An Etymological Dictionary of Astronomy and Astrophysics
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A → transcendental function. Examples are: exponential, logarithmic, and trigonometric functions.

→ non-; → algebraic + → function.

Radiation having waves that are out of phase in space and/or time; radiation which is not → coherent.

→ non-; → coherent; → radiation.

Not ionized, → neutral.

→ non-; → ionized.

A → tumbling motion of an → asteroid. See also → tumbling asteroid.

→ non-; → principal axis; → rotational; → motion.

A type of stellar pulsation in which waves run in different directions on and beneath the surface of a star.

→ non-; → radial; → pulsation.

→ non-thermal radiation.

→ non-thermal; → emission.

The electromagnetic radiation whose characteristics do not depend on the temperature of the emitting source. In contrast to → thermal radiation, it has a different spectrum from that of → blackbody radiation. The three common types of non-thermal radiation in astronomy are: → synchrotron radiation, → bremsstrahlung radiation, and → maser  → stimulated emission.

→ non-thermal; → radiation.

A plasma in which the → mean free path of the charged particles between two collisions is much larger than the size of the system containing the plasma.

→ non-; → collisional; → plasma.

An equation that is independent of the units of measurement as it only involves nondimensional numbers, parameters, and variables.

→ non-; → dimensional; → equation.

A → linear differential equation if Q(x)≠ 0 on interval I.

→ nonhomogeneous; → linear; → differential; → equation.

The quality of an atom that has neither lost nor gained any electrons.

→ non-; → ionized.

The dispersion in which a shorter wavelength is associated with a higher → refractive index. Contrasted with the → anomalous dispersion.

→ normal; → dispersion.

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.

1) A mathematical technique for adjusting a series of values (typically representing a set of measurements) according to some transformation function in order to make them comparable with some specific point of reference.
2) Process of introducing a numerical factor into an equation so that the area under the corresponding graph (if finite) shall be made equal to unity.
3) To change in scale so that the sum of squares or the integral of squares of the transformed quantity is zero.

Verbal noun of → normalize.

Representation of numbers, quantities, or other entities by symbols; a system of symbols for such a purpose.

From L. notationem (nom. notatio) "a marking, explanation," from notatus, p.p. of notare "to note."

Namâdgân, from namâd, → symbol, + -gân suffix denoting order, organization, multiplicity.

A general understanding; vague or imperfect conception or idea of something.

From L. notio "concept, conception, idea," from noscere "to know," → knowledge.

Pendâré, noun from pendâštan "to imagine, consider, think," → imaginary number.

→ nuclear burning.

→ nuclear; → combustion.

Apparent cross-section possessed by an atomic nucleus when it undergoes a particular type of collision process.

→ nuclear; → cross section.

A → nuclear reaction in which a heavy atomic nucleus splits into two or more approximately equal parts, usually as the result of the capture of a slow, or → thermal neutron by the nucleus. It is normally accompanied by the emission of further neutrons or → gamma rays and very large amounts of energy. The neutrons can continue the process as a → chain reaction, so that it becomes the source of energy in a → nuclear reactor or an atomic bomb. It may also be a trigger for → nuclear fusion in a hydrogen bomb. Fission occurs spontaneously in nuclei of uranium-235, the main fuel used in nuclear reactors.

→ nuclear; → fission.

A → nuclear reaction between atomic nuclei as a result of which a heavier → atomic nucleus is formed, a small fraction of mass is lost, and a large quantity of energy is released. Nuclear fusion is the source of the energy of stars.

→ nuclear; → fusion.