An Etymological Dictionary of Astronomy and Astrophysics
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فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 13116 Search : far
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

zenithal
  سرسویی   
sarsuyi

Fr.: zénithal   

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

zenith; → -al.

zenithal well
  چاه ِ سرسویی   
câh-e sarsuyi

Fr.: puits 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 resulting from the Earth motion around Sun. A long plumb line was attached to the top of the well. Astronomers thought they could measure the stellar shifts with respect to the plumb line. The problem was, however, the lack of stability of the images, because the well acted in fact as a chimney generating turbulence. So that the zenithal well was hardly used. See also: → zenith telescope.

zenithal; → well.

zepto-
  زپتو-   
zepto-

Fr.: zepto-   

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

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

zero
  صفر   
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.

zero polynomial
  بلنامین ِ صفر   
bolnâmin-e sefr

Fr.: polynôme nul   

A → polynomial whose → coefficients are all zero. See also → non-zero polynomial.

zero; → polynomial.

zero suppression
  نهاوش ِ صفر   
nehâveš-e sefr

Fr.: suppression de zéro   

The removal of non-significant zeroes from a number. For example, replacing 531.2300 by 531.23.

zero; → suppression.

zero-velocity surface
  رویه‌ی ِ تندای ِ صفر   
ruye-ye tondâ-ye sefr

Fr.: surface de vitesse nulle   

In the → restricted three-body problem, a surface which limits the region of space in which a small body can move. In the expression for the → Jacobi integral, the left side value is always positive or nul; hence the particle motion is confined to the region where U ≤ CJ. The surface that limits this region, defined by U = CJ, is called the zero-velocity surface.

zero; → velocity; → surface.

zeroth law of thermodynamics
  قانون ِ صفرُم ِ گرماتوانیک   
qânun-e sefrom-e garmâtavânik

Fr.: loi zéro de la thermodynamique   

Two objects that are in → thermal equilibrium with a third object will be in thermal equilibrium with each other.

zero; → law; → thermodynamics.

Zeta Ophiuchi
  زتا-مار‌افسا   
Zetâ Mâr-afsâ

Fr.: ζ Ophiuchi   

A blue star, also called HD 149757 and HR 6175, which is the nearest, and probably the most widely studied, → massive star. It is variable in several wavelength bands and has a mean visual magnitude of V = 2.58, B - V = 0.01. It lies ~ 222 pc away and has a formal spectral type of O9.5 Ve and a luminosity of 105 Lsun. ζ Ophiuchi is a very rapid rotator with a v sin i ~ 400 km s-1, i.e. ~ 85% of the → break-up velocity. It is one of the earliest prototypes of the → Be phenomenon. Moreover, it shows episodes of Hα emission variability, a common feature of Be/Oe stars. It also shows periodic non-radial pulsations and UV → P Cygni profile variability, as is evident in the periodic behavior of → discrete absorption components (DACs). It has a → mass loss rate of 10-7 Msun yr-1 and a → terminal velocity of wind v = 1550 km s-1. ζ Ophiuchi is a well-known → runaway star with a velocity of 30 km s-1. The interstellar → CH molecule and → CN molecule were first detected toward ζ Ophiuchi. It has been recognized for some time that this star lies close to the blue edge of the → beta Cephei instability strip.

Zeta (ζ), according to the → variable star designation system; Ophiuchi, → Ophiuchus.

Zeta Orionis
  زتا-شکارگر، زتا-اریون   
zetâ-Šekârgar, zetâ-Orion

Fr.: Zeta (ζ) Orionis   

Same as → Alnitak.

Zeta (ζ), Gk. letter in the → Bayer designation scheme.

zetta-
  زتا-   
zetta-

Fr.: zetta-   

A prefix of the → SI units, denoting 1021. Symbol: Z.

From L. septem, → hepta-, by replacing the initial s with z to distinguish from → zepto-. It is equal to 10007.

Zhevakin's zone
  زنار ِ ژواکین   
zonaar-e Zhavakin

Fr.: zone de Zhevakin   

One of several regions of the stellar interior where increased → opacity can provide the necessary → valve mechanism to drive → stellar pulsations. Also called → partial ionization zone.

Named after the Russian astronomer Sergei A. Zhevakin (1916-2001), who identified these zone in the 1950s; → mechanism.

<< < -es -iv -ti 21 a p abe abs abs aca acc acc acr act ada adh Adr aer aga air Alf Alg alk Alp alt alu amm ana And ang ani ano ant ant Ap apo app app Aqu Arc arg arr asc ass ast ast asy atm ato att aur aut axi B-m bad Bal bar bar Bay Bed ber Bet bif bim bin bio bis bla ble blu Bod Bol bor bou Bra Bre bro bul C-t Cal Cam can car Car Cas cat cav cel cen cer Cha cha Cha che chl Cir cir cir Cla cli clo clu co- coc coh col col col Com com com com com com com com Com con con con con con con con con con con con con coo Cor Cor cor cos cos cos Cou cou Cra Cre cri cro cub cur cyc cyl Dan dat Dav de- Deb dec dec dee def deg del Den den der det deu dew dic dif dif dil Dip dir dis dis dis dis dis diu dod Dop dou Dra dua dus dwa dyn DZ Ear ecc eco edi EHB Ein ela ele ele ele ele ell eme emp end Eng ent epi equ equ era ESP eth Eur evi exa exc exe exi exp exp ext ext ext fac fal far fec Fer fer fie fin fir fis fla Flo flu fog for for Fou fra fre fre Fro fun G s Gal gal gal Gar gau geg gen geo geo geo ger gla gly gra gra gra gra gra Gre gro GYR Had Hal hap Har HD hea hel hel Hen Her hex hig Hil hol Hoo hor hou Hub hum hyb hyd hyd hyp hys ide ign ima imp imp in- inc Ind ind ine inf inf inf ini ins ins ins int int int int Int int int int inv ion iri irr iso iso iso Jea Jor jum K c Kep Ker kin kno lab Lam Lan Lap las lat Le lef len lev lig lig lin lin lin liq Lit loc log lon lou LS lun lun Lym M s Mag mag mag mag mag mag maj man Mar mas mas mat May mea mec mel mer mes met met met mic mid mil Min Mir mix mod mod mol mon mor mov mul mur mys nan nat nav nec Nep neu New New NGC nob nom non non nor nos nuc nuc num nut obj obl obs occ oct off oli oni ope opp opt opt orb ord org orp osc out ove oxi P-w pal par par par par Pas pat pej per per per per per per pha Phe pho pho pho phy pin pla Pla pla pla pla plu poi pol pol Pol pol por pos pot Poy pre pre pre pre pri pri pri pro pro pro pro pro pro Psa pul pum Q i qua qua qua qua R A rad rad rad rad rad rad Ram Ran rat rea rea rec rec red red ref ref reg rei rel rel rem rep res res res ret rev Rho Rie ril riv rog Ros rot rul S A Sag sam sat sca sca Sch Sco Sec sec sec seg sel sem sen set Sha sha shi sho sid sig sim sin Sir ske sli Smo soc sof sol sol sol sol sou sou spa spe spe Spe spe sph spi Spi spr sta sta sta sta sta ste ste ste Sto str str sub sub sub suc sun sup sup sup sup sur swa syn syn tac tas tel tem ter tes the the the the thi thr tid til tip ton tor tou tra tra tra tra Tri tri tru tsu tur two Typ UHE ult unc uni uni uni upg ura uti val var vec Vel ver Ver vie Vir vis vis vol W-R war wav wav wea Wei wha wid win WN3 Wol wri xen yok zen zij > >>