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

A nuclear reaction that takes place at high densities and relatively low temperatures. Pycnonuclear reactions are almost temperature independent and occur even at zero temperature. These reactions are extremely slow at densities typical for normal stars but intensify with increasing density. For example, carbon burns into heavier elements at densities over 10¹⁰ g cm^-3.

Pycnonuclear, from pycno- a combining form meaning "dense, thick," from Gk. pyknos "dense, solid" + → nuclear; → reaction.

Vâžireš, → reaction; cagâl-hasteyi, from cagâl, → dense, + hasteyi, → nuclear.

General term for the class of → actinometers that measure the intensity of solar radiation received on the surface of the Earth. It functions by converting the heat of the sunlight into a voltage using a device called a thermopile, and a recording voltmeter.

From pyr-, from → pyro- + → heliometer.

A yellow → mineral which is an iron sulfide (FeS₂). It is a source of → sulfur and is used in the manufacture of sulfuric acid.

M.E., from O.Fr. pirite, from L. pyrites, from Gk. pyr "fire," → pyro-, + → -ite.

A prefix meaning "fire, heat, high temperature," used in the formation of compound words. → pyrheliometer; → pyrometer.

From Gk. pyro-, combining form of pyr "fire," cognate with O.E. fyr, O.N. fürr, M.Du. vuur, Ger. Feuer), from PIE *paewr-; cf. Mod.Pers. Lori porpor "blazing charcoal," Gilaki bur, biur "smokeless red fire" (Lori perisk, periska "spark," Kurd. biriske "spark," Lârestâni pelita "spark"); Gk. pyr "fire;" Hitt. pahhur "fire;" Skt. pū- "to cleanse."

Âzar, variants âtaš, taš "fire," from Mid.Pers. âtaxš, âtur "fire;" Av. ātar-, āθr- "fire," singular nominative ātarš-; O.Pers. ātar- "fire;" Av. āθaurvan- "fire priest;" Skt. átharvan- "fire priest;" cf. L. ater "black" ("blackened by fire"); Arm. airem "burns;" Serb. vatra "fire;" PIE base *āter- "fire."

A device used for measuring high temperatures. By comparing a source whose temperature is to be measured to a standardized source of illumination, it determines the temperature of the former source.

→ pyro- + → -meter.

One of the major groups of silicate minerals found in many igneous and metamorphic rocks. Pyroxene minerals are also common in meteorites. There are many different types of pyroxene. All of the types contain Si₂O₆ but some have sodium (Na) while others have iron (Fe), magnesium (Mg), or a combination of these three elements.

From → pyro- "fire," + xeno- a combining form meaning "alien, strange, guest," from Gk. xenos "stranger, guest." Pyroxene was originally supposed to be a foreign substance when found in igneous rocks.

The proposition that the → square of the → hypotenuse of a → right triangle is equal to the → sum of the squares of the other two sides: a² + b² = c².

After Pythagoras (c570 BC-c495BC), Greek philosopher and mathematician; → theorem.

Any group of three → integers that satisfy the relations specified by the → Pythagorean theorem. Some examples: 3, 4, and 5; 5, 12, and 13; 8, 15, 17.

→ Pythagorean theorem; → triple; → triplet.

The Compass Box. A faint constellation in the southern hemisphere, at 9h right ascension, 30° south declination, representing a mariner's compass. Its brightest star, Alpha Pyxidis, is magnitude 3.7. Abbreviation: Pyx; genitive: Pyxidis.

L. pyxis, from Gk. pyxis "box."

Qotbnamâ literally "pole indicator," from qotb, → pole, + namâ "displayer, indicator," from nemudan "to show" (Mid.Pers. nimūdan, nimây- "to show," from O.Pers./Av. ni- "down; into" (Skt. ni "down," nitaram "downward," Gk. neiothen "from below," cf. E. nether, O.E. niþera, neoþera "down, downward, below, beneath," from P.Gmc. *nitheraz, Du. neder, Ger. nieder; PIE *ni- "down, below") + māy- "to measure;" cf. Skt. mati "measures," matra- "measure;" Gk. metron "measure;" L. metrum; PIE base *me- "to measure").

In the Johnson → UBV system, a reddening-free parameter which is related to the → effective temperature of stars and thus provides a useful, but rough, discriminant for → spectral types. It is expressed as: Q = (U - B) - 0.72 (B - V).

→ index.

A two-dimensional figure that consists of four points connected by straight lines. Same as → tetragon; see also → quadrilateral.

L.L. quadrangulum, noun use of neuter of L. quadrangulus, quadriangulus "four-cornered," from quadr- variant of quadri- before a vowel "four," akin to quattuor, → four, cognate with Pers. cahâr, as below; → angle.

Cahârgušé, cârguš "four-cornered," from cahâr, câr "four," cognate with L. quattuor, → four, + gušé, guš "corner, angle;" Mid.Pers. gôšak "corner."

An obsolete → constellation created by the French astronomer Jérôme Lalande in 1795. He named it such for the main astronomical instrument, that is → mural quadrant, he used. Quadrans Muralis was located between the constellations → Boötes and → Draco. The name disappeared from astronomical catalogs, but the → meteor shower→ Quadrantids has kept that name.

→ mural quadrant.

1) A quarter of a circle; an arc of 90°.
2) Any of the four parts into which a plane is divided by a pair of rectangular axes.
3) An instrument, usually containing a graduated arc of 90°, formerly used in astronomy and navigation to measure the angles and altitudes of stars. → mural quadrant.

M.E., from L. quadrantem (nominative quadrans) "fourth part."

Cârakân, from cârak + -ân. Cârak "quarter," literally "fourth, a fourth part of one," from câr, variant of cahâr, → four, cognate with L. quattuor, + -ak, contraction of yak "one," from Mid.Pers. êwak (Proto-Iranian *aiua-ka-); O.Pers. aiva- "one, alone;" Av. aēuua- "one, alone" (cf. Skt. éka- "one, alone, single;" Gk. oios "alone, lonely;" L. unus "one;" E. one); -ân nuance suffix.

An annual → meteor shower reaching a peak about 3 January and having its → radiant in the constellation → Boötes.

From L. Quadrant-, from Quadrans Muralis , → mural quadrant.

Of or relating to or resembling a → square.
Of, relating to, or containing terms with powers no higher than the power of two.

Quadratic, adj. of quadrate, from L. quadratus p.p. of quadrare "to make square."

Câruši pertaining to câruš "square," from Av. caθruša- "four sides (of a four-sided figure)," from caθru- "four," Mod.Pers. cahâr, câr "four," cognate with L. quattuor, → four.

An equation with the general form of ax² + bx +c = 0, in which the highest power of the unknown is the second power (square).

→ quadratic; → equation.

A formula relating the unknown part of a → quadratic equation (the roots of the equation, x) to the known parts (a, b, and c): x = (-b± (b² - 4ac)^½) / 2a.

→ quadratic; → formula.

1) General: The process of making something square; the act of squaring.
2) Math.: The act or process of constructing a → square with an area equal to that of a specified surface, especially a surface bounded by a curve.
3) Astro.: The position of a planet or the Moon when it makes a 90° angle with the Sun as seen from Earth.

From L. quadratura, from quadrat(us) p.p. of quadrare "to make square."

1) Cârušeš verbal noun of cârušidan "to square," from câruš "square," from Av. caθruša-, → quadratic.
Câruši quality noun of câruš "square," as preceding.
2) Navadân, from navad "ninety," referring to the longitude difference of 90° (Mid.Pers. nawad; Av. nauuaiti- "ninety," from nauua- "nine" (Mod.Pers. noh); cf. Skt. navati- "ninety") + -ân suffix of place and time.

Constructing a square whose area equals that of a given circle. This was one of the three geometric problems of antiquity. It was finally proved to be an impossible problem when π was proven to be transcendental by Lindemann in 1882. Same as → squaring the circle.

→ quadrature; → circle.

A plane figure bounded by four straight lines.

From L. quadrilater(us) "four-sided," from L. quattuor, → four, + → lateral.