An Etymological Dictionary of Astronomy and Astrophysics

→ Titius-Bode law.

→ Titius-Bode law.

1. The physical structure of a human being or animal, including the bones, flesh, and organs.
   

2. Any material object characterized by its physical properties.

Etymology (EN): Body, from O.E. bodig “trunk, chest,” related to O.H.G. botah, of unknown origin.

Etymology (PE): 1) Tan, from Mid.Pers. tan “body, person;” O.Pers. tanūš “body,” tanūm [acc.sg.] “(to) oneself;” Av. tanū- “body, person, self,” tanūm [acc.sg.]; cf. Skt. tanūš- “body, self;” PIE base *ten-uh- “body.”

2. Jesm, from Ar. jism “body, corps.”

1. The physical structure of a human being or animal, including the bones, flesh, and organs.
   

2. Any material object characterized by its physical properties.

Etymology (EN): Body, from O.E. bodig “trunk, chest,” related to O.H.G. botah, of unknown origin.

Etymology (PE): 1) Tan, from Mid.Pers. tan “body, person;” O.Pers. tanūš “body,” tanūm [acc.sg.] “(to) oneself;” Av. tanū- “body, person, self,” tanūm [acc.sg.]; cf. Skt. tanūš- “body, self;” PIE base *ten-uh- “body.”

2. Jesm, from Ar. jism “body, corps.”

A system for the classification of → S-type stars. The system involves the designations of a C/O index and a temperature type. Moreover, when possible, it uses intensity estimates for → ZrO bands, the → TiO bands, the → Na I D-lines, the YO bands, and the Li I 6708 line.

See also: Philip C. Keenan & Patricia C. Boeshaar, 1980, ApJS, 43, 379; → classification.

A system for the classification of → S-type stars. The system involves the designations of a C/O index and a temperature type. Moreover, when possible, it uses intensity estimates for → ZrO bands, the → TiO bands, the → Na I D-lines, the YO bands, and the Li I 6708 line.

See also: Philip C. Keenan & Patricia C. Boeshaar, 1980, ApJS, 43, 379; → classification.

Niels Bohr (1885-1962), Danish physicist who made several important contributions to modern physics. He won the 1922 Nobel prize for physics in recognition of his work on the structure of atoms.

Niels Bohr (1885-1962), Danish physicist who made several important contributions to modern physics. He won the 1922 Nobel prize for physics in recognition of his work on the structure of atoms.

The simplest model of an atom according to which electrons move
around the central nucleus in circular, but well-defined, orbits. For more details
see → Bohr model.

See also: → Bohr; → atom.

The simplest model of an atom according to which electrons move
around the central nucleus in circular, but well-defined, orbits. For more details
see → Bohr model.

See also: → Bohr; → atom.

A fundamental constant, first calculated by Bohr, for the intrinsic → spin magnetic moment of the electron. It is given by: μ_B = eħ/2m_e = 9.27 x 10^-24 joule/tesla = 5.79 x 10^-5 eV/tesla, representing the minimum amount of magnetism which can be caused by the revolution of an electron around an atomic nucleus. It serves as a unit for measuring the magnetic moments of atomic particles.

See also: → Bohr; magneton, from → magnet

• → -on.

A fundamental constant, first calculated by Bohr, for the intrinsic → spin magnetic moment of the electron. It is given by: μ_B = eħ/2m_e = 9.27 x 10^-24 joule/tesla = 5.79 x 10^-5 eV/tesla, representing the minimum amount of magnetism which can be caused by the revolution of an electron around an atomic nucleus. It serves as a unit for measuring the magnetic moments of atomic particles.

See also: → Bohr; magneton, from → magnet

• → -on.

A model suggested in 1913 to explain the stability of atoms which
classical electrodynamics was unable to account for. According to the classical view of the atom, the energy of an electron moving around a nucleus must continually diminish until the electron falls onto the nucleus. The Bohr model solves this paradox with the aid of three postulates (→ Bohr’s first postulate, → Bohr’s second postulate, → Bohr’s third postulate). On the whole, an atom has stable orbits such that an electron moving in them does not radiate electromagnetic waves. An electron radiates only when making a transition from an orbit of higher energy to one with lower energy. The frequency of this radiation is related to the difference between the energies of the electron in these two orbits,
as expressed by the equation hν = ε₁ - ε₂, where h is → Planck’s constant and ν the radiation frequency. The electron needs to gain energy to jump to a higher orbit. It gets that extra energy by absorbing a quantum of light (→ photon), which excites the jump. The electron does not remain on the higher orbit and returns to its lower energy orbit releasing the extra energy as radiation.
Bohr’s model answered many scientific questions in its time though the model itself is oversimplified and, in the strictest sense, incorrect. Electrons do not orbit the nucleus like a planet orbiting the Sun; rather, they behave as → standing waves. Same as → Bohr atom.

See also: → Bohr; → model.

A model suggested in 1913 to explain the stability of atoms which
classical electrodynamics was unable to account for. According to the classical view of the atom, the energy of an electron moving around a nucleus must continually diminish until the electron falls onto the nucleus. The Bohr model solves this paradox with the aid of three postulates (→ Bohr’s first postulate, → Bohr’s second postulate, → Bohr’s third postulate). On the whole, an atom has stable orbits such that an electron moving in them does not radiate electromagnetic waves. An electron radiates only when making a transition from an orbit of higher energy to one with lower energy. The frequency of this radiation is related to the difference between the energies of the electron in these two orbits,
as expressed by the equation hν = ε₁ - ε₂, where h is → Planck’s constant and ν the radiation frequency. The electron needs to gain energy to jump to a higher orbit. It gets that extra energy by absorbing a quantum of light (→ photon), which excites the jump. The electron does not remain on the higher orbit and returns to its lower energy orbit releasing the extra energy as radiation.
Bohr’s model answered many scientific questions in its time though the model itself is oversimplified and, in the strictest sense, incorrect. Electrons do not orbit the nucleus like a planet orbiting the Sun; rather, they behave as → standing waves. Same as → Bohr atom.

See also: → Bohr; → model.

The radius of the orbit of the hydrogen electron in its ground state (0.529 Å).

See also: → Bohr; → radius.

The radius of the orbit of the hydrogen electron in its ground state (0.529 Å).

See also: → Bohr; → radius.

One of the postulates used in the → Bohr model, whereby there are certain steady states of the atom in which electrons can only travel in stable orbits. In spite of their acceleration, the electrons do not radiate electromagnetic waves when they move along stationary orbits.

See also: → Bohr; → first; → postulate.

One of the postulates used in the → Bohr model, whereby there are certain steady states of the atom in which electrons can only travel in stable orbits. In spite of their acceleration, the electrons do not radiate electromagnetic waves when they move along stationary orbits.

See also: → Bohr; → first; → postulate.

One of the three postulates advanced in the → Bohr model which led to the correct prediction of the observed line spectrum of hydrogen atom. See also → Bohr’s first postulate, → Bohr’s second postulate, → Bohr’s third postulate,

See also: → Bohr; → postulate.

One of the three postulates advanced in the → Bohr model which led to the correct prediction of the observed line spectrum of hydrogen atom. See also → Bohr’s first postulate, → Bohr’s second postulate, → Bohr’s third postulate,

See also: → Bohr; → postulate.

One of the postulates used in the → Bohr model, whereby when an atom is in the steady state an electron travelling in a circular orbit should have → quantized values of the → angular momentum which comply with the condition p = n(h/2π), where p is the angular momentum of the electron, h is → Planck’s constant, and n is a positive integer called → quantum number.

See also: → Bohr; → second; → postulate.

One of the postulates used in the → Bohr model, whereby when an atom is in the steady state an electron travelling in a circular orbit should have → quantized values of the → angular momentum which comply with the condition p = n(h/2π), where p is the angular momentum of the electron, h is → Planck’s constant, and n is a positive integer called → quantum number.

See also: → Bohr; → second; → postulate.

One of the postulates used in the → Bohr model, whereby the atom emits (absorbs) a quantum of electromagnetic energy (→ photon) when the electron passes from an orbit with a greater (lesser) n value to one with a lesser (greater) value. The energy of the quantum is equal to the difference between the energies of the electron on its orbits before and after the transition or “jump”: hν = ε₁ - ε₂, where h is the → Planck’s constant and ν the frequency of the transition.

See also: → Bohr; → third; → postulate.

One of the postulates used in the → Bohr model, whereby the atom emits (absorbs) a quantum of electromagnetic energy (→ photon) when the electron passes from an orbit with a greater (lesser) n value to one with a lesser (greater) value. The energy of the quantum is equal to the difference between the energies of the electron on its orbits before and after the transition or “jump”: hν = ε₁ - ε₂, where h is the → Planck’s constant and ν the frequency of the transition.

See also: → Bohr; → third; → postulate.

The temperature at which a liquid changes to a gas (vapor) at normal atmospheric pressure. In other words, the temperature at which the vapor pressure of a liquid is equal to the external pressure.

Etymology (EN): M.E. boillen; O.Fr. boillir, from L. bullire “to bubble, seethe,” from bulla “a bubble, knob;” → point.

Etymology (PE): Noqté, → point; juš “boiling,” present stem of jušidan “to boil;” Khotanese jis- “to boil;” Av. yaēšiiant- “boiling;” cf. Skt. yas- “to boil, become hot,” yasyati “boils, seethes;” Gk. zein “to bubble, boil, cook;” O.H.G. jesan “to ferment, foam;” Ger. Gischt “foam, froth,” gären “to ferment;” O.E. gist; E. yeast.

The temperature at which a liquid changes to a gas (vapor) at normal atmospheric pressure. In other words, the temperature at which the vapor pressure of a liquid is equal to the external pressure.

Etymology (EN): M.E. boillen; O.Fr. boillir, from L. bullire “to bubble, seethe,” from bulla “a bubble, knob;” → point.

Etymology (PE): Noqté, → point; juš “boiling,” present stem of jušidan “to boil;” Khotanese jis- “to boil;” Av. yaēšiiant- “boiling;” cf. Skt. yas- “to boil, become hot,” yasyati “boils, seethes;” Gk. zein “to bubble, boil, cook;” O.H.G. jesan “to ferment, foam;” Ger. Gischt “foam, froth,” gären “to ferment;” O.E. gist; E. yeast.

A small, roughly spherical cloud of → interstellar dust and gas that appears as a dark compact globule when viewed against the background of an → H II region. Bok globules range in mass from about 1 to 1,000 or more → solar masses, and in size from about 10,000 → astronomical units to 3 → light-years. They typically have temperatures of around 10 → Kelvin. Bok globules are thought to represent a stage in the collapse of a dense fragment of → molecular clouds that are in the process of forming new stars. → elephant trunk.

Etymology (EN): In honor of Bart Jan Bok (1906-1983), the Dutch-American astronomer, who first observed these objects. In 1947, in collaboration with Edith F. Reilly, he put forward the hypothesis that these globules were undergoing → gravitational collapse to form new stars (Bok & Reilly, 1947, ApJ 105, 255); → globule.

A small, roughly spherical cloud of → interstellar dust and gas that appears as a dark compact globule when viewed against the background of an → H II region. Bok globules range in mass from about 1 to 1,000 or more → solar masses, and in size from about 10,000 → astronomical units to 3 → light-years. They typically have temperatures of around 10 → Kelvin. Bok globules are thought to represent a stage in the collapse of a dense fragment of → molecular clouds that are in the process of forming new stars. → elephant trunk.

Etymology (EN): In honor of Bart Jan Bok (1906-1983), the Dutch-American astronomer, who first observed these objects. In 1947, in collaboration with Edith F. Reilly, he put forward the hypothesis that these globules were undergoing → gravitational collapse to form new stars (Bok & Reilly, 1947, ApJ 105, 255); → globule.

A → meteor which is extremely bright, particularly one that breaks up during its passage through the → atmosphere.
Also called → fireball.

Etymology (EN): Bolide, Fr., from L. bolis, bolidis,
from Gk. bolis, bolidos “missile, flash of lightning,” from ballein “to throw;” PIE *g^welH₁- “to throw;” → ballistics.

Etymology (PE): Garzin “arrow;” cf. Tâleši ger “meteor” (from Proto-Iranian *garH- “to throw”), cognate with Gk. ballein, as above; → ballistics.

A → meteor which is extremely bright, particularly one that breaks up during its passage through the → atmosphere.
Also called → fireball.

Etymology (EN): Bolide, Fr., from L. bolis, bolidis,
from Gk. bolis, bolidos “missile, flash of lightning,” from ballein “to throw;” PIE *g^welH₁- “to throw;” → ballistics.

Etymology (PE): Garzin “arrow;” cf. Tâleši ger “meteor” (from Proto-Iranian *garH- “to throw”), cognate with Gk. ballein, as above; → ballistics.

1. An instrument for measuring the intensity of radiant energy in amounts as small as one millionth of an erg. It uses the change in resistance of a thin conductor caused by the heating effect of the radiation. → actinometer, → photometer, →
   pyrheliometer, → pyrometer,
   radiometer.
   
2. In astronomy, an instrument that measures the amount of radiant energy received from a celestial object.

Etymology (EN): From Gk. bole “stroke, beam of light,” from ballein “to throw” + middle suffix -o- + → -meter..

Etymology (PE): Tafsanj, from taf “heat, warmth; light, brightness,” from tâbidan, “→ radiate,”

• sanj, → -meter.

1. An instrument for measuring the intensity of radiant energy in amounts as small as one millionth of an erg. It uses the change in resistance of a thin conductor caused by the heating effect of the radiation. → actinometer, → photometer, →
   pyrheliometer, → pyrometer,
   radiometer.
   
2. In astronomy, an instrument that measures the amount of radiant energy received from a celestial object.

Etymology (EN): From Gk. bole “stroke, beam of light,” from ballein “to throw” + middle suffix -o- + → -meter..

Etymology (PE): Tafsanj, from taf “heat, warmth; light, brightness,” from tâbidan, “→ radiate,”

• sanj, → -meter.

Of or relating to or measured by a → bolometer.

See also: → bolometer; → -ic.

Of or relating to or measured by a → bolometer.

See also: → bolometer; → -ic.

The difference between the → visual magnitude and → bolometric magnitude.

See also: → bolometric; → correction.

The difference between the → visual magnitude and → bolometric magnitude.

See also: → bolometric; → correction.

The total rate of energy output of an object integrated over all wavelengths.

See also: → bolometric; → luminosity.

The total rate of energy output of an object integrated over all wavelengths.

See also: → bolometric; → luminosity.

The magnitude of an astronomical object for the entire range of its electromagnetic spectrum.

See also: → bolometric; → magnitude.

The magnitude of an astronomical object for the entire range of its electromagnetic spectrum.

See also: → bolometric; → magnitude.

→ Boltzmann’s constant.

See also: → Boltzmann’s constant.

→ Boltzmann’s constant.

See also: → Boltzmann’s constant.

The factor e^-E/kT involved in the probability for atoms having an excitation energy E and temperature T, where k is Boltzmann’s constant.

See also: → Boltzmann’s constant; → factor.

The factor e^-E/kT involved in the probability for atoms having an excitation energy E and temperature T, where k is Boltzmann’s constant.

See also: → Boltzmann’s constant; → factor.

The physical constant, noted by k, relating the mean → kinetic energy of → molecules in an → ideal gas to their → absolute temperature. It is given by the ratio of the → gas constant to → Avogadro’s number.
Its value is about 1.380 x 10^-16erg K^-1.

See also: Named after the Austrian physicist Ludwig Boltzmann (1844-1906), who made important contributions to the theory of statistical mechanics; → constant.

The physical constant, noted by k, relating the mean → kinetic energy of → molecules in an → ideal gas to their → absolute temperature. It is given by the ratio of the → gas constant to → Avogadro’s number.
Its value is about 1.380 x 10^-16erg K^-1.

See also: Named after the Austrian physicist Ludwig Boltzmann (1844-1906), who made important contributions to the theory of statistical mechanics; → constant.

In → statistical thermodynamics, a probability equation relating the → entropy S of an → ideal gas to the quantity Ω, which is the number of → microstates corresponding to a given → macrostate: S = k. ln Ω. Same as → Boltzmann’s relation.

See also: → Boltzmann’s constant; → entropy; → formula.

In → statistical thermodynamics, a probability equation relating the → entropy S of an → ideal gas to the quantity Ω, which is the number of → microstates corresponding to a given → macrostate: S = k. ln Ω. Same as → Boltzmann’s relation.

See also: → Boltzmann’s constant; → entropy; → formula.

1. An equation that expresses the relative number (per unit volume) of → excited atoms in different states as a function of the temperature for a gas in → thermal equilibrium: N_u/N_l = (g_u/g_l) exp (-ΔE/kT_ex), where N_u and N_l are the upper level and lower level populations respectively, g_u and g_l the → statistical weights,
   ΔE = hν the energy difference between the states,
   k is → Boltzmann’s constant, and h  → Planck’s constant.

See also: → Boltzmann’s constant; → equation.

1. An equation that expresses the relative number (per unit volume) of → excited atoms in different states as a function of the temperature for a gas in → thermal equilibrium: N_u/N_l = (g_u/g_l) exp (-ΔE/kT_ex), where N_u and N_l are the upper level and lower level populations respectively, g_u and g_l the → statistical weights,
   ΔE = hν the energy difference between the states,
   k is → Boltzmann’s constant, and h  → Planck’s constant.

See also: → Boltzmann’s constant; → equation.

A relation between the → entropy of a given → state of a → thermodynamic system and the → probability of the state: S = k . ln Ω where S is the entropy of the system, k is → Boltzmann’s constant, and Ω the thermodynamic probability of the state. Boltzmann’s relation connects → statistical mechanics and → thermodynamics. Ω is the number of possible → microstates of the system, and it represents the → randomness of the system.
The relation also describes the statistical meaning of the → second law of thermodynamics. This expression has been carved above Boltzmann’s name on his tombstone in Zentralfreihof in Vienna. Same as → Boltzmann’s entropy formula.

See also: → Boltzmann’s constant; → relation.

A relation between the → entropy of a given → state of a → thermodynamic system and the → probability of the state: S = k . ln Ω where S is the entropy of the system, k is → Boltzmann’s constant, and Ω the thermodynamic probability of the state. Boltzmann’s relation connects → statistical mechanics and → thermodynamics. Ω is the number of possible → microstates of the system, and it represents the → randomness of the system.
The relation also describes the statistical meaning of the → second law of thermodynamics. This expression has been carved above Boltzmann’s name on his tombstone in Zentralfreihof in Vienna. Same as → Boltzmann’s entropy formula.

See also: → Boltzmann’s constant; → relation.

The → attractive force that holds together neighboring → atoms in → molecules.

Etymology (EN): Bond, variant of band, from M.E. bende, O.E. bend, from O.Fr. bande, bende, PIE *bendh- “to bind” (cf. Goth bandi “that which binds;” Av./O.Pers. band- “to bind, fetter,” banda- “band, tie” (see below);
Skt. bandh- “to bind, tie, fasten,” bandhah “a tying, bandage”).

Etymology (PE): Band “band, tie,” from Mid.Pers., O.Pers./Av. band- “to bind,” banda- “band, tie,” also present stem of bastan “to bind, shut,” → shutter.

The → attractive force that holds together neighboring → atoms in → molecules.

Etymology (EN): Bond, variant of band, from M.E. bende, O.E. bend, from O.Fr. bande, bende, PIE *bendh- “to bind” (cf. Goth bandi “that which binds;” Av./O.Pers. band- “to bind, fetter,” banda- “band, tie” (see below);
Skt. bandh- “to bind, tie, fasten,” bandhah “a tying, bandage”).

Etymology (PE): Band “band, tie,” from Mid.Pers., O.Pers./Av. band- “to bind,” banda- “band, tie,” also present stem of bastan “to bind, shut,” → shutter.

The fraction of the total amount of electromagnetic radiation falling upon a non-luminous spherical body that is reflected in all directions by that body. The bond albedo takes into account all wavelengths at all → phase angles. Compare with → geometric albedo.

See also: Named after the American astronomer George Phillips Bond (1825-1865), who proposed it; → albedo.

The fraction of the total amount of electromagnetic radiation falling upon a non-luminous spherical body that is reflected in all directions by that body. The bond albedo takes into account all wavelengths at all → phase angles. Compare with → geometric albedo.

See also: Named after the American astronomer George Phillips Bond (1825-1865), who proposed it; → albedo.

The → accretion of mass by a star (assumed as point particle) moving at a steady speed through an infinite, uniform gas cloud.
It is directly proportional to the star mass (M) and the medium density (ρ) and inversely proportional to the relative star/gas velocity (v). In its classical expression:
4πρ(G M)² / v³, where G is the → gravitational constant. See Bondi & Hoyle (1944, MNRAS 104, 273) and Bondi (1952, MNRAS 112, 195). For a recent treatment of accretion in a turbulent medium see Krumholtz et al. 2006 (ApJ 638, 369).

See also: Named after Hermann Bondi (1919-2005), an Anglo-Austrian mathematician and cosmologist and Fred Hoyle (1915-2001), British mathematician and astronomer best known as the foremost proponent and defender of the steady-state theory of the universe; → accretion.

The → accretion of mass by a star (assumed as point particle) moving at a steady speed through an infinite, uniform gas cloud.
It is directly proportional to the star mass (M) and the medium density (ρ) and inversely proportional to the relative star/gas velocity (v). In its classical expression:
4πρ(G M)² / v³, where G is the → gravitational constant. See Bondi & Hoyle (1944, MNRAS 104, 273) and Bondi (1952, MNRAS 112, 195). For a recent treatment of accretion in a turbulent medium see Krumholtz et al. 2006 (ApJ 638, 369).

See also: Named after Hermann Bondi (1919-2005), an Anglo-Austrian mathematician and cosmologist and Fred Hoyle (1915-2001), British mathematician and astronomer best known as the foremost proponent and defender of the steady-state theory of the universe; → accretion.

In the → Bondi-Hoyle accretion process, the radius where the gravitational energy owing to star is larger than the kinetic energy and, therefore,
at which material is bound to star. The Bondi-Hoyle accretion radius is given by

R_BH = 2 GM / (v² + c_s²)

where G is the gravitational constant, M is the stellar mass, v the gas/star relative velocity, and c_s is the sound speed.

See also: → Bondi-Hoyle accretion; → radius.

In the → Bondi-Hoyle accretion process, the radius where the gravitational energy owing to star is larger than the kinetic energy and, therefore,
at which material is bound to star. The Bondi-Hoyle accretion radius is given by

R_BH = 2 GM / (v² + c_s²)

where G is the gravitational constant, M is the stellar mass, v the gas/star relative velocity, and c_s is the sound speed.

See also: → Bondi-Hoyle accretion; → radius.

A catalog of 324,188 stars in the → declination zones +89 to -01 degrees. The goal of the survey was to obtain a → position and estimated → visual magnitude for every star visible with the 78 mm → refracting telescope at Bonn. Actual → magnitude estimates were made and reported to 0.1 mag for all stars down to 9.5 mag. Positions are given to the nearest 0.1 sec in → right ascension and 0.1 arcmin in declination. The survey was carried out by Friedrich W. Argelander (1799-1875) and his assistants in the years 1852-1861.

See also: The Ger. name means Bonn Survey.

A catalog of 324,188 stars in the → declination zones +89 to -01 degrees. The goal of the survey was to obtain a → position and estimated → visual magnitude for every star visible with the 78 mm → refracting telescope at Bonn. Actual → magnitude estimates were made and reported to 0.1 mag for all stars down to 9.5 mag. Positions are given to the nearest 0.1 sec in → right ascension and 0.1 arcmin in declination. The survey was carried out by Friedrich W. Argelander (1799-1875) and his assistants in the years 1852-1861.

See also: The Ger. name means Bonn Survey.

The largest gravitationally stable mass of the → Bonnor-Ebert sphere.

See also: After W.B. Bonnor (1956) and R. Ebert (1955); → mass.

The largest gravitationally stable mass of the → Bonnor-Ebert sphere.

See also: After W.B. Bonnor (1956) and R. Ebert (1955); → mass.

A sphere of interstellar gas at uniform temperature in equilibrium under its own gravitation and an external pressure. The pressure of a hotter surrounding medium causes the sphere to collapse. → Bonnor-Ebert mass.

See also: → Bonnor-Ebert mass; → sphere.

A sphere of interstellar gas at uniform temperature in equilibrium under its own gravitation and an external pressure. The pressure of a hotter surrounding medium causes the sphere to collapse. → Bonnor-Ebert mass.

See also: → Bonnor-Ebert mass; → sphere.

A bound set of printed or manuscript pages.

Etymology (EN): M.E., from O.E. boc “book, written document;” cf. Ger. Buch “book;” Du. boek; O.N. bôk; Gothic boka.

Etymology (PE): Ketâb, loanword from Ar.
Nâmé “book, letter;” Mid.Pers. nâmag “book, letter, inscription;” O.Pers./Av. nāman- “name;” cf. Skt. nama-;
Gk. onoma, onuma; L. nomen; PIE *nomen-.
Nask; Mid.Pers. nask “one of the book comprising Avesta;” Av. naska-, literally “bundle, bunch,” naskô.frasa- “one who devotes himself to the study of nasks;” cf. Skt. nah- “to tie, bind,” nahyati “he ties, binds;” L. nectere “to tie, bind,” nodus “node;” O.Ir. nasc “a tie, bond, ring,” nascim “I bind.”

A bound set of printed or manuscript pages.

Etymology (EN): M.E., from O.E. boc “book, written document;” cf. Ger. Buch “book;” Du. boek; O.N. bôk; Gothic boka.

Etymology (PE): Ketâb, loanword from Ar.
Nâmé “book, letter;” Mid.Pers. nâmag “book, letter, inscription;” O.Pers./Av. nāman- “name;” cf. Skt. nama-;
Gk. onoma, onuma; L. nomen; PIE *nomen-.
Nask; Mid.Pers. nask “one of the book comprising Avesta;” Av. naska-, literally “bundle, bunch,” naskô.frasa- “one who devotes himself to the study of nasks;” cf. Skt. nah- “to tie, bind,” nahyati “he ties, binds;” L. nectere “to tie, bind,” nodus “node;” O.Ir. nasc “a tie, bond, ring,” nascim “I bind.”

A → variable or → function which takes the value → true or → false. → Boolean algebra.

See also: After the English mathematician George Boole (1815-1864), the founder of mathematical, or symbolic, logic.

A → variable or → function which takes the value → true or → false. → Boolean algebra.

See also: After the English mathematician George Boole (1815-1864), the founder of mathematical, or symbolic, logic.

Any of a number of possible systems of mathematics that deals with → binary digits instead of numbers. In Boolean algebra, a binary value of 1 is interpreted to mean → true and a binary value of 0 means → false. Boolean algebra can equivalently be thought of as a particular type of mathematics that deals with → truth values instead of numbers.

See also: → Boolean; → algebra. The term Boolean algebra was first suggested by Sheffer in 1913.

Any of a number of possible systems of mathematics that deals with → binary digits instead of numbers. In Boolean algebra, a binary value of 1 is interpreted to mean → true and a binary value of 0 means → false. Boolean algebra can equivalently be thought of as a particular type of mathematics that deals with → truth values instead of numbers.

See also: → Boolean; → algebra. The term Boolean algebra was first suggested by Sheffer in 1913.

A → nebula displaying two nearly symmetric lobes of matter that are being ejected from a central star at a speed of about 600,000 km per hour (each lobe nearly one light-year in length). The Boomerang Nebula resides 5,000 → light-years from Earth in the direction of the Southern constellation → Centaurus.

See also: Boomerang, adapted from wo-mur-rang, boo-mer-rit, in the language of Australian aborigines; → nebula.

A → nebula displaying two nearly symmetric lobes of matter that are being ejected from a central star at a speed of about 600,000 km per hour (each lobe nearly one light-year in length). The Boomerang Nebula resides 5,000 → light-years from Earth in the direction of the Southern constellation → Centaurus.

See also: Boomerang, adapted from wo-mur-rang, boo-mer-rit, in the language of Australian aborigines; → nebula.

The Herdsman, the Ox Driver. A constellation in the northern hemisphere, at right ascension about 14h 30m, north declination about 30°. Its brightest star is → Arcturus. Abbreviation: Boo; genitive form: Boötis.

Etymology (EN): L. Boötes, from Gk. bootes “plowman,” literally “ox-driver,”
from bootein “to plow,” from bous “ox,” from
PIE *gwou- “ox, bull, cow;” compare with Av. gao-, gâuš “bull, cow, ox,” Mod.Pers. gâv, Skt. gaus, Armenian kov, O.E. cu.

Etymology (PE): Gâvrân “ox-driver,” from gâv “ox, cow” + rân “driver,” from rândan “to drive."
Gâyâr, from Lori “bull driver, plower, plow man” (Tabari goyâr),
from gâ “bull, cow,” variant of gâv, explained above, + -âr, either “driver”, Av. ar-
“to set in motion” (Skt. ir-, IER *er-), or IER *are- “to plow” (L. arare, Gk. aroun, O.C.S. orja, Lith. ariu, Goth. arjan, O.E. erian, Tokharian AB âre). Compare also with Gilaki urân " to plow,” Qâeni ordu “plow”.

The Herdsman, the Ox Driver. A constellation in the northern hemisphere, at right ascension about 14h 30m, north declination about 30°. Its brightest star is → Arcturus. Abbreviation: Boo; genitive form: Boötis.

Etymology (EN): L. Boötes, from Gk. bootes “plowman,” literally “ox-driver,”
from bootein “to plow,” from bous “ox,” from
PIE *gwou- “ox, bull, cow;” compare with Av. gao-, gâuš “bull, cow, ox,” Mod.Pers. gâv, Skt. gaus, Armenian kov, O.E. cu.

Etymology (PE): Gâvrân “ox-driver,” from gâv “ox, cow” + rân “driver,” from rândan “to drive."
Gâyâr, from Lori “bull driver, plower, plow man” (Tabari goyâr),
from gâ “bull, cow,” variant of gâv, explained above, + -âr, either “driver”, Av. ar-
“to set in motion” (Skt. ir-, IER *er-), or IER *are- “to plow” (L. arare, Gk. aroun, O.C.S. orja, Lith. ariu, Goth. arjan, O.E. erian, Tokharian AB âre). Compare also with Gilaki urân " to plow,” Qâeni ordu “plow”.

The Herdsman, the Ox Driver. A constellation in the northern hemisphere, at right ascension about 14h 30m, north declination about 30°. Its brightest star is → Arcturus. Abbreviation: Boo; genitive form: Boötis.

Etymology (EN): L. Boötes, from Gk. bootes “plowman,” literally “ox-driver,”
from bootein “to plow,” from bous “ox,” from
PIE *gwou- “ox, bull, cow;” compare with Av. gao-, gâuš “bull, cow, ox,” Mod.Pers. gâv, Skt. gaus, Armenian kov, O.E. cu.

Etymology (PE): Gâvrân “ox-driver,” from gâv “ox, cow” + rân “driver,” from rândan “to drive."
Gâyâr, from Lori “bull driver, plower, plow man” (Tabari goyâr), from gâ “bull, cow,” variant of gâv, explained above, + -âr, either “driver”, Av. ar- “to set in motion” (Skt. ir-, IER *er-), or IER *are- “to plow” (L. arare, Gk. aroun, O.C.S. orja, Lith. ariu, Goth. arjan, O.E. erian, Tokharian AB âre). Compare also with Gilaki urân " to plow,” Qâeni ordu “plow”.

The Herdsman, the Ox Driver. A constellation in the northern hemisphere, at right ascension about 14h 30m, north declination about 30°. Its brightest star is → Arcturus. Abbreviation: Boo; genitive form: Boötis.

Etymology (EN): L. Boötes, from Gk. bootes “plowman,” literally “ox-driver,”
from bootein “to plow,” from bous “ox,” from
PIE *gwou- “ox, bull, cow;” compare with Av. gao-, gâuš “bull, cow, ox,” Mod.Pers. gâv, Skt. gaus, Armenian kov, O.E. cu.

Etymology (PE): Gâvrân “ox-driver,” from gâv “ox, cow” + rân “driver,” from rândan “to drive."
Gâyâr, from Lori “bull driver, plower, plow man” (Tabari goyâr), from gâ “bull, cow,” variant of gâv, explained above, + -âr, either “driver”, Av. ar- “to set in motion” (Skt. ir-, IER *er-), or IER *are- “to plow” (L. arare, Gk. aroun, O.C.S. orja, Lith. ariu, Goth. arjan, O.E. erian, Tokharian AB âre). Compare also with Gilaki urân " to plow,” Qâeni ordu “plow”.

An instrument which was an improved form of the → reflecting circle, used for measuring angular distances. In Borda’s version the arm carrying the telescope was extended right across the circle. The telescope and a clamp and tangent screw were at one end, and the half-silvered horizon glass at the far end from the eye. In practice, with the index arm clamped, the observer first aims
directly at the right hand object and by reflection on the left, moving the telescope arm until this is achieved. He then frees the index arm, sights directly on the left hand object with the telescope arm clamped, and moves the index arm until the two coincide again. The difference in the readings of the index arm is twice the angle required, so that the final sum reading must be divided by twice the number of double operations. Borda’s instrument greatly contributed to the French success in measuring the length of the meridional arc of the Earth’s surface between Dunkirk and Barcelona (1792-1798). The operation carried out by Jean Baptiste Delambre (1749-1822) and Pierre Méchain (1744-1804) was essential for establishing the meter as the length unit.

See also: After the French physicist and naval officer Jean-Charles de Borda (1733-1799), who made several contributions to hydrodynamics and nautical astronomy. Borda was also one of the most important metrological pioneers; → circle.

An instrument which was an improved form of the → reflecting circle, used for measuring angular distances. In Borda’s version the arm carrying the telescope was extended right across the circle. The telescope and a clamp and tangent screw were at one end, and the half-silvered horizon glass at the far end from the eye. In practice, with the index arm clamped, the observer first aims
directly at the right hand object and by reflection on the left, moving the telescope arm until this is achieved. He then frees the index arm, sights directly on the left hand object with the telescope arm clamped, and moves the index arm until the two coincide again. The difference in the readings of the index arm is twice the angle required, so that the final sum reading must be divided by twice the number of double operations. Borda’s instrument greatly contributed to the French success in measuring the length of the meridional arc of the Earth’s surface between Dunkirk and Barcelona (1792-1798). The operation carried out by Jean Baptiste Delambre (1749-1822) and Pierre Méchain (1744-1804) was essential for establishing the meter as the length unit.

See also: After the French physicist and naval officer Jean-Charles de Borda (1733-1799), who made several contributions to hydrodynamics and nautical astronomy. Borda was also one of the most important metrological pioneers; → circle.

Brought forth by → birth. Past participle of bear. → born-again AGB star.

Etymology (EN): M.E., from O.E. boren, p.p. of beran “to bear, bring, wear”, from P.Gmc. *beranan (O.H.G. beran, Goth. bairan
“to carry”), from PIE root *bher- “to bear; to carry” (cf.
Av./O.Pers. bar- “to bear, carry,” bareθre “to bear (infinitive),” bareθri “a female that bears (children), a mother,” Mod.Pers. bordan “to carry,” bâr “charge, load”, bârdâr “pregnant,” Skt. bharati “he carries,” Gk. pherein).

Etymology (PE): Zâdé “born,” p.p. of zâdan “give birth” (Av. zan- “to bear, give birth to a child, be born,” infinitive zizâite, zâta- “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”).

Brought forth by → birth. Past participle of bear. → born-again AGB star.

Etymology (EN): M.E., from O.E. boren, p.p. of beran “to bear, bring, wear”, from P.Gmc. *beranan (O.H.G. beran, Goth. bairan
“to carry”), from PIE root *bher- “to bear; to carry” (cf.
Av./O.Pers. bar- “to bear, carry,” bareθre “to bear (infinitive),” bareθri “a female that bears (children), a mother,” Mod.Pers. bordan “to carry,” bâr “charge, load”, bârdâr “pregnant,” Skt. bharati “he carries,” Gk. pherein).

Etymology (PE): Zâdé “born,” p.p. of zâdan “give birth” (Av. zan- “to bear, give birth to a child, be born,” infinitive zizâite, zâta- “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”).

A → post-AGB star that undergoes a last → thermal pulse when it is already on the → white dwarf  → cooling track. The thermal pulse will expand the hot central star, whereby hydrogen will be ingested into the → helium burning shell. This will temporarily return the star to the → AGB phase it has previously left.

See also: → born; → again; → asymptotic giant branch; → star.

A → post-AGB star that undergoes a last → thermal pulse when it is already on the → white dwarf  → cooling track. The thermal pulse will expand the hot central star, whereby hydrogen will be ingested into the → helium burning shell. This will temporarily return the star to the → AGB phase it has previously left.

See also: → born; → again; → asymptotic giant branch; → star.

A → planetary nebula which is thought to have experienced a → very late thermal pulse (VLTP) when the central star (→ CSPN) was on the → white dwarf cooling track. The VLTP event occurs when the thermonuclear → hydrogen shell burning has built up a → shell of helium with the critical mass to ignite its → fusion into carbon and oxygen (→ helium shell burning). Since the → white dwarf envelope is shallow, the increase of pressure from this last helium shell flash leads to the ejection of newly processed material inside the old planetary nebula, leaving the stellar core intact. As the stellar envelope expands, its → effective temperature decreases and the star goes back to the → asymptotic giant branch (AGB) region in the → H-R diagram. The subsequent stellar evolution is fast and will return the star back to the → Post-AGB track in the H-R diagram: the envelope of the star contracts, its effective temperature and ionizing photon flux increase, and a new fast stellar wind develops (see, e.g. J. A. Toalá et al. 2015, ApJ 799, 67).

See also: → born; → again; → planetary; → nebula.

A → planetary nebula which is thought to have experienced a → very late thermal pulse (VLTP) when the central star (→ CSPN) was on the → white dwarf cooling track. The VLTP event occurs when the thermonuclear → hydrogen shell burning has built up a → shell of helium with the critical mass to ignite its → fusion into carbon and oxygen (→ helium shell burning). Since the → white dwarf envelope is shallow, the increase of pressure from this last helium shell flash leads to the ejection of newly processed material inside the old planetary nebula, leaving the stellar core intact. As the stellar envelope expands, its → effective temperature decreases and the star goes back to the → asymptotic giant branch (AGB) region in the → H-R diagram. The subsequent stellar evolution is fast and will return the star back to the → Post-AGB track in the H-R diagram: the envelope of the star contracts, its effective temperature and ionizing photon flux increase, and a new fast stellar wind develops (see, e.g. J. A. Toalá et al. 2015, ApJ 799, 67).

See also: → born; → again; → planetary; → nebula.

A soft, brown, nonmetallic chemical element; symbol B. → Atomic number 5; → atomic weight 10.81; → melting point about 2,300°C; → specific gravity 2.3 at 25°C; → valence +3. Boron occurs as borax and boric acid. It is used for hardening steel and for producing enamels and glasses. Since it absorbs slow neutrons, it is used in steel alloys for making control rods in nuclear reactors. Boron was separated in 1808 by Joseph Louis Gay Lussac (1778-1850) and Louis Jacques Thénard (1777-1857) and independently by Sir Humphry Davy (1778-1829).

Etymology (EN): From bor(ax), from M.Fr. boras, from M.L. borax, from Ar. buraq, from Pers. burah “borax, nitre, used in soldering gold” + (car)bon.

Etymology (PE): Bor, loan from Fr., as above.

A soft, brown, nonmetallic chemical element; symbol B. → Atomic number 5; → atomic weight 10.81; → melting point about 2,300°C; → specific gravity 2.3 at 25°C; → valence +3. Boron occurs as borax and boric acid. It is used for hardening steel and for producing enamels and glasses. Since it absorbs slow neutrons, it is used in steel alloys for making control rods in nuclear reactors. Boron was separated in 1808 by Joseph Louis Gay Lussac (1778-1850) and Louis Jacques Thénard (1777-1857) and independently by Sir Humphry Davy (1778-1829).

Etymology (EN): From bor(ax), from M.Fr. boras, from M.L. borax, from Ar. buraq, from Pers. burah “borax, nitre, used in soldering gold” + (car)bon.

Etymology (PE): Bor, loan from Fr., as above.

A state of matter in which a group of atoms or subatomic particles, cooled to within → absolute zero, coalesce into a single quantum mechanical entity that can be described by a → wave function. When a group of atoms are cooled down to very near absolute zero, the atoms hardly move relative to each other, because they have almost no free energy to do so. Hence the atoms clump together and enter the same → ground energy states. They become identical and the whole group starts behaving as though it were a single atom. A Bose-Einstein condensate results from a → quantum transition phase called the → Bose-Einstein condensation.

This form of matter was predicted in 1924 by Albert Einstein on the basis of the quantum formulations of the Indian physicist Satyendra Nath Bose.

Bose-Einstein condensate was created for the first time in the laboratory in 1995. The three physicist who succeeded in producing BEC, Eric A. Cornell, Wolfgang Ketterle, and Carl E. Wieman, were awarded the 2001 Nobel Prize in Physics. Cornell and Wieman managed to do that with about 2,000 → rubidium atoms cooled down to 20 nano K, while Ketterle used more than 100,000 → sodium atoms.

See also: → boson; → Einstein; → condensate.

A state of matter in which a group of atoms or subatomic particles, cooled to within → absolute zero, coalesce into a single quantum mechanical entity that can be described by a → wave function. When a group of atoms are cooled down to very near absolute zero, the atoms hardly move relative to each other, because they have almost no free energy to do so. Hence the atoms clump together and enter the same → ground energy states. They become identical and the whole group starts behaving as though it were a single atom. A Bose-Einstein condensate results from a → quantum transition phase called the → Bose-Einstein condensation.

This form of matter was predicted in 1924 by Albert Einstein on the basis of the quantum formulations of the Indian physicist Satyendra Nath Bose.

Bose-Einstein condensate was created for the first time in the laboratory in 1995. The three physicist who succeeded in producing BEC, Eric A. Cornell, Wolfgang Ketterle, and Carl E. Wieman, were awarded the 2001 Nobel Prize in Physics. Cornell and Wieman managed to do that with about 2,000 → rubidium atoms cooled down to 20 nano K, while Ketterle used more than 100,000 → sodium atoms.

See also: → boson; → Einstein; → condensate.

A → quantum phase transition during which the → bosons constituting a sufficiently cooled boson gas are all clustered in the → ground energy state. The phase transition results in a → Bose-Einstein condensate. This phenomenon occurs when the temperature becomes smaller than a critical value given by:

T_c = (2π&#295² / km)(n / 2.612)^2/3, where m is mass of each boson, &#295 is the → reduced Planck’s constant, k is → Boltzmann’s constant, and n is the particle number density. When T  ≤  T_c, the → de Broglie wavelength of bosons becomes comparable to the distance between bosons.

See also: → boson; → Einstein; → condensation.

A → quantum phase transition during which the → bosons constituting a sufficiently cooled boson gas are all clustered in the → ground energy state. The phase transition results in a → Bose-Einstein condensate. This phenomenon occurs when the temperature becomes smaller than a critical value given by:

T_c = (2π&#295² / km)(n / 2.612)^2/3, where m is mass of each boson, &#295 is the → reduced Planck’s constant, k is → Boltzmann’s constant, and n is the particle number density. When T  ≤  T_c, the → de Broglie wavelength of bosons becomes comparable to the distance between bosons.

See also: → boson; → Einstein; → condensation.

For a → population of independent → bosons, a function that specifies the number of particles in each of the allowed → energy states.

See also: → boson; → Einstein; → distribution.

For a → population of independent → bosons, a function that specifies the number of particles in each of the allowed → energy states.

See also: → boson; → Einstein; → distribution.

Same as → Bose-Einstein distribution.

See also: → boson; → Einstein; → statistics.

Same as → Bose-Einstein distribution.

See also: → boson; → Einstein; → statistics.

Any of a class of particles (such as the → photon, → pion, or → alpha particle) that have zero or integral → spin and do not obey
the → Pauli exclusion principle. The energy distribution of bosons is described by → Bose-Einstein statistics. See also: → gauge boson, → Higgs boson, → W boson, → Z boson, → intermediate boson.

Etymology (EN): Boson, in honor of the Indian-American physicist Satyendra Nath Bose (1894-1974).

Any of a class of particles (such as the → photon, → pion, or → alpha particle) that have zero or integral → spin and do not obey
the → Pauli exclusion principle. The energy distribution of bosons is described by → Bose-Einstein statistics. See also: → gauge boson, → Higgs boson, → W boson, → Z boson, → intermediate boson.

Etymology (EN): Boson, in honor of the Indian-American physicist Satyendra Nath Bose (1894-1974).

The branch of → biology that deals with → plants.

Etymology (EN): From botanic, from Fr. botanique, M.L. botanicus, from Gk. botanikos “of herbs,” from botane “herb, grass, pasture.”

Etymology (PE): Giyâhšenâsi, from giyâh, → plant,

• šenâsi, → -logy.

The branch of → biology that deals with → plants.

Etymology (EN): From botanic, from Fr. botanique, M.L. botanicus, from Gk. botanikos “of herbs,” from botane “herb, grass, pasture.”

Etymology (PE): Giyâhšenâsi, from giyâh, → plant,

• šenâsi, → -logy.

A dim, red star in the constellation → Aries; a → giant of → spectral type
K2 III at a distance of 168 light-years.

Etymology (EN): Botein, from Ar. Al-Butain “the little belly.”

Etymology (PE): Boteyn, from Ar. Al-Butain.

A dim, red star in the constellation → Aries; a → giant of → spectral type
K2 III at a distance of 168 light-years.

Etymology (EN): Botein, from Ar. Al-Butain “the little belly.”

Etymology (PE): Boteyn, from Ar. Al-Butain.

A portable vessel for liquids, typically cylindrical and often of glass or plastic
with a narrow neck that can be closed.
→ magnetic bottle, → Leyden jar.

Etymology (EN): From O.Fr. bo(u)teille, from L.L. butticula diminutive of L. buttis “a cask.”

Etymology (PE): Botri, loan from Fr. bouteille or E. bottle, as above.

A portable vessel for liquids, typically cylindrical and often of glass or plastic
with a narrow neck that can be closed.
→ magnetic bottle, → Leyden jar.

Etymology (EN): From O.Fr. bo(u)teille, from L.L. butticula diminutive of L. buttis “a cask.”

Etymology (PE): Botri, loan from Fr. bouteille or E. bottle, as above.

1. The lowest or deepest part of anything, as distinguished from the → top. The under or lower side; underside.
   → bottom-up structure formation.
   

2. → bottom quark.

Etymology (EN): M.E. botme; O.E. botm, bodan “ground, soil, lowest part” (cf. O.Fris. boden “soil,” O.N. botn, O.H.G. bodam, Ger. Boden “ground, earth, soil”), akin to Pers. bon “basis; root; foundation; bottom;” Mid.Pers. bun “root; foundation; beginning;” Av. būna- “base, depth” (Skt. bundha-, budhná- “base, bottom,” Pali bunda- “root of tree;” Gk. pythmen “foundation;” L. fundus “bottom, piece of land, farm,” O.Ir. bond “sole of the foot”).

Etymology (PE): Tah “bottom; end”
(Mid.Pers. tah “bottom.” The origin of this term is not clear. It may be related to PIE *tenegos “water bottom;” cf. Gk. tenagos “bottom, swamp,” Latvian tigas, from *tingas, from
*tenegos “depth”).
Pâyin “bottom, below; at the foot of,” from pâ(y) “foot; step” (Mid.Pers. pâd, pây; Av. pad- “foot;” cf. Skt. pat; Gk. pos, genitive podos; L. pes, genitive pedis (Fr. pied); P.Gmc. *fot (E. foot; Ger. Fuss);
PIE *pod-/*ped-); + -in a relation suffix.

1. The lowest or deepest part of anything, as distinguished from the → top. The under or lower side; underside.
   → bottom-up structure formation.
   

2. → bottom quark.

Etymology (EN): M.E. botme; O.E. botm, bodan “ground, soil, lowest part” (cf. O.Fris. boden “soil,” O.N. botn, O.H.G. bodam, Ger. Boden “ground, earth, soil”), akin to Pers. bon “basis; root; foundation; bottom;” Mid.Pers. bun “root; foundation; beginning;” Av. būna- “base, depth” (Skt. bundha-, budhná- “base, bottom,” Pali bunda- “root of tree;” Gk. pythmen “foundation;” L. fundus “bottom, piece of land, farm,” O.Ir. bond “sole of the foot”).

Etymology (PE): Tah “bottom; end”
(Mid.Pers. tah “bottom.” The origin of this term is not clear. It may be related to PIE *tenegos “water bottom;” cf. Gk. tenagos “bottom, swamp,” Latvian tigas, from *tingas, from
*tenegos “depth”).
Pâyin “bottom, below; at the foot of,” from pâ(y) “foot; step” (Mid.Pers. pâd, pây; Av. pad- “foot;” cf. Skt. pat; Gk. pos, genitive podos; L. pes, genitive pedis (Fr. pied); P.Gmc. *fot (E. foot; Ger. Fuss);
PIE *pod-/*ped-); + -in a relation suffix.

A → structure formation scenario in which small galaxies form first, and larger structures are then formed in due course. Contrary to → top-down structure formation.

See also: → bottom; → up; → structure; → formation; → galaxy.

A → structure formation scenario in which small galaxies form first, and larger structures are then formed in due course. Contrary to → top-down structure formation.

See also: → bottom; → up; → structure; → formation; → galaxy.

Geology: A → sedimentary particle that is larger than 256 mm in size. Boulders are the largest particles of sediment that occur in streams and can reach the size of a small house (geology.com/dictionary).

Etymology (EN): From late M.E. bulder, possibly from Swedish bullersten “noisy stone” (large stone in a stream, causing water to roar around it), from buller “noisy” + sten “stone.”

Etymology (PE): Gordâle “boulder” (used in various areas of Iran: Šuštar, Kermânšâh, Nahâvand, Ali-Gudarz), from gord “kidney” + similarity/relation suffix -âl, → -al.

Geology: A → sedimentary particle that is larger than 256 mm in size. Boulders are the largest particles of sediment that occur in streams and can reach the size of a small house (geology.com/dictionary).

Etymology (EN): From late M.E. bulder, possibly from Swedish bullersten “noisy stone” (large stone in a stream, causing water to roar around it), from buller “noisy” + sten “stone.”

Etymology (PE): Gordâle “boulder” (used in various areas of Iran: Šuštar, Kermânšâh, Nahâvand, Ali-Gudarz), from gord “kidney” + similarity/relation suffix -âl, → -al.

1. (adj.) Tied, confined by bonds. → bound cluster, → bound charge, → bound system.
   
2. (n) a boundary; a limit.

See also: 1) p.p. of → bind. 2) → boundary.

1. (adj.) Tied, confined by bonds. → bound cluster, → bound charge, → bound system.
   
2. (n) a boundary; a limit.

See also: 1) p.p. of → bind. 2) → boundary.

Any electric charge which is bound to an atom or molecule, in contrast to free charge, such as metallic conduction electrons, which is not. Also known as → polarization charge.

See also: → bound; → charge.

Any electric charge which is bound to an atom or molecule, in contrast to free charge, such as metallic conduction electrons, which is not. Also known as → polarization charge.

See also: → bound; → charge.

A cluster of astronomical objects, such as stars or galaxies, held together by their mutual gravitational attraction. → bound system.

Etymology (EN): Bound, p.p. of → bind; → cluster.

Etymology (PE): Xušé, → cluster; bandidé p.p. of bandidan, → bind.

A cluster of astronomical objects, such as stars or galaxies, held together by their mutual gravitational attraction. → bound system.

Etymology (EN): Bound, p.p. of → bind; → cluster.

Etymology (PE): Xušé, → cluster; bandidé p.p. of bandidan, → bind.

Any → occurrence of a → variable  x in an x-bound part of a → wff.

See also: → bound; → occurrence.

Any → occurrence of a → variable  x in an x-bound part of a → wff.

See also: → bound; → occurrence.

The orbit described by an object around a central gravitational force in a system whose total energy is negative. An elliptical orbit.

Etymology (EN): Bound, p.p. of → bind; → orbit.

Etymology (PE): Madâr, → orbit; bandidé, p.p. of bandidan, → bind.

The orbit described by an object around a central gravitational force in a system whose total energy is negative. An elliptical orbit.

Etymology (EN): Bound, p.p. of → bind; → orbit.

Etymology (PE): Madâr, → orbit; bandidé, p.p. of bandidan, → bind.

A system composed of several material bodies the total energy of which (the sum of kinetic and potential energies) is negative, e.g. a → bound cluster.

Etymology (EN): Bound, p.p. of → bind; → system.

Etymology (PE): Aâžmân, → system; bandidé p.p. of bandidan, → bind.

A system composed of several material bodies the total energy of which (the sum of kinetic and potential energies) is negative, e.g. a → bound cluster.

Etymology (EN): Bound, p.p. of → bind; → system.

Etymology (PE): Aâžmân, → system; bandidé p.p. of bandidan, → bind.

A transition between two energy levels of an electron bound to a nucleus. The electron remains tied to the nucleus before and after the transition. → bound-free transition; → free-free emission.

See also: Bound, p.p. of → bind; → transition.

A transition between two energy levels of an electron bound to a nucleus. The electron remains tied to the nucleus before and after the transition. → bound-free transition; → free-free emission.

See also: Bound, p.p. of → bind; → transition.

A transition in which a bound electron is liberated. → free-bound emission; → free-free emission.

See also: Bound, p.p. of → bind;
→ free.

A transition in which a bound electron is liberated. → free-bound emission; → free-free emission.

See also: Bound, p.p. of → bind;
→ free.

1. General: Something that indicates a border or limit; the border or limit so indicated.
   

2. Thermodynamics: A conceptual closed surface useful in separating and distinguishing a system from its surroundings.
   

3. Math.: In topology, the boundary of a subset S of a topological space X is the set of points which can be approached both from S and from the outside of S.
   

4. Electronics: An area of meeting of P-type and N-type → semiconductor materials where the → donor and → acceptor concentrations are equal.

Etymology (EN): From Fr., from O.Fr. bodne, from M.L. bodina, butina “boundary, boundary marker.”

Etymology (PE): Karân, karâné, kenâr from Mid.Pers. karânag, Av. karana- “boundary.”

1. General: Something that indicates a border or limit; the border or limit so indicated.
   

2. Thermodynamics: A conceptual closed surface useful in separating and distinguishing a system from its surroundings.
   

3. Math.: In topology, the boundary of a subset S of a topological space X is the set of points which can be approached both from S and from the outside of S.
   

4. Electronics: An area of meeting of P-type and N-type → semiconductor materials where the → donor and → acceptor concentrations are equal.

Etymology (EN): From Fr., from O.Fr. bodne, from M.L. bodina, butina “boundary, boundary marker.”

Etymology (PE): Karân, karâné, kenâr from Mid.Pers. karânag, Av. karana- “boundary.”

1. Math: Restriction on the limits of applicability of an equation. In a differential equation, conditions that allow to fix the constant of integration and reach a unique solution. The number of boundary conditions necessary to determine a solution matches the order of the equation.
   

2. Physics: Conditions needed to determine the evolution of a system, given the physical laws.

See also: → boundary; → condition.

1. Math: Restriction on the limits of applicability of an equation. In a differential equation, conditions that allow to fix the constant of integration and reach a unique solution. The number of boundary conditions necessary to determine a solution matches the order of the equation.
   

2. Physics: Conditions needed to determine the evolution of a system, given the physical laws.

See also: → boundary; → condition.

An effect that forbids or invalidate locally the use of an idealized model of a system in which one or several of its dimensions are supposed to be infinite.

See also: → boundary; → effect.

An effect that forbids or invalidate locally the use of an idealized model of a system in which one or several of its dimensions are supposed to be infinite.

See also: → boundary; → effect.

A layer of fluid that is formed wherever a fluid flows past a solid surface and the effects of → viscosity are important. The boundary level forms because as the fluid moves past the object, the molecules which are in direct contact with the surface stick to the surface. The molecules just above the surface are slowed down in their collisions with the molecules sticking to the surface. These molecules in turn slow down the flow just above them, but less effectively. This creates a thin layer of fluid near the surface in which the velocity changes from zero at the surface to the free stream value away from the surface. The boundary layer may be either → laminar or → turbulent in character,
depending on the value of the → Reynolds number. The concept of boundary level was first put forward by Ludwig Prandlt (1875-1953) in 1904.

See also: → boundary; → layer.

A layer of fluid that is formed wherever a fluid flows past a solid surface and the effects of → viscosity are important. The boundary level forms because as the fluid moves past the object, the molecules which are in direct contact with the surface stick to the surface. The molecules just above the surface are slowed down in their collisions with the molecules sticking to the surface. These molecules in turn slow down the flow just above them, but less effectively. This creates a thin layer of fluid near the surface in which the velocity changes from zero at the surface to the free stream value away from the surface. The boundary layer may be either → laminar or → turbulent in character,
depending on the value of the → Reynolds number. The concept of boundary level was first put forward by Ludwig Prandlt (1875-1953) in 1904.

See also: → boundary; → layer.

General: Having bounds or limits.
Math.: Of a function, having a range with an upper bound and a lower bound.

See also: Adj. from → bound.

General: Having bounds or limits.
Math.: Of a function, having a range with an upper bound and a lower bound.

See also: Adj. from → bound.

The function y = f(x) in a given range of the argument x if there exists a positive number M such that for all values of x in the range under consideration the inequality | f(x) | ≤ M will be fulfilled. → unbounded function.

Etymology (EN): → bounded; → function.

The function y = f(x) in a given range of the argument x if there exists a positive number M such that for all values of x in the range under consideration the inequality | f(x) | ≤ M will be fulfilled. → unbounded function.

Etymology (EN): → bounded; → function.

A simplification in the equations of → hydrodynamics that treats the density as constant except in the → buoyancy term. This approximation is motivated by the fact that when pressure and temperature differences in a flow are small, then it follows from the thermodynamic → equation of state that a change in the density is also small.

See also: Named after Joseph Valentin Boussinesq (1842-1929), a French physicist
who made significant contributions to the theory of hydrodynamics, vibration, light, and heat; → approximation.

A simplification in the equations of → hydrodynamics that treats the density as constant except in the → buoyancy term. This approximation is motivated by the fact that when pressure and temperature differences in a flow are small, then it follows from the thermodynamic → equation of state that a change in the density is also small.

See also: Named after Joseph Valentin Boussinesq (1842-1929), a French physicist
who made significant contributions to the theory of hydrodynamics, vibration, light, and heat; → approximation.

1a) A bent, curved, or arched object.

1b) A weapon made of a curved, flexible strip of material
and a cord connecting the two ends that is used to launch an arrow.

2. The front of a ship or boat; prow; opposite to stern or poop, → Puppis.

Etymology (EN): 1) M.E., from O.E. boga “archery bow, arch, rainbow” (cf. O.Norse bogi, Du. boog, Ger. Bogen “bow”); PIE root *bheug- “to bend;” cf. Skt. bhujati “bends;” O.H.G. boug, O.E. beag “a ring”).

2. M.E. boue, from O.N. bogr or M.Du. boech “bow of a ship.”

Etymology (PE): 1) Kamân “bow, arc,”
from Mid.Pers. kamân, related to xam “curve,” cf. Breton kamm “curved, bent,” Gk. kampe “a corner, a joint,” L. campus “a field,” Lith. kampus “corner,” PIE *kamb- “to bend, crook.”

Farâl, from farâ “forward” (farâ raftan “to go forward, proceed,” farâ rândan “to drive forward”), equivalent to → pro-, + relation suffix -âl, → -al. Compare farâl with prow “bow,” Fr. la proue “prow, bow,” from dialectal It. proa, prua, from L. prora “bow,” from Gk. proira, related to pro “before, forward.”

1a) A bent, curved, or arched object.

1b) A weapon made of a curved, flexible strip of material
and a cord connecting the two ends that is used to launch an arrow.

2. The front of a ship or boat; prow; opposite to stern or poop, → Puppis.

Etymology (EN): 1) M.E., from O.E. boga “archery bow, arch, rainbow” (cf. O.Norse bogi, Du. boog, Ger. Bogen “bow”); PIE root *bheug- “to bend;” cf. Skt. bhujati “bends;” O.H.G. boug, O.E. beag “a ring”).

2. M.E. boue, from O.N. bogr or M.Du. boech “bow of a ship.”

Etymology (PE): 1) Kamân “bow, arc,”
from Mid.Pers. kamân, related to xam “curve,” cf. Breton kamm “curved, bent,” Gk. kampe “a corner, a joint,” L. campus “a field,” Lith. kampus “corner,” PIE *kamb- “to bend, crook.”

Farâl, from farâ “forward” (farâ raftan “to go forward, proceed,” farâ rândan “to drive forward”), equivalent to → pro-, + relation suffix -âl, → -al. Compare farâl with prow “bow,” Fr. la proue “prow, bow,” from dialectal It. proa, prua, from L. prora “bow,” from Gk. proira, related to pro “before, forward.”

A → shock wave created in front of an object moving through a medium with a velocity higher than that of the → sound waves in that medium. See, for example, → magnetosphere.

See also: → bow; → shock.

A → shock wave created in front of an object moving through a medium with a velocity higher than that of the → sound waves in that medium. See, for example, → magnetosphere.

See also: → bow; → shock.

The wave which appears in front of a speeding boat and goes out behind it in a distinctive “V”. It is due to the fact that waves pile up on each other before they can move away.

See also: → bow; → wave.

The wave which appears in front of a speeding boat and goes out behind it in a distinctive “V”. It is due to the fact that waves pile up on each other before they can move away.

See also: → bow; → wave.

A mechanism, made possible by certain chance coincidences between → spectral lines of He II, O III and N III in some → planetary nebulae ,
that explains the presence with a high intensity of a selected group of O III and N III lines
while all other lines of these elements are missing.

See also: After I. S. Bowen who first discovered this mechanism in 1935; → fluorescence; → mechanism.

A mechanism, made possible by certain chance coincidences between → spectral lines of He II, O III and N III in some → planetary nebulae ,
that explains the presence with a high intensity of a selected group of O III and N III lines
while all other lines of these elements are missing.

See also: After I. S. Bowen who first discovered this mechanism in 1935; → fluorescence; → mechanism.

A container, case, or receptacle, usually rectangular, of wood, metal, cardboard, etc. (Dictionary.com).
→ box-peanut bulge.

Etymology (EN): M.E., O.E., probably from L.L. buxis, from L. buxis, from Gk. pyxis “boxwood box,” from pyxos “box tree,” of uncertain origin.

Etymology (PE): Ja’bé, from Ar. ja’bah; quti, from Turk.

A container, case, or receptacle, usually rectangular, of wood, metal, cardboard, etc. (Dictionary.com).
→ box-peanut bulge.

Etymology (EN): M.E., O.E., probably from L.L. buxis, from L. buxis, from Gk. pyxis “boxwood box,” from pyxos “box tree,” of uncertain origin.

Etymology (PE): Ja’bé, from Ar. ja’bah; quti, from Turk.

A → galaxy bulge that shows
a boxy or peanut-like morphology. These bulges are usually featureless and show no signs of → dust obscuration,
young → stellar populations,
or → star-forming regions. They are also kinematically cold and usually referred to as → pseudo-bulges. A number of studies have shown that these structures are just the inner parts of → bars that grow vertically thick due to vertical → resonances.
They have basically the same dynamics and stellar content as bars, just their geometry is somewhat different. Box/peanut bulges are not seen if the galaxy is not inclined enough. In a → face-on galaxy, if it has a box/peanut, it will be seen as part of the bar. The → Milky Way shows a box/peanut bulge. Another remarkable case is that of → M31, known to have a bar, with its box/peanut inner part (Combes & Sanders 1981, A&A 96, 164; Combes et al. 1990, A&A 233, 82; Kormendy & Kennicutt, 2004, ARA&A 42, 603).

See also: → box; → peanut; → bulge.

A → galaxy bulge that shows
a boxy or peanut-like morphology. These bulges are usually featureless and show no signs of → dust obscuration,
young → stellar populations,
or → star-forming regions. They are also kinematically cold and usually referred to as → pseudo-bulges. A number of studies have shown that these structures are just the inner parts of → bars that grow vertically thick due to vertical → resonances.
They have basically the same dynamics and stellar content as bars, just their geometry is somewhat different. Box/peanut bulges are not seen if the galaxy is not inclined enough. In a → face-on galaxy, if it has a box/peanut, it will be seen as part of the bar. The → Milky Way shows a box/peanut bulge. Another remarkable case is that of → M31, known to have a bar, with its box/peanut inner part (Combes & Sanders 1981, A&A 96, 164; Combes et al. 1990, A&A 233, 82; Kormendy & Kennicutt, 2004, ARA&A 42, 603).

See also: → box; → peanut; → bulge.

In a → perfect gas where mass and temperature are kept constant, the volume of the gas will vary inversely with the absolute pressure. The law can be expressed as PV = constant, where P = absolute pressure and V = volume.

See also: After Robert Boyle (1627-1691), an Irish philosopher, chemist, and physicist, and Edme Mariotte (1620-1684), a French physicist and pioneer of neurophysiology, who discovered the law independently, the first one in 1662 and the second one in 1676; → law.

In a → perfect gas where mass and temperature are kept constant, the volume of the gas will vary inversely with the absolute pressure. The law can be expressed as PV = constant, where P = absolute pressure and V = volume.

See also: After Robert Boyle (1627-1691), an Irish philosopher, chemist, and physicist, and Edme Mariotte (1620-1684), a French physicist and pioneer of neurophysiology, who discovered the law independently, the first one in 1662 and the second one in 1676; → law.