Meh Romb, rombeš-e farjâmin
Fr.: big crunch
The state of extremely high density and temperature into which a closed → Universe would → collapse in the distant future. If the Universe has a mass density exceeding the critical threshold, then gravity will eventually halt the expansion and cause the Big Crunch.
→ big; crunch "to crush, grind, or tread noisily; the act or sound of crunching," alteration of craunch, possibly of imitative origin.
Fr.: méthode de Biruni
A method devised by the Iranian astronomer Biruni (973-1048) to measure the Earth radius, using trigonometric calculations. In contrast to foregoing → Eratosthenes' method and → Mamun's method, which required expeditions to travel long distances, Biruni's method was on-site. He carried out the measurement when he was at Nandana Fort (at the southern end of the pass through the Salt Range, near Baghanwala in the Punjab). He first calculated the height of a hill (321.5 m). To do this he used the usual method of observing the summit from two places in a straight line from the hill top. He measured the distance, d, between the two places and the angles θ1 and θ2 to the hill top from the two points, respectively. He made both measurements using an astrolabe. The formula that relates these angles to the hill height is: h = (d. tan θ1 . tan θ2) / (tan θ2 - tan θ1). He then climbed to the hill top, where he measured the → dip angle (θ), that is the angle of the line of sight to the horizon. He applied the values he obtained for the dip angle and the hill's height to the following trigonometric formula to derive the Earth radius: R = h cosθ / (1 - cos θ). The result for the Earth radius was 12,851,369.845 cubits (or 6335.725 km, using favorable conversion units). Despite the fact that the method is very ingenious, such a precise value is only by chance, because of several drawbacks: The plane was not perfectly flat to serve as the smooth surface of the sea. A measuring instrument more accurate than the alleged 5 arc minutes was needed. And the method suffered from the → atmospheric refraction (See, e.g., Gomez, A. G., 2010, Journal of Scientific and Mathematical Research).
Abu Rayhân Mohammad Biruni (973-1048 A.D.), one of the greatest scholars of the medieval era, was an Iranian of the Khwarezm region; → method.
Bonner Durchmusterung (BD)
Fr.: Bonner Durchmusterung
A catalog of 324,188 stars in the → declination zones +89 to -01 degrees. The goal of the survey was to obtain a → position and estimated → visual magnitude for every star visible with the 78 mm → refracting telescope at Bonn. Actual → magnitude estimates were made and reported to 0.1 mag for all stars down to 9.5 mag. Positions are given to the nearest 0.1 sec in → right ascension and 0.1 arcmin in declination. The survey was carried out by Friedrich W. Argelander (1799-1875) and his assistants in the years 1852-1861.
The Ger. name means Bonn Survey.
Fr.: fréquence de Brunt-Väisälä
The frequency at which an air parcel will oscillate when subjected to an infinitesimal perturbation in a stably stratified atmosphere. For a medium with a continuous density gradient, it is expressed by the formula: N2 = -(g/ρ)∂ρ/∂z , where g is the → gravitational acceleration, ρ is density, and z geometric height. The stability condition is N > 0. It is also sometimes referred to as the buoyancy frequency. The higher the value of N the more stable the flow.
Named aster David Brunt (1886-1965), British meteorologist (1927, Q.J.R.Met.Soc. 53, 30) and Vilho Väisälä (1889-1969), Finnish meteorologist (1925, Soc. Sci. Fenn. Commental. Phys. Math. 2 (19), 19); → frequency.
kolkard-e disk, ~ gerdé
Fr.: troncature de disque
In models of magnetized → accretion disks, the process whereby the disk is disrupted at a radius where the → magnetic pressure overcomes the → ram pressure of the accreted material. This occurs at a distance typically 3-7 stellar radii, below the → corotation radius.
Fr.: trompe d'éléphant
An elongated structure of → interstellar dust and gas which absorbs the radiation from background stars in an → H II region. These structures are the denser remnants of → molecular clouds from which → massive stars are formed. Elephant trunks are eventually dissipated by the action of the → ionizing radiation and → stellar wind of the associated massive stars. A remarkable example of these structures is displayed by the → HST image of the → Eagle Nebula as → pillars of obscuring matter protruding from the interior wall of a dark molecular cloud. Some → Bok globules may represent the remaining densest fragments of elephant trunks.
M.E. elephant, from O.Fr. olifant, from L. elephantus, from Gk. elephas "elephant, ivory," probably from a non-I.E. language, likely via Phoenician; trunk, from M.E. trunke, O.Fr. tronc, from L. truncus "stem, trunk, stump."
Xortum "the proboscis of an elephant," loanword from Ar. xartum; fil, pil "elephant," from Mid.Pers. pil "elephant;" O.Pers. piru- "ivory."
Elephant's Trunk Nebula
miq-e xortum-e fil
Fr.: Nébuleuse de la trompe d'éléphant
An elongated dark structure of gas and dust in the → H II region IC 1396. It spans about 5 degrees on the sky in the constellation → Cepheus, about 2400 → light-years from the Earth. The Elephant Trunk Nebula is believed to be site of star formation, containing several very young stars. It is an example of → elephant trunks associated with star forming regions.
Fr.: gérondif, substantif verbal
A noun formed from a verb, denoting an action or state. In English, the gerund is the "-ing" form of a verb when it functions grammatically as a noun in a sentence; it is identical in appearance to the present participle.
From L.L. gerundium, from gerundum "to be carried out," gerundive of gerere "to bear, carry."
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.: période d'observation
A period of telescope time for observations allocated to a science project.
An interval or period during which something, as a machine, operates or continues operating. → observing run.
Run, noun from verb, from M.E. ronnen, alteration of rinnen, (from O.E. rinnan and O.N. rinna) and of rennen, from O.N. renna; akin to O.H.G. rinnan; Ger. rinnen "to flow, run;" Skt. rinati "he causes to flow," and probably to L. rivus "stream;" PIE base *rei- "to flow."
Dâv "a move, a turn (at play)," dâv zadan (kardan) "to make a move (at game)," variant dow (e.g. dow bé dast-e kasi oftâdan), maybe related to dow "run," from davidan, dav- "to run;" Mid.Pers. dawidan, daw- "to run;" cf. Skt. dhāv- "to walk, hurry, flow," dhāvati "flows, runs;" Gk. thoos "fast, quick;" O.E. deaw; E. dew; PIE base *dheu- "to flow."
Fr.: étoile en fuite
A massive, young, and hot star that is moving quickly through space. Runaways are probably propelled through space from a binary star when its companion has exploded as a supernova, or ejected from a stellar cluster by the dynamical interactions in the system.
Setâré, → star; gorizân present participle of goriz-, gorixtan "to escape; to flee, run away;" Mid.Pers. virextan; Proto-Iranian *vi-raik, from vi- "apart, asunder" + *raik; Av. raek- "to leave, set free, let off;" Mid./Mod.Pers. reg/rig (in mordé-rig "inheritance"); Skt. ric- "to leave," rinakti "gives up, evacuates;" Gk. leipein "to leave;" L. linquere "to leave;" from PIE *linkw-, from *leikw- "to leave behind" (cf. Goth. leihvan; O.E. lænan "to lend;" O.H.G. lihan "to borrow;" O.N. lan "loan").
The water or other liquids that drains or flows from the land into streams and rivers, eventually into seas.
Ravânâb, literally "flowing water," from ravân "flowing, running," pr.p. of raftan "to go, walk; to flow" (Mid.Pers. raftan, raw-, Proto-Iranian *rab/f- "to go; to attack" + âb, → water.
vâžireš-e garmâhaste-yi-e legâm gosixté
Fr.: emballement thermonucléaire
Vâžireš, → reaction; garmâhaste-yi, → thermonuclear; legâm gosixté literally "rampant, unrestrained," from legâm "bridle, rein" + gosixté "broken off, torn away," p.p. of gosixtan "to tear away, to break off."
To shorten by cutting off a part.
From L. truncatus "cut off," p.p. of truncare "to maim, cut off," from truncus "mutilated, cut off."
Kol kardan "to cut off the end of; to dock a tail," from kol "docked, short," variants in a large number of dialects: kola, kalta, kel, kelma, koc, kall, kor, kul in Gilaki, Tâleši, Lori, Malâyeri, Hamedâni, Qâeni, and others, cf. Av. kaurvô- "bald, docked," kaurvôduma- "with a bald tail," kaurvôgaoša- "with bald ears;" cf. Gk. kol(os) "docked" (kolouros "dock-tailed;" L. colurus) + kardan "to do, to make" (Mid.Pers. kardan, O.Pers./Av. kar- "to do, make, build," Av. kərənaoiti "makes," cf. Skt. kr- "to do, to make," krnoti "makes," karma "act, deed;" PIE base kwer- "to do, to make").
The act or process of truncating, as → disk truncation.
Verbal noun from → truncate.