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

Having the form of a parabola.

of or pertaining to → parabola.

An antenna comprising a parabolic reflector with a receiving and/or transmitting element positioned at or near its focal point.

→ parabolic; → antenna.

A concave mirror that has the form of a paraboloid of revolution.

→ parabolic; → mirror.

An orbit whose overall shape is like a parabola; it is the limiting case between an elliptical orbit (eccentricity less than 1) and a hyperbolic orbit (eccentricity larger than 1). The speed necessary to form a parabolic orbit is known as the escape velocity.

→ parabolic; → orbit.

The speed necessary to form a parabolic orbit around a gravitational center. It is also the minimum speed necessary to escape from the gravitational pull of a body.

→ parabolic; → velocity.

A solid formed by the revolution of a parabola about its axis.

From parabol(a), → parabola, + → -oid.

1) General: A typical example of something.
2) Grammar: A set of word forms giving all of the possible inflections (declensions, conjugations) of a word.
3) Philosophy of science: A framework of concepts, results, and procedures within which subsequent work is carried out, as defined by the influential Thomas Kuhn (1922-1996) in his classic The Structure of Scientific Revolutions (1962). "Normal science" proceeds within such a framework or paradigm. When a paradigm has to be changed (→ paradigm shift), there comes about a crisis and then scientific revolution. For example, Newton's mechanical paradigm was replaced by the paradigm of Einstein's relativistic universe. Each paradigm is an interpretation of the world, rather than an objective explanation. For criticism of Kuhn's views, see, e.g., Stanford Encyclopedia of Philosophy.
4) Term now occurring frequently in every kind of discourse, usually to mean something like "way of thinking" or "approach to a problem."

L.L. paradigma "pattern, example," especially in grammar, from Gk. paradeigma "pattern, model," from paradeiknynai "to exhibit, show side by side," from → para- "beside" + deiknynai "to show," related to dokein "to appear, seem, think," cognate with Av. daēs- "to show" (Mod.Pers. andišé, andiš "thought, think," see below); Skt. diś- "to show, point out," diśati "he shows;" L. dicere "to utter;" PIE base *deik- "to show, to pronounce."

Parâdiš, pârâdiš, from parâ-, pârâ, → para- + diš "to show," as in andiš, andišidan "to → think" (related to dis, disé, → form); Sogd. andiš "to seem," andêš "to show," andêšik "appearing;" ultimately from Av. daēs- "to show," s-aorist forms dāiš-, dôiš-, diš-, akin to Gk. deiknynai "to show," as above, dike "manner, custom;" Skt. diś- "to show, point out;" L. dicere "to utter, say;" O.H.G. zeigon, Ger. zeigen "to show;" O.E. teon "to accuse," tæcan "to teach."

1) Philosophy of science: A process of revolutionary change in scientific → paradigms, whereby established scientific ideas are replaced by new ones. For instance, Copernicus' evidence that the Earth revolved around the Sun caused a paradigm shift in astronomy.
2) The idea of paradigm shift has been transferred from the sciences to other areas of society and culture, referring to a fundamental reorganization of how people think about an entire topic.

→ paradigm; → shift; → change.

A statement, proposition, or situation that seems self-contradictory or absurd but in reality is or may be true. → Fermi paradox; → faint early Sun paradox; → twins paradox; → paradox of youth.

From L. paradoxum "contrary to expectation," from Gk. paradoxon, from neuter of adj. paradoxos "contrary to common opinion, unbelievable," from → para- "contrary to" + dox(a) "opinion, belief" + -os adj. suffix. The main component dox, from dokein "to appear, seem, think," is cognate with Av. daēs- "to show;" Skt. diś- "to show, point out," diśati "he shows;" L. dicere "to utter;" PIE base *deik- "to show, pronounce solemnly."

Pârâdaxš (on the model of Gk. paradoxos), from pârâ-, → para-, + daxš, from Av. daxš- "to reveal, instruct, point out," fradaxštar- "teacher," *daxšārə "revelations;" Mod.Pers. daxš "task, effort;" cf. Skt. daks- "to be able," dáksa- "able, expert."

The observed presence of young stars in the immediate vicinity of the → supermassive black hole (SMBH), → Sgr A*, residing in the center of our Galaxy. The stellar population within 1 pc of the SMBH contains a variety of young and → massive stars orbiting the SMBH. Some of them are only about 20 Myr old and get as close as a few light-days to the SMBH, while from 0.1 to 0.4 pc even younger stars are found with ages of 3-7 Myr. The presence of these stars so near to the SMBH is a paradox. Their → in situ formation should be almost impossible, since the environment is too hostile for these stars to form. Indeed the strong → tidal influence of the SMBH should hamper their formation. On the other hand, the scenario considering their → migration from other places does not seem to be adequate. The time required for the migration from > 1 pc by dynamical friction would exceed their inferred ages unless the migration rate were somehow accelerated. This apparent contradiction was termed "paradox of youth" by Ghez et al. (2003, ApJ 586, L127). See also Genzel et al. (2010, Rev.Mod.Phys. 82, 3121, also at astro-ph/1006.0064).

Youth, the condition of being → young; → paradox.

Molecular hydrogen in which the nuclei (protons) of the two hydrogen atoms contained in the molecule have spins in opposite directions. → orthohydrogen

→ para-; + → hydrogen.

Of or pertaining to a parallax.

Adj. form of → parallax.

Of an object in the sky, the angle between the → celestial pole, the object, and the → zenith. Since parallactic angle describes the orientation on the sky of the object for a particular observer, it can be an important quantity in some observations.

→ parallactic; → angle.

The path on the sky of the apparent position of a star as seen from the Earth, due to the Earth's annual motion around the Sun.

→ parallactic; → ellipse.

An irregularity in the Moon's motion caused by the Sun's gravitational attraction, which sets the Moon ahead or behind its normal orbital position. The Moon is about 2 arcminutes ahead of its expected position at first quarter, and a similar amount behind at last quarter.

→ parallactic; → inequality.

The proper motion of a star due to the effect of the Sun's motion relative to the → local standard of rest.

→ parallactic; → motion.

The apparent → shift of a nearby object's → position in relation to more distant ones when the nearby object is observed from different → viewing angles. See also → stellar parallax.

From M.Fr. parallaxe, from Gk. parallaxis "change, alteration," from parallassein "to alter, make things alternate," from → para- "beside" + allassein "to change," from allos "other;" → alias.

Didgašt, literally "view change," from did "sight, view; eye," from didan "to see" (Mid.Pers. ditan "to see, regard, catch sight of, contemplate, experience;" O.Pers. dī- "to see;" Av. dā(y)- "to see," didāti "sees;" cf. Skt. dhī- "to perceive, think, ponder; thought, reflection, meditation," dādhye; Gk. dedorka "have seen") + gašt "change, alteration," past stem of gaštan, gardidan "to turn, to change" (Mid.Pers. vartitan; Av. varət- "to turn, revolve;" Skt. vrt- "to turn, roll," vartate "it turns round, rolls;" L. vertere "to turn;" O.H.G. werden "to become;" PIE base *wer- "to turn, bend").

The angular displacement associated with → parallax.

→ parallax; → angle.

1) Said of two or more things, such as lines or planes, that are equally distant from one another at all points.
2) Electricity: An arrangement of the components in an electric circuit so that the same voltage is applied to each component. Compare → series.

From M.Fr. parallèle, from L. parallelus, from Gk. parallelos "parallel," from para allelois "beside one another," from → para- "beside" + allelois "each other," from allos "other," → alias.

Parâsu, from parâ-, → para-, + su "direction, side," from Mid.Pers. sôk "direction, side."

The → moment of inertia of a body about any given axis is the moment of inertia about a parallel axis through the center of mass, plus the moment of inertia about the given axis if the mass were located at the center of mass. same as → Steiner's theorem.

→ parallel; → axis; → theorem.