An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 55 Search : point
South point
  نقطه‌ی ِ دشتر   
noqte-ye daštar

Fr.: point Sud   

The point on → horizon in direction of → geographic south pole.

south; → point.

stagnation point
  نقطه‌ی ِ ناروانی   
noqte-ye nâravâni

Fr.: point de stagnation   

A point where the → flow  → velocity is → zero. For example a point around an obstacle where a → flow tube splits into two portions.

stagnation; → point.

stationary point
  نقطه‌ی ِ ایست‌ور   
noqte-ye istvar

Fr.: point critique, ~ stationnaire   

1) Math.: For a → function y = f(x), a point at which the → tangent to the graph is horizontal. In other words, a point where the → slope is zero: dy/dx = 0.
2) Of a planet, the position at which the rate of change of its apparent → right ascension is momentarily zero.

stationary; → point.

subsolar point
  نقطه‌ی ِ زیر-خورشیدی   
noqte-ye zir-xoršidi

Fr.: point subsolaire   

The point of the surface of a celestial body (including the Earth) at which the Sun is directly overhead at a particular time.

sub-; → solar; → point.

substellar point
  نقطه‌ی ِ زیر-ستاره‌ای   
noqte-ye zir-setâre-yi

Fr.: point substellaire   

The point on the Earth, or other body, at which a particular star is directly overhead at a given time.

substellar; → point.

subterrestrial point
  نقطه‌ی ِ زیر-زمینی   
noqte-ye zir-zamini

Fr.: point subterrestre   

The point on the surface of a celestial body where the star is perceived to be directly overhead (in zenith). The sublunar point and subsolar point are the equivalent points for the Moon and Sun, respectively.

sub-; → terrestrial.

telescope pointing accuracy
  رشمندی ِ آماجش ِ دوربین، ~ ~ تلسکوپ   
rašmandi-ye âmâješ-e durbin, ~ ~ teleskvp

Fr.: précision du pointage de télescope   

The accuracy with which a telescope can be pointed to a particular coordinate in the sky.

telescope; → pointing; accuracy.

triple point
  نقطه‌ی ِ سه‌گانه   
noqte-ye segâné (#)

Fr.: point triple   

The definite pressure and temperature at which all three phases of a substance coexist in → phase equilibrium. The triple point of water has a pressure of 4.58 mm of Hg and a temperature of 273.16 °K.

triple; → point.

Noqté, → triple; segâné, from three + -gâné suffix forming plural entities, from Mid.Pers. -gânag, -gâna.

turning point
gaštgâh (#)

Fr.: tournant   

The closest point in the path of a sound wave to the center of a star, as studied in → asteroseismology. Starting from the surface, the sound wave first moves into the star almost straight toward the center. Its path then deflects, because of the increasing → sound speed, so that it misses the center of the star. After the turning point, the wave moves out again until it reaches the surface, where it is reflected. If exactly an integer number of wavelengths fits between two reflections at the surface, the sound wave corresponds to a → standing wave with a specific pattern of → node lines on the surface.

turn; → point.

turnoff point
  نقطه‌ی ِ رهگشت   
noqte-ye rahgašt

Fr.: tournant final de la séquence principale   

Same as → main-sequence turnoff.

turnoff; → point.

vernal point
  نقطه‌ی ِ بهاری   
noqte-ye bahâri

Fr.: point vernal   

The intersection point between the → celestial equator and the → ecliptic from where the Sun apparently enters into the northern celestial hemisphere.

vernal; → point.

  نقطه‌ی ِ X   
noqte-te X

Fr.: point X   

A configuration of magnetic field lines around a → magnetic null point resembling a cross. See also → O-point.

X, the letter of alphabet whose shape evokes the configuration; → point.

yield point
  نقطه‌ی ِ وادهی، ~ واداد   
noqte-ye vâdahi, ~ vâdâd

Fr.: limite d'élasticite   

The point at which the → strain caused by a → stress on a material begins to increase without further increase in the stress. This point marks the end of → elastic deformation and the beginning of → plastic deformation. Same as → elastic limit.

yield; → point.

zero point
  نقطه‌ی ِ صفر   
noqte-ye sefr

Fr.: point zéro   

1) General: A starting point for making a measurement.
2) A basic parameter on which a → photometric system relies and must be determined each night. The zero points of → magnitudes and color indices (→ color index) depend on atmospheric transparency that varies from night to night.

zero; → point.

zero point energy
  کاروژ ِ نقطه‌ی ِ صفر   
kâruž-e noqte-ye sefr

Fr.: énergie du point zéro, point zéro   

The lowest possible energy that a → quantum mechanical system may possess. It is the energy of the → ground state of the system. The term "zero point" refers to the observed fact that → vacuum fluctuations persist at → absolute zero temperature. Same as → vacuum energy.

zero; → point; → energy.

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