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

A galaxy with a stellar mass of M ≥ 10¹¹Msun and an → effective radius of R_e ≤ 1.5 kpc. Many studies have shown that massive galaxies with low → star formation rates were remarkably compact at a → redshift of z≥ 2. At fixed stellar mass of Mstars ≅ 10¹¹Msun, quiescent galaxies are a factor of ~ 4 smaller at z = 2 than at z = 0. As the stellar mass of the galaxies also evolves, the inferred size growth of individual galaxies is even larger. It is unlikely that all massive galaxies in the present-day Universe had a compact progenitor. However, the vast majority of CMGs that are observed at z = 2 ended up in the center of a much larger galaxy today. Their size growth after z = 2 is probably dominated by minor → mergers. Such mergers are expected because other mechanisms cannot easily produce the observed scaling between size growth and mass growth (P. G. van Dokkum1 et al., 2015, ApJ 813, 23).

→ compact; → massive; → galaxy.

An astronomical object that is substantially denser or more compact than most objects of its class. More specifically, a → neutron star or a → stellar black hole.

→ compact; → object.

A star whose spectrum shows striking similarities to → B[e] stars and is evolving into a → planetary nebula (→ preplanetary nebula).

→ compact; → planetary; → nebula; → B[e] star.

An object emitting intense energy in radio wavelength from a small, unresolved central region.

→ compact; → radio source.

A topological space for which every collection of open sets that covers the space has a finite subset that also covers the space.

→ compact; → space.

1) Math.: A process applied to topological spaces having many dimensions to make them compact spaces.
2) Physics: In string theory, the process of "curling up" the extra dimensions (six in the superstring theory). According to these theories, the Universe actually has 10 spatial dimensions but that 7 of them have become "compactified" down to subatomic size and thus are unobservable.

Compactification, n. from → compactify.

Verbal form of → compactification.

Compactify, from → compact + -ify "cause to become," M.E. -fien, from O.Fr. -fier, from L. -ficare, root of facere "to make, do;" PIE base *dhe- "to put, to do" (cf. Skt. dadhati "puts, places;" Av. dadaiti "he puts," O.Pers. ada "he made," Gk. tithenai "to put, set, place."

1) The act of compacting or the state of being compacted.
2) Geology: The physical process whereby the volume of a fixed mass of sediment reduces either by the weight of overlying deposits or by the pressure of earth movements.

→ compact; → -tion.

1) General: The quality of being compact.
2) For a → compact object, a rough measure of the importance of gravity, defined by a dimension-less quantity which is the ratio between its gravitational radius (→ Schwarzschild radius) and its physical radius. It is expressed as φ = 2 GM / c² R, where M and R are the mass and radius of the object respectively, and G and c are the → gravitational constant and speed of light respectively. For a → black hole  φ is of order unity (by definition), for a → white dwarf it is of order 10^-4, and for a → neutron star  φ is around 0.5.

→ compact + → -ness.

The fainter of the two components in a → binary system.

Companion from O.Fr. compaignon "fellow, mate," from L.L. companionem, lit. "bread fellow, messmate," from L. → com- "with" + panis "bread."

Hamdam "bearthing together, i.e. an intimate companion, friend," from ham- "with", → com- + dam "breath," Mod.Pers./Mid.Pers. damidan "to breathe, blow," Av. dāδmainya- "blowing up," cp. Skt. dham- "to blow," dhamati "he bows," Proto-Indo-Iranian *dhamH-, Proto-Iranian *damH- "to blow, breathe; to swell," PIE *dhemH- "to blow."

A faint star of 8th magnitude in a binary system with → Sirius. Called also Sirius B, it is a → white dwarf with a mass comparable to that of the Sun, but with a diameter smaller than that of the Earth. The mean distance between the stars is about 20 A.U. (angular separation 4.6 seconds of arc), and their period of revolution about 50 years. This star was discovered in 1844 by Friedrich Bessel, who noticed that Sirius had a slight wobbling motion, as if it was orbiting an unseen object. In 1863, the optician and telescope maker Alvan Clark spotted the companion. The star was later determined to be a → white dwarf.

→ companion; → Sirius.

1) Of or relating to comparison.
2) Proceeding by, founded on, or using comparison as a method of study.
3) Grammar: Being, noting, or pertaining to the intermediate degree of the comparison of adjectives, as better and more beautiful, the comparative forms of good and beautiful, and of adverbs, as nearer and more carefully, the comparative forms of near and carefully (Dictionary.com).

→ comparison; → -ive.

A device that compares the measured property of an object (position, shape, color, brightness) with a standard. → blink comparator.

L.L. comparator "comparer," from compara, → compare, + -tor suffix forming personal agent nouns, cf. Gk. -tor, Skt. -tar.

Hamsanjgar, agent noun from hamsanjidan→ comparison.

To examine in order to note similarities and differences.

From O.Fr. comparer, from L. comparare "to match, make equal with, liken," from → com- "with" + parare "to make or esteem equal," from par "equal."

Sanjidan "to compare; to measure," from Mid.Pers. sanjidan "to weigh," from present tense stem sanj-, Av. θanj- "to draw, pull;" Proto-Iranian *θanj-. Other terms from this base in Pers.: lanjidan "to pull up," hanjidan, âhanjidan "to draw out," farhang "education, culture."

The act of comparing or the process of being compared.

From O.Fr. comparaison from L. comparationem, from p.p. stem of comparare, → compare.

Hamsanješ, from hamsanj present tense stem of hamsanjidan, → compare, + -š verbal noun suffix.

A spectrum of known substances used as a standard of comparison for investigating spectra of celestial objects.

→ comparison; → spectrum.

A non-variable star used to monitor the variations of another nearby star.

→ comparison; → star.

A device for determining directions, as by means of a freely rotating → magnetic needle that indicates → magnetic north.

M.E. compas, from O.Fr. compas "circle, pair of compasses," from compasser "to go around, measure," from V.L. *compassare "to pace out," from L. → com- "together" + passus "a step."

Qotbnemâ, literally "pole indicator," from qotb, → pole, + nemâ "indicator, showing," from nemudan "to show," → display.

The needle in a → magnetic compass.

→ compass; → needle.

An instrument that consists of two arms, joined at the top, one arm of which serves as a stationary reference point or pivot, while the other describes a circle or is extended. It is used for measuring angles, transferring lengths, and drawing circumferences. Also pair of compasses.

→ compass.

Pargâr "a pair of compasses," from Proto-Ir. *pari-kar- "to draw around, to plough around," from *pari- "around, round about" (Mod.Pers. par-, pirâ-, cognate with Gk. peri-), → circum-, + *kar-, karš- "to draw (a furrow), till, plant" (Mod.Pers. kašidan "to draw," kâštan, kâridan "to plant"); Lori, Hamadâni kerr "line, scratch;" Laki keronen, Hamadâni kerândan "to pull along, drag;" Tâleši kernye; Tabari kərəš "to drag;" cf. Av. pairikara- "a furrow round about," Skt. parikara- "girdle, waist-band, zone."