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 to meter conversion
hâgard-e hertz bé metr
Fr.: conversion hertz / mètre
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.
Fr.: trou de Hertzsprung
Named after the Danish astronomer Ejnar Hertzsprung (1873-1967), who first noticed this phenomenon; → gap
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
(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.
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.
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.
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 setâré→ star + 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."
Fr.: collaboration HESS
Fr.: diagramme de Hess
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.
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."
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.
girande-ye heterodini (#)
Fr.: récepteur hétérodyne
Fr.: technique hétérodyne
Noun from → heterogeneous.
1) Composed of parts of different kinds; having widely dissimilar elements or constituents.
See also → homogeneous,
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.
šešbar (#), šešguš (#)
A six-sided → polygon.
Hickson Compact Group (HCG)
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.
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").