An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

An image which is dim, indistinct, or vague in appearance, for instance when the optics is not well-focused or when the seeing is poor. The same as → unsharp image, contrary to → sharp image.

Blurred, p.p. of → blur; → image.

In → galactic dynamics models, the → scattering of stars at radii substantially away from → corotation resonance, especially at the → Lindblad resonances, leading to a higher → eccentricity. The → spiral wave response of a → galactic disk to a co-orbiting mass → clump blurs the distinction between scattering by → spiral arms and by mass clumps. See also → churning (J. A. Sellwood & J. J. Binney, 2002, astro-ph/0203510 and references therein).

Verbal noun of → blur.

→ 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.

Body, from O.E. bodig "trunk, chest," related to O.H.G. botah, of unknown origin.

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.

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.

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.

→ 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.

→ 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.

→ Bohr; → model.

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

→ 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.

→ 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,

→ 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.

→ 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.

→ 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.

M.E. boillen; O.Fr. boillir, from L. bullire "to bubble, seethe," from bulla "a bubble, knob;" → point.

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.

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.

Bolide, Fr., from L. bolis, bolidis, from Gk. bolis, bolidos "missile, flash of lightning," from ballein "to throw;" PIE *g^welH₁- "to throw;" → ballistics.

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.

From Gk. bole "stroke, beam of light," from ballein "to throw" + middle suffix -o- + → -meter..

Tafsanj, from taf "heat, warmth; light, brightness," from tâbidan, "→ radiate," + sanj, → -meter.

Of or relating to or measured by a → bolometer.

→ bolometer; → -ic.

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

→ bolometric; → correction.