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

Chemistry: The process by which a solid, gas, or liquid is dispersed homogeneously in a gas, solid, or a liquid.

Verbal noun of → dissolve.

Same as → metric.

→ distance + → function.

1) The act or an instance of distinguishing or differentiating.
2) A distinguishing feature.
3) The state of being different or distinguishable.
4) Special honor, recognition, or fame (The FreeDictionary.com).

→ distinct; → -tion.

1) Extent to which a system, optical, acoustic, or electronic, fails to reproduce accurately at its output the characteristics of the input.
2) Optics: An optical imperfection caused by a → lens or → system of lenses which results in → magnification differences between different points on the → image. The points on the → object are misplaced in the image relative to the → center of the → field. See also → barrel distortion; → pincushion distortion.

Verbal noun of → distort.

An act or instance of distributing; the state or manner of being distributed; something that is distributed. → binomial distribution, → Bose-Einstein distribution, → brightness distribution, → chi-square distribution, → cumulative distribution function, → distribution function, → Gaussian distribution, → Gibbs canonical distribution, → lognormal distribution, → Maxwell-Boltzmann distribution, → normal distribution, → Poisson distribution, → power-law distribution, → probability distribution, → spectral energy distribution.

Verbal noun of → distribute

A function that gives the relative frequency with which the value of a statistical variable may be expected to lie within any specified interval. For example, the Maxwellian distribution of velocities gives the number of particles, in different velocity intervals, in a unit volume.

→ distribution; → function.

The aberration of a star's position due to the rotation of the Earth. Its value depends on the latitude of the observer, and is only 0''.32 in the case of an observer at the equator, where the rotational velocity is greatest.

→ diurnal; → aberration.

Daily geometrical libration of the Moon arising from the fact that observers at different points on the Earth see the Moon from slightly different angles. As the Moon rises in the east, you are positioned on one side of our planet, and by the time it sets in the west. Earth's rotation has carried you to the other side. This change in position produces a slight → parallax effect that adds about another 1° of libration in longitude. Two other geometrical libration are → libration in longitude and → libration in latitude. See also → physical libration.

→ diurnal; → libration.

The daily apparent motion of all celestial objects, due to Earth's rotation.

→ diurnal; → motion.

1) The act or process of dividing; state of being divided.
Math.: An operation in which a dividend is divided by a divisor to give a quotient and a remainder.
2) Something that marks a division; a separation.

From O.Fr. division, from L. divisionem (nom. divisio), from divid-, stem of dividere "to cleave, distribute," from → dis- "apart" + -videre "to separate," from PIE base *widh- "to separate."

1) Baxš "portion, part, division," baxšidan "to divide, distribute, grant;" Mod./Mid.Pers. baxt "fortune, fate," baxtan, baxšidan "to distribute, divide," bâq "garden," initially "piece or patch of land," baq "god, lord;" Av. bag- "to attribute, allot, distribute," baxš- "to apportion, divide, give to," baxta- "what is allotted (luck, fortune)," baxədra- "part, portion," baγa- "master, god;" O.Pers. bāji- "tribute, tax;" cf. Skt. bhaj- "to share, divide, distribute, apportion," bhájati "divides," bhakta- "allotted; occupied with; a share; food or a meal, time of eating?" pitu-bháj- "enjoying food;" Gk. phagein"to eat (to have a share of food)"; PIE base *bhag- "to share out, apportion."
2) Šekâf "a fissure, crack, slit," šekâftan "to divide into two long strips, split, break," Mid.Pers. škâftan.

A symbol placed between two quantities (dividend and the divisor) to indicate the division of the first by the second. The division sign is written as a horizontal line with dot above and dot below, ÷ (→ obelus), or a slash or horizontal line.

→ division; → sign.

1) The use of documentary evidence.
2) A furnishing with documents, as to substantiate a claim or the data in a book or article.
3) Computers: Manuals, listings, diagrams, and other hard- or soft-copy written and graphic materials that describe the use, operation, maintenance, or design of software or hardware (Dictionary.com).

→ document; → -tion.

A segment of the → zodiac extending 2.5 degrees, as considered in Babylonian and Hellenistic astrology; plural: dodekatemoria. Dodekatemoria result from a subdivision of each → zodiacal sign into twelve equal parts, each given the name of a → sign, beginning with the name of the sign being divided and continuing throughout the other eleven sequentially. Each zodiacal sign therefore contained a micro-zodiac within its own 30° span. Textual evidence for the micro-zodiac does not antedate the sixth century BC (F. Rochberg, 2010, In the Path of the Moon, BRILL).

From Gk. dodekatemorion "twelfth part," from dodekate "twelfth" (from dodeka "twelve") + morion "part."

Davâzdahân, from Mid.Pers. dwâzdahân "the twelve ones," from dwâzdah (Mod.Pers. davâzdah) "twelve;" Av. dvadasa, from dva "→ two" + dasa "→ ten."

An act or instance of dominating.

Verbal noun of → dominate.

Formation of two refracted rays of light from a single incident ray; property of certain crystals, notably calcite.

→ double; → refraction.

Same as → diplopia.

→ double; → vision.

An instability involving two layers of fluid with opposite gradients of properties. Same as → fingering instability. See also → salt finger. Double-diffusive instabilities commonly occur in any astrophysical fluid that is stable according to the → Ledoux criterion, as long as the entropy and chemical stratifications have opposing contributions to the dynamical stability of the system. They drive weak forms of convection, and can cause substantial heat and compositional → mixing. Two cases can be distinguished. In fingering convection, entropy is stably stratified (∇ - ∇ad < 0), but chemical composition is unstably stratified (∇μ < 0); it is often referred to as → thermohaline convection by analogy with the oceanographic context in which the instability was first discovered. In oscillatory double-diffusive convection, entropy is unstably stratified (∇ - ∇ad > 0), but chemical composition is stably stratified (∇μ > 0); it is related to semiconvection, but can occur even when the → opacity is independent of composition (P. Garaud, 2014, arXiv:1401.0928).

→ double;→ diffusive; → system.

An atom that has lost two of its external electrons, for example O⁺⁺ ([O III]).

→ doubly; → ionized.

A probabilistic argument used to estimate the number of → intelligent, communicating → extraterrestrial civilizations in the → Milky Way galaxy. The Drake equation is:
N = R_* . f_p . n_e . f_l . f_i . f_c . L, where:
N = the number of → civilizations in our Galaxy with which → communication might be possible,
R_* = the average rate of → star formation in our Galaxy,
f_p = the fraction of those stars that have → planets,
n_e = the average number of planets that can potentially support → life per star that has planets,
f_l = the fraction of planets that could develop life at some point,
f_i = the fraction of planets with life that actually go on to develop intelligent life,
f_c = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space,
L = the length of time for which such civilizations release detectable signals into space.
The first three terms of the equation have been successfully investigated by astronomers and are to some extent known. In contrast, values for the last four are very speculative. Drake himself estimates that N might be as high as 10,000. Carl Sagan was more optimistic, and came up with the value of a million or more for N. These estimates may be too optimistic. A pessimistic choice of parameters leads to N smaller than 1, which means that we might be the only technically sophisticated civilization in the Galaxy.

Frank Donald Drake (1930-); → equation.

An act or instance of duplicating; the state of being duplicated.

Verbal noun of → duplicate.