An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 1010
precessed coordinates
  هم‌آراهای ِ پیشایانیده   
hamârâhâ-ye pišâyânidé

Fr.: coordonnées précessées, ~ corrigées de la précession   

The apparent position of a celestial object corrected for the epoch → precession.

Precessed, p.p. of → precess; → coordinates.


Fr.: précession   

The periodic motion of the → rotation axis of a body such as a → spinning top in which the axis of rotation gradually sweeps out a conical shape. In the case of the spinning Earth, it is due to the combined → gravitational attractions of the → Sun, the → Moon, and → planets on Earth's → equatorial bulge. Since the Earth's axis is tilted to its → orbital plane or → ecliptic, the gravitational force of the Sun and the Moon on the Earth's equatorial bulge tend to pull it back toward the plane of ecliptic. As a result, the axis → precesses. Earth's axis of rotation precesses with a period of about 25,770 years, describing one complete circle on the → celestial sphere (→ precession constant). This circle has a radius of approximately 23°.5, equal to the → inclination of the Earth's orbit. Since the → vernal equinox is the reference direction for the → equatorial coordinate system, the coordinates of "fixed" objects change with time and must therefore be referred to an → epoch at which they are correct. → sign of zodiac.
See also → general precession; → precession of the ecliptic; → precession of the equator; → precession of the equinoxes; → precessional circle; → precession time; → geodetic precession; → general precession in longitude; → general precession in right ascension; → orbital precession; → perihelion precession; → planetary precession; → precession period.

L.L. præcissionem "a coming before," from L. præcessus, p.p. of præcedere "to happen before," from the fact that the equinoxes occur earlier each year with respect to the preceding year, from præ- "before," → pre-, + cedere "to walk, to go, to happen."

Pišâyân, literally "coming before," from piš- "before" → pre- + ây- (present stem of âmadan "to come, arrive, become"), from Av. ay- "to go, to come," aēiti "goes;" O.Pers. aitiy "goes;" Skt. e- "to come near," eti "arrival;" L. ire "to go;" Goth. iddja "went," Lith. eiti "to go;" Rus. idti "to go;" + -ân suffix of space and time.

precession constant
  پایای ِ پیشایان   
pâyâ-ye pišâyân

Fr.: constante de précession   

The amount by which the equinoctial points drift westward annually due to precession. Its value for epoch J2000.0 is 50''.26, resulting from the westward → precession of the equator (50".38), and the eastward → precession of the ecliptic (0".12).

precession; → constant.

precession of the ecliptic
  پیشایان ِ هورپه   
pišâyân-e hurpeh

Fr.: précession de l'écliptique   

The component of general precession caused by the gravitational attraction of the planets on the Earth's center of mass. It causes the equinox to move eastward by about 0''.12 per year in the opposite direction to the → precession of the equator. This terminology replaces → planetary precession, according to an IAU resolution adopted in August 2006.

precession; → ecliptic.

precession of the equator
  پیشایان ِ هموگار   
pišâyân-e hamugâr

Fr.: précession de l'équateur   

That component of general precession caused by the combined effect of the Moon, the Sun and the planets on the equatorial protuberance of the Earth, producing a westward motion of the equinoxes along the ecliptic about 50'' per year. According to an IAU resolution adopted in August 2006, the present terminology replaces lunisolar precession.

precession; → equator.

precession of the equinoxes
  پیشایان ِ هموگان‌ها   
pišâyân-e hamugânhâ

Fr.: précession des équinoxes   

The slow motion of the equinoxes along the ecliptic, resulting from the combined motion of the equator (→ precession of the equator) and the ecliptic (→ precession of the ecliptic), or in other words the precession of the Earth's axis of rotation. Also know as → general precession. The First Point of Aries moves westward along the ecliptic at 50.38 arcseconds per year (1 degree every 71.6 years), causing the equinoxes to occur about twenty minutes earlier each sidereal year. See also → nutation.

precession; → equinox.

precession of the nodes
  پیشایان ِ گره‌ها   
pišâyân-e gereh-hâ

Fr.: précession des nœuds   

The gradual change in he orbital planes of a binary system.

precession; → node.

precession period
  دوره‌ی ِ پیشایان   
dowre-ye pišâyân

Fr.: période de précession   

The interval with which a rotating body precesses. The precession period of the Earth is 25,770 years. For a → spinning top it is given by: Tp = (4π2I)/(mgrTs), where I is the → moment of inertia, m the mass of the top, g gravity, r the distance between the center of mass and the contact point, and Ts is the spinning period of the top.

precession; → period.

precession time
  زمان ِ پیشایان   
zamân-e pišâyân

Fr.: temps de précession   

A time interval over which an orbit precesses by 2π radians in its plane.

precession; → time.


Fr.: précessionnel   

Of or pertaing to → precession.

precession; → -al.

precessional circle
  پرهون ِ پیشایانی   
parhun-e pišâyâni

Fr.: circle précessionnel   

The path of either → celestial poles around the → ecliptic pole due to the → precession of equinox. It takes about 26,000 years for the celestial pole to complete path.

precessional; → circle.

  ۱) بارش، ریزش؛ ۲) ته‌نشست   
1) bâreš (#), rizeš (#); 2) tahnešast (#)

Fr.: précipitation   

1) Meteo.: Any form of water, such as rain, snow, sleet, or hail, that falls to the Earth's surface. The quantity of such water falling in a specific area within a specific period.
2) Chemistry: The process of separating a solid substance from a solution.

From M.Fr. précipitation, from L. præcipitationem "act or fact of falling headlong, haste," from præcipitare "fall, be hasty," from præceps "steep, headlong, headfirst," from præ- "forth" + caput, → head.

1) Bâreš, verbal noun of bâridan "to rain," bârân "rain;" Mid.Pers. vâritan, vârân; Av. vār- "rain; to rain;" cf. Skt. vār- "rain, water; to rain;" PIE base *uer- "water, rain, river."
Rizeš, verbal noun of rixtan "to flow, to pour," → overflow.
2) Tahnešast "to settle down, precipitate," from tah "→ bottom, end;" + nešast past stem of nešastan "to sit down; to settle down; to sink," → sit.


Fr.: précis   

1) Definitely or sharply stated, or defined.
2) Designating → precision.
See also: → accurate, → exact.

M.E., from M.Fr. précis "cut short" from M.L. precisus, from L. præcisus "abridged, cut off," p.p. of præcidere "to cut off, shorten," from præ- "in front," → pre-, + cædere "to cut down, chop, beat, hew, slay."

Parsun literally "cut around" (compare with Skt. pariccheda "precise, accurate definition, exact discrimination," from pari- + cheda "cut, cutting off," from chid- "to cut, split"), from par-, variant of pirâ- "around, about," → peri-, + sun "to cut;" cf. Kurd. Sorani su, sun "to sharpen, whet;" Kurd. Kurmanji (prefixed ha-, contraction of *ham-) hasun "to sharpen, whet;" Mod.Pers. sân "whetstone," variants fasân, afsân, awsân; Av. si-, sā- "to cut;" cf. Skt. śā- "to sharpen, whet" (see also → concrete).


Fr.: précisement   

In a precise manner.

precise; → -ly.


Fr.: précision   

The quality or state of being very accurate.

precise; → -ness.


Fr.: précision   

1) The state or quality of being → precise.
2) The degree to which repeated measurements of a quantity give the same results under unchanged conditions. Not the same as → accuracy, but often confused as such. See → accuracy for the difference between precision and accuracy.

Verbal noun from → precise.

pišgâm (#)

Fr.: précurseur   

1) A person or thing that comes before another of the same kind; a forerunner.
2) A substance from which another is formed, especially by metabolic reaction (

M.E., from L. præcursor "forerunner," from præcursus, p.p. of præcurrere, from præ- "before," → pre-, + currere "to run," → current.

Pišgâm, from piš- "before," → pre-, + gâm "step, pace," → stage.

precursor pulse
  تپ ِ پیشگام   
tap-e pišgâm

Fr.: pulse précurseur   

A component of a → pulsar pulse that appears shortly in advance of the main pulse.

precursor; → pulse.

  ۱) فراسن؛ ۲) فراسندن   
1) farâsan; 2) farâsandan

Fr.: prédicat   

1a) Grammar: The part of a → sentence or → clause stating something about the → subject and usually consisting of a → verb. For example, in the sentence "The man opened the door," the subject is "the man" and the predicate is "opened the door."
1b) Logic: Something which is affirmed or denied concerning the subject in a → proposition.

1c) Math.: A → function whose values are statements about n-tuples of objects forming the values of its → arguments. For n =1 a predicate is called a "property" , for n> 1 a → relation; propositions may be regarded as zero-place predicates (
2a) To state, affirm, or assert (something) about the subject of a proposition.
2b) To make (a term, expression, etc.) the predicate of a proposition.

M.E., from M.Fr. predicat, from L. praedicatus "declared, proclaimed," p.p. of praedicare, from prae "beforehand," → pre-, + dicare "proclame," from stem of dicere "to speak, to say," from PIE root *deik- "to point out, to show," cognate with Pers. dis, → form, and andišidan, → think.

Farâsan from farâ- "before; toward, along; above, upon, over," → pro-, + san Proto-Ir. *sanh- "to declare, explain," related to soxan, → speech and pâsox, → response, sahân, → sentence.

predicate logic
  گوییک ِ فراسنی، ~ فراسنها   
guyik-e farâsani, ~ farâsanhâ

Fr.: logique des prédicats   

The generic term for systems of → formal logic like → first-order logic and → second-order logic. Predicate logic contains → variables which can be quantified (→ quantify, → quantification).

predicate; → logic.

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