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

Math.: The fact that no → solution exists for a given → problem. In mathematics, nonexistence usually is a matter of impossibility.

→ non-; → existence.

A theoretical frequency distribution for a set of variable data, usually represented by a bell-shaped curve with a mean at the center of the curve and tail widths proportional to the standard deviation of the data about the mean. Same as → Gaussian distribution.

→ normal; → distribution.

In → nucleosynthesis models, the condition in which all nuclear species are in equilibrium under exchange of → protons and → neutrons. Matter in nuclear statistical equilibrium is characterized by a large abundance of iron peak nuclei. In such equilibria abundance of each nuclide can be calculated from repeated application of → Saha equation.

→ nuclear; → statistical; → equilibrium.

A person who is trained or expert in the science of nutrition.

→ nutrition; → -ist.

The mean square noise voltage across a resistance in thermal equilibrium is four times the product of the resistance, Boltzmann's constant, the absolute temperature, and the frequency range within which the voltage is measured. → Johnson-Nyquist noise.

Named after Harry Nyquist (1889-1976), a Swedish-born American physicist, who made important contributions to information theory. → Johnson-Nyquist noise; → formula.

The highest frequency that can be determined in a Fourier analysis of a discrete sampling of data.

→ Nyquist formula; → frequency.

The minimum number of resolution elements required to properly sample a signal, such as a star image, without causing erroneous effects known as aliasing. For electronic imaging, this number is generally taken as 2 pixels across the seeing disk diameter at the half intensity points. Also called → Shannon's sampling theorem and → sampling theorem.

Named after Harry Nyquist (1889-1976), a Swedish-born American physicist, who made important contributions to information theory, and Claude Elwood Shannon (1916-2001), an American mathematician and pioneer of information theory; → theorem.

A person who adapts his actions, responses, etc, to take advantage of opportunities, circumstances, etc. (Dictionary.com).

→ opportune + → -ist.

The study of compounds that contain carbon chemically bound to hydrogen.

→ organic; → chemistry.

1) A person who adheres to or believes in → perfectionism.
2) A person who demands perfection of himself, herself, or others (Dictionary.com).

→ perfection; → -ist.

The distance between the → Sun and an → object in orbit around it when they are at their closest approach.

→ perihelion; → distance.

1) To continue steadfastly or firmly in some state, purpose, course of action, or the like, especially in spite of opposition, remonstrance, etc.
2) To last or endure tenaciously (Dictionary.com).

M.Fr. persister, from L. persistere "abide, continue steadfastly," from → per- "thoroughly" + sistere "come to stand, cause to stand still," → resist.

Paristâdan from par-, → per-, + istâdan "to stand," → resist.

The act or fact of persisting; the quality of being persistent.

Verbal noun from → persist.

Persisting, especially in spite of opposition, obstacles, discouragement, etc.; persevering (Dictionary.com).

Adjective from → persist.

A hypothetical substance that, prior to the discovery of → oxygen, was thought to be released during → combustion. → phlogiston theory.

From New Latin, from Gk. phlogiston, neuter of phlogistos "inflammable, burnt up," from phlogizein "to set on fire, burn," from phlox "flame, blaze;" from PIE root *bhel- "to shine, burn."

Fložiston, loan from Fr, as above.

An obsolete theory of combustion in which all flammable objects were supposed to contain a substance called → phlogiston, which was released when the object burned. The existence of this hypothetical substance was proposed in 1669 by Johann Becher, who called it terra pinguis "fat earth." For example, as wood burns it releases phlogiston into the air, leaving ash behind. Ash was therefore wood minus phlogiston. In the early 18th century Georg Stahl renamed the substance phlogiston. The theory was disproved by Antoine Lavoisier in 1783, who proved the principle of conservation of mass, refuted the phlogiston theory and proposed the oxygen theory of burning.

→ phlogiston; → theory.

The study of the chemical and physical changes occurring when a molecule or atom absorbs photons of light.

→ photo- + → chemistry.

The branch of chemistry dealing with the relations between the physical properties of substances and their chemical composition and transformations.

→ physical; → chemistry.

A specialist in → physics.

From physic, → physics, + → -ist.

Fizikdân, from fizik, → physics, + -dân "knower," present stem of dânestan "to know," → science.

An → aberration of a → lens  → system in which → magnification increases with → distance from the → optical axis, whereby → horizontal and → vertical lines bend inward toward the → center of the → field. Opposite of → barrel distortion.

Pincushion, from pin, from M.E. pinne, O.E. pinn "peg;" cf. D. pin, Ger. Pinne; perhaps from L. pinna "feather, quill" + cushion, M.E. cuisshin, O.Fr. coissin (Fr. coussin) a variant of V.L. *coxinum, either from L. coxa "hip, thigh," or from L. culcita "mattress;" → distortion.

Cowlegi, → distortion; bâleštaki, adj. of bâleštak, diminutive of bâlešt, variant bâleš "cushion, pillow," Mid.Pers. bâlišn, bâlên "cushion, pillow;" Av. barəiš- "pillow, cushion;" cf. Skt. barhis- "straw, a bed or layer of kusa grass strewed over the sacrificial ground."