An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



<< < Z b zer > >>

Number of Results: 37
Z boson
  بوسون ِ Z   
boson-e Z

Fr.: boson Z   

An electrically neutral subatomic particle that along with → W boson mediates the → weak nuclear force. Like the photon, the Z boson is its own antiparticle.


Z Canis Majoris (Z CMa)

Fr.: Z CMa   

A luminous → FU Orionis object consisting of two young stars in a → binary system, a → Herbig Be star embedded in a dust cocoon and a less massive component located 0.1 arcsecond south-east. It is associated with a very large-scale and high-velocity → bipolar outflow extending in total 3.6 pc (for a distance of 1150 pc) with radial velocities up to -620 km/sec. The outflow is traced by a → jet and at least 15 → Herbig-Haro objects. In 2008 Z CMa showed the largest "outburst" ever reported in the past 90 years.

Canis Major.

Z source
  خن ِ Z   
xan-e Z

Fr.: source Z   

A member of a class of → low-mass X-ray binary systems containing low-magnetic field → neutron stars. See also → atoll source.

The name derives from the fact that on X-ray → color-color diagrams Z sources usually form a Z shape that is traced on timescales of hours to days; → source

  عدد ِ اتمی   
adad-e atomi (#)

Fr.: nombre atomique   

Same as → atomic number.

Z, from the German word Zahl "number, numeral, figure," which was used to specify an element's numerical place in the → periodic table; → number.

Zanstra method
  روش ِ زنسترا   
raveš-e Zanstra

Fr.: méthode de Zanstra   

The method of using the nebular observations to estimate the stellar ultraviolet radiation and the temperature of the central star in a planetary nebula. The basic assumptions are that the flux from a star could be approximately represented by the Planck function and that the nebula absorbs all the ultraviolet photons from the star which can cause ionization. For each ultraviolet photon absorbed an Hα photon is emitted when the ionized hydrogen subsequently recombines with an electron. Thus the strength of the Hα line is related to the ultraviolet flux of the star. However, modern theoretical work on stellar atmospheres shows that there are important deviations between the emergent fluxes from stars and Planck functions. Moreover, some of the stellar ultraviolet photons may be missed.

Named after the Dutch astrophysicist Herman Zanstra (1894-1972), who first introduced the method in 1927.

Zeeman effect
  اُسکر ِ زیمن   
oskar-e Zeeman

Fr.: effet Zeeman   

The splitting of spectral lines into closely-spaced components when the radiating substance is placed in a strong → magnetic field. Distinction is made between the normal and → anomalous Zeeman effects, and also the longitudinal and transverse Zeeman effects. In the normal → longitudinal Zeeman effect each spectral line is split into two components with frequencies ν ± Δν. In the normal → transverse Zeeman effect un un-displaced line is observed along with a doublet, i.e. three lines in all, with the frequencies ν and ν ±Δν. In the classical theory of the normal Zeeman effect, the motion of an electron in an atom is regarded as the harmonic oscillation of a linear harmonic oscillator. Arbitrary linearly polarized oscillation of the electron can be resolved into two oscillations: one along the magnetic field and the other in a plane perpendicular to this field. The latter can be further resolved into two oscillations, circularly polarized with opposite directions of rotation that occur in the Larmor precession frequency. Classical theory cannot explain the anomalous Zeeman effect. Both effects are accounted for in quantum mechanics as the result of changes in the energy levels of atomic electrons due to the interaction of their → orbital angular momentum and → spin angular momentum with each other and with the external magnetic field. See also → inverse Zeeman effect.

Named after Pieter Zeeman (1865-1943), Dutch physicist who discovered the phenomenon; → effect.

sarsu (#)

Fr.: zénith   

The point on the celestial sphere directly above the observer's head, opposite to the direction in which gravity acts. Opposite of → nadir.

M.E. cenith, from O.Fr. cenith, from M.L. cenit, senit, incorrect transliteration of Ar. samt (سمت) "path, direction," abbreviation of samt ar-ras (سمت‌الرأس), literally "road above one's head."

Sarsu, literally "the way over the head," from sarhead + su, → direction.

zenith distance
  دورای ِ سرسو، دوری ِ ~   
durâ-ye sarsu, duri-ye ~

Fr.: distance zénithale   

The angular distance of a celestial body from the zenith. The zenith distance is 90° minus the body's altitude above the horizon (i.e. the complement of the altitude) and hence is also known as coaltitude.

zenith; → distance

zenith hour rate (ZHR)
  نرخ در ساعت در سرسو   
nerx- dar sâ'at dar sarsu

Fr.: taux par heure au zénith   

The number of → meteors expected to be seen under ideal conditions if the → radiant of the → meteoroid stream is at the → zenith of the → observer.

zenith; → hour; → rate.

zenith telescope
  تلسکوپ ِ سرسو، دوربین ِ ~   
teleskop-e sarsu, dvrbin-e ~

Fr.: télescope zénithal   

A → telescope that is mounted on a → vertical axis or moves only a small amount from the vertical. It is primarily used to determine positional measurement of stars moving near the → zenith. The advantage is that there is no → atmospheric refraction occurring at the zenith. If a star on one night passes through the center of eyepiece, one must observe it six month later, and see if the star has been offset by the center. A shift would mean a measure of parallax. See also: → zenithal well.

zenith; → telescope


Fr.: zénithal   

Of or relating to the → zenith; located at or near the zenith.

zenith; → -al.

zenithal well
  چاه ِ سرسویی   
câh-e sarsuyi

Fr.: puit zénithal   

1) A well used in Antiquity from bottom of which the sky could be observed during the day with a better contrast. The aperture of the well reduced the light diffused by the sky.
2) A vertical tunnel in → Paris Observatory (built in 1667), from the top roof to the underground vaults, 55m deep. This well had the purpose of observing the stars near the → zenith and measure their → parallaxes. The problem was the lack of stability of the images so that the zenithal well was hardly used. See also: → zenith telescope.

zenithal; → well.


Fr.: zepto-   

A prefix of the → SI units, denoting 10-21. Symbol z.

From L. septem, → hepta-, since it is equal to 1/10007.

sefr (#)

Fr.: zéro   

1) The cardinal number of a class that has no members.
2) The only integer that is neither negative nor positive.
3) The → identity element for addition.

From Fr. zéro, from It. zero, from M.L. zephirum, from Ar. sifr (صفر) "cipher," translation of Skt. śūnya "empty place, void, naught." The rules governing the use of zero appeared for the first time in the Indian mathematician Brahmagupta's book Brahmasputha Siddhanta "The Opening of the Universe," written in 628.

zero age horizontal branch star (ZAHB)
  ستاره‌ی ِ شاخه‌ی ِ افقی با سن ِ صفر   
setâre-ye šâxe-ye ofoqi bâ senn-e sefr

Fr.: étoile de la branche horizontale d'âge zéro   

A star that has arrived on the → horizontal branch after leaving the → red giant branch. It begins → helium burning in its core.

zero; → age; → horizontal; → branch; → star.

zero age main sequence (ZAMS)
  رشته‌ی ِ فریست با سن ِ صفر   
rešte-ye farist bâ senn-e sefr

Fr.: séquence principale d'âge zéro   

The position on the → Hertzsprung-Russell diagram for newborn stars which have just started → hydrogen burning in their cores. The ZAMS forms the lower luminosity boundary of of the → main sequence strip. See also → terminal age main sequence (TAMS).

zero; → age; → main sequence.

zero matrix
  ماتریس ِ صفر   
mâtris-e zefr

Fr.: matrice nulle   

Same as → null matrix.

zero; → matrix.

zero method
  روش ِ صفر   
raveš-e sefr

Fr.: méthode de zéro   

same as → null method.

zero; → method.

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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