An Etymological Dictionary of Astronomy and Astrophysics
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A plot representing the evolution of the internal structure of a star as a function of time. The x-axis indicates the time, the y-axis the mass, and a color or shading specifies convective regions. A vertical line through the graph corresponds to a model at a particular time.

Named after Rudolf Kippenhahn (1926-), a German astrophysicist; → diagram

An approximate expression for deriving the → opacity that depends upon temperature with a power law: κ ∝ ρT^-3.5, where ρ represents the density. In → partial ionization zones, a part of the energy released during a layer's compression can be used for further ionization, rather than raising the temperature of the gas. As the temperature of the compressed layer has not substantially increased, the increase in density produces a corresponding increase in the opacity of the layer. Likewise, during the expansion phase, the temperature does not decrease significantly since the ions release energy when they recombine with electrons.

Derived in 1923 by the Dutch physicist Henrik Kramers (1894-1952); → law.

Same as → Kramers' law.

Named after Henrik Kramers (1894-1952); → law.

A diagram used to plot trajectories in → space-time near a → black hole. The vertical and horizontal axes are two complicated functions of time and distance from the black hole. Lines of constant time radiate from the origin of the diagram, with steeper slopes corresponding to later times. Lines of constant distance are hyperbolas, lines of constant time pass through the origin; photons always travel along diagonal lines at ±45° to the vertical. The trajectory of an object falling into the black hole is shown as a curving line moving upward on the diagram at less than 45° to the vertical.

Named after the American physicist Martin David Kruskal (1925-2006); → diagram.

A procedure for finding the maximum or minimum of a → linear function where the → arguments are subject to linear → constraints. For problems involving more than two variables or problems involving a large number of constraints, solution methods used are those that are adaptable to computers. A well-known such → algorithm is the → simplex method.

→ linear; → programmings.

A coordinate system or frame of reference defined in the vicinity of the Earth in which Newton's first law of motion is valid; that is, a non-rotating and non-accelerating reference frame.

→ local; → inertial; → time.

A diagram that uses special symbols called logic symbols to represent the detailed functioning of electronic logic circuits. The symbols do not represent the type of electronics used, but only their functions.

→ logic; → diagram.

An algorithm for detecting and characterizing periodic signals in unevenly-sampled data. The Lomb-Scargle periodogram has a particularly wide use within the astronomy community. This method allows efficient computation of a Fourier-like → power spectrum estimator from such unevenly-sampled data, resulting in an intuitive means of determining the period of oscillation (see VanderPlas, 2017, astro-ph/1703.09824 and references therein).

Named after Lomb, N. R. 1976, Ap&SS 39, 447 and Scargle, J. D. 1982, ApJ 263, 835; → periodogram.

A graphic representation of solar magnetic field strengths and polarity.

From → magneto- + → -gram.

Same as → space-time diagram.

→ Minkowski metric; → diagram.

In the → mixing length theory, a parameter, α, that relates the → mixing length, l, to the → pressure scale height: α = l/H_P. It is usually supposed that α is of order unity. Changes in α correspond to variations in the efficiency of the → convection, hence the transfer of heat.

→ mixing; → length; → parameter.

A → frame of reference that moves relative to the observer. The moving frame may be → inertial or → non-inertial. See also → rest frame.

→ moving; → frame.

Any frame of reference in which the law of inertia does not apply, such as in accelerating and rotating frames. For example, the Earth is a non-inertial frame because it is rotating about its axis. But the rotation is so slow that the associated acceleration is negligible compared to other accelerations commonly encountered in everyday life. However, the non-inertial nature of the Earth appears in, e.g., the → Coriolis effect. → inertial reference frame.

→ non-; → inertial; → frame.

A dimensionless parameter expressed by h(z) = H(z)/H₀, where H(z) is the → Hubble parameter at → redshift z and H₀ is the → Hubble constant.

→ normalized; → Hubble; → parameter.

In computer science a programming technique that uses → objects and their interactions to design applications and programs.

→ object; oriented, p.p. from the verb of → orientation; → programming.

Barnâme-sâzi, → programming; barâxt, → object; gerâ agent adj. of gerâyidan "to incline toward; to intend; to make for." The stem gerâ may be a variant of Mod.Pers. kil "bent, inclined" (k/g and l/r interchanges), from PIE base *klei- "to lean, incline," cognate with L. clinare "to bend" (E. declination, inclination, etc.), Gk. klinein "to cause to slope, slant, incline," Skt. sri- "to lean," O.Pers. θray-, Av. sray- "to lean," P.Gmc. *khlinen (Ger. lehnen, E. lean).

→ orbital element.

→ orbital; → parameter.

A four-sided → polygon whose opposite sides are parallel. A parallelogram all of whose angles are right angles is a → rectangle.

From Fr. parallélogramme, from L. parallelogrammum, from Gk. parallelogrammon "bounded by parallel lines," from parallelos, → parallel, + gramme "line," related to graphein "to write, draw" → -graph.

Parâsubar, from parâsu, → parallel, + bar, → side.

A paramagnetic substance, which possesses → paramagnetism.

→ para- + → magnet.

Relative to or characterized by → paramagnetism.

→ para- + → magnetic

The property of a substance that possesses a → magnetic permeability greater than that of a vacuum but significantly less than that exhibited by → ferromagnetism. In the absence of an external magnetic field the atomic → magnetic moments of the substance are randomly oriented and thus cancel each other out with no net total magnetic moment. Moreover the coupling between neighboring moments is weak. However, when a magnetic field is applied magnetic moments align with the direction of the field and so the magnetic moments add together. Therefore paramagnetic substances affect external fields in a positive way, by attraction to the field resulting in a local increase in the magnetic field. The → magnetization vanishes when the field is removed.

→ para- + → magnetism