An Etymological Dictionary of Astronomy and Astrophysics
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The extent of → coherence of an → electromagnetic wave, as indicated by a → dimensionless number. Since interference takes place when waves are → coherent, using a → Young's experiment, the degree of coherence is measured from the → fringe  → visibility, V. It is defined as the ratio V = (I_max - I_min) / (I_max + I_min), where I_max is the intensity at a maximum of the → interference pattern, and I_min is the intensity at a minimum of the interference pattern. The electromagnetic wave is considered to be highly coherent when the degree of coherence is about 1, incoherent for nearly zero values, and partially coherent for values between 0 and 1.

→ degree; → coherence.

Of a → mechanical system, the number of → independent variables needed to describe its configuration.

→ degree; → freedom.

The number of electrons a neutral atom has lost in an ionizing physical process (radiation, shock, collision). In spectroscopy, the degree of ionization is indicated by a Roman numeral following the symbol for the element. A neutral atom is indicated by the Roman numeral I, a singly ionized atom, one which has lost one electron, is indicated by II, and so on. Thus O VI indicates an oxygen atom which has lost five electrons.

→ degree; → ionization.

The ratio of the intensity of polarized portion of light to the total intensity at a point in the beam.

→ degree; → polarization.

Statics: The → energy that must be expended to permanently disturb a specific state of → equilibrium of a body.

→ degree; → stability.

The → number of → edges incident on the → vertex.

→ degree; → vertex.

An opaque region of a → molecular cloud (A_V  10 mag) which is considered to be the progenitor of → star formation. Dense cores have temperatures of about 10 K and masses of roughly 1 to 10Msun each and in which the → molecular hydrogen density is roughly 10⁴-10⁵ cm^-3 and size 0.1 pc. The → self-gravity of a dense core plays a central part in star formation. See also → hot molecular core.

→ dense; → core.

→ core mass function.

→ dense; → core; → mass; → function.

An → H II region which lacks enough matter to absorb all → Lyman continuum photons of the → exciting star(s). In such an H II region a part of the ionizing photons escape into the → interstellar medium. See also → ionization-bounded H II region.

→ density; → bounded; → region.

An act of attacking or plundering.

→ de-; → predation.

1) Navigation:→ dip.
2) Meteorology: An area of low atmospheric pressure.
3) Geology: An area of the Earth's crust sunken or depressed below the surrounding area, formed by various mechanisms.

Depression, verbal noun of depress, from O.Fr. depresser, from L.L. depressare, frequentative of pressus, p.p. of deprimere "press down," from → de- "down" + premere "to press."

1) Našib-e ofoq, from našib "declivity, descent; lowness of ground, slope of any place" (Mid.Pers. nišēp "declivity, (astrology) dejection," Av. *nixšvaēpā-, xšvaēpā- "bottom, rear") + ofoq→ horizon. 2) Forubâr, from foru "down, downward; below; beneath," → de- + bâr "load, pressure, charge," → charge. 3) Našiblâx, from našib, as above, in item 1, + -lâx place suffix.

An → interference process in which the → amplitude of the the amplitude of the resultant wave is less than that of either individual waves. See also → constructive interference.

Destructive, from O.Fr. destructif, from L.L. destructivus, from destruct-, p.p. stem of destruere, from → de- + struere "to build," → structure; → interference.

Andarzaneš, → interference; virângar "destructive," from virân, "destroyed, ruined."

The quality or condition of being different.
Math.: the amount by which one quantity is greater or less than another.
Of two sets A and B, the set consisting of all elements of A which do not belong to B.

Noun form of → differ.

Not alike in character or quality; differing; dissimilar.

Adj. of → difference.

Of a mathematical function, the quality of being → differentiable.

Noun from → differentiable.

Capable of being → differentiated. → differentiable function.

From → differentiate + → -able.

Property of a mathematical function if it has a → derivative at a given point.

From → differentiable; → function.

1) Noun.
1a) General: A difference or the amount of difference, as in rate, cost, quantity, degree, or quality, between things that are comparable.
1b) Math.: An infinitesimally small change in a variable; a function of two variables that is obtained from a given function, y = f(x), and that expresses the increment in the given function as the derivative of the function, f'(x), times the increment in the independent variable, written as dy = f'(x) dx.
1c) Electronics: Referring to a circuit, device, or machine whose principle of operation depends on the difference between two opposing effects.
2) Adjective.
2a) General: Of, relating to, or constituting a difference.
2b) Physics: Pertaining to or involving the difference of two or more motions, forces, etc.
2c) Math.: Pertaining to or involving a → derivative or derivatives.

From M.L. differentialis, from differenti(a), → difference, + → -al.

Degarsâné, from degarsân, → different + noun suffix -é.

The two branches of mathematics that make up the → calculus. → differential calculus; → integral calculus.

→ differential; → integral; → calculus.

A branch of calculus which is concerned with the instantaneous rate of change of quantities with respect to other quantities, or more precisely, the local behavior of functions. → integral calculus.

→ differential; → calculus.