An Etymological Dictionary of Astronomy and Astrophysics

Prefix denoting “two, both, twice.”

Etymology (EN): From L. bi-, cognate of Gk. di-, O.E. twi-; cf. Av. bi- “two,” biš “twice,” Mod.Pers. do “two,” PIE *dwo- “two.”

Etymology (PE): Do, Mid.Pers. do, Av. dva-, Skt. dvi-, Gk. duo, L. duo, E. two, Ger. zwei, Fr. deux.

Prefix denoting “two, both, twice.”

Etymology (EN): From L. bi-, cognate of Gk. di-, O.E. twi-; cf. Av. bi- “two,” biš “twice,” Mod.Pers. do “two,” PIE *dwo- “two.”

Etymology (PE): Do, Mid.Pers. do, Av. dva-, Skt. dvi-, Gk. duo, L. duo, E. two, Ger. zwei, Fr. deux.

A cosmological model based on the theory of → general relativity, which is homogeneous but → anisotropic. There are actually ten dinstinct Bianchi types, classified according to the particular kinds of symmetry they posses.

See also: Luigi Bianchi (1856-1928), Italian mathematician; → cosmological; → model.

A cosmological model based on the theory of → general relativity, which is homogeneous but → anisotropic. There are actually ten dinstinct Bianchi types, classified according to the particular kinds of symmetry they posses.

See also: Luigi Bianchi (1856-1928), Italian mathematician; → cosmological; → model.

1. General: Leaning of the mind toward or away from something; especially: a personal and sometimes unreasoned judgment.
   Statistics: A → systematic error introduced by selecting items from a wrong population, favoring some of the elements of a population, or poorly phrasing questions.
   

2. Electronics: A → voltage applied to a device to establish a reference level for operation. Same as initial voltage, initial tension (Ger. die Vorspannung).
   In a → CCD detector, electronic → offset which prevents negative signal.
   

3a) General: To give a settled and often prejudiced outlook to.

3b) Electronics: To apply a small voltage to a device to control its operation. See also: → bias error, → bias frame, → bias offset, → bias voltage, → biased, → biased estimate, → biased galaxy formation, → biased sample, → biased statistics, → debias, → kinematic bias, → Lutz-Kelker bias, → Malmquist bias, → observational bias, → sampling bias, → unbiased, → unbiased estimator.

Etymology (EN): From M.Fr. biais “slant,” perhaps ultimately from Gk. epikarsios “slanting, oblique,” from epi- “upon” + karsios “oblique.”

Etymology (PE): Varak, from var “side, direction”

• -ak suffix denoting relation, affinity, similarity (as in dastak, poštak, pašmak, xarak, nâxonak, mušak, eynak). Note also var in yekvar “slanting, inclined”.
  
  Pištaneš, only in the electronic sense, from piš, → pre- + taneš, → tension.
  Varak dâdan, from varak + dâdan “to give,” → datum.

1. General: Leaning of the mind toward or away from something; especially: a personal and sometimes unreasoned judgment.
   Statistics: A → systematic error introduced by selecting items from a wrong population, favoring some of the elements of a population, or poorly phrasing questions.
   

2. Electronics: A → voltage applied to a device to establish a reference level for operation. Same as initial voltage, initial tension (Ger. die Vorspannung).
   In a → CCD detector, electronic → offset which prevents negative signal.
   

3a) General: To give a settled and often prejudiced outlook to.

3b) Electronics: To apply a small voltage to a device to control its operation. See also: → bias error, → bias frame, → bias offset, → bias voltage, → biased, → biased estimate, → biased galaxy formation, → biased sample, → biased statistics, → debias, → kinematic bias, → Lutz-Kelker bias, → Malmquist bias, → observational bias, → sampling bias, → unbiased, → unbiased estimator.

Etymology (EN): From M.Fr. biais “slant,” perhaps ultimately from Gk. epikarsios “slanting, oblique,” from epi- “upon” + karsios “oblique.”

Etymology (PE): Varak, from var “side, direction”

• -ak suffix denoting relation, affinity, similarity (as in dastak, poštak, pašmak, xarak, nâxonak, mušak, eynak). Note also var in yekvar “slanting, inclined”.
  
  Pištaneš, only in the electronic sense, from piš, → pre- + taneš, → tension.
  Varak dâdan, from varak + dâdan “to give,” → datum.

A measurement error that remains constant in magnitude for all observations; for example an incorrectly set zero adjustment.

See also: → bias; → error.

A measurement error that remains constant in magnitude for all observations; for example an incorrectly set zero adjustment.

See also: → bias; → error.

CCD frame with exposure time set to zero and giving the bias level.

Etymology (EN): → bias; → frame.

Etymology (PE): Nurdâd, → exposure; varak→ bias

CCD frame with exposure time set to zero and giving the bias level.

Etymology (EN): → bias; → frame.

Etymology (PE): Nurdâd, → exposure; varak→ bias

In → CCD detectors, same as → bias and → offset.

See also: → bias; → offset.

In → CCD detectors, same as → bias and → offset.

See also: → bias; → offset.

A voltage applied or developed between two electrodes as a bias.

See also: → bias; → voltage.

A voltage applied or developed between two electrodes as a bias.

See also: → bias; → voltage.

Marked by or exhibiting bias; characterized by settled and often prejudiced outlook.

Etymology (EN): Biased, from → bias + adj. suffix -ed.

Etymology (PE): Varakdâr, from varak, → bias + -dâr “possessing, having,” from dâštan “to possess, to have.”

Marked by or exhibiting bias; characterized by settled and often prejudiced outlook.

Etymology (EN): Biased, from → bias + adj. suffix -ed.

Etymology (PE): Varakdâr, from varak, → bias + -dâr “possessing, having,” from dâštan “to possess, to have.”

Of a population parameter, if the mean or expectation of the statistics is not equal to the parameter.

Etymology (EN): → biased; → estimate.

Etymology (PE): barâvard, → estimate; varakdâr→ biased.

Of a population parameter, if the mean or expectation of the statistics is not equal to the parameter.

Etymology (EN): → biased; → estimate.

Etymology (PE): barâvard, → estimate; varakdâr→ biased.

The theory that bright galaxies form preferentially from anomalously overdense perturbations in the → early Universe.

See also: → biased; → galaxy; → formation.

The theory that bright galaxies form preferentially from anomalously overdense perturbations in the → early Universe.

See also: → biased; → galaxy; → formation.

A sample that is not a true representative of a → statistical population to which generalizations are to be made. A sample which is not → randomly constituted.

See also: → biased; → sample.

A sample that is not a true representative of a → statistical population to which generalizations are to be made. A sample which is not → randomly constituted.

See also: → biased; → sample.

A statistics based on a → biased sample.

See also: → biased; → statistics.

A statistics based on a → biased sample.

See also: → biased; → statistics.

A birefrigent crystal, such as mica, that is characterized by having two optical axes along which light is propagated with equal velocities.

See also: Biaxial, from → bi- “two” + axial, from → axe; → crystal.

A birefrigent crystal, such as mica, that is characterized by having two optical axes along which light is propagated with equal velocities.

See also: Biaxial, from → bi- “two” + axial, from → axe; → crystal.

A → microwave → polarimeter designed specifically to target the → B-mode signature of → inflation in the → cosmic microwave background polarization. BICEP2 observed from the South Pole for three seasons from 2010 to 2012. This 26 cm aperture → telescope comprised an all-cold refracting optical system equipped with a → bolometer array of 512 → detectors (256 pixels) operating at 150 GHz.

See also: BICEP2, the upgraded version of the first BICEP, short for Background Imaging of Cosmic Extragalactic Polarization.

A → microwave → polarimeter designed specifically to target the → B-mode signature of → inflation in the → cosmic microwave background polarization. BICEP2 observed from the South Pole for three seasons from 2010 to 2012. This 26 cm aperture → telescope comprised an all-cold refracting optical system equipped with a → bolometer array of 512 → detectors (256 pixels) operating at 150 GHz.

See also: BICEP2, the upgraded version of the first BICEP, short for Background Imaging of Cosmic Extragalactic Polarization.

Describing a lens with two concave faces.

See also: → bi-; → concave; → lens.

Describing a lens with two concave faces.

See also: → bi-; → concave; → lens.

A → spherical lens with two convex faces. The radii of curvature for the two surfaces may or may not be the same.

See also: → bi-; → convex; → lens.

A → spherical lens with two convex faces. The radii of curvature for the two surfaces may or may not be the same.

See also: → bi-; → convex; → lens.

A comet having a short period of 6.62 years discovered by Biela.
It broke up on its 1846 return and subsequently gave rise to a spectacular meteor shower.

Etymology (EN): In honor of Wilhelm von Biela (1782-1856), Austrian military officer and amateur astronomer, who re-discovered the comet Biela in 1826, although it had been seen first in 1772. → comet.

A comet having a short period of 6.62 years discovered by Biela.
It broke up on its 1846 return and subsequently gave rise to a spectacular meteor shower.

Etymology (EN): In honor of Wilhelm von Biela (1782-1856), Austrian military officer and amateur astronomer, who re-discovered the comet Biela in 1826, although it had been seen first in 1772. → comet.

A → meteor shower, originating from → Biela’s comet, whose → radiant lies in the constellation → Andromeda; also called → Andromidids.

Etymology (EN): Bielids, From Biel(a) + → -ids suffix denoting “descendant of, belonging to the family of.”

A → meteor shower, originating from → Biela’s comet, whose → radiant lies in the constellation → Andromeda; also called → Andromidids.

Etymology (EN): Bielids, From Biel(a) + → -ids suffix denoting “descendant of, belonging to the family of.”

1. To divide into two branches.
   

2. Divided into two branches.

Etymology (EN): M.L. bifurcatus, from L. → bi- “two,”

• furca “pitchfork; fork used in cooking,” of uncertain origin.

Etymology (PE): Dogalidan, from Gilaki dogal “fork, two-branched,” cf. Tabari dekal, dokkal, doqâla, from do, → two, + gal, kal “branch, part,” cf. Kurd. (Kurmanji) kar “part, piece,” cognate with Pers. kârd “knife,” (+ *niš-) nišgarda “cobbler’s knife;” Mid.Pers. kârt “knife,” karēnītan, karītan “to cut,”
(+ *fra-) fragard “chapter, section;” Av. karət- “to cut;” Proto-Iranian kart- “to cut;” cf. Skt. kart- “to cut;”
Gk. karpos “fruit;” L. carpere “to cut, divide, pluck;” PIE base (s)ker- “to cut;” + -idan infinitive suffix. See also → shear.

1. To divide into two branches.
   

2. Divided into two branches.

Etymology (EN): M.L. bifurcatus, from L. → bi- “two,”

• furca “pitchfork; fork used in cooking,” of uncertain origin.

Etymology (PE): Dogalidan, from Gilaki dogal “fork, two-branched,” cf. Tabari dekal, dokkal, doqâla, from do, → two, + gal, kal “branch, part,” cf. Kurd. (Kurmanji) kar “part, piece,” cognate with Pers. kârd “knife,” (+ *niš-) nišgarda “cobbler’s knife;” Mid.Pers. kârt “knife,” karēnītan, karītan “to cut,”
(+ *fra-) fragard “chapter, section;” Av. karət- “to cut;” Proto-Iranian kart- “to cut;” cf. Skt. kart- “to cut;”
Gk. karpos “fruit;” L. carpere “to cut, divide, pluck;” PIE base (s)ker- “to cut;” + -idan infinitive suffix. See also → shear.

1. A branching or division into two parts; a splitting apart.
   

2. A sudden qualitative change in the behavior of a → dynamical system.
   The equation describing the evolution of the system finds several solutions for certain values of a parameter. Systems undergoing a bifurcation do not necessarily return to their original state, even if the parameter returns to its nominal value. See also → chaos.

See also: Verbal noun of → bifurcate.

1. A branching or division into two parts; a splitting apart.
   

2. A sudden qualitative change in the behavior of a → dynamical system.
   The equation describing the evolution of the system finds several solutions for certain values of a parameter. Systems undergoing a bifurcation do not necessarily return to their original state, even if the parameter returns to its nominal value. See also → chaos.

See also: Verbal noun of → bifurcate.

The point or moment in the evolution of a → dynamical system that occurs if a parameter passes through a critical point. At this point the system branches into any number of qualitatively new types of behavior.

See also: → bifurcation; → point.

The point or moment in the evolution of a → dynamical system that occurs if a parameter passes through a critical point. At this point the system branches into any number of qualitatively new types of behavior.

See also: → bifurcation; → point.

1. A theory which studies how, in certain nonlinear systems, there may be paths and shifts in behavior dependent on small changes in circumstances or the current position of the system.
   

2. Math.: The study of the behavior of a solution of a nonlinear problem in the neighborhood of a known solution, particularly as a parameter varies.

See also: → bifurcation; → theory.

1. A theory which studies how, in certain nonlinear systems, there may be paths and shifts in behavior dependent on small changes in circumstances or the current position of the system.
   

2. Math.: The study of the behavior of a solution of a nonlinear problem in the neighborhood of a known solution, particularly as a parameter varies.

See also: → bifurcation; → theory.

Of considerable size, number, quantity, large.

Etymology (EN): M.E., northern England dialect, of unknown origin.

Etymology (PE): Bozorg, → large.

Meh “great, large;” Mid.Pers. meh, mas; Av. maz-, masan-, mazant- “great, important,” mazan- “greatness, majesty,” mazišta- “greatest;” cf. Skt. mah-, mahant-; Gk. megas; L. magnus; PIE *meg- “great.”

Of considerable size, number, quantity, large.

Etymology (EN): M.E., northern England dialect, of unknown origin.

Etymology (PE): Bozorg, → large.

Meh “great, large;” Mid.Pers. meh, mas; Av. maz-, masan-, mazant- “great, important,” mazan- “greatness, majesty,” mazišta- “greatest;” cf. Skt. mah-, mahant-; Gk. megas; L. magnus; PIE *meg- “great.”

A theory which states that the → Universe came into existence in an “instantaneous” event some 14 billion years ago. Matter
was created in that initial event and as time has gone by the Universe has expanded and the contents evolved into the galaxies and stars and of today. The Big Bang is sometimes described as an “explosion.” However, matter and energy did not erupt into a pre-existing space, since they came into being simultaneously with space and time.

Etymology (EN): → big;
bang “a sudden loud noise, as of an explosion” (probably of Scandinavian origin; akin to Icelandic banga “to hammer”). The term was coined by Fred Hoyle in 1950 in the course of discussions entitled “the Nature of the Universe” broadcasted by BBC. Hoyle’s intention was a pejorative term in order to ridicule the theory which his own → steady state theory contested.

Etymology (PE): Meh Bâng, from meh “great, large,” → big, + bâng “voice, sound, clamour,” (Mid.Pers. vâng, Av. vaocanghê “to declare (by means of speech”), vacah- “word,” from vac- “to speak, say,” cf. Mod.Pers. vâžé “word,” âvâz “voice, sound, song,” Skt. vakti “speaks, says,” vacas- “word;”
Gk. epos “word,” L. vox “voice;” PIE base *wek- “to speak”).

A theory which states that the → Universe came into existence in an “instantaneous” event some 14 billion years ago. Matter
was created in that initial event and as time has gone by the Universe has expanded and the contents evolved into the galaxies and stars and of today. The Big Bang is sometimes described as an “explosion.” However, matter and energy did not erupt into a pre-existing space, since they came into being simultaneously with space and time.

Etymology (EN): → big;
bang “a sudden loud noise, as of an explosion” (probably of Scandinavian origin; akin to Icelandic banga “to hammer”). The term was coined by Fred Hoyle in 1950 in the course of discussions entitled “the Nature of the Universe” broadcasted by BBC. Hoyle’s intention was a pejorative term in order to ridicule the theory which his own → steady state theory contested.

Etymology (PE): Meh Bâng, from meh “great, large,” → big, + bâng “voice, sound, clamour,” (Mid.Pers. vâng, Av. vaocanghê “to declare (by means of speech”), vacah- “word,” from vac- “to speak, say,” cf. Mod.Pers. vâžé “word,” âvâz “voice, sound, song,” Skt. vakti “speaks, says,” vacas- “word;”
Gk. epos “word,” L. vox “voice;” PIE base *wek- “to speak”).

→ Big Bang; → model.

→ Big Bang; → model.

The production of → light elements, roughly three minutes after the → Big Bang when the temperature of the → Universe dropped from 10³² K to approximately 10⁹ K. In a short time interval → protons and → neutrons collided to produce → deuterium. Most of the deuterium then fused with other protons and neutrons to produce → helium and a small amount of → tritium. The element
→ lithium 7 could also arise form the coalescence of one tritium and two deuterium nuclei. According to the Big Bang nucleosynthesis theory, roughly 25% of the mass of the Universe consists of helium. It also predicts about 0.01% deuterium, and even smaller quantities of lithium. These predictions depend critically on the → baryon-photon ratio. Same as → primordial nucleosynthesis.

See also: → Big Bang; → nucleosynthesis.

The production of → light elements, roughly three minutes after the → Big Bang when the temperature of the → Universe dropped from 10³² K to approximately 10⁹ K. In a short time interval → protons and → neutrons collided to produce → deuterium. Most of the deuterium then fused with other protons and neutrons to produce → helium and a small amount of → tritium. The element
→ lithium 7 could also arise form the coalescence of one tritium and two deuterium nuclei. According to the Big Bang nucleosynthesis theory, roughly 25% of the mass of the Universe consists of helium. It also predicts about 0.01% deuterium, and even smaller quantities of lithium. These predictions depend critically on the → baryon-photon ratio. Same as → primordial nucleosynthesis.

See also: → Big Bang; → nucleosynthesis.

A hypothetical state of → infinite energy density representing an infinite → gravitational field and infinite → space-time curvature.

The singularity arises from using Einstein’s theory of → general relativity concerning gravity. We know, however, that when the density and heat become extremely large, quantum physics of gravity becomes important. Yet Einstein’s equations ignore quantum effects. In other words, in certain extreme conditions, Einstein’s equations do not apply.

See also: → Big Bang; → singularity.

A hypothetical state of → infinite energy density representing an infinite → gravitational field and infinite → space-time curvature.

The singularity arises from using Einstein’s theory of → general relativity concerning gravity. We know, however, that when the density and heat become extremely large, quantum physics of gravity becomes important. Yet Einstein’s equations ignore quantum effects. In other words, in certain extreme conditions, Einstein’s equations do not apply.

See also: → Big Bang; → singularity.

→ Big Bang; → theory.

→ Big Bang; → theory.

The broad continuum feature dominating the optical-ultraviolet spectra of AGNs. Most current models attribute the big blue bump to thermal emission from an optically thick accretion disk.

See also: → big; → blue; bump, → bump Cepheid.

The broad continuum feature dominating the optical-ultraviolet spectra of AGNs. Most current models attribute the big blue bump to thermal emission from an optically thick accretion disk.

See also: → big; → blue; bump, → bump Cepheid.

The state of extremely high density and temperature into which a closed → Universe would → collapse in the distant future. If the Universe has a mass density exceeding the critical threshold, then gravity will eventually halt the expansion and cause the Big Crunch.

Etymology (EN): → big; crunch “to crush, grind, or tread noisily; the act or sound of crunching,” alteration of craunch, possibly of imitative origin.

Etymology (PE): Meh “large, big,” → big; romb, → collapse, from rombidan “to collapse;” rombeš-e farjâmin “final collapase,” from rombeš verbal noun of rombidan; farjâmin, → late.

The state of extremely high density and temperature into which a closed → Universe would → collapse in the distant future. If the Universe has a mass density exceeding the critical threshold, then gravity will eventually halt the expansion and cause the Big Crunch.

Etymology (EN): → big; crunch “to crush, grind, or tread noisily; the act or sound of crunching,” alteration of craunch, possibly of imitative origin.

Etymology (PE): Meh “large, big,” → big; romb, → collapse, from rombidan “to collapse;” rombeš-e farjâmin “final collapase,” from rombeš verbal noun of rombidan; farjâmin, → late.

A group of seven stars, an → asterism, lying inside the Northern constellation → Ursa Major. They are:
→ Dubhe, → Merak, → Phad, → Megrez, → Alioth, → Mizar, and → Alkaid. The group is also known as the Plough in Great Britain.

Etymology (EN): → big; dipper a popular U.S. name for the asterism known in Britain as The Plough or Charles’ Wain, from dip O.E. dyppan “immerse,” from P.Gmc. *dupjanan.

Etymology (PE): Haft barâdarân “the seven brothers,” from haft “seven” (Mid.Pers. haft, Av. hapta, cf. Skt. sapta, Gk. hepta, L. septem, P.Gmc. *sebun, Du. zeven, O.H.G. sibun, Ger. sieben, E. seven; PIE *septm)

• barâdarân, plural of barâdar “brother” (Mid.Pers. brad, bardar, O.Pers./Av. brātar-, cf. Skt. bhrátar-, Gk. phrater, L. frater, P.Gmc. *brothar; PIE base *bhrater- “brother”).
  Haftowrang, Mid.Pers. haptôiring, from Av. haptôiringa- “with seven marks,” from hapto- “seven,“as above, + iringa- “mark,” cf. Skt. linga- “mark, token, sign.”
  Camcé “a spoon, ladle; a wooden bowl or cup;”
  bozorg “big, large.”

A group of seven stars, an → asterism, lying inside the Northern constellation → Ursa Major. They are:
→ Dubhe, → Merak, → Phad, → Megrez, → Alioth, → Mizar, and → Alkaid. The group is also known as the Plough in Great Britain.

Etymology (EN): → big; dipper a popular U.S. name for the asterism known in Britain as The Plough or Charles’ Wain, from dip O.E. dyppan “immerse,” from P.Gmc. *dupjanan.

Etymology (PE): Haft barâdarân “the seven brothers,” from haft “seven” (Mid.Pers. haft, Av. hapta, cf. Skt. sapta, Gk. hepta, L. septem, P.Gmc. *sebun, Du. zeven, O.H.G. sibun, Ger. sieben, E. seven; PIE *septm)

• barâdarân, plural of barâdar “brother” (Mid.Pers. brad, bardar, O.Pers./Av. brātar-, cf. Skt. bhrátar-, Gk. phrater, L. frater, P.Gmc. *brothar; PIE base *bhrater- “brother”).
  Haftowrang, Mid.Pers. haptôiring, from Av. haptôiringa- “with seven marks,” from hapto- “seven,“as above, + iringa- “mark,” cf. Skt. linga- “mark, token, sign.”
  Camcé “a spoon, ladle; a wooden bowl or cup;”
  bozorg “big, large.”

A type of → interstellar dust grains with a size ranging from 150 to 1000 Å. Big grains consist of graphite and silicates. They
are in → thermal equilibrium with the radiation field and their emission can be described by a modified → blackbody radiation following from → Kirchhoff’s law.

See also: → big; → grain.

A type of → interstellar dust grains with a size ranging from 150 to 1000 Å. Big grains consist of graphite and silicates. They
are in → thermal equilibrium with the radiation field and their emission can be described by a modified → blackbody radiation following from → Kirchhoff’s law.

See also: → big; → grain.

A cosmological hypothesis regarding the ultimate fate of the → Universe whereby in a far future galaxies and stellar systems would be torn apart due to the → accelerating expansion of the Universe depending on the kind of the → dark energy content of the Universe. According to this hypothesis, after the disruption of galaxies, stars, and planets even atoms might not be able to withstand the internal force of the expansion imposed by the dark energy.

Etymology (EN): → big; M.E. rippen, origin obscure, cf. Frisian rippe “to tear, rip,” M.Du. reppen, rippen “to pull, jerk,” Swed. reppa, Dan. rippe “to tear, rip.”

Etymology (PE): Meh “large, big,” see under → big; gosast stem of gosastan “to tear, cut, break,” from Mid.Pers. wisistan “to break, split,” Av. saed-, sid- “to split, break,” asista- “unsplit, unharmed,” Skt. chid- “to split, break, cut off,” PIE base *skei- “to cut, split,” cf. Gk. skhizein “to split,” L. scindere “to split,” Goth. skaidan, O.E. sceadan “to divide, separate.”

A cosmological hypothesis regarding the ultimate fate of the → Universe whereby in a far future galaxies and stellar systems would be torn apart due to the → accelerating expansion of the Universe depending on the kind of the → dark energy content of the Universe. According to this hypothesis, after the disruption of galaxies, stars, and planets even atoms might not be able to withstand the internal force of the expansion imposed by the dark energy.

Etymology (EN): → big; M.E. rippen, origin obscure, cf. Frisian rippe “to tear, rip,” M.Du. reppen, rippen “to pull, jerk,” Swed. reppa, Dan. rippe “to tear, rip.”

Etymology (PE): Meh “large, big,” see under → big; gosast stem of gosastan “to tear, cut, break,” from Mid.Pers. wisistan “to break, split,” Av. saed-, sid- “to split, break,” asista- “unsplit, unharmed,” Skt. chid- “to split, break, cut off,” PIE base *skei- “to cut, split,” cf. Gk. skhizein “to split,” L. scindere “to split,” Goth. skaidan, O.E. sceadan “to divide, separate.”

A → mapping  f from a → set  A onto a set B which is both an → injection and a → surjection. More explicitly, for every element b of B there is a unique element a of A for which f(a) = b. Also known as → bijective mapping.

See also: From bi- + → injection.

A → mapping  f from a → set  A onto a set B which is both an → injection and a → surjection. More explicitly, for every element b of B there is a unique element a of A for which f(a) = b. Also known as → bijective mapping.

See also: From bi- + → injection.

Of or pertaining to a → bijection.

See also: → bi-; → injection.

Of or pertaining to a → bijection.

See also: → bi-; → injection.

Same as → bijection.

See also: → bijective; → mapping.

Same as → bijection.

See also: → bijective; → mapping.

Same as → isomorphism.

See also: → bijective; → morphism.

Same as → isomorphism.

See also: → bijective; → morphism.

Having or providing two modes, methods, systems, etc., in particular having or occurring with two statistical modes.

See also: → bi-; → modal.

Having or providing two modes, methods, systems, etc., in particular having or occurring with two statistical modes.

See also: → bi-; → modal.

A concept of → star formation in which → high-mass stars and → low-mass stars form in different physical conditions involving different → molecular clouds.

Following the pioneering suggestion of Herbig (1962), successive investigations have generally supported the idea that star formation proceeds bimodally with respect to stellar mass. The star formation rate appears to differ both spatially and temporally for low mass and → massive stars. This is of considerable importance for galactic evolution, since the low-mass stars lock up mass and are long-lived, low luminosity survivors to the present epoch, whereas massive stars are short-lived, recycle and enrich interstellar gas, and leave dark remnants while producing a high luminosity per unit of mass (Silk, J., 1988, in Galactic and Extragalactic Star Formation, p. 503, eds. R. E. Pudritz and M. Fich).

See also: → bimodal; → star; → formation.

A concept of → star formation in which → high-mass stars and → low-mass stars form in different physical conditions involving different → molecular clouds.

Following the pioneering suggestion of Herbig (1962), successive investigations have generally supported the idea that star formation proceeds bimodally with respect to stellar mass. The star formation rate appears to differ both spatially and temporally for low mass and → massive stars. This is of considerable importance for galactic evolution, since the low-mass stars lock up mass and are long-lived, low luminosity survivors to the present epoch, whereas massive stars are short-lived, recycle and enrich interstellar gas, and leave dark remnants while producing a high luminosity per unit of mass (Silk, J., 1988, in Galactic and Extragalactic Star Formation, p. 503, eds. R. E. Pudritz and M. Fich).

See also: → bimodal; → star; → formation.

The quality or state of being → bimodal.

See also: → bimodal; → -ity.

The quality or state of being → bimodal.

See also: → bimodal; → -ity.

1a) General:A box or enclosed space for storing grain, coal, or the like.

1b) Electronics: In a → CCD detector, a square or rectangular group of adjacent → pixels
used collectively to transport the → electron charges.

1c) In a statistical → histogram, the range of → distribution → intervals. The bin widths (or the number of bins) affect a histogram.

2. To place in a → bin; to create → binning.

Etymology (EN): M.E. binne, O.E. binn(e) “manger, crib,” perhaps from O.Celt. *benna, akin to Welsh benn “a cart, especially one with a woven wicker body.” The same Celtic word seems to be preserved in It. benna “dung cart,” Fr. benne “a sort of box for transporting materials, especially in mines,” Du. benne “large basket,” from L.L. benna.

Etymology (PE): Bâvin “a basket, more precisely a small basket which contains the cotton to be spun;” bâvinidan infinitive from bâvin.

1a) General:A box or enclosed space for storing grain, coal, or the like.

1b) Electronics: In a → CCD detector, a square or rectangular group of adjacent → pixels
used collectively to transport the → electron charges.

1c) In a statistical → histogram, the range of → distribution → intervals. The bin widths (or the number of bins) affect a histogram.

2. To place in a → bin; to create → binning.

Etymology (EN): M.E. binne, O.E. binn(e) “manger, crib,” perhaps from O.Celt. *benna, akin to Welsh benn “a cart, especially one with a woven wicker body.” The same Celtic word seems to be preserved in It. benna “dung cart,” Fr. benne “a sort of box for transporting materials, especially in mines,” Du. benne “large basket,” from L.L. benna.

Etymology (PE): Bâvin “a basket, more precisely a small basket which contains the cotton to be spun;” bâvinidan infinitive from bâvin.

The quality or condition of being binary.

See also: → binary; → -ity.

The quality or condition of being binary.

See also: → binary; → -ity.

General: Characterized by or consisting of two parts or components.
Math.: Of or relating to a system of numeration having 2 as its base.
Astro.: Physically associated pair of astronomical objects.

Etymology (EN): Binary, from L.L. binarius, from bini “two-by-two,” from bis “twice, two times;” cf. Av. biš- “twice,” bi- “two,” Mod.Pers. do “two,” PIE *dwo- “two.”

Etymology (PE): Dorin, from Mid.Pers. dorin “double, pair,” from do (Av. dva-, Skt. dvi-, Gk. duo, L. duo, E. two, Der. zwei, Fr. deux) “two” + rin “time, turn.”
Dodoyi “two-by-two,” from do, → two.

General: Characterized by or consisting of two parts or components.
Math.: Of or relating to a system of numeration having 2 as its base.
Astro.: Physically associated pair of astronomical objects.

Etymology (EN): Binary, from L.L. binarius, from bini “two-by-two,” from bis “twice, two times;” cf. Av. biš- “twice,” bi- “two,” Mod.Pers. do “two,” PIE *dwo- “two.”

Etymology (PE): Dorin, from Mid.Pers. dorin “double, pair,” from do (Av. dva-, Skt. dvi-, Gk. duo, L. duo, E. two, Der. zwei, Fr. deux) “two” + rin “time, turn.”
Dodoyi “two-by-two,” from do, → two.

A system of calculation in which the only numerals used are 0 and 1. All the real numbers are represented in terms of powers of 2.

See also: → binary; → arithmetic.

A system of calculation in which the only numerals used are 0 and 1. All the real numbers are represented in terms of powers of 2.

See also: → binary; → arithmetic.

A member of a population of double objects in the main → Asteroid Belt or the → Kuiper Belt which are gravitationally bound together. So far about 200 such binary systems have been identified, while their number is increasing.
243 Ida was the first binary asteroid to be discovered during the Galileo spacecraft flyby in 1993. Other examples are
→ Antiope and Kalliope in the main belt and QG₂₉₈ in the Kuiper Belt.
The importance of these objects resides in the fact that
systems with well measured orbital parameters allow the total mass to be estimated. If the sizes of the components are known then their densities can be accurately calculated. Density is an important parameter since it yields information about composition and internal structure.

See also: → binary; → asteroid.

A member of a population of double objects in the main → Asteroid Belt or the → Kuiper Belt which are gravitationally bound together. So far about 200 such binary systems have been identified, while their number is increasing.
243 Ida was the first binary asteroid to be discovered during the Galileo spacecraft flyby in 1993. Other examples are
→ Antiope and Kalliope in the main belt and QG₂₉₈ in the Kuiper Belt.
The importance of these objects resides in the fact that
systems with well measured orbital parameters allow the total mass to be estimated. If the sizes of the components are known then their densities can be accurately calculated. Density is an important parameter since it yields information about composition and internal structure.

See also: → binary; → asteroid.

A → binary system consisting of two → black holes in close orbit around each other. Same as → black hole binary.

See also: → binary; → black; → hole.

A → binary system consisting of two → black holes in close orbit around each other. Same as → black hole binary.

See also: → binary; → black; → hole.

Either of the digits 0 or 1, used in the → binary number system.

See also: → binary, → digit.

Either of the digits 0 or 1, used in the → binary number system.

See also: → binary, → digit.

The fraction of stars that have at least one → companion. It is at least 50%. The binary fraction appears to increase with increasing → primary star mass, at least among the more massive stars: the → O stars and → B stars have a companion frequency of at least 70%, while for the → G stars the binary frequency is around 50% and the → M stars may have an even lower binary frequency of around 30-40%. Brown dwarfs are rare as companions to lower-main-sequence stars, although brown-dwarf binaries appear not to be rare. An increase in binary frequency with mass would be expected if most stars form in → multiple systems that disintegrate, since the more massive stars would then preferentially remain in binaries while the less massive ones would preferentially be ejected as single stars (see Richard B. Larson, 2001, in IAU Symposium 200, p. 93 and references therein).

See also: → binary; → frequency.

The fraction of stars that have at least one → companion. It is at least 50%. The binary fraction appears to increase with increasing → primary star mass, at least among the more massive stars: the → O stars and → B stars have a companion frequency of at least 70%, while for the → G stars the binary frequency is around 50% and the → M stars may have an even lower binary frequency of around 30-40%. Brown dwarfs are rare as companions to lower-main-sequence stars, although brown-dwarf binaries appear not to be rare. An increase in binary frequency with mass would be expected if most stars form in → multiple systems that disintegrate, since the more massive stars would then preferentially remain in binaries while the less massive ones would preferentially be ejected as single stars (see Richard B. Larson, 2001, in IAU Symposium 200, p. 93 and references therein).

See also: → binary; → frequency.

A pair of galaxies in orbit around each other.

Etymology (EN): → binary; → galaxy.

Etymology (PE): Kahkašân, → galaxy; dorin→ binary.

A pair of galaxies in orbit around each other.

Etymology (EN): → binary; → galaxy.

Etymology (PE): Kahkašân, → galaxy; dorin→ binary.

A → numeral system that has 2 as its base and uses only two digits, 0 and 1. The positional value of each digit in a binary number is twice the place value of the digit of its right side. Each binary digit is known as a bit. The decimal numbers from 0 to 10 are thus in binary 0, 1, 10, 11, 100, 101, 110, 111, 1000, 1001, and 1010. And, for example, the binary number 11101₂ represents the decimal number (1 × 2⁴) + (1 × 2³)

• (1 × 2²) + (0 × 2¹) + (1 × 2⁰), or 29. In electronics, binary numbers are the flow of information in the form of zeros and ones used by computers. Computers use it to manipulate and store all of their data including numbers, words, videos, graphics, and music.

See also: → binary; → number; → system.

A → numeral system that has 2 as its base and uses only two digits, 0 and 1. The positional value of each digit in a binary number is twice the place value of the digit of its right side. Each binary digit is known as a bit. The decimal numbers from 0 to 10 are thus in binary 0, 1, 10, 11, 100, 101, 110, 111, 1000, 1001, and 1010. And, for example, the binary number 11101₂ represents the decimal number (1 × 2⁴) + (1 × 2³)

• (1 × 2²) + (0 × 2¹) + (1 × 2⁰), or 29. In electronics, binary numbers are the flow of information in the form of zeros and ones used by computers. Computers use it to manipulate and store all of their data including numbers, words, videos, graphics, and music.

See also: → binary; → number; → system.

A mathematical operation that combines two numbers, quantities, sets, etc., to give a third. For example, multiplication of two numbers is a binary operation.

A binary operation * on a set S is → commutative if a * b = b * a for all a, b∈ S.

A binary operation * on a set S is → associative if (a * b) * c = a * (b * c) for all a, b, c∈ S.

See also: → binary; → operation.

A mathematical operation that combines two numbers, quantities, sets, etc., to give a third. For example, multiplication of two numbers is a binary operation.

A binary operation * on a set S is → commutative if a * b = b * a for all a, b∈ S.

A binary operation * on a set S is → associative if (a * b) * c = a * (b * c) for all a, b, c∈ S.

See also: → binary; → operation.

A pulsar in a → binary system, the companion of which often being a → neutron star or a → white dwarf. The only known binary system with two pulsars
components is the → double pulsar. As of 2010 about 70 binary pulsars have been identified. They are ideal laboratories for testing and studying the effects predicted by → general relativity, such as → spin precession, → Shapiro time delay, and → gravitational waves. The prototype, called PSR 1913+16, was discovered in 1974 by
Russell A. Hulse and Joseph H. Taylor, Jr., who received the Nobel Prize for Physics in 1993. → Hulse-Taylor pulsar.

See also: → binary; → pulsar.

A pulsar in a → binary system, the companion of which often being a → neutron star or a → white dwarf. The only known binary system with two pulsars
components is the → double pulsar. As of 2010 about 70 binary pulsars have been identified. They are ideal laboratories for testing and studying the effects predicted by → general relativity, such as → spin precession, → Shapiro time delay, and → gravitational waves. The prototype, called PSR 1913+16, was discovered in 1974 by
Russell A. Hulse and Joseph H. Taylor, Jr., who received the Nobel Prize for Physics in 1993. → Hulse-Taylor pulsar.

See also: → binary; → pulsar.

Two stars gravitationally bound to each other, so that they revolve around their common center of gravity. → double star; → spectroscopic binary.

Etymology (EN): → binary; → star.

Etymology (PE): Setâré, → star; dorin, → binary.

Two stars gravitationally bound to each other, so that they revolve around their common center of gravity. → double star; → spectroscopic binary.

Etymology (EN): → binary; → star.

Etymology (PE): Setâré, → star; dorin, → binary.

A → dual supermassive black hole whose components are separated by a few parsecs.

See also: → binary; → supermassive; → black; → hole.

A → dual supermassive black hole whose components are separated by a few parsecs.

See also: → binary; → supermassive; → black; → hole.

Two astronomical objects revolving around their common center of mass.

Etymology (EN): → binary; → system.

Etymology (PE): Râžmân, → system; dorin→ binary.

Two astronomical objects revolving around their common center of mass.

Etymology (EN): → binary; → system.

Etymology (PE): Râžmân, → system; dorin→ binary.

In → graph theory, an → ordered tree with all → nodes having at most two → children.

See also: → binary; → tree.

In → graph theory, an → ordered tree with all → nodes having at most two → children.

See also: → binary; → tree.

To tie, to fasten, to cause ti stick together.

Etymology (EN): O.E. bindan “to tie up with bonds,”
PIE base *bhendh- “to bind;” cf. Av./O.Pers. band- “to bind, fetter,” banda- “band, tie,” Skt. bandh- “to bind, tie, fasten,” bandhah “a tying, bandage.”

Etymology (PE): Bandidan “to bind, confine” [Mo’in, Dehxodâ], from band “band, tie” + -idan infinitive suffix; cognate with E. bind, as explained above.

To tie, to fasten, to cause ti stick together.

Etymology (EN): O.E. bindan “to tie up with bonds,”
PIE base *bhendh- “to bind;” cf. Av./O.Pers. band- “to bind, fetter,” banda- “band, tie,” Skt. bandh- “to bind, tie, fasten,” bandhah “a tying, bandage.”

Etymology (PE): Bandidan “to bind, confine” [Mo’in, Dehxodâ], from band “band, tie” + -idan infinitive suffix; cognate with E. bind, as explained above.

1. Of a gravitational system, the difference in energies between the hypothetical state where all bodies of the system are infinitely separated from each other and the actual bound state.
   
2. The energy which must be supplied to a nucleus in order to cause it to decompose into its constituent neutrons and protons.

Etymology (EN): Binding, noun from → bind; → energy.

Etymology (PE): Kâruž, → energy; bandeš noun from bandidan, → bind.

1. Of a gravitational system, the difference in energies between the hypothetical state where all bodies of the system are infinitely separated from each other and the actual bound state.
   
2. The energy which must be supplied to a nucleus in order to cause it to decompose into its constituent neutrons and protons.

Etymology (EN): Binding, noun from → bind; → energy.

Etymology (PE): Kâruž, → energy; bandeš noun from bandidan, → bind.

Combining a few adjacent CCD pixels in bins, during readout; the method used to assemble the bins and transfer the charge by means of an electronic clock. Binning improves signal-to-noise ratio at the expense of spatial resolution.

Etymology (EN): Binning, from → bin.

Etymology (PE): Bâvineš, from bâvin, → bin.

Combining a few adjacent CCD pixels in bins, during readout; the method used to assemble the bins and transfer the charge by means of an electronic clock. Binning improves signal-to-noise ratio at the expense of spatial resolution.

Etymology (EN): Binning, from → bin.

Etymology (PE): Bâvineš, from bâvin, → bin.

A small optical instrument with two tubes that is used to magnify the view of distant or astronomical objects. → prism binoculars.

Etymology (EN): From Fr. binoculaire, from binocle, from L. bini “double” (L. bis, bi- “twice,” Av. biš “twice”) + ocularis “of the eye,” from oculus “eye” (compare with Av. axš-, aš- “eye,” Skt. akshi- “eye,” Gk. ops “eye,” opsis “sight, appearance,” from PIE okw- “to see;” also O.E. ege, eage, from P.Gmc. *augon, Goth. augo, Lith. akis, Armenian aku).

Etymology (PE): Docašmi “binocular,” from do, → two

• cašm, → eye, + -i adj. suffix; durbin, → telescope.

A small optical instrument with two tubes that is used to magnify the view of distant or astronomical objects. → prism binoculars.

Etymology (EN): From Fr. binoculaire, from binocle, from L. bini “double” (L. bis, bi- “twice,” Av. biš “twice”) + ocularis “of the eye,” from oculus “eye” (compare with Av. axš-, aš- “eye,” Skt. akshi- “eye,” Gk. ops “eye,” opsis “sight, appearance,” from PIE okw- “to see;” also O.E. ege, eage, from P.Gmc. *augon, Goth. augo, Lith. akis, Armenian aku).

Etymology (PE): Docašmi “binocular,” from do, → two

• cašm, → eye, + -i adj. suffix; durbin, → telescope.

1a) An algebraic expression containing 2 terms, as x + y and 2x² - 3x. In other words, a → polynomial with 2 terms.

1b) Biology: A pair of Latin (or latinized) words forming a scientific name for organisms. The first word represents the genus, and the second the species.

2. Of, pertaining to, or consisting of a binomial.

See also: From L.L. binomi(us) “having two names,” + → -al, → nominal.

1a) An algebraic expression containing 2 terms, as x + y and 2x² - 3x. In other words, a → polynomial with 2 terms.

1b) Biology: A pair of Latin (or latinized) words forming a scientific name for organisms. The first word represents the genus, and the second the species.

2. Of, pertaining to, or consisting of a binomial.

See also: From L.L. binomi(us) “having two names,” + → -al, → nominal.

The factor multiplying the variable in a term of a → binomial expansion. For example, in (x + y)⁴ = x⁴ + 4x³y + 6x²y² + 4xy³ + y⁴ the binomial coefficients are 1, 4, 6, 4, and 1. In general, the r-th binomial coefficient in the expression
(x + y)ⁿ is: (n,r) = n!/[r!(n - r)!].

See also: → binomial; → coefficient.

The factor multiplying the variable in a term of a → binomial expansion. For example, in (x + y)⁴ = x⁴ + 4x³y + 6x²y² + 4xy³ + y⁴ the binomial coefficients are 1, 4, 6, 4, and 1. In general, the r-th binomial coefficient in the expression
(x + y)ⁿ is: (n,r) = n!/[r!(n - r)!].

See also: → binomial; → coefficient.

An expression of the form x^m(a + bxⁿ)^pdx, where m, n, p, a, and b are constants.

See also: → binomial; → differential.

An expression of the form x^m(a + bxⁿ)^pdx, where m, n, p, a, and b are constants.

See also: → binomial; → differential.

A probability distribution for independent events for which there are only two possible outcomes i.e., success and failure.

The probability of x successes in n trials is: P(x) = [n!/x!(n - x)!] p^x.q^{n - x}, where p is the probability of success and q = 1 - p the probability of failure on each trial. These probabilities are given in terms of the → binomial theorem expansion of (p + q)ⁿ.

See also: → binomial; → distribution.

A probability distribution for independent events for which there are only two possible outcomes i.e., success and failure.

The probability of x successes in n trials is: P(x) = [n!/x!(n - x)!] p^x.q^{n - x}, where p is the probability of success and q = 1 - p the probability of failure on each trial. These probabilities are given in terms of the → binomial theorem expansion of (p + q)ⁿ.

See also: → binomial; → distribution.

A rule for the expansion of an expression of the form (x + y)ⁿ. The variables x and y can be any → real numbers and n is an → integer. The general formula is known as the → binomial theorem.

See also: → binomial; → expansion.

A rule for the expansion of an expression of the form (x + y)ⁿ. The variables x and y can be any → real numbers and n is an → integer. The general formula is known as the → binomial theorem.

See also: → binomial; → expansion.

A system introduced by Carl von Linné (1707-1778), the Swedish botanist, in which each organism is identified by two names. The first is the name of the genus (generic name), written with a capital letter. The second is the name of the species (specific name). The generic and specific names are in Latin and are printed in italic type. For example, human beings belong to species
Homo sapiens.

See also: → binomial; → nomenclature.

A system introduced by Carl von Linné (1707-1778), the Swedish botanist, in which each organism is identified by two names. The first is the name of the genus (generic name), written with a capital letter. The second is the name of the species (specific name). The generic and specific names are in Latin and are printed in italic type. For example, human beings belong to species
Homo sapiens.

See also: → binomial; → nomenclature.

A rule for writing an equivalent expansion of an expression such as (a + b)ⁿ without having to perform all multiplications involved. → binomial expansion. The general expression is

(a + b)ⁿ = &Sigma (n,k)a^kb^{n - k}, where the summation is from k = 0 to n, and (n,k) = n!/[r!(n - k)!]. For n = 2, (a + b)² = a² + 2ab + b².

Historically, the binomial theorem as applied to (a + b)² was known to Euclid (320 B.C.) and other early Greek mathematicians. In the tenth century the Iranian mathematician Karaji (953-1029) knew the binomial theorem and its accompanying table of → binomial coefficients, now known as → Pascal’s triangle. Subsequently Omar Khayyam (1048-1131) asserted that he could find the 4th, 5th, 6th, and higher roots of numbers by a special law which did not depend on geometric figures. Khayyam’s treatise concerned with his findings is lost. In China there appeared in 1303 a work containing the binomial coefficients arranged in triangular form.
The complete generalization of the binomial theorem for all values of n, including negative integers, was established by Isaac Newton (1642-1727).

See also: → binomial; → theorem.

A rule for writing an equivalent expansion of an expression such as (a + b)ⁿ without having to perform all multiplications involved. → binomial expansion. The general expression is

(a + b)ⁿ = &Sigma (n,k)a^kb^{n - k}, where the summation is from k = 0 to n, and (n,k) = n!/[r!(n - k)!]. For n = 2, (a + b)² = a² + 2ab + b².

Historically, the binomial theorem as applied to (a + b)² was known to Euclid (320 B.C.) and other early Greek mathematicians. In the tenth century the Iranian mathematician Karaji (953-1029) knew the binomial theorem and its accompanying table of → binomial coefficients, now known as → Pascal’s triangle. Subsequently Omar Khayyam (1048-1131) asserted that he could find the 4th, 5th, 6th, and higher roots of numbers by a special law which did not depend on geometric figures. Khayyam’s treatise concerned with his findings is lost. In China there appeared in 1303 a work containing the binomial coefficients arranged in triangular form.
The complete generalization of the binomial theorem for all values of n, including negative integers, was established by Isaac Newton (1642-1727).

See also: → binomial; → theorem.

Etymology (EN): Bio-, Gk., from bios “life,” from PIE base *gweie- “to live;” cf. O.Pers./Av. gay- “to live,” Av. gaya- “life,” gaeθâ- “being, world, mankind,” jivya-, jva- “aliving, alive,” Skt. jivah “alive, living;” Mid.Pers. zivastan “to live,” zivik, zivandag “alive, living,” L. vivus “living, alive,” vita “life,” O.E. cwic “alive,” E. quick, Lith. gyvas “living, alive.”

Etymology (PE): Zist “life, existence,” from zistan “to live,” Mid.Pers. zivastan “to live,” zivižn “life,” O.Pers./Av. gay-, as explained above.

Etymology (EN): Bio-, Gk., from bios “life,” from PIE base *gweie- “to live;” cf. O.Pers./Av. gay- “to live,” Av. gaya- “life,” gaeθâ- “being, world, mankind,” jivya-, jva- “aliving, alive,” Skt. jivah “alive, living;” Mid.Pers. zivastan “to live,” zivik, zivandag “alive, living,” L. vivus “living, alive,” vita “life,” O.E. cwic “alive,” E. quick, Lith. gyvas “living, alive.”

Etymology (PE): Zist “life, existence,” from zistan “to live,” Mid.Pers. zivastan “to live,” zivižn “life,” O.Pers./Av. gay-, as explained above.

A common branch of astronomy and biology dealing with the study of life throughout the Universe; synonymous with → astrobiology and → exobiology.

Etymology (EN): Bioastronomy, from → bio- + → astronomy.

Etymology (PE): Zistaxtaršenâsi, from zist-, → bio-,

• axtaršenâsi, → astronomy.

A common branch of astronomy and biology dealing with the study of life throughout the Universe; synonymous with → astrobiology and → exobiology.

Etymology (EN): Bioastronomy, from → bio- + → astronomy.

Etymology (PE): Zistaxtaršenâsi, from zist-, → bio-,

• axtaršenâsi, → astronomy.

The → variety of → plant and → animal → species in a particular → environment.

See also: → bio-; → diversity.

The → variety of → plant and → animal → species in a particular → environment.

See also: → bio-; → diversity.

The retrieval and analysis of biochemical and biological data using mathematics and computer science, as in the study of genomes (Dictionary.com).

See also: → bio-; → informatics.

The retrieval and analysis of biochemical and biological data using mathematics and computer science, as in the study of genomes (Dictionary.com).

See also: → bio-; → informatics.

An expert or specialist in biology.

See also: Biologist, from → biology + → -ist.

An expert or specialist in biology.

See also: Biologist, from → biology + → -ist.

The study of living organisms and their interactions with the non living world.

See also: Biology, from → bio- + → -logy.

The study of living organisms and their interactions with the non living world.

See also: Biology, from → bio- + → -logy.

The production and emission of light by a living organism as the result of a chemical reaction (→ chemiluminescence). In other words, bioluminescence is chemiluminescence from living organisms. It is widespread in the marine environment, but rare in terrestrial and especially freshwater environments.

See also: → chemi-; → luminescence.

The production and emission of light by a living organism as the result of a chemical reaction (→ chemiluminescence). In other words, bioluminescence is chemiluminescence from living organisms. It is widespread in the marine environment, but rare in terrestrial and especially freshwater environments.

See also: → chemi-; → luminescence.

A biologic feature that is measured and evaluated as an indicator of normal biological processes, pathogenic processes, or pharmacological responses to a therapeutic intervention. For example, prostate specific antigen (PSA) is a biomarker for cancer of the prostate.

See also: → bio-; → marker.

A biologic feature that is measured and evaluated as an indicator of normal biological processes, pathogenic processes, or pharmacological responses to a therapeutic intervention. For example, prostate specific antigen (PSA) is a biomarker for cancer of the prostate.

See also: → bio-; → marker.

A specialist in → biophysics.

See also: → bio-; → physicist.

A specialist in → biophysics.

See also: → bio-; → physicist.

The science that deals with biological structures and processes involving the application of physical principles and methods.

Etymology (EN): Biophysics, from → bio- + → physics.

Etymology (PE): Zistfizik, from zist-, → bio- + fizik→ physics.

The science that deals with biological structures and processes involving the application of physical principles and methods.

Etymology (EN): Biophysics, from → bio- + → physics.

Etymology (PE): Zistfizik, from zist-, → bio- + fizik→ physics.

A substance or phenomenon whose presence in an object such as a → meteorite or an → exoplanet indicates the existence of life.

See also: → bio-; → signature.

A substance or phenomenon whose presence in an object such as a → meteorite or an → exoplanet indicates the existence of life.

See also: → bio-; → signature.

The part of a planet or moon within which life can occur. It may include the crust, oceans, and atmosphere.

Etymology (EN): Biosphere, from → bio- + → sphere.

Etymology (PE): Zistsepehr, from zizt-, → bio-, + sepehr→ sphere.

The part of a planet or moon within which life can occur. It may include the crust, oceans, and atmosphere.

Etymology (EN): Biosphere, from → bio- + → sphere.

Etymology (PE): Zistsepehr, from zizt-, → bio-, + sepehr→ sphere.

The → magnetic field due to → electric current flowing in a long straight conductor is directly proportional to the current and inversely proportional to the distance of the point of observation from the conductor. The law is derivable from → Ampere’s law, but was obtained experimentally by the authors.

Etymology (EN): Named after the French physicists Jean-Baptiste Biot (1774-1862) and Félix Savart (1791-1841); → law.

The → magnetic field due to → electric current flowing in a long straight conductor is directly proportional to the current and inversely proportional to the distance of the point of observation from the conductor. The law is derivable from → Ampere’s law, but was obtained experimentally by the authors.

Etymology (EN): Named after the French physicists Jean-Baptiste Biot (1774-1862) and Félix Savart (1791-1841); → law.

Ecology: The environment consisting of living organisms, which interact with each other and with their non-living surroundings.

See also: Biotic adj. of → biotics; of → environment.

Ecology: The environment consisting of living organisms, which interact with each other and with their non-living surroundings.

See also: Biotic adj. of → biotics; of → environment.

The science concerned with the functions of life, or vital activity and force.

See also: From biotic, from Gk. biotikos “of or pertaining to life,” from → bio- + -tic a suffix equivalent in meaning to → -ic.

The science concerned with the functions of life, or vital activity and force.

See also: From biotic, from Gk. biotikos “of or pertaining to life,” from → bio- + -tic a suffix equivalent in meaning to → -ic.

Having two poles; having two opposite main structures or components.

Etymology (EN): Bipolar, from → bi- + → polar, from → pole.

Etymology (PE): Doqotbi, from do-, → bi-, + qotbi,
→ polar, from qotb, → pole.

Having two poles; having two opposite main structures or components.

Etymology (EN): Bipolar, from → bi- + → polar, from → pole.

Etymology (PE): Doqotbi, from do-, → bi-, + qotbi,
→ polar, from qotb, → pole.

Same as → bipolar outflow.

See also: → bipolar; → flow.

Same as → bipolar outflow.

See also: → bipolar; → flow.

One of two beams of high-temperature, ionized gas ejected in two opposite directions associated with a → protostar. The collimated jets, a consequence of the → accretion process, can extend over distances of several
→ light-years.

See also: → bipolar; → jet.

One of two beams of high-temperature, ionized gas ejected in two opposite directions associated with a → protostar. The collimated jets, a consequence of the → accretion process, can extend over distances of several
→ light-years.

See also: → bipolar; → jet.

An interstellar cloud of ionized gas with two main lobes which lie symmetrically on either side of a central star. The bipolar shape is generally due to the ejection of material by the central star in opposing directions.

Etymology (EN): → bipolar; → nebula.

An interstellar cloud of ionized gas with two main lobes which lie symmetrically on either side of a central star. The bipolar shape is generally due to the ejection of material by the central star in opposing directions.

Etymology (EN): → bipolar; → nebula.

A flow of gaseous material in two opposite directions emanating from protostellar regions or from → evolved stars
during the early post-→ AGB evolution. In protostellar regions → molecular outflows are pushed by → bipolar jets.

Etymology (EN): → bipolar; → outflow.

Etymology (PE): Ostacân, → outflow; doqotbi→ bipolar.

A flow of gaseous material in two opposite directions emanating from protostellar regions or from → evolved stars
during the early post-→ AGB evolution. In protostellar regions → molecular outflows are pushed by → bipolar jets.

Etymology (EN): → bipolar; → outflow.

Etymology (PE): Ostacân, → outflow; doqotbi→ bipolar.

A property of some crystalline materials (e.g. calcite, quartz) which have different indices of refraction associated with different crystallographic directions. Therefore, the crystal splits incident transmitted light into two beams, each polarized perpendicularly to the other. Also called double refraction.

Etymology (EN): Birefringence, from → bi- + refringence, from L. refringere “to break up,” from → re- “back” + combination form of frangere “to break.”

Etymology (PE): Došekast, from do- “two,” → bi- + šekast “breaking,” from šekastan “to break up,” Mid.Pers. škastan, Av. skand- “to break.”

A property of some crystalline materials (e.g. calcite, quartz) which have different indices of refraction associated with different crystallographic directions. Therefore, the crystal splits incident transmitted light into two beams, each polarized perpendicularly to the other. Also called double refraction.

Etymology (EN): Birefringence, from → bi- + refringence, from L. refringere “to break up,” from → re- “back” + combination form of frangere “to break.”

Etymology (PE): Došekast, from do- “two,” → bi- + šekast “breaking,” from šekastan “to break up,” Mid.Pers. škastan, Av. skand- “to break.”

Of or relating to → birefringence.

Of or relating to → birefringence.

A type of narrow-band filter that uses the birefringence to produce selective absorption of polarized light.

See also: → birefringent; → filter.

A type of narrow-band filter that uses the birefringence to produce selective absorption of polarized light.

See also: → birefringent; → filter.

Empty space undergoing → vacuum birefringence.

See also: → birefringent; → vacuum.

Empty space undergoing → vacuum birefringence.

See also: → birefringent; → vacuum.

For a four dimensional → space-time, the → Schwarzschild metric is the only solution of → Einstein’s field equations which describes the gravitational field created by a spherically symmetrical distribution of mass. The theorem implies that the gravitational field outside a sphere is necessarily static, and that the metric inside a spherical shell of matter is necessarily flat.

See also: The theorem was first demonstrated in 1923 by George David Birkhoff (1884-1944), an American mathematician; → theorem

For a four dimensional → space-time, the → Schwarzschild metric is the only solution of → Einstein’s field equations which describes the gravitational field created by a spherically symmetrical distribution of mass. The theorem implies that the gravitational field outside a sphere is necessarily static, and that the metric inside a spherical shell of matter is necessarily flat.

See also: The theorem was first demonstrated in 1923 by George David Birkhoff (1884-1944), an American mathematician; → theorem

1. The act or process of bearing or bringing forth offspring.
   

2. The act or fact of being born.
   

3. The coming into existence of something.

Etymology (EN): M.E. byrthe; O.E. gebyrd; cf. O.H.G. giburt,
Ger. geburt; PIE *bhrto, from *bher- “to bear.”

Etymology (PE): 1) Zâymân, from zây present stem of zâyidan, zâdan “to give birth”
(Mid.Pers. zâtan; Av. zan- “to bear, give birth to a child, be born,” infinitive zazāite, zāta- “born;” cf. Skt. janati “begets, bears;” Gk. gignesthai “to become, happen;” L. gignere “to beget,” gnasci “to be born;” PIE base *gen- “to give birth, beget”) + -mân a suffix forming verbal nouns, → organization.

2. Zâd, past stem of zâyidan, zâdan, as above; zâdmân with prefix -mân, as above.
   

3. Zâyeš, from zây, present stem of zâyidan + -eš suffix of verbal nouns, → -tion.

1. The act or process of bearing or bringing forth offspring.
   

2. The act or fact of being born.
   

3. The coming into existence of something.

Etymology (EN): M.E. byrthe; O.E. gebyrd; cf. O.H.G. giburt,
Ger. geburt; PIE *bhrto, from *bher- “to bear.”

Etymology (PE): 1) Zâymân, from zây present stem of zâyidan, zâdan “to give birth”
(Mid.Pers. zâtan; Av. zan- “to bear, give birth to a child, be born,” infinitive zazāite, zāta- “born;” cf. Skt. janati “begets, bears;” Gk. gignesthai “to become, happen;” L. gignere “to beget,” gnasci “to be born;” PIE base *gen- “to give birth, beget”) + -mân a suffix forming verbal nouns, → organization.

2. Zâd, past stem of zâyidan, zâdan, as above; zâdmân with prefix -mân, as above.
   

3. Zâyeš, from zây, present stem of zâyidan + -eš suffix of verbal nouns, → -tion.

In star formation models, the population of binary components formed via random pairing of stars distributed according to the → canonical IMF.

See also: → birth; → binary; → population.

In star formation models, the population of binary components formed via random pairing of stars distributed according to the → canonical IMF.

See also: → birth; → binary; → population.

The path in the → H-R diagram that continuously → accreting stars follow. Stars on the birthline are difficult to observe, because they are hidden by the → accretion disk and a dense → cocoon of → interstellar matter. The star becomes visible once a sufficient amount of the surrounding matter has been dispersed. It follows that the young starsare observed generally between the birthline and the → zero-age main sequence (ZAMS). Before hydrogen ignition, gravitational contraction and deuterium burning are the main energy sources for the star. The localization of the birthline depends on the deuterium → accretion rate.
First introduced by R. Behrend & A. Maeder, 2001 (A&A 373, 190).

See also: → birth; → line.

The path in the → H-R diagram that continuously → accreting stars follow. Stars on the birthline are difficult to observe, because they are hidden by the → accretion disk and a dense → cocoon of → interstellar matter. The star becomes visible once a sufficient amount of the surrounding matter has been dispersed. It follows that the young starsare observed generally between the birthline and the → zero-age main sequence (ZAMS). Before hydrogen ignition, gravitational contraction and deuterium burning are the main energy sources for the star. The localization of the birthline depends on the deuterium → accretion rate.
First introduced by R. Behrend & A. Maeder, 2001 (A&A 373, 190).

See also: → birth; → line.

A method devised by the Iranian astronomer Biruni (973-1048) to measure the Earth radius, using trigonometric calculations. In contrast to foregoing → Eratosthenes’ method and → Mamun’s method, which required expeditions to travel long distances, Biruni’s method was on-site. He carried out the measurement when he was at Nandana Fort (at the southern end of the pass through the Salt Range, near Baghanwala in the Punjab).

He first calculated the height of a hill (321.5 m). To do this he used the usual method of observing the summit from two places in a straight line from the hill top. He measured the distance, d, between the two places and the angles θ₁ and θ₂ to the hill top from the two points, respectively. He made both measurements using an astrolabe. The formula that relates these angles to the hill height is: h = (d. tan θ₁ . tan θ₂) / (tan θ₂ - tan θ₁).
He then climbed to the hill top, where he measured the → dip angle (θ), that is the angle of the line of sight to the horizon. He applied the values he obtained for the dip angle and the hill’s height to the following trigonometric formula to derive the Earth radius:

R = h cosθ / (1 - cos θ).

The result for the Earth radius was 12,851,369.845 cubits (or 6335.725 km, using favorable conversion units). Despite the fact that the method is very ingenious, such a precise value is only by chance, because of several drawbacks: The plane was not perfectly flat to serve as the smooth surface of the sea. A measuring instrument more accurate than the alleged 5 arc minutes was needed. And the method suffered from the → atmospheric refraction (See, e.g., Gomez, A. G., 2010, Journal of Scientific and Mathematical Research).

See also: Abu Rayhân Mohammad Biruni (973-1048 A.D.), one of the greatest scholars of the medieval era, was an Iranian of the Khwarezm region; → method.

A method devised by the Iranian astronomer Biruni (973-1048) to measure the Earth radius, using trigonometric calculations. In contrast to foregoing → Eratosthenes’ method and → Mamun’s method, which required expeditions to travel long distances, Biruni’s method was on-site. He carried out the measurement when he was at Nandana Fort (at the southern end of the pass through the Salt Range, near Baghanwala in the Punjab).

He first calculated the height of a hill (321.5 m). To do this he used the usual method of observing the summit from two places in a straight line from the hill top. He measured the distance, d, between the two places and the angles θ₁ and θ₂ to the hill top from the two points, respectively. He made both measurements using an astrolabe. The formula that relates these angles to the hill height is: h = (d. tan θ₁ . tan θ₂) / (tan θ₂ - tan θ₁).
He then climbed to the hill top, where he measured the → dip angle (θ), that is the angle of the line of sight to the horizon. He applied the values he obtained for the dip angle and the hill’s height to the following trigonometric formula to derive the Earth radius:

R = h cosθ / (1 - cos θ).

The result for the Earth radius was 12,851,369.845 cubits (or 6335.725 km, using favorable conversion units). Despite the fact that the method is very ingenious, such a precise value is only by chance, because of several drawbacks: The plane was not perfectly flat to serve as the smooth surface of the sea. A measuring instrument more accurate than the alleged 5 arc minutes was needed. And the method suffered from the → atmospheric refraction (See, e.g., Gomez, A. G., 2010, Journal of Scientific and Mathematical Research).

See also: Abu Rayhân Mohammad Biruni (973-1048 A.D.), one of the greatest scholars of the medieval era, was an Iranian of the Khwarezm region; → method.

A white, crystalline, brittle metallic chemical element with a pinkish tinge; symbol Bi. → Atomic number 83; → atomic weight 208.9804; → melting point 271.3°C; → boiling point about 1,560°C; → specific gravity 9.75 at 20°C; → valence +3 or +5.

Bismuth is the most → diamagnetic of all metals. Its
thermal conductivity is lower than any metal, except → mercury.
There is only one naturally occurring → isotope of bismuth, ²⁰⁹Bi. Bismuth is used in a number of very different applications, chiefly in bismuth alloys, and in pharmaceuticals and chemicals.

See also: From Ger. Bismuth, Wismut, Wissmuth, probably from weisse Masse
“white mass,” indicating how the element appears in nature.

A white, crystalline, brittle metallic chemical element with a pinkish tinge; symbol Bi. → Atomic number 83; → atomic weight 208.9804; → melting point 271.3°C; → boiling point about 1,560°C; → specific gravity 9.75 at 20°C; → valence +3 or +5.

Bismuth is the most → diamagnetic of all metals. Its
thermal conductivity is lower than any metal, except → mercury.
There is only one naturally occurring → isotope of bismuth, ²⁰⁹Bi. Bismuth is used in a number of very different applications, chiefly in bismuth alloys, and in pharmaceuticals and chemicals.

See also: From Ger. Bismuth, Wismut, Wissmuth, probably from weisse Masse
“white mass,” indicating how the element appears in nature.

Of or relating to a → leap year or to the extra day falling in a leap year.

Etymology (EN): L.L. bissextlis (annus) “year containing an intercalary day,” from bisextus, from bis “twice, two, doubled” + sextus “sixth,” because in the → Julian calendar the sixth day before the Calends of March was doubled every four years. Same as → leap and
→ intercalary day.

Etymology (PE): Andarheli, of or relating to andarhel→ intercalation.

Note. Some authors have used the Pers. term behizaki for “bissextile,” however this is problematic as far as the
calendar history is concerned. The term comes from Mid.Pers. vihezagig or vihezakik “movable,” which was the name of the additional whole month of 30 days which Iranians used in their calendar system in the Sasanid era. In fact they did not use an intercalary day every four years, but instead added a whole month after a period of 120 years. The operation was called vihezag. The term originates from Mid.Pers. vihez-
“to move, progress,” vihezag(k) “movement, progression.” Therefore, this dictionary cautions against equating behizaki and bissextile. → embolismic month.

Of or relating to a → leap year or to the extra day falling in a leap year.

Etymology (EN): L.L. bissextlis (annus) “year containing an intercalary day,” from bisextus, from bis “twice, two, doubled” + sextus “sixth,” because in the → Julian calendar the sixth day before the Calends of March was doubled every four years. Same as → leap and
→ intercalary day.

Etymology (PE): Andarheli, of or relating to andarhel→ intercalation.

Note. Some authors have used the Pers. term behizaki for “bissextile,” however this is problematic as far as the
calendar history is concerned. The term comes from Mid.Pers. vihezagig or vihezakik “movable,” which was the name of the additional whole month of 30 days which Iranians used in their calendar system in the Sasanid era. In fact they did not use an intercalary day every four years, but instead added a whole month after a period of 120 years. The operation was called vihezag. The term originates from Mid.Pers. vihez-
“to move, progress,” vihezag(k) “movement, progression.” Therefore, this dictionary cautions against equating behizaki and bissextile. → embolismic month.

The condition in which a physical system is capable of assuming either of two stable states.

See also: → bi-; → stable.

The condition in which a physical system is capable of assuming either of two stable states.

See also: → bi-; → stable.

An abrupt discontinuity in the → stellar wind properties of → hot stars near → effective temperatures about 21,000 K and 10,000 K, corresponding to O9.5-B3 supergiants (Castor et al. 1975, ApJ 195, 157; Lamers et al., 1995, ApJ 455, 269). At these temperatures the → terminal velocity of the wind drops steeply by about a factor two and the → mass loss rate increases steeply by about a factor three to five, when going from high to low temperatures. Bistability jump is related to the degree of ionization in the wind. With a little drop in the temperature, the dominant driving element (Fe) will recombine to lower ionization stages which produces a lower terminal velocity and a relatively high density in the wind. → wind momentum. Additional bistability jumps may occur at higher temperatures where CNO may provide the dominant line driving, especially for low metallicity stars (Vink et al. 2001, A&A 369, 574). However, a recent study using a larger sample finds that there is a gradual decline in the wind terminal velocities of early B supergiants and not a “jump” (Crowther et al. 2006, A&A 446, 279).

See also: → bistability; → jump.

An abrupt discontinuity in the → stellar wind properties of → hot stars near → effective temperatures about 21,000 K and 10,000 K, corresponding to O9.5-B3 supergiants (Castor et al. 1975, ApJ 195, 157; Lamers et al., 1995, ApJ 455, 269). At these temperatures the → terminal velocity of the wind drops steeply by about a factor two and the → mass loss rate increases steeply by about a factor three to five, when going from high to low temperatures. Bistability jump is related to the degree of ionization in the wind. With a little drop in the temperature, the dominant driving element (Fe) will recombine to lower ionization stages which produces a lower terminal velocity and a relatively high density in the wind. → wind momentum. Additional bistability jumps may occur at higher temperatures where CNO may provide the dominant line driving, especially for low metallicity stars (Vink et al. 2001, A&A 369, 574). However, a recent study using a larger sample finds that there is a gradual decline in the wind terminal velocities of early B supergiants and not a “jump” (Crowther et al. 2006, A&A 446, 279).

See also: → bistability; → jump.

The mechanism that accounts for the → bistability jump.

See also: → bistability; → mechanism.

The mechanism that accounts for the → bistability jump.

See also: → bistability; → mechanism.

A contraction of → binary digit, either 0 or 1.

See also: Bit, from binary + digit

A contraction of → binary digit, either 0 or 1.

See also: Bit, from binary + digit

1. Chem.: Having a → valence of two or having two valences.
   

2. → bivalent logic.

See also: → bi-; → valence.

1. Chem.: Having a → valence of two or having two valences.
   

2. → bivalent logic.

See also: → bi-; → valence.

A logical system, such as → classical logic,
in which every declarative sentence expressing a → proposition has exactly one → truth value, either → true or → false. Bivalent logic is just a sub-set of a more powerful type of logic known as → fuzzy logic. See also → polyvalent logic.

See also: → bivalent; → logic.

A logical system, such as → classical logic,
in which every declarative sentence expressing a → proposition has exactly one → truth value, either → true or → false. Bivalent logic is just a sub-set of a more powerful type of logic known as → fuzzy logic. See also → polyvalent logic.

See also: → bivalent; → logic.