An Etymological Dictionary of Astronomy and Astrophysics
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Any → transformation preserving → collinearity.

→ affine; → transformation.

Any of the four main → proposition forms treated in Aristotle's → syllogism:
The A form (universal affirmative): All P's are Q's,
The E form (universal negative): No P's are Q's,
The I form (particular affirmative): Some P's are Q's, and
The O form (particular negative) Some P's are not Q's.

Greek philosopher Aristotle (384-322 BC); → form.

A special solution of the mathematical formula which represents the wavelengths of the various spectral series of hydrogen in which the lower energy level is n = 2.

→ Balmer; → formula.

The mathematical expression giving the → entropy, S, of a → black hole as a function of the area of its → event horizon, A: S = (kc³A)/(4Għ), where k is → Boltzmann's constant, ħ is the → reduced Planck's constant, and G the → gravitational constant. It can also be expressed by S = (kA)/(4l_P²), where l_P is the → Planck length. The existence of this entropy led to the prediction of the → Hawking radiation, because an entropy is associated with a temperature and a temperature to a → thermal radiation. The entropy of a black hole increases continuously because the fall of material into it increases its area.

For Jacob D. Bekenstein (1947-), an Israeli theoretical physicist, who contributed to the foundation of black hole thermodynamics; → formula.

The theory that bright galaxies form preferentially from anomalously overdense perturbations in the → early Universe.

→ biased; → galaxy; → formation.

A concept of → star formation in which → high-mass stars and → low-mass stars form in different physical conditions involving different → molecular clouds. Following the pioneering suggestion of Herbig (1962), successive investigations have generally supported the idea that star formation proceeds bimodally with respect to stellar mass. The star formation rate appears to differ both spatially and temporally for low mass and → massive stars. This is of considerable importance for galactic evolution, since the low-mass stars lock up mass and are long-lived, low luminosity survivors to the present epoch, whereas massive stars are short-lived, recycle and enrich interstellar gas, and leave dark remnants while producing a high luminosity per unit of mass (Silk, J., 1988, in Galactic and Extragalactic Star Formation, p. 503, eds. R. E. Pudritz and M. Fich).

→ bimodal; → star; → formation.

The retrieval and analysis of biochemical and biological data using mathematics and computer science, as in the study of genomes (Dictionary.com).

→ bio-; → informatics.

In → statistical thermodynamics, a probability equation relating the → entropy S of an → ideal gas to the quantity Ω, which is the number of → microstates corresponding to a given → macrostate: S = k. ln Ω. Same as → Boltzmann's relation.

→ Boltzmann's constant; → entropy; → formula.

A → structure formation scenario in which small galaxies form first, and larger structures are then formed in due course. Contrary to → top-down structure formation.

→ bottom; → up; → structure; → formation; → galaxy.

An intense → star formation activity in a region of → interstellar medium or, more globally, in a → galaxy. It is characterized by a → star formation rate which is much higher than the corresponding average. Same as → starburst.

→ burst; → star; → formation.

The simplest expression of an equation, statement, or rule.

→ canonical; → form.

The fraction of → star formation which happens in → bound clusters. It is defined as the ratio between the → cluster formation rate and → star formation rate (Bastian, 2008, MNRAS 390, 759, arxiv/0807.4687).

→ cluster; → formation; → efficiency.

A parameter used in star formation models representing the ratio of the total mass in → star clusters to the corresponding age range (Bastian, 2008, MNRAS 390, 759, arxiv/0807.4687).

→ cluster; → formation; → rate.

The chemical reaction that gives rise to → carbon monoxide in the → interstellar medium. According to models, several processes may lead to CO formation. For example, HCO⁺ + e → CO + H. The molecule HCO⁺ is itself produced through several paths, for example: H₃⁺ + C → CH₂⁺ + H, CH₂⁺ + H₂ → CH₃⁺ + H, CH₃⁺ + O → HCO⁺ + H. Alternatively: C⁺ + H₂O → HCO⁺ + H. Another possibility: C⁺ + OH → CO⁺ + H, CO⁺ + H₂→ HCO⁺ + H.

→ carbon monoxide; → formation.

A theory according to which the Earth and Moon formed from the → protoplanetary disk at the same time. See also → giant impact hypothesis, → capture theory, → fission theory.

→ co-; → formation; → theory.

Formation of stars, especially → massive stars, in group as opposed to individual formation.

→ collective; → star; → formation.

Empirical mathematical transformation applied to the observed magnitudes in order to convert them into a standard system, or into a different system.

→ color; → transformation.

One of eight equations that give the → trigonometric functions of → compound angles.
sin(A± B) = sinA.cosnd angleB± cosA.sinB
cos(A + B) = cosA.cosB - sinA.sinB
cos(A - B) = cosA.cosB + sinA.sinB
tan(A + B) = (tanA + tanB)/(1 - tanA.tanB)
tan(A - B) = (tanA - tanB)/(1 + tanA.tanB).

→ compound; → angle; → formula.

1a) To make similar in form, nature, or character.
1b) To bring into agreement, correspondence, or harmony.
2a) To act in accordance or harmony; comply (usually followed by to).
2b) To be or become similar in form, nature, or character (Dictionary.com).

→ con-; → form.

1) That conforms, especially to the shape of something.
2) Math.: Of, pertaining to, or specifying a mapping of a surface upon another surface so that all angles between intersecting curves remain unchanged.

→ con- + → form + → -al.