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

The Fishes. An extensive but faint constellation of the → Zodiac, representing a pair of fishes, located in the northern hemisphere, at 1h right ascension, 15° north declination. Abbreviation: Psc; genitive: Piscium.

L., plural of piscis "fish," cognate with Goth. fisks, O.E. fisc.

Mâhi "fish," from Mid.Pers. mâhik; Av. masya-; cf. Skt. matsya-, Pali maccha-.

The Southern Fish. A small constellation in the southern hemisphere, at 22h 30m right ascension, 30° south declination. Its brightest star, → Fomalhaut, has apparent visual magnitude 1.3. Abbreviation: PsA; genitive: Piscis Austrini.

L. piscis "fish," cognate with Goth. fisks, O.E. fisc; austrinus "southern."

Mâhi "fish," → Pisces; daštari "southern," → south.

A disk or cylindrical part tightly fitting and moving within a cylinder, either to compress or move a fluid collected in the cylinder, as air or water, or to transform energy imparted by a fluid entering or expanding inside the cylinder, as compressed air, explosive gases, or steam, into a rectilinear motion usually transformed into rotary motion by means of a connecting rod (Dictionary.com).

From Fr. piston, from M.Fr. piston "large pestle," from O.It. pistone "a piston," from pestare "to pound," from L.L. pistare, from pistare "to pound."

The sensation of a sound frequency; the relative highness or lowness that we hear in a sound. A high pitch sound corresponds to a high frequency sound wave and a low pitch sound corresponds to a low frequency sound wave. In music, a sound that has a definite pitch is called a → tone. Sounds may be generally characterized by pitch, → loudness, and → quality.

M.E. picchen "to thrust, pierce, set;" maybe akin to pick.

Dong "voice, sound," variants bâng, vâng, vang, zang, Tabari šong "cry;" related to vâž, → word.

A natural ore consisting mainly of → uranium oxide, U₃O₈, with small amounts of → radium, of which is the principal source. It usually contains some → lead and variable amounts of → thorium and → rare-earth elements.

From Ger. Pechblende, from Pech "pitch" (from its black color) + Blende "a mineral."

A → device used to → measure the → velocity of a flowing → fluid. The Pitot tube is used on → aircrafts to determine their → speed. It is also used to meaure water speed of a boat as well as liquid, air, and gas velocities in industrial applications. It is a small tube that has two holes on it. The front hole is placed in the airstream to measure the → stagnation pressure. The side hole measures the → static pressure. The difference between these pressures gives the → dynamic pressure, which can be used to calculate airspeed. See also the → Bernoulli equation.

Named after the French inventor Henri Pitot (1695-1771), a hyraulic engineer; → tube.

The smallest useful element of image information.

From pix, plural of pic, short for → picture + el, from → element.

An area, position, or portion of space. → mean place

O.E. from O.Fr. place, from M.L. placea "place, spot," from L. platea "courtyard, open space, broad street," from Gk. plateia (hodos) "broad (way)," feminine of platus "broad;" cognate with Av. pərəθu- "broad;" Skt. prthú- "broad, wide;" Lith. platus "broad;" Ger. Fladen "flat cake;" O.Ir. lethan "broad;" PIE base *plat- "to spread."

Jâ "place" (from Mid.Pers. giyag "place;" O.Pers. ā-vahana- "place, village;" Av. vah- "to dwell, stay," vanhaiti "he dwells, stays;" Skt. vásati "he dwells;" Gk. aesa (nukta) "to pass (the night);" Ossetic wat "room; bed; place;" Tokharian B wäs- "to stay, wait;" PIE base ues- "to stay, live, spend the night").

A mathematical notation system in which the → numerals get different values depending on their position relative to the other numerals. Same as → positional notation and → positional number system.

→ place; → value; → notation.

A bright cloud-like feature that appears in the vicinity of a sunspot. Plages represent regions of higher temperature and density within the chromosphere. They are particularly visible when photographed through filters passing the spectral light of hydrogen or calcium.

From Fr., from It. piaggia, from L.L. plagia "shore;" noun use of the feminine of plagius "horizontal;" frpm Gk. plagios "slanting, sideways" from plag(os) "side" + -ios adj. suffix.

Plâž, loan from Fr., as above.

Any of the → feldspar minerals consisting of a mixture of → sodium and → calcium  → aluminium  → silicates in triclinic crystalline form. Members of the plagioclase group are the most common rock-forming minerals. They are important or dominant minerals in most → igneous rocks of the → Earth's crust.

From Ger. Plagioclase, from Gk. plagio- a combining form meaning "oblique," + clase a suffix used in the formation of compound words that denote minerals with a particular cleavage, as specified by the initial element.

An extent of flat land not noticeably diversified with mountains, hills, or valleys.

M.E. from O.Fr. plain, from L. planum "level ground, plain."

Dašt, from Mid.Pers. dašt "plain, open ground."

1a) A scheme or method of acting, doing, proceeding, making, etc., developed in advance.
1b) A representation of a thing drawn on a plane, as a map or diagram.
2a) To arrange a method or scheme beforehand for.
2b) To make plans for (Dictionary.com).

M.E., from Fr. plan "ground plan, map," literally "plane surface," from L. planum "level or flat surface," noun use of adjective planus "level, flat" (from PIE root *pele- "flat; to spread;" Gk. plassein "to mold," plasma "something molded or created;" L. planus "flat, level, even, plain, clear;" Lith. plonas "thin;" O.C.S. polje "flat land, field," Russ. polyi "open;" O.E. feld, M.Du. veld "field."

Pišgâr, literally "beforehand written, painted in advance," from piš- "before, in front," → pre-, + gâr present stem of negâridan, negâštan "to paint, write," → graph.

Variant of → plano-.

→ plano-.

Short for Max Planck (1858-1947), German physicist, great authority on thermodynamics and creator of the quantum theory.

A physical constant that determines the energy of quantum as a function of its frequency; symbol h. Also called → Planck's constant. On 16 November 2018, the International Bureau of Weights and Measures (BIPM) voted to redefine the kilogram by fixing the value of the Planck constant, thereby defining the kilogram in terms of the second and the speed of light. Starting 20 May 2019, the new value is exactly 6.626 070 15 × 10^-34 J s. The → reduced Planck constant, ħ = h / 2π, is also called the → Dirac constant.

→ Planck; → constant.

Same as → blackbody curve.

→ Planck; → curve.

The density corresponding to a → Planck mass in a cubic region of edge length given by the → Planck length: ρ_P = c⁵/(ħG²) ≅ 5.16 x 10⁹³ g cm^-3, where c is the → speed of light, ħ is the → reduced Planck's constant, and G is the → gravitational constant.

→ Planck; → density.

The distribution of radiation with wavelength for a blackbody, given by → Planck's radiation law.

→ Planck; → distribution.

The unit of energy in the system of Planck units. E_P = √ (ħ c⁵/G) ≅ 1.22 x 10¹⁹ GeV. It can also be defined as E_P = ħ / t_P, where t_P is the Planck time. This is an extraordinarily large amount of energy on the subatomic scale and particle accelerators have yet to produce a particle with this magnitude of energy. Understanding the properties of a subatomic particle that contains the Planck Energy is helpful in developing a Unified Field Theory which encompasses the realms of Quantum Theory and Relativity, although this too has evaded complete scientific understanding.

→ Planck; → energy.