An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 442
Hertz experiment
  آزمایش ِ هرتز   
âzmâyeš-e Hertz (#)

Fr.: expérience de Hertz   

A laboratory experiment carried out by Heinrich Hertz in 1888 to generate and detect → electromagnetic waves for the first time. It involved a high voltage power source, consisting of two → capacitors, each provided with a conducting rod. The rods were separated by a small → spark gap and connected to an → induction coil. When the electrodes were raised to a sufficiently high → potential difference, a spark passed across the gap, and an oscillating discharge took place. A group of waves with a wavelength of a few meters were emitted at each discharge. A wire loop provided with a detecting spark gap, held away from the oscillating sparks, produced sparks upon arrival of the oscillating electric and magnetic fields.

hertz (Hz); → experiment.

hertz to meter conversion
  هاگرد ِ هرتز به متر   
hâgard-e hertz bé metr

Fr.: conversion hertz / mètre   

frequency to wavelength conversion.

hertz; → meter; → conversion.

Hertzian oscillator
  نوشگر ِ هرتزی   
navešgar-e Hertzi

Fr.: oscillateur hertzien   

An electrical system used for the production of → electromagnetic waves. It consists of two equal → capacitors connected to two electrodes with a → spark gap between the electrodes. The system is connected to an → induction coil. When the induction coil is activated, electromagnetic waves are generated across the spark gap. See also → Hertz experiment.

hertz (Hz); → oscillator.

Hertzsprung gap
  گاف ِ هرتسپرونگ   
gâf-e Hertzsprung

Fr.: trou de Hertzsprung   

A region of the → Hertzsprung-Russell diagram, between the → main sequence and the → giant branch, occupied by very few stars. It corresponds to a very short period in stellar evolution.

Named after the Danish astronomer Ejnar Hertzsprung (1873-1967), who first noticed this phenomenon; → gap

Hertzsprung-Russell diagram
  نمودار ِ هرتسپرونگ-راسل   
nemudâr-e Hertzsprung-Russell (#)

Fr.: diagramme de Hertzsprung-Russell   

A display of stellar properties using a plot of → effective temperature (or instead → color or → spectral type) along the abscissa versus → luminosity (or → absolute magnitude). The temperature is plotted in the inverse direction, with high temperatures on the left and low temperatures on the right. On the diagram the majority of stars are concentrated in a diagonal strip running from upper left to lower right, i.e. from high temperature-high luminosity → massive stars to low temperature-low luminosity → low-mass stars. This feature is known as the → main sequence. This is the locus of stars burning hydrogen in their cores (→ proton-proton chain). The lower edge of this strip, known as the → zero age main sequence (ZAMS), designates the positions where stars of different mass first begin to burn hydrogen in their cores. Well below the main sequence there is a group of stars that, despite being very hot, are so small that their luminosity is very small as a consequence. These are the class of → white dwarfs. These objects represent old and very evolved stars that have shed their outer layers to reveal a very small but extremely hot inner core. They are no longer generating energy but are merely emitting light as they cool (→ white dwarf cooling track). Stars with high luminosities but relatively low temperatures occupy a wide region above the main sequence. The majority of them have used up all the hydrogen in their cores and have expanded and cooled as a result of internal readjustment. Called → red giants, they are still burning helium in their cores (→ helium burning, → carbon burning). There are also stars with very high luminosities, resulting from their enormous outputs of energy, because they are burning their fuel at a prodigious rate. These are the → supergiants. They can be hot or cool, hence blue or red in color. Same as → H-R diagram.
See also:
asymptotic giant branch, → blue horizontal branch star, → extreme horizontal branch star, → field horizontal branch star, → Hayashi track, → horizontal branch, → post-asymptotic giant branch star, → red giant branch, → supra-horizontal branch star, → zero age horizontal branch star, → Humphreys-Davidson limit.

Named after the Danish Ejnar Hertzsprung (1873-1967) and the American Henry Norris Russell (1877-1957). However, the first H-R diagram was published not by Hertzpurung neither Russell, but by a PhD student of Karl Schwarzschild at Göttingen. The student was Hans Rosenberg (1879-1940), who in 1910 published the diagram for stars in the → Pleiades (Astronomische Nachrichten, Vol. 186 (4445), p. 71, 1910). Although Hertzpurung had a very preliminary diagram in 1908, his first proper diagram was published in 1911. Likewise, Russell published his version only in 1915 with the better and more numerous data then available (Nielsen, A.V., 1969, Centaurus 9, 219; Valls-Gabaud, D., 2002, Observed HR diagrams and stellar evolution, ASP Conf. Proceedings, Vol. 274. Edited by Thibault Lejeune and João Fernandes); → diagram.

Hesperian era
  دوران ِ هسپریسی   
dowrân-e hesperisi

Fr.: ère hespérienne   

The Martian geologic era after the Noachian Era which lasted from about 3500 million to 2500 million years ago. During this period Martian climate began to change to drier, dustier conditions. Water that flowed on the Martian surface during the Noachian Era may have frozen as underground ice deposits, and most river channels probably experienced their final flow episodes during this era. → Noachian era; → Amazonian era.

Named after the Martian plains of Hesperis; → era.

  ستاره‌ی ِ شامگاه   
setâre-ye šâmgâh (#)

Fr.: étoile du soir   

An → evening star, especially the planet Venus in its appearance as the evening star.

M.E., from L., from Gk. hesperos "evening, western;" → west.

Setâre-ye šâmgâh "evening star," from setâréstar + šâmgâh "evening," from šâm "evening, evening meal" + gâh "time." The first component, šâm, from Mid.Pers. šâm "evening meal, supper," from Av. xšāfnya- "evening meal," from Av. xšap-, xšapā-, xšapan-, xšafn- "night" (O.Pers. xšap- "night," Mid.Pers. šap, Mod.Pers. šab "night"); cf. Skt. ksap- "nigh, darkness;" Hittite ispant- "night." The second component gâh "time," Mid.Pers. gâh, gâs "time," O.Pers. gāθu-, Av. gātav-, gātu- "place, throne, spot;" cf. Skt. gâtu- "going, motion; free space for moving; place of abode;" PIE *gwem- "to go, come."

HESS collaboration
  همکاری ِ HESS   
hamkâri-ye HESS

Fr.: collaboration HESS   

High Energy Stereoscopic System (H.E.S.S.).

H.E.S.S.; → collaboration.

Hess diagram
  نمودار ِ هس   
nemudâr-e Hess

Fr.: diagramme de Hess   

A diagram showing the relative density of occurrence of stars at various → color-magnitude positions of the → Hertzsprung-Russell diagram for a given → galaxy.

Named after R. Hess who originated it in 1924: "Die Verteilungsfunktion der absoluten Helligkeiten in ihrer Abhängigkeit vom Spektrum". Probleme der Astronomie. Festschrift fur Hugo v. Seeliger. Springer, Berlin. p. 265; → diagram.

degar- (#)

Fr.: hétéro-   

Prefix denoting "other, different."

From Gk. heteros "the other (of two), another, different."

Degar "another, other;" from Mid.Pers. dit, ditikar "the other, the second;" O.Pers. duvitiya- "second," Av. daibitya-, bitya- "second;" Skt. dvitiya- "second," PIE *duitiio- "second."

heterodin (#)

Fr.: hétérodyne   

1) Originally, the technique invented by the Canadian engineer Reginald Fessenden (1866-1932) to combine two signals to produce a third audible tone. However, heterodyne reception was not fully practical for a decade after it was invented. It required producing a stable local signal, which awaited the advent of the oscillating vacuum tube.
2) The term heterodyne is often loosely used instead of → superheterodyne in the radio frequency field.

Heterodyne, from → hetero- + -dyne, from Gk. dynamicsdynamics; → receiver.

heterodyne receiver
  گیرنده‌ی ِ هترودینی   
girande-ye heterodini (#)

Fr.: récepteur hétérodyne   

superheterodyne receiver.

heterodyne; → receiver.

heterodyne technique
  تشنیک ِ هترودین   
tašnik-e heterodin

Fr.: technique hétérodyne   

superheterodyne technique.

heterodyne; → technique.


Fr.: hétérogénéité   

The quality or state of being → heterogeneous. See also → homogeneity, → inhomogeneity.

Noun from → heterogeneous.


Fr.: hétérogène   

1) Composed of parts of different kinds; having widely dissimilar elements or constituents. See also → homogeneous, → inhomogeneous.
2) Chemistry: A mixture that does not have uniform composition and properties throughout; composed of different substances or the same substance in different phases.

hetero- + -genous, → homogeneous.


Fr.: heuristique   

Methodology, Math.: Pertaining to a method of analyzing outcome through comparison to previously recognized patterns in the absence of an → algorithm for formal proof.

From L. heuristicus (from Gk. heuretikos "inventive," related to heuriskein "to find," from heur-) + -isticus, → -ic.

Yâftik, from yâft past tense of yâftan, yâb- "to → find" + -ik, → -ic.

šeš- (#)

Fr.: hexa-   

A prefix meaning → six. → hexagon.


  شش‌بر، شش‌گوش   
šešbar (#), šešguš (#)

Fr.: hexagone   

A six-sided → polygon.

hexa-; → -gon;.

Hickson Compact Group (HCG)
  گروه ِ همپک ِ هیکسون   
goruh-e hampak-e Hickson

Fr.: groupe compact de Hickson   

A list of 100 compact groups of galaxies that were identified by a systematic search of the → Palomar Observatory Sky Survey red prints. Each group contains four or more galaxies, has an estimated mean surface brightness brighter than 26.0 magnitude per arcsec2 and satisfies an isolation criterion.

Hickson, Paul, 1982, ApJ 255, 382; → compact; → group.

penhân (#)

Fr.: caché   

Being out of sight; concealed.

From M.E., from O.E. hydan, from W.Gmc. *khuthjanan, from PIE *keudh- (cf. Gk. keuthein "to hide, conceal"), from base *(s)keu- "to cover, conceal."

Penhân "hidden," from Mid.Pers. pad nihân, from pad "to, at, for, in" (from O.Pers. paity; Av. paiti "to, toward, in, at;" cf. Skt. práti; Gk. poti) + nihân "concealment, secrecy, hiding place" (Mod.Pers. nahân), from Proto-Iranian *ni-dāna-, from ni- "down; into," → ni- (PIE), + dā- "to put; to establish; to give" (dadâiti "he gives;" cf. Skt. dadâti "he gives;" Gk. didomi "I give;" L. do "I give;" PIE base *do- "to give").

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