PE): Hidrur, loan from Fr.

A combining form (hydr- before a vowel) originally meaning “water,” but also “liquid, gas.” In chemical nomenclature, often denotes a compound of hydrogen.

Etymology (EN): Gk. hydro-, combining form of hydor “water,” cognate with Skt. udá- “water;” Khotanese ūtcā “water;” Hittite uātar; L. unda “wave;”
O.C.S., Rus. voda; Lith. vanduo; P.Gmc. *watar (cf. Du. water; O.H.G. wazzar; Ger. Wasser; Goth. wato; O.E. wæter; E. water); from PIE base *wed- “water; wet.”

Etymology (PE): Hidro-, loanword from Gk., as above. Âb- “water,” from
Mid.Pers. âb “water;” O. Pers. ap- “water;” Av. ap- “water;” cf. Skt. áp- “water;”
Hitt. happa- “water;” PIE āp-, ab- “water, river;”
cf. Gk. Apidanos, proper noun, a river in Thessalia; L. amnis “stream, river” (from *abnis); O.Ir. ab “river,” O.Prus. ape “stream,” Lith. upé “stream;” Latv. upe “brook.”

A combining form (hydr- before a vowel) originally meaning “water,” but also “liquid, gas.” In chemical nomenclature, often denotes a compound of hydrogen.

Etymology (EN): Gk. hydro-, combining form of hydor “water,” cognate with Skt. udá- “water;” Khotanese ūtcā “water;” Hittite uātar; L. unda “wave;”
O.C.S., Rus. voda; Lith. vanduo; P.Gmc. *watar (cf. Du. water; O.H.G. wazzar; Ger. Wasser; Goth. wato; O.E. wæter; E. water); from PIE base *wed- “water; wet.”

Etymology (PE): Hidro-, loanword from Gk., as above. Âb- “water,” from
Mid.Pers. âb “water;” O. Pers. ap- “water;” Av. ap- “water;” cf. Skt. áp- “water;”
Hitt. happa- “water;” PIE āp-, ab- “water, river;”
cf. Gk. Apidanos, proper noun, a river in Thessalia; L. amnis “stream, river” (from *abnis); O.Ir. ab “river,” O.Prus. ape “stream,” Lith. upé “stream;” Latv. upe “brook.”

Any of a class of compounds containing only → hydrogen and → carbon. Hydrocarbons are organic compounds found in coal, petroleum, natural gas, and plant life. They are used as fuels, solvents, and as raw materials for numerous products such as dyes, pesticides, and plastics. Petroleum is a mixture of several hydrocarbons.

See also: → hydro- + → carbon.

Any of a class of compounds containing only → hydrogen and → carbon. Hydrocarbons are organic compounds found in coal, petroleum, natural gas, and plant life. They are used as fuels, solvents, and as raw materials for numerous products such as dyes, pesticides, and plastics. Petroleum is a mixture of several hydrocarbons.

See also: → hydro- + → carbon.

Same as → hydrogen cyanide.

See also: → hydro-; → cyano-; → acid.

Same as → hydrogen cyanide.

See also: → hydro-; → cyano-; → acid.

Of or pertaining to → hydrodynamics.

See also: → hydro- + → dynamic.

Of or pertaining to → hydrodynamics.

See also: → hydro- + → dynamic.

Fluid mechanics: A → partial differential equation which describes the motion of an element of fluid subjected to different forces such as pressure, gravity, and frictions.

See also: → hydrodynamic; → equation.

Fluid mechanics: A → partial differential equation which describes the motion of an element of fluid subjected to different forces such as pressure, gravity, and frictions.

See also: → hydrodynamic; → equation.

The state of a star when all its internal forces are in equilibrium. The main forces are gas pressure, radiation pressure due to thermonuclear fusion that tends to disrupt the star, and the opposing gravity. → hydrostatic equilibrium.

See also: → hydrodynamic; → equilibrium.

The state of a star when all its internal forces are in equilibrium. The main forces are gas pressure, radiation pressure due to thermonuclear fusion that tends to disrupt the star, and the opposing gravity. → hydrostatic equilibrium.

See also: → hydrodynamic; → equilibrium.

The branch of physics dealing with the motion, energy, and pressure of neutral → fluids.

See also: → hydro- + → dynamics.

The branch of physics dealing with the motion, energy, and pressure of neutral → fluids.

See also: → hydro- + → dynamics.

The most abundant → chemical element in the Universe. Symbol H; → atomic number 1; → atomic weight 1.00794; → melting point -259.14°C; → boiling point -252.87°C.
It was discovered by the English physicist Henry Cavendish in 1766, who called it the “inflammable air.”

See also:
→ antihydrogen, → atomic hydrogen, → heavy hydrogen, → hydrogen bond, → hydrogen burning, → hydrogen coma, → hydrogen cyanide, → hydrogen fusion, → hydrogen ion, → hydrogen line, → hydrogen shell burning, → hydrogenate, → hydrogenation, → hydrogenize, → ionized hydrogen region, → metallic hydrogen, → molecular hydrogen, → neutral hydrogen, → orthohydrogen, → parahydrogen, → triatomic hydrogen molecular ion.

See also: Hydrogen, from Fr. hydrogène, from Gk. hydro-, combining form of hydor “water” → hydro-

• Fr. -gène “producing,” → -gen;
  coined in 1787 by the French chemist Guyton de Morveau (1737-1816) because it forms water when exposed to oxygen.

The most abundant → chemical element in the Universe. Symbol H; → atomic number 1; → atomic weight 1.00794; → melting point -259.14°C; → boiling point -252.87°C.
It was discovered by the English physicist Henry Cavendish in 1766, who called it the “inflammable air.”

See also:
→ antihydrogen, → atomic hydrogen, → heavy hydrogen, → hydrogen bond, → hydrogen burning, → hydrogen coma, → hydrogen cyanide, → hydrogen fusion, → hydrogen ion, → hydrogen line, → hydrogen shell burning, → hydrogenate, → hydrogenation, → hydrogenize, → ionized hydrogen region, → metallic hydrogen, → molecular hydrogen, → neutral hydrogen, → orthohydrogen, → parahydrogen, → triatomic hydrogen molecular ion.

See also: Hydrogen, from Fr. hydrogène, from Gk. hydro-, combining form of hydor “water” → hydro-

• Fr. -gène “producing,” → -gen;
  coined in 1787 by the French chemist Guyton de Morveau (1737-1816) because it forms water when exposed to oxygen.

The attractive force between the hydrogen attached to an electronegative atom of one molecule and an electronegative atom of a different molecule. Usually the electronegative atom is oxygen, nitrogen, or fluorine, which has a partial negative charge. The hydrogen then has the partial positive charge.

See also: → hydrogen; → bond.

The attractive force between the hydrogen attached to an electronegative atom of one molecule and an electronegative atom of a different molecule. Usually the electronegative atom is oxygen, nitrogen, or fluorine, which has a partial negative charge. The hydrogen then has the partial positive charge.

See also: → hydrogen; → bond.

→ proton-proton chain.

See also: → hydrogen; → burning.

→ proton-proton chain.

See also: → hydrogen; → burning.

The cometary cloud of hydrogen, detectable in ultraviolet light, that is immensely bigger than even the huge visible coma it surrounds. It is produced by the dissociation of water into hydrogen and oxygen and by other processes set into motion by solar radiation and and the solar wind.

See also: → hydrogen, → coma.

The cometary cloud of hydrogen, detectable in ultraviolet light, that is immensely bigger than even the huge visible coma it surrounds. It is produced by the dissociation of water into hydrogen and oxygen and by other processes set into motion by solar radiation and and the solar wind.

See also: → hydrogen, → coma.

A colorless or light blue liquid or gas, a triatomic cyanide,
which is extremely flammable. HCN is an important industrial chemical and over a million tonnes are produced yearly in the world. It is produced industrially by reacting methane and ammonia in air at high temperature. A wide range of combustion processes produce HCN gas in the smoke or fumes. HCN is found naturally throughout the environment at low levels as it is released from volcanoes and certain plants and bacteria. Hydrogen cyanide is abundant in all kinds of astronomical environments, from dark clouds to star-forming regions and circumstellar envelopes. The first detection of interstellar HCN (at 88.6 GHz) and H¹³N (at 86.3 GHz)
was reported by Buhl & Snyder (1971, ApJ 163, L47). Also called → hydrocyanic acid and → prussic acid.

See also: → hydrogen; → cyanide.

A colorless or light blue liquid or gas, a triatomic cyanide,
which is extremely flammable. HCN is an important industrial chemical and over a million tonnes are produced yearly in the world. It is produced industrially by reacting methane and ammonia in air at high temperature. A wide range of combustion processes produce HCN gas in the smoke or fumes. HCN is found naturally throughout the environment at low levels as it is released from volcanoes and certain plants and bacteria. Hydrogen cyanide is abundant in all kinds of astronomical environments, from dark clouds to star-forming regions and circumstellar envelopes. The first detection of interstellar HCN (at 88.6 GHz) and H¹³N (at 86.3 GHz)
was reported by Buhl & Snyder (1971, ApJ 163, L47). Also called → hydrocyanic acid and → prussic acid.

See also: → hydrogen; → cyanide.

A → nuclear reaction where hydrogen (H) nuclei combine to form helium (⁴He) nuclei. Same as the → proton-proton chain.

See also: → hydrogen; → fusion.

A → nuclear reaction where hydrogen (H) nuclei combine to form helium (⁴He) nuclei. Same as the → proton-proton chain.

See also: → hydrogen; → fusion.

Chemistry: The → positively charged hydrogen atom, H⁺, formed by removal of the orbital electron. Same as → proton.

See also: → hydrogen; → ion.

Chemistry: The → positively charged hydrogen atom, H⁺, formed by removal of the orbital electron. Same as → proton.

See also: → hydrogen; → ion.

An → emission or → absorption line in the spectra of various astronomical objects produced by the presence of hydrogen atoms in particular physical conditions.

See also: → hydrogen, → line.

An → emission or → absorption line in the spectra of various astronomical objects produced by the presence of hydrogen atoms in particular physical conditions.

See also: → hydrogen, → line.

A phase in the life of a star that has left the → main sequence. When no more hydrogen is available in the core, the core will start to contract as it is no longer releasing the necessary energy whose pressure supports the surrounding layers. As a result of this contraction, gravitational energy is converted into thermal energy and the temperature will rise. Therefore a shell of unprocessed material surrounding the original core will be heated sufficiently for hydrogen burning to start. During the evolution of → asymptotic giant branch stars hydrogen shell burning occurs alternatively with helium shell burning. → double shell burning.

See also: → hydrogen; → shell; → burning.

A phase in the life of a star that has left the → main sequence. When no more hydrogen is available in the core, the core will start to contract as it is no longer releasing the necessary energy whose pressure supports the surrounding layers. As a result of this contraction, gravitational energy is converted into thermal energy and the temperature will rise. Therefore a shell of unprocessed material surrounding the original core will be heated sufficiently for hydrogen burning to start. During the evolution of → asymptotic giant branch stars hydrogen shell burning occurs alternatively with helium shell burning. → double shell burning.

See also: → hydrogen; → shell; → burning.

To undergo or cause to undergo a reaction with hydrogen. Same as → hydrogenize.

See also: → hydrogen; → -ate.

To undergo or cause to undergo a reaction with hydrogen. Same as → hydrogenize.

See also: → hydrogen; → -ate.

The process of combining or exposing to → hydrogen.

The process of combining or exposing to → hydrogen.

→ hydrogenate.

See also: → hydrogen; → -ize.

→ hydrogenate.

See also: → hydrogen; → -ize.

The study, measurement, and description of depths and currents in open seas, lakes, estuaries, and rivers.

See also: → hydro- + → -graphy.

The study, measurement, and description of depths and currents in open seas, lakes, estuaries, and rivers.

See also: → hydro- + → -graphy.

The vertical and horizontal transport of water in all its states between the earth, the atmosphere, and the seas; often called the water cycle.

See also: Hydrologic, pertaining to → hydrology;
→ cycle.

The vertical and horizontal transport of water in all its states between the earth, the atmosphere, and the seas; often called the water cycle.

See also: Hydrologic, pertaining to → hydrology;
→ cycle.

The study of the waters of the earth, especially with relation to the effects of precipitation and evaporation upon the occurrence and character of water in streams, lakes, and on or below the land surface.

See also: Hydrology, from → hydro-; + → -logy.

The study of the waters of the earth, especially with relation to the effects of precipitation and evaporation upon the occurrence and character of water in streams, lakes, and on or below the land surface.

See also: Hydrology, from → hydro-; + → -logy.

Same as → magnetohydrodynamics.

Etymology (EN): → hydro-; → magnetics.

Same as → magnetohydrodynamics.

Etymology (EN): → hydro-; → magnetics.

The general name for the atomic hydrogen → cation H⁺.

See also: → hydro-; → -on.

The general name for the atomic hydrogen → cation H⁺.

See also: → hydro-; → -on.

A → water, → molecule with an additional hydrogen ion (H₃O⁺). Also called hydronium ion. Hydronium is an abundant molecular ion in the interstellar diffuse and dense molecular clouds (→ Sagittarius B2, → Orion molecular cloud OMC-1) as well as the plasma tails of → comets (→ Halley, → Hale-Bopp).

See also: From hydr-, → hydro- + -onium a suffix used in the names of complex cations, extrcated from ammonium “ionized ammonia” (NH₄⁺).

A → water, → molecule with an additional hydrogen ion (H₃O⁺). Also called hydronium ion. Hydronium is an abundant molecular ion in the interstellar diffuse and dense molecular clouds (→ Sagittarius B2, → Orion molecular cloud OMC-1) as well as the plasma tails of → comets (→ Halley, → Hale-Bopp).

See also: From hydr-, → hydro- + -onium a suffix used in the names of complex cations, extrcated from ammonium “ionized ammonia” (NH₄⁺).

A term denoting the water portion of the Earth’s surface.

See also: → hydro-; → sphere.

A term denoting the water portion of the Earth’s surface.

See also: → hydro-; → sphere.

Of or pertaining to → hydrostatics.

See also: → hydro- + → static.

Of or pertaining to → hydrostatics.

See also: → hydro- + → static.

The equation describing the → hydrostatic equilibrium in a star, expressed as: dP/dr = -GMρ/r², where
P and M are the mass and pressure of a spherical shell with thickness dr at some distance r around the center of the star, ρ is the density of the gas, and G the → gravitational constant.

See also: → hydrostatic; → equation.

The equation describing the → hydrostatic equilibrium in a star, expressed as: dP/dr = -GMρ/r², where
P and M are the mass and pressure of a spherical shell with thickness dr at some distance r around the center of the star, ρ is the density of the gas, and G the → gravitational constant.

See also: → hydrostatic; → equation.

1. The physical situation reached in a fluid when complete balance exists between the internal pressure at any point and the weight of the material above the point.
   

2. For a star, the balance between the inward → gravitational force and the outward gas pressure everywhere in the star. → hydrostatic equation. See also → hydrodynamic equilibrium.

See also: → hydrostatic; → equilibrium.

1. The physical situation reached in a fluid when complete balance exists between the internal pressure at any point and the weight of the material above the point.
   

2. For a star, the balance between the inward → gravitational force and the outward gas pressure everywhere in the star. → hydrostatic equation. See also → hydrodynamic equilibrium.

See also: → hydrostatic; → equilibrium.

A model of the → Milky Way galaxy in which the → Galactic halo (composed of → gas, → magnetic fields, and → cosmic rays) is assumed to be in → hydrostatic equilibrium. Parker (1966) presented the first study of stability considerations between gas, magnetic fields and cosmic rays in an equilibrium configuration. He found that it is difficult to maintain a stable configuration due to magnetohydrodynamic self-attraction (→ Parker instability). Subsequent works taking into account turbulent motions showed that turbulent pressure can mitigate the influence of Parker instabilities. This enabled new attempts to find conditions under which a stable equilibrium configuration of the Galaxy could exist.

See also: → hydrostatic; → halo.

A model of the → Milky Way galaxy in which the → Galactic halo (composed of → gas, → magnetic fields, and → cosmic rays) is assumed to be in → hydrostatic equilibrium. Parker (1966) presented the first study of stability considerations between gas, magnetic fields and cosmic rays in an equilibrium configuration. He found that it is difficult to maintain a stable configuration due to magnetohydrodynamic self-attraction (→ Parker instability). Subsequent works taking into account turbulent motions showed that turbulent pressure can mitigate the influence of Parker instabilities. This enabled new attempts to find conditions under which a stable equilibrium configuration of the Galaxy could exist.

See also: → hydrostatic; → halo.

The term ρgz in the → Bernoulli equation. It is not pressure in a real sense, because its value depends on the reference level selected.

See also: → hydrostatic; → pressure.

The term ρgz in the → Bernoulli equation. It is not pressure in a real sense, because its value depends on the reference level selected.

See also: → hydrostatic; → pressure.

A branch of physics that deals with the characteristics of → fluids at rest and especially with the pressure in a fluid or exerted by a fluid on an immersed body.

See also: → hydro- + → statics.

A branch of physics that deals with the characteristics of → fluids at rest and especially with the pressure in a fluid or exerted by a fluid on an immersed body.

See also: → hydro- + → statics.

Geology: Relating to or caused by high temperature underground water or gas
heated by natural processes.

See also: → hydro-; → thermal.

Geology: Relating to or caused by high temperature underground water or gas
heated by natural processes.

See also: → hydro-; → thermal.

A diatomic ion containing one oxygen and one hydrogen atom with chemical formula OH^-.

See also: → hydr-; → oxide.

A diatomic ion containing one oxygen and one hydrogen atom with chemical formula OH^-.

See also: → hydr-; → oxide.

The univalent radical or group consisting of one hydrogen and one oxygen atom, forming a part of a molecule of a compound.

See also: From → hydro- + ox(y)- a combining form meaning “sharp, acute, pointed, acid,” used in the formation of compound words, from Gk, oxys “sharp, keen, acid” + -yl a suffix used in the names of chemical radicals, from Fr. -yle, from Gk. hyle “matter, substance;” → group.

The univalent radical or group consisting of one hydrogen and one oxygen atom, forming a part of a molecule of a compound.

See also: From → hydro- + ox(y)- a combining form meaning “sharp, acute, pointed, acid,” used in the formation of compound words, from Gk, oxys “sharp, keen, acid” + -yl a suffix used in the names of chemical radicals, from Fr. -yle, from Gk. hyle “matter, substance;” → group.

The Male Water Snake. A minor constellation with three main stars, one of the 15 → circumpolar constellations in the southern hemisphere. It first appeared in Johann Bayer’s Uranometria of 1603. It is often confused with → Hydra, the large constellation further north. It is also referred to as “male Hydra” or “little Hydra.” Abbreviation: Hyi; genitive: Hydri.

Etymology (EN): From L., from Gk. hydros “water serpent.”

Etymology (PE): Âbmâr “water snake,” from âb “water” (Mid.Pers. âb “water;” O. Pers. ap- “water;” Av. ap- “water;” cf. Skt. áp- “water;”
Hitt. happa- “water;” PIE āp-, ab- “water, river;”
cf. Gk. Apidanos, proper noun, a river in Thessalia; L. amnis “stream, river” (from *abnis); O.Ir. ab “river,” O.Prus. ape “stream,” Lith. upé “stream;” Latv. upe “brook”)

• mâr “snake, serpent” (Mid.Pers. mâr “snake;” Av. mairya- “snake, serpent”).

The Male Water Snake. A minor constellation with three main stars, one of the 15 → circumpolar constellations in the southern hemisphere. It first appeared in Johann Bayer’s Uranometria of 1603. It is often confused with → Hydra, the large constellation further north. It is also referred to as “male Hydra” or “little Hydra.” Abbreviation: Hyi; genitive: Hydri.

Etymology (EN): From L., from Gk. hydros “water serpent.”

Etymology (PE): Âbmâr “water snake,” from âb “water” (Mid.Pers. âb “water;” O. Pers. ap- “water;” Av. ap- “water;” cf. Skt. áp- “water;”
Hitt. happa- “water;” PIE āp-, ab- “water, river;”
cf. Gk. Apidanos, proper noun, a river in Thessalia; L. amnis “stream, river” (from *abnis); O.Ir. ab “river,” O.Prus. ape “stream,” Lith. upé “stream;” Latv. upe “brook”)

• mâr “snake, serpent” (Mid.Pers. mâr “snake;” Av. mairya- “snake, serpent”).

A combining form meaning “wet, moist, moisture,” used in the formation of compound words: → hygrogram; → hygrograph; → hygrometer .

Etymology (EN): Hygro-, from Gk, combining form of hygros “wet, moist.”

Etymology (PE): Nam “humidity, moisture” + -negâšt, → -gram. The first component nam, from Mid.Pers. nam, namb “moisture;” Av. napta- “moist,” nabās-câ- “cloud,” nabah- “sky;” cf. Skt. nábhas- “moisture, cloud, mist;” Gk. nephos “cloud, mass of clouds,” nephele “cloud;” L. nebula “mist,” nimbus “rainstorm, rain cloud;” O.H.G. nebul; Ger. Nebel “fog;” O.E. nifol “dark;” from PIE *nebh- “cloud, vapor, fog, moist, sky.”

A combining form meaning “wet, moist, moisture,” used in the formation of compound words: → hygrogram; → hygrograph; → hygrometer .

Etymology (EN): Hygro-, from Gk, combining form of hygros “wet, moist.”

Etymology (PE): Nam “humidity, moisture” + -negâšt, → -gram. The first component nam, from Mid.Pers. nam, namb “moisture;” Av. napta- “moist,” nabās-câ- “cloud,” nabah- “sky;” cf. Skt. nábhas- “moisture, cloud, mist;” Gk. nephos “cloud, mass of clouds,” nephele “cloud;” L. nebula “mist,” nimbus “rainstorm, rain cloud;” O.H.G. nebul; Ger. Nebel “fog;” O.E. nifol “dark;” from PIE *nebh- “cloud, vapor, fog, moist, sky.”

The graphical record made by a → hygrograph.

See also: → hygro- + → -gram.

The graphical record made by a → hygrograph.

See also: → hygro- + → -gram.

An instrument that records the hygrometer’s measure of water vapor.

See also: → hygro- + → -graph.

An instrument that records the hygrometer’s measure of water vapor.

See also: → hygro- + → -graph.

An instrument that measures the relative humidity of the air.

See also: → hygro- + → -meter.

An instrument that measures the relative humidity of the air.

See also: → hygro- + → -meter.

A member of a class of equations of state used in some models concerned with the evolution of a hypothetical supermassive star. The supermassive star is assumed to consist of a → convective core, which obeys a
→ polytropic law, and an envelope,
which contains most of the whole mass, and follows the hylotropic → equation of state. This equation is expressed by P = A ρ^4/3M^α, where A is a constant, ρ the density, M the mass, and α an index.
First introduced by Mitchell C. Begelman (2010, MNRAS 402, 673).

See also: From → hylotropic, on the model of → polytrope.

A member of a class of equations of state used in some models concerned with the evolution of a hypothetical supermassive star. The supermassive star is assumed to consist of a → convective core, which obeys a
→ polytropic law, and an envelope,
which contains most of the whole mass, and follows the hylotropic → equation of state. This equation is expressed by P = A ρ^4/3M^α, where A is a constant, ρ the density, M the mass, and α an index.
First introduced by Mitchell C. Begelman (2010, MNRAS 402, 673).

See also: From → hylotropic, on the model of → polytrope.

Physical chemistry: Describing a substance that is capable of undergoing a change in phase (as from a liquid to a gas), with no change in chemical composition. If the substance is hylotropic over a limited range of pressure and temperatures, it is a pure chemical substance. If it is hylotropic over all pressure and temperatures except the most extreme ones, it is a → chemical element. See also → hylotrope.

Etymology (EN): First suggested by Wilhelm Ostwald (1904, in Annalen der Naturphilosophie 3, 355), from Gk. hylo-, combining form of hyle “matter; wood,” because of the dependence on the composition, + → -tropic.

Etymology (PE): Mâdegard, from mâdé, → matter,

• gard, → -tropic.

Physical chemistry: Describing a substance that is capable of undergoing a change in phase (as from a liquid to a gas), with no change in chemical composition. If the substance is hylotropic over a limited range of pressure and temperatures, it is a pure chemical substance. If it is hylotropic over all pressure and temperatures except the most extreme ones, it is a → chemical element. See also → hylotrope.

Etymology (EN): First suggested by Wilhelm Ostwald (1904, in Annalen der Naturphilosophie 3, 355), from Gk. hylo-, combining form of hyle “matter; wood,” because of the dependence on the composition, + → -tropic.

Etymology (PE): Mâdegard, from mâdé, → matter,

• gard, → -tropic.

Physical chemistry: The fact or condition of being → hylotropic.

See also: → hylotropic; → -tropy.

Physical chemistry: The fact or condition of being → hylotropic.

See also: → hylotropic; → -tropy.

A prefix appearing in loanwords from Greek meaning:

1. “Over,” like → super-, and sometimes implying:
   

2. “Excess higher than that denoted by super-;” e.g. → hypernova.

Etymology (EN): From Gk. hyper, preposition and adverb, “over, beyond, overmuch, above;” cognate with L. super- and Pers. abar-, as below.

Etymology (PE): 1) Mid.Pers. abar; O.Pers. upariy “above; over, upon, according to;” Av. upairi “above, over,” upairi.zəma- “located above the earth;” cf. Gk. hyper- “over, above;” L. super-; O.H.G. ubir “over;” PIE base *uper “over.”
2) hiper, loanword from Gk.

A prefix appearing in loanwords from Greek meaning:

1. “Over,” like → super-, and sometimes implying:
   

2. “Excess higher than that denoted by super-;” e.g. → hypernova.

Etymology (EN): From Gk. hyper, preposition and adverb, “over, beyond, overmuch, above;” cognate with L. super- and Pers. abar-, as below.

Etymology (PE): 1) Mid.Pers. abar; O.Pers. upariy “above; over, upon, according to;” Av. upairi “above, over,” upairi.zəma- “located above the earth;” cf. Gk. hyper- “over, above;” L. super-; O.H.G. ubir “over;” PIE base *uper “over.”
2) hiper, loanword from Gk.

A two-branched open curve, a type of conic section, defined as the intersection between a right circular conical surface and a plane which cuts through both halves of the cone.

Etymology (EN): From Gk. hyperbole “excess, exaggeration” literally “a throwing beyond,” from hyperballein “to throw over or beyond,” from → hyper- “beyond” + bol-, nom. stem of ballein “to throw.”

Etymology (PE): Hozluli, loanword from Ar.

A two-branched open curve, a type of conic section, defined as the intersection between a right circular conical surface and a plane which cuts through both halves of the cone.

Etymology (EN): From Gk. hyperbole “excess, exaggeration” literally “a throwing beyond,” from hyperballein “to throw over or beyond,” from → hyper- “beyond” + bol-, nom. stem of ballein “to throw.”

Etymology (PE): Hozluli, loanword from Ar.

Of or pertaining to a → hyperbola.

See also: From hyperbol-, → hyperbola, + → -ic.

Of or pertaining to a → hyperbola.

See also: From hyperbol-, → hyperbola, + → -ic.

A function, denoted cosh x, defined for all real values of x, by the relation: cosh x = (1/2) (e^x + e^-x).

See also: → hyperbolic; → cosine.

A function, denoted cosh x, defined for all real values of x, by the relation: cosh x = (1/2) (e^x + e^-x).

See also: → hyperbolic; → cosine.

Any of the six functions sinh, cosh, tanh, coth, csch, and sech that are related to the → hyperbola in the same way the → trigonometric functions relate to the → circle. Many of the formulae satisfied by the hyperbolic functions are similar to corresponding formulae for the trigonometric functions,
except for + and - signs. For example: cosh²x - sinh²x = 1. See also: → hyperbolic cosine, → hyperbolic sine. Hyperbolic functions were first introduced by the Swiss mathematician Johann Heinrich Lambert (1728-1777).

See also: → hyperbolic; → function.

Any of the six functions sinh, cosh, tanh, coth, csch, and sech that are related to the → hyperbola in the same way the → trigonometric functions relate to the → circle. Many of the formulae satisfied by the hyperbolic functions are similar to corresponding formulae for the trigonometric functions,
except for + and - signs. For example: cosh²x - sinh²x = 1. See also: → hyperbolic cosine, → hyperbolic sine. Hyperbolic functions were first introduced by the Swiss mathematician Johann Heinrich Lambert (1728-1777).

See also: → hyperbolic; → function.

An orbit that is an open curve whose ends get wider apart at any rate between that of an ellipse and a straight line. Some comets’ orbits become hyperbolic through the gravitational influence of a planet the comet passes near.

See also: → hyperbolic; → orbit.

An orbit that is an open curve whose ends get wider apart at any rate between that of an ellipse and a straight line. Some comets’ orbits become hyperbolic through the gravitational influence of a planet the comet passes near.

See also: → hyperbolic; → orbit.

A function, denoted cosh x, defined for all real values of x, by the relation: cosh x = (1/2) (e^x - e^-x).

See also: → hyperbolic; → sine.

A function, denoted cosh x, defined for all real values of x, by the relation: cosh x = (1/2) (e^x - e^-x).

See also: → hyperbolic; → sine.

A three-dimensional space whose geometry resembles that of a saddle-shaped surface and is said to have negative curvature.

See also: → hyperbolic; → space.

A three-dimensional space whose geometry resembles that of a saddle-shaped surface and is said to have negative curvature.

See also: → hyperbolic; → space.

A surface or body obtained by rotating a hyperbola about its axis of symmetry.

Etymology (EN): Hyperboloid, from hyperbol(a) + → -oid a suffix meaning “resembling, like.”

Etymology (PE): Hozlulivâr, from hozluli, → hyperbola, + -vâr a suffix of similarity.

A surface or body obtained by rotating a hyperbola about its axis of symmetry.

Etymology (EN): Hyperboloid, from hyperbol(a) + → -oid a suffix meaning “resembling, like.”

Etymology (PE): Hozlulivâr, from hozluli, → hyperbola, + -vâr a suffix of similarity.

Extremely fine or thin, especially of a → spectral line split into two or more very thin components. → hyperfine structure; → hyperfine transition.

See also: → hyper-, → fine structure.

Extremely fine or thin, especially of a → spectral line split into two or more very thin components. → hyperfine structure; → hyperfine transition.

See also: → hyper-, → fine structure.

In spectroscopy, the → splitting of a spectral line into a number of very thin components. It results from a small perturbation in the energy levels of atoms or molecules due to the magnetic dipole-dipole interaction arising from the interaction of the nuclear → magnetic moment with the → spin of the electron. It can be observed only at high spectral dispersion. → fine structure.

See also: → hyperfine; → structure.

In spectroscopy, the → splitting of a spectral line into a number of very thin components. It results from a small perturbation in the energy levels of atoms or molecules due to the magnetic dipole-dipole interaction arising from the interaction of the nuclear → magnetic moment with the → spin of the electron. It can be observed only at high spectral dispersion. → fine structure.

See also: → hyperfine; → structure.

An → atomic transition involving a → hyperfine structure.

See also: → hyperfine; → transition.

An → atomic transition involving a → hyperfine structure.

See also: → hyperfine; → transition.

A system consisting of a dominant → spiral galaxy associated with → dwarf satellite galaxies and intergalactic matter. Examples in the → Local Group are our Galaxy and the → Andromeda galaxy.

See also: → hyper- + → galaxy.

A system consisting of a dominant → spiral galaxy associated with → dwarf satellite galaxies and intergalactic matter. Examples in the → Local Group are our Galaxy and the → Andromeda galaxy.

See also: → hyper- + → galaxy.

A high luminosity star with absolute visual magnitude around -10, about 10⁶ times as luminous as the Sun. Hypergiant stars are evolved → massive stars belonging to the luminosity class Ia+ or Ia0. Their spectra show very broadened emission and absorption lines resulting from the high luminosity and low surface gravity which favor strong → stellar wind. See also → Humphreys-Davidson limit; → yellow hypergiant.

See also: → hyper-; → giant.

A high luminosity star with absolute visual magnitude around -10, about 10⁶ times as luminous as the Sun. Hypergiant stars are evolved → massive stars belonging to the luminosity class Ia+ or Ia0. Their spectra show very broadened emission and absorption lines resulting from the high luminosity and low surface gravity which favor strong → stellar wind. See also → Humphreys-Davidson limit; → yellow hypergiant.

See also: → hyper-; → giant.

The sixteenth of → Saturn’s known → natural satellites. It is shaped like a potato with dimensions of 410 x 260 x 220 km and has a bizarre porous,
sponge-like appearance.

Many of the sponge holes or craters have bright walls, which suggests an abundance of → water  → ice. The crater floors are mostly the areas of the lowest → albedo and greatest red coloration. This may be because the average temperature of roughly -180 °C might be close enough to a temperature that would cause → volatiles to → sublimate, leaving the darker materials accumulated on the crater floors. Hyperion is one of the largest bodies in the → Solar System known to be so irregular. Its density is so low that it might house a vast system of caverns inside. Hyperion rotates chaotically and revolves around Saturn at a mean distance of 1,481,100 km.
It was discovered by two astronomers independently in 1848, the American William C. Bond (1789-1859) and the British William Lassell (1799-1880).

See also: Hyperion, in Gk. mythology was the
Titan god of light, one of the sons of Ouranos (Heaven) and Gaia (Earth), and the father of the lights of heaven, Eos the Dawn, Helios the Sun, and Selene the Moon.

The sixteenth of → Saturn’s known → natural satellites. It is shaped like a potato with dimensions of 410 x 260 x 220 km and has a bizarre porous,
sponge-like appearance.

Many of the sponge holes or craters have bright walls, which suggests an abundance of → water  → ice. The crater floors are mostly the areas of the lowest → albedo and greatest red coloration. This may be because the average temperature of roughly -180 °C might be close enough to a temperature that would cause → volatiles to → sublimate, leaving the darker materials accumulated on the crater floors. Hyperion is one of the largest bodies in the → Solar System known to be so irregular. Its density is so low that it might house a vast system of caverns inside. Hyperion rotates chaotically and revolves around Saturn at a mean distance of 1,481,100 km.
It was discovered by two astronomers independently in 1848, the American William C. Bond (1789-1859) and the British William Lassell (1799-1880).

See also: Hyperion, in Gk. mythology was the
Titan god of light, one of the sons of Ouranos (Heaven) and Gaia (Earth), and the father of the lights of heaven, Eos the Dawn, Helios the Sun, and Selene the Moon.

A condition of the eye that occurs when light rays entering the eye are focused behind the retina; also called farsightedness, hyperopia, long sight (opposed to → myopia).

Etymology (EN): From Gk. hupermetros “beyond measure,” from → hyper- + metron “measure;” → meter + -opia a combining form denoting a condition of sight or of the visual organs hemeralopia; myopia.

Etymology (PE): Durbini “farsightedness,” from dur “far” (Mid.Pers. dūr “far, distant, remote;” O.Pers. dūra- “far (in time or space),” dūraiy “afar, far away, far and wide;” Av. dūra-, dūirē “far,” from dav- “to move away;” cf. Skt. dūrá- “far; distance (in space and time);” PIE base *deu- “to move forward, pass;” cf. Gk. den “for a long time,” deros “lasting long”) + bin- “to see” (present stem of didan;
Mid.Pers. wyn-;
O.Pers. vain- “to see;” Av. vaēn- “to see;”
Skt. veda “I know;” Gk. oida “I know,” idein “to see;” L. videre “to see;” PIE base *weid- “to know, to see”) + -i noun suffix.

A condition of the eye that occurs when light rays entering the eye are focused behind the retina; also called farsightedness, hyperopia, long sight (opposed to → myopia).

Etymology (EN): From Gk. hupermetros “beyond measure,” from → hyper- + metron “measure;” → meter + -opia a combining form denoting a condition of sight or of the visual organs hemeralopia; myopia.

Etymology (PE): Durbini “farsightedness,” from dur “far” (Mid.Pers. dūr “far, distant, remote;” O.Pers. dūra- “far (in time or space),” dūraiy “afar, far away, far and wide;” Av. dūra-, dūirē “far,” from dav- “to move away;” cf. Skt. dūrá- “far; distance (in space and time);” PIE base *deu- “to move forward, pass;” cf. Gk. den “for a long time,” deros “lasting long”) + bin- “to see” (present stem of didan;
Mid.Pers. wyn-;
O.Pers. vain- “to see;” Av. vaēn- “to see;”
Skt. veda “I know;” Gk. oida “I know,” idein “to see;” L. videre “to see;” PIE base *weid- “to know, to see”) + -i noun suffix.

A highly energetic → supernova explosion. This phenomenon, which is more violent than a typical → supernova event, is accompanied by a → gamma-ray burst.

See also: → hyper-; → nova.

A highly energetic → supernova explosion. This phenomenon, which is more violent than a typical → supernova event, is accompanied by a → gamma-ray burst.

See also: → hyper-; → nova.

An unstable elementary particles, belonging to the class called → baryons, which have greater mass than the neutron but very short lives (10^-8 to 10^-10 seconds).

See also: From → hyper- + → -on
a suffix used in the names of elementary particles (gluon; meson; neutron; graviton, and so on).

An unstable elementary particles, belonging to the class called → baryons, which have greater mass than the neutron but very short lives (10^-8 to 10^-10 seconds).

See also: From → hyper- + → -on
a suffix used in the names of elementary particles (gluon; meson; neutron; graviton, and so on).

In aerodynamics, adjective used to describe a → sound speed in excess of Mach 5. See also → supersonic.

See also: Hypersonic, from → hyper- + → sonic.

In aerodynamics, adjective used to describe a → sound speed in excess of Mach 5. See also → supersonic.

See also: Hypersonic, from → hyper- + → sonic.

A star whose velocity is so great that it will escape the → gravitational potential of our → Galaxy. Depending on the location and direction of motion, this criterion typically corresponds to a stellar velocity in the Galactic → rest frame larger than 400 km s^-1, and up to about 1200 km s^-1.
The nature of the HVSs spans a wide range of types from → OB stars, to metal-poor → F-type stars and G/K dwarfs. While there is evidence from many late-type B HVSs in the → halo to originate from the Galactic → supermassive black hole (SMBH), other HVSs seem to originate from the → galactic disk.

HVSs can obtain their large velocities from a number of different processes:

1. → Tidal disruption of
   → close binary stars by the central SMBH of the Milky Way. In this process one star is captured by the SMBH while the other is ejected at high speed via the → gravitational slingshot mechanism.
   

2. Exchange encounters in other dense stellar environments between hard binaries (→ hard binary) and → massive stars may cause stars to be ejected and escape our Galaxy.
   

3. Disruption of close binaries via → supernova explosions. The → runaway velocities of both ejected stars can reach large values when asymmetric supernovae are considered, i.e. when the newborn → neutron star
   receives a momentum kick at birth.
   (see, e.g., T. M. Tauris, 2014, and references therein, arXiv:1412.0657).

See also: → hyper-; → velocity; → star.

A star whose velocity is so great that it will escape the → gravitational potential of our → Galaxy. Depending on the location and direction of motion, this criterion typically corresponds to a stellar velocity in the Galactic → rest frame larger than 400 km s^-1, and up to about 1200 km s^-1.
The nature of the HVSs spans a wide range of types from → OB stars, to metal-poor → F-type stars and G/K dwarfs. While there is evidence from many late-type B HVSs in the → halo to originate from the Galactic → supermassive black hole (SMBH), other HVSs seem to originate from the → galactic disk.

HVSs can obtain their large velocities from a number of different processes:

1. → Tidal disruption of
   → close binary stars by the central SMBH of the Milky Way. In this process one star is captured by the SMBH while the other is ejected at high speed via the → gravitational slingshot mechanism.
   

2. Exchange encounters in other dense stellar environments between hard binaries (→ hard binary) and → massive stars may cause stars to be ejected and escape our Galaxy.
   

3. Disruption of close binaries via → supernova explosions. The → runaway velocities of both ejected stars can reach large values when asymmetric supernovae are considered, i.e. when the newborn → neutron star
   receives a momentum kick at birth.
   (see, e.g., T. M. Tauris, 2014, and references therein, arXiv:1412.0657).

See also: → hyper-; → velocity; → star.

A Gk. prefix denoting “under.”

Etymology (EN): Gk. hypo “under” (prep.), “below” (adv.); cognate with L. sub- and
O.Pers./Av. upā, as below.

Etymology (PE): Upâ-, from O.Pers. upā (prep.) “under, with;” Av. upā, upa (prep.; prevb) “toward, with, on, in” (upā.gam- “to arrive at,” upāpa- “living in the water,” upa.naxturušu “bordering on the night”); Mod.Pers. bâ “with,” from abâ; cf. Skt. úpa (adv., prevb., prep.) “toward, with, under, on;” cognate with Gk. hypo, as above.

A Gk. prefix denoting “under.”

Etymology (EN): Gk. hypo “under” (prep.), “below” (adv.); cognate with L. sub- and
O.Pers./Av. upā, as below.

Etymology (PE): Upâ-, from O.Pers. upā (prep.) “under, with;” Av. upā, upa (prep.; prevb) “toward, with, on, in” (upā.gam- “to arrive at,” upāpa- “living in the water,” upa.naxturušu “bordering on the night”); Mod.Pers. bâ “with,” from abâ; cf. Skt. úpa (adv., prevb., prep.) “toward, with, under, on;” cognate with Gk. hypo, as above.

A curve generated by the trace of a fixed point on a small circle that rolls within a larger circle.

See also: Hypocycloid, from → hypo- +
→ cycloid.

A curve generated by the trace of a fixed point on a small circle that rolls within a larger circle.

See also: Hypocycloid, from → hypo- +
→ cycloid.

In a → right triangle, the side opposite to the right angle.

Etymology (EN): L.L. hypotenusa, from Gk. hypoteinousa “stretching under” (the right angle), from hypoteinein, from → hypo- “under” + teinein “to stretch,” → tension.

Etymology (PE): Vatar loan from Ar.

In a → right triangle, the side opposite to the right angle.

Etymology (EN): L.L. hypotenusa, from Gk. hypoteinousa “stretching under” (the right angle), from hypoteinein, from → hypo- “under” + teinein “to stretch,” → tension.

Etymology (PE): Vatar loan from Ar.

The failure of the body to maintain adequate production of heat under conditions of extreme cold.

Etymology (EN): Hypothermia, from → hypo- + therm,
from Gk. therme “heat,” from PIE *ghwerm-/*ghworm- “warm;” cf. Pers. garm “warm;” L. fornax “an oven;” O.E. wearm “warm” + -ia a noun suffix.

Etymology (PE): Upâgarmâyi, from upâ-, → hypo-, + garmâ “heat, warmth,” from Mid.Pers. garmâg; O.Pers./Av. garəma- “hot, warm;” cf. Skt. gharmah “heat;” Gk. thermos “warm;” L. formus “warm,” fornax “oven;” P.Gmc. *warmaz; O.E. wearm; E. warm; O.H.G., Ger. warm; PIE *ghworm-/*ghwerm- “warm” + -yi noun suffix.

The failure of the body to maintain adequate production of heat under conditions of extreme cold.

Etymology (EN): Hypothermia, from → hypo- + therm,
from Gk. therme “heat,” from PIE *ghwerm-/*ghworm- “warm;” cf. Pers. garm “warm;” L. fornax “an oven;” O.E. wearm “warm” + -ia a noun suffix.

Etymology (PE): Upâgarmâyi, from upâ-, → hypo-, + garmâ “heat, warmth,” from Mid.Pers. garmâg; O.Pers./Av. garəma- “hot, warm;” cf. Skt. gharmah “heat;” Gk. thermos “warm;” L. formus “warm,” fornax “oven;” P.Gmc. *warmaz; O.E. wearm; E. warm; O.H.G., Ger. warm; PIE *ghworm-/*ghwerm- “warm” + -yi noun suffix.

A statement which is based on previous observations and which serves as a starting point for further investigation by which it may be proved or disproved. See also → theory, → model, → ad hoc hypothesis, → Kant-Laplace hypothesis, → arge number hypothesis, → nebular hypothesis, → null hypothesis, → statistical hypothesis, → statistical hypothesis testing.

Etymology (EN): Hypothesis, from M.Fr. hypothèse, from L.L. hypothesis, from Gk. hypothesis “base, basis of an argument, supposition,” literally “a placing under,” from → hypo- “under” + thesis “a placing, proposition,”
from root of tithenai “to place, put, set,” didomi “I give;”
from PIE base *dhe- “to put, to do;” cf.
Mod.Pers. dâdan “to give,”
Mid.Pers. dâdan “to give,” O.Pers./Av. dā- “to give, grant, yield,” dadāiti “he gives;” Skt. dadáti “he gives;” L. dare “to give, offer,” facere “to do, to make;” Rus. delat’ “to do;” O.H.G. tuon, Ger. tun, O.E. don “to do.”

Etymology (PE): Engâré, from engâridan, engâštan “to → suppose.”
Upâdâyan, from upâ-, → hypo-, + dâyan, → thesis.

A statement which is based on previous observations and which serves as a starting point for further investigation by which it may be proved or disproved. See also → theory, → model, → ad hoc hypothesis, → Kant-Laplace hypothesis, → arge number hypothesis, → nebular hypothesis, → null hypothesis, → statistical hypothesis, → statistical hypothesis testing.

Etymology (EN): Hypothesis, from M.Fr. hypothèse, from L.L. hypothesis, from Gk. hypothesis “base, basis of an argument, supposition,” literally “a placing under,” from → hypo- “under” + thesis “a placing, proposition,”
from root of tithenai “to place, put, set,” didomi “I give;”
from PIE base *dhe- “to put, to do;” cf.
Mod.Pers. dâdan “to give,”
Mid.Pers. dâdan “to give,” O.Pers./Av. dā- “to give, grant, yield,” dadāiti “he gives;” Skt. dadáti “he gives;” L. dare “to give, offer,” facere “to do, to make;” Rus. delat’ “to do;” O.H.G. tuon, Ger. tun, O.E. don “to do.”

Etymology (PE): Engâré, from engâridan, engâštan “to → suppose.”
Upâdâyan, from upâ-, → hypo-, + dâyan, → thesis.

To form a → hypothesis.

Etymology (EN): Hypothesize, from hypothes(is), → hypothesis

• -ize a verb-forming suffix, from M.E. -isen, from O.Fr. -iser, from L.L. -izare, from Gk. -izein.

Etymology (PE): Engâré sâxtan, from engâré, → hypothesis

• sâxtan, sâzidan “to adapt, adjust, be fit; to build, make, fashion,” Mid.Pers. sâxtan, sâz-, Manichean Parthian s’c’dn “to prepare, to form,” Av. sak- “to understand, to mark,” sâcaya- (causative) “to teach.”
  Upâdâyanidan, infinitive from upâdâyan, → hypothesis.

To form a → hypothesis.

Etymology (EN): Hypothesize, from hypothes(is), → hypothesis

• -ize a verb-forming suffix, from M.E. -isen, from O.Fr. -iser, from L.L. -izare, from Gk. -izein.

Etymology (PE): Engâré sâxtan, from engâré, → hypothesis

• sâxtan, sâzidan “to adapt, adjust, be fit; to build, make, fashion,” Mid.Pers. sâxtan, sâz-, Manichean Parthian s’c’dn “to prepare, to form,” Av. sak- “to understand, to mark,” sâcaya- (causative) “to teach.”
  Upâdâyanidan, infinitive from upâdâyan, → hypothesis.

Of, pertaining to, or involving a → hypothesis; supposed.

See also: → hypothesis; → -al.

Of, pertaining to, or involving a → hypothesis; supposed.

See also: → hypothesis; → -al.

The phenomenon exhibited by a body (especially a ferromagnetic or imperfectly elastic material) in reacting to changes in the forces, especially magnetic forces, affecting it.

In ferromagnetic materials, the lag in the change in the magnetic induction B behind the change in the intensity of the external magnetizing field, due to the dependence of B on its previous values (past history).

Etymology (EN): Hysteresis, from Gk. hysteresis “being behind or late,” from
hystere-, stem of hysterein “to come late, lag behind” + -sis a suffix forming abstract nouns of action.

Etymology (PE): Pasmând “lagging behind,” from pas “behind” (Mid.Pers. pas “behind, before, after;” O.Pers. pasā “after;” Av. pasca “behind (of space); then, afterward (of time);” cf. Skt. pazca “behind, after, later,”
L. post “behind, in the rear; after, afterward;” O.C.S. po “behind, after;” Lith. pas “at, by;”
PIE *pos-, *posko-) + mând stem of mândan “to remain; to be fatigued,” mân “house, family” (Mid.pers. mândan “to remain, stay;” O.Pers. mān- “to remain, dwell;” Av. man- “to remain, dwell; to wait;” cf. Gk. menein “to remain;” L. manere “to stay, remain, abide,” mansio “a staying, a remaining, night quarters, station” (Fr. maison, ménage; E. manor, mansion, permanent); PIE *men- “to remain, wait for.”

The phenomenon exhibited by a body (especially a ferromagnetic or imperfectly elastic material) in reacting to changes in the forces, especially magnetic forces, affecting it.

In ferromagnetic materials, the lag in the change in the magnetic induction B behind the change in the intensity of the external magnetizing field, due to the dependence of B on its previous values (past history).

Etymology (EN): Hysteresis, from Gk. hysteresis “being behind or late,” from
hystere-, stem of hysterein “to come late, lag behind” + -sis a suffix forming abstract nouns of action.

Etymology (PE): Pasmând “lagging behind,” from pas “behind” (Mid.Pers. pas “behind, before, after;” O.Pers. pasā “after;” Av. pasca “behind (of space); then, afterward (of time);” cf. Skt. pazca “behind, after, later,”
L. post “behind, in the rear; after, afterward;” O.C.S. po “behind, after;” Lith. pas “at, by;”
PIE *pos-, *posko-) + mând stem of mândan “to remain; to be fatigued,” mân “house, family” (Mid.pers. mândan “to remain, stay;” O.Pers. mān- “to remain, dwell;” Av. man- “to remain, dwell; to wait;” cf. Gk. menein “to remain;” L. manere “to stay, remain, abide,” mansio “a staying, a remaining, night quarters, station” (Fr. maison, ménage; E. manor, mansion, permanent); PIE *men- “to remain, wait for.”

A closed curve showing the change in magnetic induction of a ferromagnetic body to which an external field is applied as the intensity of this field is varied from +H_s to -H_s and back again, where H_s is the magnetic field intensity corresponding to saturation.

See also: → hysteresis; → loop.

A closed curve showing the change in magnetic induction of a ferromagnetic body to which an external field is applied as the intensity of this field is varied from +H_s to -H_s and back again, where H_s is the magnetic field intensity corresponding to saturation.

See also: → hysteresis; → loop.

Dissipation of energy which occurs, due to magnetic hysteresis, when the magnetic material is subject to changes of magnetization.

See also: → hysteresis; → loss.

Dissipation of energy which occurs, due to magnetic hysteresis, when the magnetic material is subject to changes of magnetization.

See also: → hysteresis; → loss.