An Etymological Dictionary of Astronomy and Astrophysics

Another name for → frost.

Another name for → frost.

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.

See also: Named after Hoba West, the farm it was discovered; → meteorite.

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.

See also: Named after Hoba West, the farm it was discovered; → meteorite.

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).

See also: → Hohmann transfer orbit.

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).

See also: → Hohmann transfer orbit.

An elliptical orbit that is the most economical path for a spacecraft to take from one planet to another. In the case of Earth-Mars travel, the desired orbit’s → perihelion will be at the distance of Earth’s orbit, and the → aphelion will be at the distance of Mars’ orbit. The portion of the solar orbit that takes the spacecraft from Earth to Mars is called its trajectory. Earth and Mars align properly for a Hohmann transfer once every 26 months. → Hohmann transfer.

See also: Named after Walter Hohmann (1880-1945), German engineer, who developed basic principles and created advanced tools necessary for the conquest of space. In 1925 he published The Attainability of the Heavenly Bodies in which he described the mathematical principles that govern space vehicle motion, in particular spacecraft transfer between two orbits.

An elliptical orbit that is the most economical path for a spacecraft to take from one planet to another. In the case of Earth-Mars travel, the desired orbit’s → perihelion will be at the distance of Earth’s orbit, and the → aphelion will be at the distance of Mars’ orbit. The portion of the solar orbit that takes the spacecraft from Earth to Mars is called its trajectory. Earth and Mars align properly for a Hohmann transfer once every 26 months. → Hohmann transfer.

See also: Named after Walter Hohmann (1880-1945), German engineer, who developed basic principles and created advanced tools necessary for the conquest of space. In 1925 he published The Attainability of the Heavenly Bodies in which he described the mathematical principles that govern space vehicle motion, in particular spacecraft transfer between two orbits.

1. General: An opening through something; an area where something is missing; a serious discrepancy.
   

2. Astro.: → black hole; → coronal hole.
   

3. Electronics: The absence of an electron in the valency structure of a crystalline semiconductor, behaving like a positive charge carrier.

Etymology (EN): 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.

Etymology (PE): 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.”
Câlé, câl “hole,” from câh “a well, pit,” from Mid.Pers. câh “a well;” Av. cāt- “a well,” from kan- “to dig,” uskən- “to dig out” (O.Pers. kan- “to dig,” akaniya- “it was dug;” Mod.Pers. kandan “to dig”); cf. Skt. khan- “to dig,” khanati “he digs,” kha- “cavity, hollow, cave, aperture.”

1. General: An opening through something; an area where something is missing; a serious discrepancy.
   

2. Astro.: → black hole; → coronal hole.
   

3. Electronics: The absence of an electron in the valency structure of a crystalline semiconductor, behaving like a positive charge carrier.

Etymology (EN): 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.

Etymology (PE): 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.”
Câlé, câl “hole,” from câh “a well, pit,” from Mid.Pers. câh “a well;” Av. cāt- “a well,” from kan- “to dig,” uskən- “to dig out” (O.Pers. kan- “to dig,” akaniya- “it was dug;” Mod.Pers. kandan “to dig”); cf. Skt. khan- “to dig,” khanati “he digs,” kha- “cavity, hollow, cave, aperture.”

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.

See also: → hole; → injection.

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.

See also: → hole; → injection.

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.
   
2. Any day of exemption from work.
   
3. (in plural form) A period of cessation from work or one of recreation; vacation.

Etymology (EN): O.E. haligdæg, from halig “holy,” → heiligenschein,

• dæg, → day.

Etymology (PE): 1) Sepantruz, from sepant “holy,” → heiligenschein, + ruz, → day.

2. Âsudruz, from âsud, âsudan “to rest, repose,” from Mid.Pers. âsutan, Av. ā- + saē- (saii-) “to lie down, go to sleep;”

• ruz, → day.
  

3. Âsudgân, from âsud, as before, + -gân suffix forming plurals.

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.
   
2. Any day of exemption from work.
   
3. (in plural form) A period of cessation from work or one of recreation; vacation.

Etymology (EN): O.E. haligdæg, from halig “holy,” → heiligenschein,

• dæg, → day.

Etymology (PE): 1) Sepantruz, from sepant “holy,” → heiligenschein, + ruz, → day.

2. Âsudruz, from âsud, âsudan “to rest, repose,” from Mid.Pers. âsutan, Av. ā- + saē- (saii-) “to lie down, go to sleep;”

• ruz, → day.
  

3. Âsudgân, from âsud, as before, + -gân suffix forming plurals.

A combining form meaning “complete, entire, total, whole,” used in the formation of compound words: → holonomic, → holography, holomorphic.

Etymology (EN): 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.

Etymology (PE): 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.”

A combining form meaning “complete, entire, total, whole,” used in the formation of compound words: → holonomic, → holography, holomorphic.

Etymology (EN): 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.

Etymology (PE): 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.”

1. A great or complete devastation or destruction, especially by fire.
   

2. (usually initial capital letter, preceded by the) The systematic mass slaughter of European Jews in Nazi concentration camps during World War II (Dictionary.com).

Etymology (EN): M.E., from L.L. holocaustum, from Gk. holokaustos “burnt whole;” see → holo- “complete, entire, total,” → caustic “burning; burnt.”

Etymology (PE): Harusuc “entirely burnt;” → holo-,
→ caustic “burning; burnt.”

1. A great or complete devastation or destruction, especially by fire.
   

2. (usually initial capital letter, preceded by the) The systematic mass slaughter of European Jews in Nazi concentration camps during World War II (Dictionary.com).

Etymology (EN): M.E., from L.L. holocaustum, from Gk. holokaustos “burnt whole;” see → holo- “complete, entire, total,” → caustic “burning; burnt.”

Etymology (PE): Harusuc “entirely burnt;” → holo-,
→ caustic “burning; burnt.”

A three-dimensional image produced with the technique of → holography.

See also: → holo-; → -gram.

A three-dimensional image produced with the technique of → holography.

See also: → holo-; → -gram.

Of, relating to, or produced using → holography; three-dimensional.

See also: → holo- + → -graphic.

Of, relating to, or produced using → holography; three-dimensional.

See also: → holo- + → -graphic.

A → diffraction grating produced from
a series of constructive → interference fringes. The fringes, whose intensities vary in a sinusoidal pattern, correspond to the grooves of the grating. They are recorded on a photosensitive substrate and subsequently treated using a chemical procedure. Since the grooves are created by the interference of light, such a grating is free from the random and periodic errors present in → ruled gratings.

See also: → holographic; → grating.

A → diffraction grating produced from
a series of constructive → interference fringes. The fringes, whose intensities vary in a sinusoidal pattern, correspond to the grooves of the grating. They are recorded on a photosensitive substrate and subsequently treated using a chemical procedure. Since the grooves are created by the interference of light, such a grating is free from the random and periodic errors present in → ruled gratings.

See also: → holographic; → grating.

A technique for making three-dimensional images by recording → interference patterns from a split → laser beam on a medium such as photographic film. One of the → coherent beams irradiates the object, the second beam illuminates a recording medium. The two beams produce an interference pattern, called → hologram, on the film. The hologram contains information on both → phase and → amplitude of the object. However, this information is in a coded form, and the image must be reconstructed. When the object is removed and the hologram is illuminated by the laser from the original direction, a 3-dimensional image of the object appears where the object was originally, as if it were not removed. The visible object seems so real that the observer can detect → parallax by changing the position of one’s head.

See also: From → holo- “whole” + → -graphy. By using the term holography, Dennis Gabor (1900-1979), the Hungarian-British electrical engineer and inventor, wanted to stress that the technique records complete information about a wave, both about its amplitude and its phase, in contrast to the usual photography in which only the distribution of the amplitude is recorded.

A technique for making three-dimensional images by recording → interference patterns from a split → laser beam on a medium such as photographic film. One of the → coherent beams irradiates the object, the second beam illuminates a recording medium. The two beams produce an interference pattern, called → hologram, on the film. The hologram contains information on both → phase and → amplitude of the object. However, this information is in a coded form, and the image must be reconstructed. When the object is removed and the hologram is illuminated by the laser from the original direction, a 3-dimensional image of the object appears where the object was originally, as if it were not removed. The visible object seems so real that the observer can detect → parallax by changing the position of one’s head.

See also: From → holo- “whole” + → -graphy. By using the term holography, Dennis Gabor (1900-1979), the Hungarian-British electrical engineer and inventor, wanted to stress that the technique records complete information about a wave, both about its amplitude and its phase, in contrast to the usual photography in which only the distribution of the amplitude is recorded.

A material system in which the → constraints can be expressed in the form of an equation relating the coordinates.

See also: From Gk. → holo- “whole” + -nomic, related to nomos
“law, managing, governing, custom,” → -nomy; → system.

A material system in which the → constraints can be expressed in the form of an equation relating the coordinates.

See also: From Gk. → holo- “whole” + -nomic, related to nomos
“law, managing, governing, custom,” → -nomy; → system.

1. Respect or reverence paid or rendered.
   

2. Something done or given in acknowledgment or consideration of the worth of another (Dictionary.com).

Etymology (EN): M.E. (h)omage, from O.Fr. homage
“allegiance or respect for one’s feudal lord,” from homme “man,” → human, + -age.

Etymology (PE): Bozordgâšt, literally “considered to be great,” from bozorg “large, magnificent, great,” → magnify, + dâšt, dâštan “to maintain, consider, possess, keep in mind, hold, have,” → property.

1. Respect or reverence paid or rendered.
   

2. Something done or given in acknowledgment or consideration of the worth of another (Dictionary.com).

Etymology (EN): M.E. (h)omage, from O.Fr. homage
“allegiance or respect for one’s feudal lord,” from homme “man,” → human, + -age.

Etymology (PE): Bozordgâšt, literally “considered to be great,” from bozorg “large, magnificent, great,” → magnify, + dâšt, dâštan “to maintain, consider, possess, keep in mind, hold, have,” → property.

A combining form meaning “same” used in the formation of compound words. Also, especially before a vowel, hom-.

Etymology (EN): Homo-, from Gk. homos “one and the same,” also “belonging to two or more jointly,” from PIE *somos;
cf. Pers. ham-, as below; Lith. similis “like,” Goth. sama “the same,” samana “together.”

Etymology (PE): Ham- “together, with; same, equally, even,” Mid.Pers. ham-, like L. com- and Gk. syn- with neither of which it is cognate. O.Pers./Av. ham-, Skt. sam-; also O.Pers./Av. hama- “one and the same,” Skt. sama-, Gk. homos-; originally identical with PIE numeral *sam- “one,” from *som-. The Av. ham- appears in various forms: han- (before gutturals, palatals, dentals) and also hem-, hen-.

A combining form meaning “same” used in the formation of compound words. Also, especially before a vowel, hom-.

Etymology (EN): Homo-, from Gk. homos “one and the same,” also “belonging to two or more jointly,” from PIE *somos;
cf. Pers. ham-, as below; Lith. similis “like,” Goth. sama “the same,” samana “together.”

Etymology (PE): Ham- “together, with; same, equally, even,” Mid.Pers. ham-, like L. com- and Gk. syn- with neither of which it is cognate. O.Pers./Av. ham-, Skt. sam-; also O.Pers./Av. hama- “one and the same,” Skt. sama-, Gk. homos-; originally identical with PIE numeral *sam- “one,” from *som-. The Av. ham- appears in various forms: han- (before gutturals, palatals, dentals) and also hem-, hen-.

Concentric → spheres of Eudoxus.

See also: → homo-; → center; → -ic; → sphere.

Concentric → spheres of Eudoxus.

See also: → homo-; → center; → -ic; → sphere.

Of, or pertaining to the process of combining two waves, such as → electromagnetic waves, of the same → frequency. See also: → heterodyne.

See also: Homodyne, from → homo- + -dyne, from Gk. dynamics→ dynamics.

Of, or pertaining to the process of combining two waves, such as → electromagnetic waves, of the same → frequency. See also: → heterodyne.

See also: Homodyne, from → homo- + -dyne, from Gk. dynamics→ dynamics.

State or quality of having a uniform appearance or composition, being homogeneous

See also: → homogeneous + → -ity.

State or quality of having a uniform appearance or composition, being homogeneous

See also: → homogeneous + → -ity.

1. Of uniform composition or having a common property throughout.
   

2. Math.: Of the same kind so as to be commensurable. Of the same degree or dimension.

→ anisotropic homogeneous cosmological model, → homogeneous fluid, → homogeneous linear differential equation, → homogeneous Universe, → homogeneous turbulence, → inhomogeneous, → nonhomogeneous, → nonhomogeneous linear differential equation.

Etymology (EN): Homogeneous, from M.L. homogeneus, from Gk. homogenes “of the same kind,” from homos “same,” → homo-,

• genos “race, kind,” gonos “birth, offspring,” from PIE base *gen-/*gon-/*gn- “to produce, beget, be born,” cf. Av. zan- “to bear, give birth to a child, be born,” infinitive zazāite, zāta- “born,” zana- “race” (in sruuô.zana- “belonging to the race of the horned ones”), O.Pers. zana- “tribe” (in paru-zana- “consisting of many tribes”),
  Skt. janati “begets, bears,” jana- “creature, human being, race, tribe, people;” L. genus “race, stock, kind,” gignere “to beget.”

Etymology (PE): Hamgen “of the same kind, like each other; friend, partner,”
from ham-, → homo-, + gen “kind,” O.Pers./Av. zana- “race; tribe,” cognate with L. genus, as above). Alternatively, gen may be a variant of Mid./Mod.Pers. gôn/gun “kind, type; manner; color, skin color,” from Av. gaona- “hair, hair color, color.”

1. Of uniform composition or having a common property throughout.
   

2. Math.: Of the same kind so as to be commensurable. Of the same degree or dimension.

→ anisotropic homogeneous cosmological model, → homogeneous fluid, → homogeneous linear differential equation, → homogeneous Universe, → homogeneous turbulence, → inhomogeneous, → nonhomogeneous, → nonhomogeneous linear differential equation.

Etymology (EN): Homogeneous, from M.L. homogeneus, from Gk. homogenes “of the same kind,” from homos “same,” → homo-,

• genos “race, kind,” gonos “birth, offspring,” from PIE base *gen-/*gon-/*gn- “to produce, beget, be born,” cf. Av. zan- “to bear, give birth to a child, be born,” infinitive zazāite, zāta- “born,” zana- “race” (in sruuô.zana- “belonging to the race of the horned ones”), O.Pers. zana- “tribe” (in paru-zana- “consisting of many tribes”),
  Skt. janati “begets, bears,” jana- “creature, human being, race, tribe, people;” L. genus “race, stock, kind,” gignere “to beget.”

Etymology (PE): Hamgen “of the same kind, like each other; friend, partner,”
from ham-, → homo-, + gen “kind,” O.Pers./Av. zana- “race; tribe,” cognate with L. genus, as above). Alternatively, gen may be a variant of Mid./Mod.Pers. gôn/gun “kind, type; manner; color, skin color,” from Av. gaona- “hair, hair color, color.”

A fluid with uniform properties throughout, but meteorologists sometimes designate as homogeneous a fluid with constant density.

See also: → homogeneous, → fluid.

A fluid with uniform properties throughout, but meteorologists sometimes designate as homogeneous a fluid with constant density.

See also: → homogeneous, → fluid.

A → linear differential equation if the right-hand member is zero, Q(x) = 0, on interval I.

See also: → homogeneous; → linear; → differential; → equation.

A → linear differential equation if the right-hand member is zero, Q(x) = 0, on interval I.

See also: → homogeneous; → linear; → differential; → equation.

→ Turbulence in which spatial derivatives of all mean turbulent quantities are negligible.

See also: → homogeneous, → turbulence.

→ Turbulence in which spatial derivatives of all mean turbulent quantities are negligible.

See also: → homogeneous, → turbulence.

A model Universe which is homogeneous and → isotropic on large scales.
It is modeled by a → Robertson-Walker cosmology. A homogeneous Universe is filled with a constant density and negligible pressure. Any small spatial region is characteristic for the whole Universe.

See also: → homogeneous; → Universe.

A model Universe which is homogeneous and → isotropic on large scales.
It is modeled by a → Robertson-Walker cosmology. A homogeneous Universe is filled with a constant density and negligible pressure. Any small spatial region is characteristic for the whole Universe.

See also: → homogeneous; → Universe.

A → mapping between two mathematical → objects that preserves the object structure. A general → morphism.

See also: → homo-; → morphism.

A → mapping between two mathematical → objects that preserves the object structure. A general → morphism.

See also: → homo-; → morphism.

A molecule that is composed of only one type of → chemical element, e.g. the → molecular hydrogen and → ozone.

See also: → homo-; → nuclear; → molecule.

A molecule that is composed of only one type of → chemical element, e.g. the → molecular hydrogen and → ozone.

See also: → homo-; → nuclear; → molecule.

The altitude at which → molecular diffusion replaces → eddy diffusion as the dominant vertical transport mechanism. Light gases separate out from heavier ones above this altitude. The flux of hydrogen through the homopause is limited by diffusion.

Etymology (EN): → homo-; + pause “break, cessation, stop,” from M.Fr. pause, from L. pausa “a halt, stop, cessation,” from Gk. pausis “stopping, ceasing,” from pauein “to stop, to cause to cease.”

Etymology (PE): Hamgen, → homogeneous, + marz “frontier, border, boundary,” → frontier. frontier.

The altitude at which → molecular diffusion replaces → eddy diffusion as the dominant vertical transport mechanism. Light gases separate out from heavier ones above this altitude. The flux of hydrogen through the homopause is limited by diffusion.

Etymology (EN): → homo-; + pause “break, cessation, stop,” from M.Fr. pause, from L. pausa “a halt, stop, cessation,” from Gk. pausis “stopping, ceasing,” from pauein “to stop, to cause to cease.”

Etymology (PE): Hamgen, → homogeneous, + marz “frontier, border, boundary,” → frontier. frontier.

Based on chemical composition, the Earth atmosphere is divided into two broad layers: the homosphere and the → heterosphere. The homosphere extends from the surface of the Earth up to the height of about 90 km. It is characterized by an almost homogeneous composition of nitrogen (78%), oxygen (21%), argon (10%), carbon dioxide as well as traces of constituents like dust particles, → aerosols and cloud droplets.

See also: → homo-; → shere.

Based on chemical composition, the Earth atmosphere is divided into two broad layers: the homosphere and the → heterosphere. The homosphere extends from the surface of the Earth up to the height of about 90 km. It is characterized by an almost homogeneous composition of nitrogen (78%), oxygen (21%), argon (10%), carbon dioxide as well as traces of constituents like dust particles, → aerosols and cloud droplets.

See also: → homo-; → shere.

A nebula of gas and dust (about 17" x 12" in size), which surrounds the massive star Eta Carinae and lies about 7500 light-years away.
The surrounding material was ejected by the massive star in 1843 during its violent eruption, and is now expanding at about 500 km/sec.

Etymology (EN): Homunculus, “a diminutive human being; little man” (since the nebula resembled a small human to early observers),
from L. homin-, homun-, homo “eartly being,” humus “the earth” (cf. Pers. zamin “earth, ground,” Mid.Pers. zamig “earth;”
Av. zam- “the earth;” Skt. ksam; Gk. khthôn, khamai “on the ground;” PIE root *dh(e)ghom “earth”) + → -ula, -ule; → nebula.

Etymology (PE): Miq, → nebula; âdamak “little man.”

A nebula of gas and dust (about 17" x 12" in size), which surrounds the massive star Eta Carinae and lies about 7500 light-years away.
The surrounding material was ejected by the massive star in 1843 during its violent eruption, and is now expanding at about 500 km/sec.

Etymology (EN): Homunculus, “a diminutive human being; little man” (since the nebula resembled a small human to early observers),
from L. homin-, homun-, homo “eartly being,” humus “the earth” (cf. Pers. zamin “earth, ground,” Mid.Pers. zamig “earth;”
Av. zam- “the earth;” Skt. ksam; Gk. khthôn, khamai “on the ground;” PIE root *dh(e)ghom “earth”) + → -ula, -ule; → nebula.

Etymology (PE): Miq, → nebula; âdamak “little man.”

1. A curved or bent piece of metal or other hard material for catching, holding, or hanging something.
   

2. Something curved or bent like a hook.

Etymology (EN): M.E. hoke, O.E. hoc “hook, angle;” cf. M.Du. hoek, Du. haak, Ger. Haken “hook.”

Etymology (PE): Qollab “a hook, a hooked device,” probably ultimately from Proto-Ir. gart- “to turn;” cf. Pers. gard-, gardidan, gaštan “to turn, to wind;” cognate with dialectal qellidan “to roll.”

1. A curved or bent piece of metal or other hard material for catching, holding, or hanging something.
   

2. Something curved or bent like a hook.

Etymology (EN): M.E. hoke, O.E. hoc “hook, angle;” cf. M.Du. hoek, Du. haak, Ger. Haken “hook.”

Etymology (PE): Qollab “a hook, a hooked device,” probably ultimately from Proto-Ir. gart- “to turn;” cf. Pers. gard-, gardidan, gaštan “to turn, to wind;” cognate with dialectal qellidan “to roll.”

The law stating that if a body is deformed the → strain produced is directly proportional to the applied → stress. If the elastic limit is not exceeded, the material returns to its original shape and size on the removal of the stress. Hooke’s law forms the basis of the theory of → elasticity.

More specifically, within certain limits, the force required to stretch an elastic object such as a metal spring is directly proportional to the extension of the spring. It is commonly written: F = -kx, where F is the force, x is the length of extension/compression and k is a constant of proportionality known as the spring constant.

See also: Named after Robert Hooke (1635-1703), British scientist who described the relationship in 1676; → law.

The law stating that if a body is deformed the → strain produced is directly proportional to the applied → stress. If the elastic limit is not exceeded, the material returns to its original shape and size on the removal of the stress. Hooke’s law forms the basis of the theory of → elasticity.

More specifically, within certain limits, the force required to stretch an elastic object such as a metal spring is directly proportional to the extension of the spring. It is commonly written: F = -kx, where F is the force, x is the length of extension/compression and k is a constant of proportionality known as the spring constant.

See also: Named after Robert Hooke (1635-1703), British scientist who described the relationship in 1676; → law.

1. To move by a quick springy leap or in a series of leaps. (Of a person) Move by jumping on one foot. (Of a bird or other animal) move by jumping with two or all feet at once.
   

2. An act of hopping; short leap.

Etymology (EN): M.E. hoppen; O.E. hoppian; cognate with Ger. hopfen, O.N. hoppa.

Etymology (PE): Kopidan, from kop; cf. (Bašâgardi) kup, (Lârestâni) komp, (Bardesiri) gopak, (Sistâni) job, (Kermâni) pok, pokidan “jump, leap.”

1. To move by a quick springy leap or in a series of leaps. (Of a person) Move by jumping on one foot. (Of a bird or other animal) move by jumping with two or all feet at once.
   

2. An act of hopping; short leap.

Etymology (EN): M.E. hoppen; O.E. hoppian; cognate with Ger. hopfen, O.N. hoppa.

Etymology (PE): Kopidan, from kop; cf. (Bašâgardi) kup, (Lârestâni) komp, (Bardesiri) gopak, (Sistâni) job, (Kermâni) pok, pokidan “jump, leap.”

1. An imaginary circle that delimits the sky and the Earth.
   

2. The fundamental great circle of the → horizon system,
   defined by the intersection of the → celestial sphere and a level plane passing through the observer.
   → celestial horizon.
   

3. In → Robertson-Walker models, the boundary separating objects already observed from those not yet observed, or the boundary separating objects observable from unobservable (J. Plebanski, A. Krasinski, 2006, An Introduction to General Relativity and Cosmology, Cambridge Univ. Press).
   

4. → cosmic horizon.
   

5. → event horizon.
   

See also:
→ apparent horizon, → artificial horizon, → astronomical horizon, → dip of the horizon, → distance to the horizon, → geometric horizon, → horizon coordinate system, → horizon problem, → horizon system, → particle horizon, → sea horizon, → sensible horizon, → sound horizon, → true horizon, → visible horizon.

Etymology (EN): From O.Fr. orizon, from orizonte, from L. horizontem (nom. horizon), from Gk. horizon kyklos “bounding circle,” from horizein “bound, limit, divide, separate,” from horos “boundary.”

Etymology (PE): Ofoq, from Ar.

1. An imaginary circle that delimits the sky and the Earth.
   

2. The fundamental great circle of the → horizon system,
   defined by the intersection of the → celestial sphere and a level plane passing through the observer.
   → celestial horizon.
   

3. In → Robertson-Walker models, the boundary separating objects already observed from those not yet observed, or the boundary separating objects observable from unobservable (J. Plebanski, A. Krasinski, 2006, An Introduction to General Relativity and Cosmology, Cambridge Univ. Press).
   

4. → cosmic horizon.
   

5. → event horizon.
   

See also:
→ apparent horizon, → artificial horizon, → astronomical horizon, → dip of the horizon, → distance to the horizon, → geometric horizon, → horizon coordinate system, → horizon problem, → horizon system, → particle horizon, → sea horizon, → sensible horizon, → sound horizon, → true horizon, → visible horizon.

Etymology (EN): From O.Fr. orizon, from orizonte, from L. horizontem (nom. horizon), from Gk. horizon kyklos “bounding circle,” from horizein “bound, limit, divide, separate,” from horos “boundary.”

Etymology (PE): Ofoq, from Ar.

The coordinate system based on the position of the observer. The horizontal plane is the fundamental plane and the coordinates are
→ altitude and → azimuth.

See also: → horizon; → coordinate; → system.

The coordinate system based on the position of the observer. The horizontal plane is the fundamental plane and the coordinates are
→ altitude and → azimuth.

See also: → horizon; → coordinate; → system.

A problem with the standard cosmological model of the Big Bang related to the observational fact that regions of the Universe that are separated by vast distances nevertheless have nearly identical properties such as temperature. This contradicts the fact that light moves with a finite speed and, as a result, certain events which occur in the Universe are completely independent of each other. Inflationary cosmology offers a possible solution.

See also: → horizon; → problem.

A problem with the standard cosmological model of the Big Bang related to the observational fact that regions of the Universe that are separated by vast distances nevertheless have nearly identical properties such as temperature. This contradicts the fact that light moves with a finite speed and, as a result, certain events which occur in the Universe are completely independent of each other. Inflationary cosmology offers a possible solution.

See also: → horizon; → problem.

Same as → horizon coordinate system.

See also: → horizon; → system.

Same as → horizon coordinate system.

See also: → horizon; → system.

1. Of or pertaining to the → horizon.
   

2. At right angles to the → vertical; parallel to level ground.
   

See also:
→ blue horizontal branch star, → extreme horizontal branch star, → field horizontal branch star, → horizontal branch, → horizontal branch star, → horizontal eclipse, → horizontal parallax, → horizontal refraction, → red horizontal branch star, → supra-horizontal branch star, → zero age horizontal branch star.

See also: From → horizon + → -al.

1. Of or pertaining to the → horizon.
   

2. At right angles to the → vertical; parallel to level ground.
   

See also:
→ blue horizontal branch star, → extreme horizontal branch star, → field horizontal branch star, → horizontal branch, → horizontal branch star, → horizontal eclipse, → horizontal parallax, → horizontal refraction, → red horizontal branch star, → supra-horizontal branch star, → zero age horizontal branch star.

See also: From → horizon + → -al.

A set of roughly horizontal points in the → Hertzsprung-Russell diagram of a typical → globular cluster. It displays a stage of stellar evolution which immediately follows the → red giant branch (RGB) in stars with an initial mass < 1.2 Msun. When the star’s ascent of the RGB is terminated by the → helium flash, it moves down to the HB. The star’s → effective temperature on the HB is higher than it was on the RGB, but the luminosity is considerably less than at the helium flash. Usually HB stars have two energy sources: in addition to the → helium burning in their cores, they experience → hydrogen fusion in a surrounding shell. The thickness of the shell determines the color of the HB stars. A thin shell, involving low → opacity, makes the star look blue. The HB domain encompasses a very large effective temperature range with several members:
→ extreme HB, → blue HB, → RR Lyrae, → red HB, and
→ red clump stars. The locations depend on many parameters, including stellar mass, metallicity, age, helium abundance, and rotation.

See also: → horizontal; → branch.

A set of roughly horizontal points in the → Hertzsprung-Russell diagram of a typical → globular cluster. It displays a stage of stellar evolution which immediately follows the → red giant branch (RGB) in stars with an initial mass < 1.2 Msun. When the star’s ascent of the RGB is terminated by the → helium flash, it moves down to the HB. The star’s → effective temperature on the HB is higher than it was on the RGB, but the luminosity is considerably less than at the helium flash. Usually HB stars have two energy sources: in addition to the → helium burning in their cores, they experience → hydrogen fusion in a surrounding shell. The thickness of the shell determines the color of the HB stars. A thin shell, involving low → opacity, makes the star look blue. The HB domain encompasses a very large effective temperature range with several members:
→ extreme HB, → blue HB, → RR Lyrae, → red HB, and
→ red clump stars. The locations depend on many parameters, including stellar mass, metallicity, age, helium abundance, and rotation.

See also: → horizontal; → branch.

A star lying on the → horizontal branch.

See also: → horizontal; → branch; → star.

A star lying on the → horizontal branch.

See also: → horizontal; → branch; → star.

A type of → lunar eclipse that occurs when both the Sun and the eclipsed Moon can be observed at the same time. This is possible only when lunar eclipse occurs just before sunset or just after sunrise. At that case, both bodies will appear just above the horizon at nearly opposite points in the sky.
Also called → selenelion and → selenehelion.

See also: → horizontal; → eclipse.

A type of → lunar eclipse that occurs when both the Sun and the eclipsed Moon can be observed at the same time. This is possible only when lunar eclipse occurs just before sunset or just after sunrise. At that case, both bodies will appear just above the horizon at nearly opposite points in the sky.
Also called → selenelion and → selenehelion.

See also: → horizontal; → eclipse.

The angle under which the radius of the Earth at the place of observation would be seen from a celestial body when it is in the horizon (at the instant of rising or setting). The amount varies with the latitude since the Earth is not exactly spherical, and is greatest at equator.

See also: → horizontal; → parallax.

The angle under which the radius of the Earth at the place of observation would be seen from a celestial body when it is in the horizon (at the instant of rising or setting). The amount varies with the latitude since the Earth is not exactly spherical, and is greatest at equator.

See also: → horizontal; → parallax.

The angular distance of an object below the horizon when it appears to lie on the horizon.

See also: → horizontal; → refraction.

The angular distance of an object below the horizon when it appears to lie on the horizon.

See also: → horizontal; → refraction.

In computer science, a scaling in which the processing power is increased/decreased by adding/removing nodes with similar resources.
See also → vertical scaling.

See also: → horizontal; → scaling.

In computer science, a scaling in which the processing power is increased/decreased by adding/removing nodes with similar resources.
See also → vertical scaling.

See also: → horizontal; → scaling.

1a) The bony pointed outgrowth, usually in pairs, on the heads of some animals.

1b) Astro.: Either of the ends of the → crescent Moon.

2. Something resembling a horn.
   

3. A wind instrument, originally an animal horn used as a wind instrument.
   

See also: → feedhorn

Etymology (EN): M.E. horn(e), from O.E. horn “horn of an animal,” also “wind instrument” (originally made from animal horns), from P.Gmc. *khurnaz (cf. Ger. Horn, Du. horen), from PIE *ker- “head, horn, top, summit” (cf. Pers. soru “horn,” sar “head,” Gk. kara “head,” karena “head, top,” keras “horn;”
L. cornu “horn,” cerebrum “brain;” Skt. śiras- “head, chief”).

Etymology (PE): 1, 2) Mid.Pers šâk; cf. Skt. sakha- “a branch, a limb;” Arm. cax; Lith. šaka; O.S. soxa;
PIE *kakhâ “branch.”

3. Karnâ “a trumpet-like wind instrument,” variant sornâ “a wind instrument,” probably related to soru, sorun “horn,” sar “head;” Mid.Pers. sar “head,” sru “horn;” Av. sarah- “head,” srū- “horn, nail;” cognate with E. horn, as above, from PIE *ker- “head, horn.”

1a) The bony pointed outgrowth, usually in pairs, on the heads of some animals.

1b) Astro.: Either of the ends of the → crescent Moon.

2. Something resembling a horn.
   

3. A wind instrument, originally an animal horn used as a wind instrument.
   

See also: → feedhorn

Etymology (EN): M.E. horn(e), from O.E. horn “horn of an animal,” also “wind instrument” (originally made from animal horns), from P.Gmc. *khurnaz (cf. Ger. Horn, Du. horen), from PIE *ker- “head, horn, top, summit” (cf. Pers. soru “horn,” sar “head,” Gk. kara “head,” karena “head, top,” keras “horn;”
L. cornu “horn,” cerebrum “brain;” Skt. śiras- “head, chief”).

Etymology (PE): 1, 2) Mid.Pers šâk; cf. Skt. sakha- “a branch, a limb;” Arm. cax; Lith. šaka; O.S. soxa;
PIE *kakhâ “branch.”

3. Karnâ “a trumpet-like wind instrument,” variant sornâ “a wind instrument,” probably related to soru, sorun “horn,” sar “head;” Mid.Pers. sar “head,” sru “horn;” Av. sarah- “head,” srū- “horn, nail;” cognate with E. horn, as above, from PIE *ker- “head, horn.”

The Clock. A faint constellation in the southern hemisphere, at about 3h right ascension, 55° south declination. Its brightest star, α Horologii, is of magnitude 3.9. Abbreviation: Hor; Genitive: Horologii.

Etymology (EN): Horologium “clock,” from L., from Gk. horologion, from horolog(os) “timeteller,” from horo-, combining form of hora “hour” (→ year)

• -log-, stem of legein “to speak, tell” (+ -os adj. suffix) + -ion diminutive suffix.
  Originally named Horologium Oscillitorium by Abbé Nicolas Louis de Lacaille (1713-1762) to honour the inventor of the pendulum clock, Christian Huygens (1629-1695).

Etymology (PE): Sâ’at “clock,” from Ar.

The Clock. A faint constellation in the southern hemisphere, at about 3h right ascension, 55° south declination. Its brightest star, α Horologii, is of magnitude 3.9. Abbreviation: Hor; Genitive: Horologii.

Etymology (EN): Horologium “clock,” from L., from Gk. horologion, from horolog(os) “timeteller,” from horo-, combining form of hora “hour” (→ year)

• -log-, stem of legein “to speak, tell” (+ -os adj. suffix) + -ion diminutive suffix.
  Originally named Horologium Oscillitorium by Abbé Nicolas Louis de Lacaille (1713-1762) to honour the inventor of the pendulum clock, Christian Huygens (1629-1695).

Etymology (PE): Sâ’at “clock,” from Ar.

A schematic drawing showing the positions of the Sun, Moon, and planets at the time of a person’s birth for baseless astrological purposes.

Etymology (EN): From M.Fr. horoscope, from L. horoscopus, from Gk. horoskopos “nativity, horoscope,” also “one who casts a horoscope,” from hora “hour” + skopos “watching.”

Etymology (PE): Zâyecé “horoscope, thema,” from Mid.Pers. zâycag “horoscope,” from zâyidan, zâdan, “to give birth, bring forth;”
Av. zan-
“to bear, give birth to a child, be born,” infinitive zazāite, zāta- “born;” cf. Skt. jan- “to produce, create; to be born,”
janati “begets, bears;” Gk. gignomai “to happen, become, be born;” L. gignere “to beget;” PIE base *gen- “to give birth, beget.”

A schematic drawing showing the positions of the Sun, Moon, and planets at the time of a person’s birth for baseless astrological purposes.

Etymology (EN): From M.Fr. horoscope, from L. horoscopus, from Gk. horoskopos “nativity, horoscope,” also “one who casts a horoscope,” from hora “hour” + skopos “watching.”

Etymology (PE): Zâyecé “horoscope, thema,” from Mid.Pers. zâycag “horoscope,” from zâyidan, zâdan, “to give birth, bring forth;”
Av. zan-
“to bear, give birth to a child, be born,” infinitive zazāite, zāta- “born;” cf. Skt. jan- “to produce, create; to be born,”
janati “begets, bears;” Gk. gignomai “to happen, become, be born;” L. gignere “to beget;” PIE base *gen- “to give birth, beget.”

1. A large, solid-hoofed, herbivorous quadruped, Equus caballus, domesticated since prehistoric times.
   

2. In a → planispheric astrolabe, the small prominence that, inserted into a slit in the pin, prevents the parts of the instrument from coming loose when in use. The part owes its name to the fact that astrolabe-makers would often shape it into a horse’s head (online museo galileo, VirtualMuseum).
   

See also:

→ horse latitude, → Horsehead Nebula, → horsepower, → horseshoe mounting, → horseshoe orbit.

Etymology (EN): Horse, O.E. hors, from P.Gmc. *khursa- (cf. M.Du. ors, Du. ros, O.H.G. hros, Ger. Roß “horse”), of unknown origin; → latitude.

Etymology (PE): Asb “horse,” from Mid.Pers. asp; O.Pers. asa- “horse;” Av. aspa- “horse,” aspā- “mare,” aspaiia- “pertaining to the horse;” cf. Skt. áśva- “horse, steed;” Gk. hippos;
L. equus; O.Ir. ech; Goth. aihwa-; O.E. eoh “horse;” PIE base *ekwo- “horse.”

1. A large, solid-hoofed, herbivorous quadruped, Equus caballus, domesticated since prehistoric times.
   

2. In a → planispheric astrolabe, the small prominence that, inserted into a slit in the pin, prevents the parts of the instrument from coming loose when in use. The part owes its name to the fact that astrolabe-makers would often shape it into a horse’s head (online museo galileo, VirtualMuseum).
   

See also:

→ horse latitude, → Horsehead Nebula, → horsepower, → horseshoe mounting, → horseshoe orbit.

Etymology (EN): Horse, O.E. hors, from P.Gmc. *khursa- (cf. M.Du. ors, Du. ros, O.H.G. hros, Ger. Roß “horse”), of unknown origin; → latitude.

Etymology (PE): Asb “horse,” from Mid.Pers. asp; O.Pers. asa- “horse;” Av. aspa- “horse,” aspā- “mare,” aspaiia- “pertaining to the horse;” cf. Skt. áśva- “horse, steed;” Gk. hippos;
L. equus; O.Ir. ech; Goth. aihwa-; O.E. eoh “horse;” PIE base *ekwo- “horse.”

The belts of latitude over the oceans, located around 30° north and south of the equator, characterized by predominantly calm or light winds and hot and dry weather.

See also: → horse; → latitude.

The origin of the term horse latitudes is not clear, despite numerous speculations. A likely explanation appears in Spanish in a natural history text (Historia General y Natural de las Indias by Lopez de Gomara)
published in 1535. Therefore, the term derives from El Golfo de las Yeguas, which translates to “The Mares’ Sea.” The sailors called it this because in the 1500’s there was active shipping of horses, particularly brood mares, from Spain to the Canary Islands, and many of the horses died during the transit of this area.

The belts of latitude over the oceans, located around 30° north and south of the equator, characterized by predominantly calm or light winds and hot and dry weather.

See also: → horse; → latitude.

The origin of the term horse latitudes is not clear, despite numerous speculations. A likely explanation appears in Spanish in a natural history text (Historia General y Natural de las Indias by Lopez de Gomara)
published in 1535. Therefore, the term derives from El Golfo de las Yeguas, which translates to “The Mares’ Sea.” The sailors called it this because in the 1500’s there was active shipping of horses, particularly brood mares, from Spain to the Canary Islands, and many of the horses died during the transit of this area.

A huge → dark cloud of → interstellar dust that is shaped like a horse’s head. It is luminous at its edges because it is in front of the bright → emission nebula IC 434. Its height and width are about 5
and 2.5 → light-years respectively. It is located at a distance of about 1500 light-years in the constellation → Orion. Also known as Barnard 33.

See also: → horse; → head;
→ nebula.

A huge → dark cloud of → interstellar dust that is shaped like a horse’s head. It is luminous at its edges because it is in front of the bright → emission nebula IC 434. Its height and width are about 5
and 2.5 → light-years respectively. It is located at a distance of about 1500 light-years in the constellation → Orion. Also known as Barnard 33.

See also: → horse; → head;
→ nebula.

A unit that is used to measure the → power of engines and motors.

1. Metric horsepower is equal to the power required to carry a load of 75 kg over a distance
   of one meter in one second. It is equivalent to 746 → watts.
   

2. British (US) horsepower is the rate of work when 33,000 foot-pounds of work are done per minute.

The horsepower was defined by James Watt (1736-1819), the inventor of the steam engine, to compare the output of steam engines with the power of draft horses. He determined that a horse is typically capable of a power of 550 foot-pounds per second.

Etymology (EN): → horse; → power.

Etymology (PE): Asb-e boxâr “vapor horse,” translation of Fr. cheval-vapeur, from asb, → horse, + boxâr, → vapor.

A unit that is used to measure the → power of engines and motors.

1. Metric horsepower is equal to the power required to carry a load of 75 kg over a distance
   of one meter in one second. It is equivalent to 746 → watts.
   

2. British (US) horsepower is the rate of work when 33,000 foot-pounds of work are done per minute.

The horsepower was defined by James Watt (1736-1819), the inventor of the steam engine, to compare the output of steam engines with the power of draft horses. He determined that a horse is typically capable of a power of 550 foot-pounds per second.

Etymology (EN): → horse; → power.

Etymology (PE): Asb-e boxâr “vapor horse,” translation of Fr. cheval-vapeur, from asb, → horse, + boxâr, → vapor.

An equatorial mounting in which the upper end of the polar axis frame is made into a horseshoe shape to accommodate the telescope tube.

Etymology (EN): Horseshoe, from → horse + shoe, from
O.E. scoh “shoe,” from P.Gmc. *skokhaz (cf. Dan., Swed. sko, O.S. skoh, Du. schoen, O.H.G. scuoh, Ger. Schuh); → mounting.

Etymology (PE): Barnešând, → mounting; na’l “horseshoe, shoe,” loanword from Ar.

An equatorial mounting in which the upper end of the polar axis frame is made into a horseshoe shape to accommodate the telescope tube.

Etymology (EN): Horseshoe, from → horse + shoe, from
O.E. scoh “shoe,” from P.Gmc. *skokhaz (cf. Dan., Swed. sko, O.S. skoh, Du. schoen, O.H.G. scuoh, Ger. Schuh); → mounting.

Etymology (PE): Barnešând, → mounting; na’l “horseshoe, shoe,” loanword from Ar.

A periodic orbit which passes around the → Lagrangian points L4, L3, and L5, but neither of the two primaries. This orbit is shaped like a horseshoe when viewed in a reference frame rotating with the primaries. Such orbits occur in the solar system, for example in the case of the satellites → Janus and → Epimetheus, which share the same orbit around → Saturn. The smaller Epimetheus encompasses both the L4 and L5 points associated with the larger Janus and performs a horseshoe orbit relative to Saturn and Janus. The satellites experience a close approach every 4 years during which their orbits are exchanged. → tadpole orbit.

See also: → horseshoe mounting; → orbit.

A periodic orbit which passes around the → Lagrangian points L4, L3, and L5, but neither of the two primaries. This orbit is shaped like a horseshoe when viewed in a reference frame rotating with the primaries. Such orbits occur in the solar system, for example in the case of the satellites → Janus and → Epimetheus, which share the same orbit around → Saturn. The smaller Epimetheus encompasses both the L4 and L5 points associated with the larger Janus and performs a horseshoe orbit relative to Saturn and Janus. The satellites experience a close approach every 4 years during which their orbits are exchanged. → tadpole orbit.

See also: → horseshoe mounting; → orbit.

A flexible → pipe for conveying a → liquid.

Etymology (EN): M.E., O.E. akin to Du. hoos, O.N. hosa, Ger. Hose.

Etymology (PE): Šilang, probably loan from Russ. шлаиг (shlang) “hose.”

A flexible → pipe for conveying a → liquid.

Etymology (EN): M.E., O.E. akin to Du. hoos, O.N. hosa, Ger. Hose.

Etymology (PE): Šilang, probably loan from Russ. шлаиг (shlang) “hose.”

One that receives or entertains guests especially in his own home. → host galaxy.

Etymology (EN): M.E. (h)oste, from O.Fr. hoste “guest, host,” from L. hospitem (nom. hospes) “guest, host,” lit. “lord of strangers,” from hostis “stranger.”

Etymology (PE): Mizbân “host,” from Mid.Pers. mezdbân “host,” from mêzd “offering, meal,” Mod.Pers. miz “guest; offering; meal” + -bân a suffix denoting “keeper, guard,” sometimes forming agent nouns or indicating relation (e.g. keštibân “sailor;” bâdbân “a sail;” mehrabân “affectionate;” mizbân “host;” âsiyâbân “a miller;” bâqbân “gardener”). This suffix derives from O.Pers. -pāvan- (as in xšaça.pāvan- “satrap”); Av. -pāna- (as in pəšu.pāna- “keeping the passage, bridge guard”), from Proto-Iranian *pa- “to prtotect, keep,” → observe,

• suffix *-van-; cf. Skt. -pāna- (as in tanū.pāna- “protection of the body”).

One that receives or entertains guests especially in his own home. → host galaxy.

Etymology (EN): M.E. (h)oste, from O.Fr. hoste “guest, host,” from L. hospitem (nom. hospes) “guest, host,” lit. “lord of strangers,” from hostis “stranger.”

Etymology (PE): Mizbân “host,” from Mid.Pers. mezdbân “host,” from mêzd “offering, meal,” Mod.Pers. miz “guest; offering; meal” + -bân a suffix denoting “keeper, guard,” sometimes forming agent nouns or indicating relation (e.g. keštibân “sailor;” bâdbân “a sail;” mehrabân “affectionate;” mizbân “host;” âsiyâbân “a miller;” bâqbân “gardener”). This suffix derives from O.Pers. -pāvan- (as in xšaça.pāvan- “satrap”); Av. -pāna- (as in pəšu.pāna- “keeping the passage, bridge guard”), from Proto-Iranian *pa- “to prtotect, keep,” → observe,

• suffix *-van-; cf. Skt. -pāna- (as in tanū.pāna- “protection of the body”).

A usually faint galaxy in which a remarkable phenomenon, such as a → supernova event, occurs.

See also: → host; → galaxy.

A usually faint galaxy in which a remarkable phenomenon, such as a → supernova event, occurs.

See also: → host; → galaxy.

Having a relatively high temperature.
→ hot accretion flow, → hot core, → hot corino, → hot dark matter , → hot dust-obscured galaxy, → hot Jupiter, → hot molecular core, → hot pixel, → hot star.

Etymology (EN): Hot, O.E. hat, “hot; fervent, fierce,” from P.Gmc. *haitoz (cf. Du. heet, Ger. heiß “hot,” Goth. heito “heat of a fever”).

Etymology (PE): Dâq “hot; brand, marking,” from Mid.Pers. dâq, dâk “hot,” dažitan “to burn, scorch,” dažišn “burning” (Mod.Pers. dežan (دژن) “acid, pugnent”), from Av. dag-, daž- “to burn;” cf. Skt. dah- “to burn;” L. fovere “to warm, heat; " Arm. dažan “violent, wild;” Lith. degu “to burn;” O.E. fefor; E. fever. PIE base *dhegh- “to burn.”

Having a relatively high temperature.
→ hot accretion flow, → hot core, → hot corino, → hot dark matter , → hot dust-obscured galaxy, → hot Jupiter, → hot molecular core, → hot pixel, → hot star.

Etymology (EN): Hot, O.E. hat, “hot; fervent, fierce,” from P.Gmc. *haitoz (cf. Du. heet, Ger. heiß “hot,” Goth. heito “heat of a fever”).

Etymology (PE): Dâq “hot; brand, marking,” from Mid.Pers. dâq, dâk “hot,” dažitan “to burn, scorch,” dažišn “burning” (Mod.Pers. dežan (دژن) “acid, pugnent”), from Av. dag-, daž- “to burn;” cf. Skt. dah- “to burn;” L. fovere “to warm, heat; " Arm. dažan “violent, wild;” Lith. degu “to burn;” O.E. fefor; E. fever. PIE base *dhegh- “to burn.”

A type of → accretion flow by a → compact object such as a → black hole which has a high → virial temperature, is → optically thick, and occurs at lower mass → accretion rates compared with
→ cold accretion flows.

In a hot accretion flow with a very low mass accretion rate, the electron mean free path is very large, and so the accreting → plasma is nearly collisionless. In this type of accretion flow, thermal conduction transports the energy from the inner to the outer regions. As the gas temperature in the outer regions can be increased above the → virial temperature , the gas in the outer regions can escape from the gravitational potential of the central black hole and form outflows, significantly decreasing the mass accretion rate.

See also: → cold; → accretion; → flow.

A type of → accretion flow by a → compact object such as a → black hole which has a high → virial temperature, is → optically thick, and occurs at lower mass → accretion rates compared with
→ cold accretion flows.

In a hot accretion flow with a very low mass accretion rate, the electron mean free path is very large, and so the accreting → plasma is nearly collisionless. In this type of accretion flow, thermal conduction transports the energy from the inner to the outer regions. As the gas temperature in the outer regions can be increased above the → virial temperature , the gas in the outer regions can escape from the gravitational potential of the central black hole and form outflows, significantly decreasing the mass accretion rate.

See also: → cold; → accretion; → flow.

Same as → hot molecular core.

See also: → hot; → core.

Same as → hot molecular core.

See also: → hot; → core.

A warm, compact → molecular clump found in the inner envelope of a → Class 0 → protostar. Hot corinos are low-mass analogs of → hot molecular cores (HMCs) occurring in → massive star formation sites. With a typical size of ≤ 150 → astronomical units, hot corinos are two orders of magnitude smaller than HMCs. They have densities ≥ 10⁷ cm^-3 and temperatures ≥ 100 K (Ceccarelli, C. 2004, ASP Conf. Ser. 323, 195).

See also: → hot; corino, from → core + -ino a diminutive suffix in It.

A warm, compact → molecular clump found in the inner envelope of a → Class 0 → protostar. Hot corinos are low-mass analogs of → hot molecular cores (HMCs) occurring in → massive star formation sites. With a typical size of ≤ 150 → astronomical units, hot corinos are two orders of magnitude smaller than HMCs. They have densities ≥ 10⁷ cm^-3 and temperatures ≥ 100 K (Ceccarelli, C. 2004, ASP Conf. Ser. 323, 195).

See also: → hot; corino, from → core + -ino a diminutive suffix in It.

Any form of → dark matter which had a significant velocity dispersion (comparable to the velocity of light), when the Universe first became → matter-dominated.

See also: → hot; → dark;
→ matter.

Any form of → dark matter which had a significant velocity dispersion (comparable to the velocity of light), when the Universe first became → matter-dominated.

See also: → hot; → dark;
→ matter.

A member of the most extreme galaxies in terms of their luminosities and unusual hot → dust temperatures. The → infrared emission from HDOGs is dominated by obscured accretion onto a central → supermassive black hole (SMBH), in most cases without significant contribution from → star formation. The large contrast between the underlying → host galaxy and the hyper-luminous emission from the → active galactic nucleus (AGN) implies that either the SMBH is much more massive than expected for the stellar mass of its host, or is radiating well above its → Eddington limit. The most extreme of these remarkable systems known is → W2246-0526.

See also: → hot; → dust; → obscure; → galaxy.

A member of the most extreme galaxies in terms of their luminosities and unusual hot → dust temperatures. The → infrared emission from HDOGs is dominated by obscured accretion onto a central → supermassive black hole (SMBH), in most cases without significant contribution from → star formation. The large contrast between the underlying → host galaxy and the hyper-luminous emission from the → active galactic nucleus (AGN) implies that either the SMBH is much more massive than expected for the stellar mass of its host, or is radiating well above its → Eddington limit. The most extreme of these remarkable systems known is → W2246-0526.

See also: → hot; → dust; → obscure; → galaxy.

Same as → Schottky diode

See also: → hot; → electron; → diode.

Same as → Schottky diode

See also: → hot; → electron; → diode.

A giant, gaseous, Jupiter-like planet lying too close to its parent star and having
an orbital period from a few days to a few weeks. The existence of hot Jupiters is usually interpreted in terms of planetary migration. These planets can, in principle, be formed at larger distances from their stars and migrate to the inner regions due to dynamical interaction with the proto-planetary disk.

See also: → hot; → Jupiter.

A giant, gaseous, Jupiter-like planet lying too close to its parent star and having
an orbital period from a few days to a few weeks. The existence of hot Jupiters is usually interpreted in terms of planetary migration. These planets can, in principle, be formed at larger distances from their stars and migrate to the inner regions due to dynamical interaction with the proto-planetary disk.

See also: → hot; → Jupiter.

A relatively small, dense, and hot → molecular clump occurring in regions of → massive star formation. HMCs have diameters ≤ 0.1 pc, densities ≥ 10⁷ cm^-3, and temperatures ≥ 100 K.
The densest hot cores are traced in → ammonia (NH₃) and possess densities of 10⁸ cm^-3, sizes down to 0.05 pc and temperatures of up to 250 K. Hot molecular cores are generally associated with → compact H II regions and → ultracompact H II regions. High angular resolution observations suggest that HMCs are internally heated by embedded sources, since temperature and density increases toward the center as expected if star formation is occurring close to the core center. Same as → hot core.

See also: → hot; → molecular; → core.

A relatively small, dense, and hot → molecular clump occurring in regions of → massive star formation. HMCs have diameters ≤ 0.1 pc, densities ≥ 10⁷ cm^-3, and temperatures ≥ 100 K.
The densest hot cores are traced in → ammonia (NH₃) and possess densities of 10⁸ cm^-3, sizes down to 0.05 pc and temperatures of up to 250 K. Hot molecular cores are generally associated with → compact H II regions and → ultracompact H II regions. High angular resolution observations suggest that HMCs are internally heated by embedded sources, since temperature and density increases toward the center as expected if star formation is occurring close to the core center. Same as → hot core.

See also: → hot; → molecular; → core.

Of a → CCD detector, a pixel that has higher charge loss. Hot pixels are a type of noise affecting almost every CCD camera. They are caused by small contamination or production faults in the CCD sensor area.

See also: → hot; → pixel.

Of a → CCD detector, a pixel that has higher charge loss. Hot pixels are a type of noise affecting almost every CCD camera. They are caused by small contamination or production faults in the CCD sensor area.

See also: → hot; → pixel.

A compact, highly luminous region in a cataclysmic binary located in the accretion disk where the stream of material hits it.

See also: → hot; → spot.

A compact, highly luminous region in a cataclysmic binary located in the accretion disk where the stream of material hits it.

See also: → hot; → spot.

A member of a class of stars having high → effective temperatures (above some 15,000 K); mainly → massive stars, but also including → exciting stars of → planetary nebulae, → white dwarfs, and → symbiotic stars.

See also: → hot; → star.

A member of a class of stars having high → effective temperatures (above some 15,000 K); mainly → massive stars, but also including → exciting stars of → planetary nebulae, → white dwarfs, and → symbiotic stars.

See also: → hot; → star.

The 24th part of a day; 60 minutes.
An angular unit of right ascension, equivalent to 15°.

Etymology (EN): Hour, from M.E. houre, from O.Fr. hore, from L. hora “hour, time, season,” from Gk. hora “any limited time,” used of day, hour, season, year; cognate E. → year.

Etymology (PE): Sâ’at, from Ar.

The 24th part of a day; 60 minutes.
An angular unit of right ascension, equivalent to 15°.

Etymology (EN): Hour, from M.E. houre, from O.Fr. hore, from L. hora “hour, time, season,” from Gk. hora “any limited time,” used of day, hour, season, year; cognate E. → year.

Etymology (PE): Sâ’at, from Ar.

A telescope based coordinate specifying the angle, in the equatorial plane, from the meridian to a plane containing the celestial object and the north and south celestial poles.

See also: → hour; → angle.

A telescope based coordinate specifying the angle, in the equatorial plane, from the meridian to a plane containing the celestial object and the north and south celestial poles.

See also: → hour; → angle.

A great circle passing through an object and the → celestial poles intersecting the → celestial equator at right angles.

See also: → hour; → circle.

A great circle passing through an object and the → celestial poles intersecting the → celestial equator at right angles.

See also: → hour; → circle.

A device for measuring time; it consists of a glass container having two compartments from the uppermost of which a quantity of sand runs in an hour into the lower one through a narrow tube.

Etymology (EN): Hour glass, from → hour + → glass.

Etymology (PE): Sâat-e šeni, from sâat, → hour +
šeni, adj. of šen “sand.”

A device for measuring time; it consists of a glass container having two compartments from the uppermost of which a quantity of sand runs in an hour into the lower one through a narrow tube.

Etymology (EN): Hour glass, from → hour + → glass.

Etymology (PE): Sâat-e šeni, from sâat, → hour +
šeni, adj. of šen “sand.”

1. A building in which people live.
   

2. A building for any purpose. → greenhouse.

Etymology (EN): M.E. h(o)us, from O.E. hus “dwelling, shelter, house;” cf. O.N. hus; Du. huis; Ger. Haus .

Etymology (PE): Xâné “house,” from Mid.Pers. xânak, xân, xôn; Aftari dialect kiye “house, home;” Xonsâri ki “house;” Anâraki xiya, Tâti Karingân kâ, Sangesari keh “house, home;” cf. L. cunae “cradle; bed;” Gk. kome “village;” PIE base *kei- “bed; to lie, to settle; beloved” (other cognates: O.E. ham “dwelling, house, village;” E. home; Ger. Heim; L. civis “townsman;” Fr. cité; E. city; Skt. śiva- “auspicious, dear”).

1. A building in which people live.
   

2. A building for any purpose. → greenhouse.

Etymology (EN): M.E. h(o)us, from O.E. hus “dwelling, shelter, house;” cf. O.N. hus; Du. huis; Ger. Haus .

Etymology (PE): Xâné “house,” from Mid.Pers. xânak, xân, xôn; Aftari dialect kiye “house, home;” Xonsâri ki “house;” Anâraki xiya, Tâti Karingân kâ, Sangesari keh “house, home;” cf. L. cunae “cradle; bed;” Gk. kome “village;” PIE base *kei- “bed; to lie, to settle; beloved” (other cognates: O.E. ham “dwelling, house, village;” E. home; Ger. Heim; L. civis “townsman;” Fr. cité; E. city; Skt. śiva- “auspicious, dear”).

1. To remain in one place in the air by rapidly beating the wings.
   

2. Computers: To place (a pointer) over a particular area of a computer screen (such as a hyperlink on a webpage) so as to cause a pop-up box to appear or other change to occur, without clicking a button on the device.

Etymology (EN): M.E. hoveren, frequentative of hoven “hover, tarry, linger,” of unknown origin.

Etymology (PE): Parjâ zadan (on the model of darjâ zadan “to march in the same place, moving one’s legs up and down without going forward”), from par zadan darjâ “to beat the wings at the same place,” from par zadan “to beat the wings,” from par “wing, → feather,” zadan, → beat,

• darjâ “in the same place,” from dar, → in, + jâ, → place.

1. To remain in one place in the air by rapidly beating the wings.
   

2. Computers: To place (a pointer) over a particular area of a computer screen (such as a hyperlink on a webpage) so as to cause a pop-up box to appear or other change to occur, without clicking a button on the device.

Etymology (EN): M.E. hoveren, frequentative of hoven “hover, tarry, linger,” of unknown origin.

Etymology (PE): Parjâ zadan (on the model of darjâ zadan “to march in the same place, moving one’s legs up and down without going forward”), from par zadan darjâ “to beat the wings at the same place,” from par zadan “to beat the wings,” from par “wing, → feather,” zadan, → beat,

• darjâ “in the same place,” from dar, → in, + jâ, → place.

A vehicle capable of travelling over land or water on a cushion of air.

See also: → space; → craft.

A vehicle capable of travelling over land or water on a cushion of air.

See also: → space; → craft.

The act of one who hovers.

See also: → hover; → -ing.

The act of one who hovers.

See also: → hover; → -ing.

An → excited state in the → triple alpha process leading to the production of the most abundant → isotope of → carbon. The existence of this state is of extreme astrophysical importance concerning the → nucleosynthesis of ¹²C in stellar → cores:
⁴He + ⁴He ↔ ⁸Be,
⁸Be + ⁴He ↔ ¹²C,
¹²C→ ¹²C + γ.

The process proceeds as follows. First the unstable
→ ground state of ⁸Be is formed in the collision of two → alpha particles. Since ⁸Be exists roughly 7 x 10^-17 sec, it must fuse with an alpha particle before breaking up. However, the probability of three bodies merging simultaneously is extremely low. Hoyle showed that the ¹²C nucleus needs an excited state or resonance at 7.68 MeV to provide for a high reaction probability. The Hoyle state was soon found at 7.65 MeV with the predicted → spin and → parity.

See also: In honor of the British astrophysicist Fred Hoyle (1915-2001), who predicted this state in 1953 (Hoyle et al. 1953, Physical Review 92, 1095); it was discovered by W. A. Fowler in 1957; → state.

An → excited state in the → triple alpha process leading to the production of the most abundant → isotope of → carbon. The existence of this state is of extreme astrophysical importance concerning the → nucleosynthesis of ¹²C in stellar → cores:
⁴He + ⁴He ↔ ⁸Be,
⁸Be + ⁴He ↔ ¹²C,
¹²C→ ¹²C + γ.

The process proceeds as follows. First the unstable
→ ground state of ⁸Be is formed in the collision of two → alpha particles. Since ⁸Be exists roughly 7 x 10^-17 sec, it must fuse with an alpha particle before breaking up. However, the probability of three bodies merging simultaneously is extremely low. Hoyle showed that the ¹²C nucleus needs an excited state or resonance at 7.68 MeV to provide for a high reaction probability. The Hoyle state was soon found at 7.65 MeV with the predicted → spin and → parity.

See also: In honor of the British astrophysicist Fred Hoyle (1915-2001), who predicted this state in 1953 (Hoyle et al. 1953, Physical Review 92, 1095); it was discovered by W. A. Fowler in 1957; → state.