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

A slender, straight, generally pointed missile or weapon made to be shot from a bow and equipped with feathers at the end of the shaft near the → nock, for controlling flight (Dictionary.com). → Sagitta.

M.E. arewe, arwe, O.E. earh, possibly borrowed from O.N. ör; ultimately from PIE *arku- "bow and/or arrow," → arc.

Peykân "arrow, javelin" (cognate with afkan-, afkandan "to throw, cast away," parâkan-, parâkandan "to scatter, to disperse"), ultimately from Proto-Iranian *paiti-kan- "to throw against," from *paiti- "against, opposite, back" (cf. Mod.Pers. pâd- "against, contrary to;" Mid.Pers. pât-; O.Pers. paity "against, back, opposite to, toward, face to face, in front of;" Av. paiti; Skt. práti "toward, against, again, back, in return, opposite;" Pali pati-; Gk. proti, pros "face to face with, toward, in addition to, near;" PIE *proti) + *kan- "to throw."

A dusky color between red and black.

M.E. broun, from O.E. brun "dark," cf. Du. bruin, Ger. braun; PIE base *bher- "shining, brown," related to *bheros "dark animal" (cf. beaver, bear).

Qahvei-yi, color of qahvé "coffee."

A star-like object whose mass is too small to sustain → hydrogen fusion in its interior and become a star. Brown dwarfs are → substellar objects and occupy an intermediate regime between those of stars and giant planets. With a mass less than 0.08 times that of the Sun (about 80 → Jupiter masses), nuclear reactions in the core of brown dwarfs are limited to the transformation of → deuterium into ³He. The reason is that the cores of these objects are supported against → gravitational collapse by electron → degeneracy pressure (at early spectral types) and → Coulomb pressure (at later spectral types). Brown dwarfs, as ever cooling objects, will have late M dwarf spectral types within a few Myrs of their formation and gradually evolve as L, T and Y dwarfs → brown dwarf cooling. As late-M and early-L dwarfs, they overlap in temperature with the cool end of the stellar → main sequence (→ M dwarf, → L dwarf, → T dwarf, → Y dwarf). In contrast to the OBAFGKM sequence, the M-L-T-Y sequence is an evolutionary one. These objects were first postulated by Kumar (1963, ApJ 137, 1121 & 1126) and Hayashi & Nakano (1963, Prog. Theor.Phys. 30, 460).

The term brown dwarf was first used by Jill Tarter in her 1975 PhD thesis; → brown; → dwarf.

The process whereby a → brown dwarf cools over time after the → deuterium burning phase, which lasts a few 10⁷ years. The → effective temperature and luminosity decrease depending on the mass, age, and → metallicity. Even though massive brown dwarfs may start out with star-like luminosity (≥ 10^-3→ solar luminosities), they progressively fade with age to the point where, after 0.5 Gyr all → substellar objects are less luminous than the dimmest, lowest mass stars. More explicitly, brown dwarfs may start as star-like objects hotter than 2200 K, with → M dwarf spectral types, and, as they get older, pass through the later and cooler L, T, and Y spectral types (→ L dwarf, → T dwarf, → Y dwarf).

→ brown; → dwarf; → cooling.

The observational result indicating a deficit in the frequency of → brown dwarf companions to Sun-like stars, either relative to the frequency of less massive planetary companions or relative to the frequency of more massive stellar companions. However, this desert exists mainly for low-separation brown dwarfs detected using orbital velocity surveys. No brown dwarf desert is noticed at wide separations (J. E. Gizis et al. 2001, ApJ 551, L163).

→ brown; → dwarf; → desert.

The continuous random motion of solid microscopic particles immersed in a fluid, which is due to bombardment by the atoms and molecules of the medium. It is named after the botanist Robert Brown, who in 1827 first noticed that pollen seeds suspended in water moved in an irregular motion. While there were suspicions that the motion was caused by the collision of atoms against the particles, the first quantitative explanation of the phenomenon, based on the kinetic theory of gases, was forwarded by A. Einstein in 1905. When Einstein's paper appeared, the notion of atoms and molecules was still a subject of heated scientific debate. Ernst Mach and the physical chemist Wilhelm Ostwald were among those who chose to deny their existence.

Named after Robert Brown (1773-1858), a Scottish botanist, who first in 1827 noticed the erratic motion of pollen grains suspended in water. → motion.

Tiny fluctuations in the intensity of the → cosmic microwave background radiation (CMBR) as a function of angular position over the sky, first discovered in the → Cosmic Background Explorer (COBE) observations. At a level of 1 part in 100,000, these temperature variations trace the distribution of matter and energy when the Universe was very young, about 380,000 years old. Since the CMB spectrum is described to a high precision by a → blackbody law with temperature T₀, it is usual to express the anisotropies in terms of temperature fluctuations ΔT/T₀ and expand them on the sky in → spherical harmonic series ΔT/T₀ (θ,φ) = Σ a_lmY_lm(θ,φ), where θ and φ are the → spherical polar coordinates, Y_lm is the spherical harmonic functions with → multipole index l, and the sum runs over l = 1, 2, ..., ∞, m = -l, ..., l, giving 2l + 1 values of m for each l, and a_lm is the multipole moment of the decomposition. The power spectrum of the anisotropies is defined as C_l≡ mean | a_lm |² = 1/(2l + 1) Σ mean | a_lm |². See also → CMB angular power spectrum.

→ cosmic; → microwave; → background; → anisotropy.

The polarization of the → cosmic microwave background radiation due to → Thomson scattering by → free electrons during the → recombination era. The polarization can greatly enhance the precision with which the parameters associated with → acoustic oscillations are derived; because it carries directional information on the sky. When an → electromagnetic wave is incident on a free electron, the scattered wave is polarized perpendicular to the incidence direction. If the incident radiation were → isotropic or had only a → dipole variation, the scattered radiation would have no net polarization. However, if the incident radiation from perpendicular directions (separated by 90°) had different intensities, a net → linear polarization would result. Such → anisotropy is called → quadrupole because the poles of anisotropy are 360°/4 = 90° apart.

→ cosmic; → microwave; → background; → polarization.

The diffuse → electromagnetic radiation in the → microwave band, coming from all directions in the sky, which consists of relic photons left over from the very hot, early phase of the → Big Bang. More specifically, the CMBR belong to the → recombination era, when the → Universe was about 380,000 years old and had a temperature of about 3,000 K, or a → redshift of about 1,100. The photons that last scattered at this epoch have now cooled down to a temperature of 2.73 K. They have a pure → blackbody spectrum as they were at → thermal equilibrium before → decoupling. The CMB was discovered serendipitously in 1965 by Penzias and Wilson (ApJ L 142, 419) and was immediately interpreted as a relic radiation of the Big Bang by Dicke et al. (1965, ApJL 142, 383). Such a radiation had been predicted before by Gamow (1948, Nature 162, 680) and by Alpher and Herman (1948, Nature 162, 774). This discovery was a major argument in favor of the Big Bang theory. In 1992, the satellite → Cosmic Background Explorer (COBE) discovered the first anisotropies in the temperature of the CMB with an amplitude of about 30 µK. See also: → cosmic microwave background anisotropy, → dipole anisotropy, → CMB lensing, → CMB angular power spectrum, → acoustic peak, → baryon acoustic oscillation, → WMAP.

→ cosmic; → microwave; → background; → radiation.

Any of several large oscine birds of the genus Corvus, of the family Corvidae, having a long, stout bill, lustrous black plumage, and a wedge-shaped tail (Dictionary.com).

O.E. crawe, imitative of the bird's cry; cf. O.Saxon kraia; Du. kraai; O.H.G. chraja; Ger. Kräke; L. corvus "a raven," Gk. korax; cognate with Pers. kalâq, → raven.

Zâq "crow, raven," of unknown origin.

1a) A large number of persons gathered closely together; throng.
1b) Any large number of persons.
1c) Any group or set of persons with something in common.
2) To gather in large numbers; throng; swarm (Dictionary.com).
→ crowded, → crowded field, → crowding.

M.E. crowden, from O.E. crudan "to press, crush;" akin to M.Du. cruden "to press, push," M.H.G. kroten "to press, oppress," Norwegian kryda "to crowd."

Capiré (Dehxodâ), variants cabiré, capar "crowd, troop, people gathered for something." Capiré, from capir, from capar, ultimately from Proto-Ir. *ui-par-, from *par- "to fill;" cf. Av. pər- "to fill, stuff with," pouru- "full, much, many;" O.Pers. paru- "much, many;" Pers. anbâr "ricks, storehouse," por, bol "full, much, many;" PIE *pel- "to fill;" → population.

Filled so that there is little or no room for anyone or anything else. → crowded field.

Past participle of → crowd.

An area on the sky where a large number of objects, commonly stars, are seen gathered together, usually as revealed by imaging.

→ crowded; → field.

1) The state or action of filling a particular place in large numbers.
2) For a → field of view, state of containing a large number of objects.

Verbal noun of → crowd.

The process of procuring needed services by soliciting a large group of people outside the demanding company, society, or institute. Two examples of crowdsourcing in astronomy involve → variable star studies and search for → meteorites.

Combination of → crowd and → outsourcing.

An optical, alkali-lime glass which is harder than → flint glass, and has a lower → index of refraction and lower → dispersion. It is used in the production of → compound lenses.

Such named because of the crown-like shape given to the blank after the process of blowing the glass; M.E. coroune, from O.Fr. corone, from L. corona "crown," originally "wreath, garland;" cf. Gk. korone "anything curved, kind of crown;" → glass.

A plot showing how the → equivalent width of an → absorption line, or the radiance of an → emission line, increases as a → function of the → number of → atoms that produce the line.

→ curve; → growth.

An increase in the output that an economy produces over a period of time.

→ economic; → growth.

Of, relating to, or being the → unification of → electromagnetism and the → weak interaction.

→ electro-; → weak.

A period in the early history of the Universe lasting from 10^-36 to 10^-12 seconds after the → Big Bang. The electroweak epoch begins at the same time as cosmic → inflation is triggered. This is also the time when the → strong force breaks from the → grand unified force and ends with another → phase transition will occur in which the → weak interaction breaks from the → electroweak force.

→ electroweak; → epoch.