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: 13176 Search : in
Lyman continuum
  پیوستار ِ لایمن   
peyvastâr-e Lyman (#)

Fr.: continuum de Lyman   

A continuous range of wavelengths in the spectrum of hydrogen at wavelengths less than the → Lyman limit. The Lyman continuum results from transitions between the → ground state of hydrogen and → excited states in which the single electron is freed from the atom by photons having an energy of 13.6 eV or higher.

Lyman; → continuum.

Lyman continuum escape
  گریز ِ پیوستار ِ لایمن   
goriz-e peyvastâr-e Lyman

Fr.: échappement du continuum de Lyman   

The process whereby → Lyman continuum photons produced by → massive stars escape from a galaxy without being absorbed by interstellar material. Some observations indicate that the Lyman continuum escape fraction evolves with → redshift.

Lyman; → continuum; → escape.

Lyman ghost
  پرهیب ِ لایمن   
parhib-e Lyman (#)

Fr.: image fantôme de Lyman   

In spectroscopy, a false image of a spectral line formed by irregularities in the ruling of diffraction gratings.

Lyman, → ghost.

Lyman limit
  حد ِ لایمن   
hadd-e Lyman

Fr.: limite de Lyman   

The short-wavelength end of the hydrogen Lyman series, at 912 Å. Also called → Lyman continuum. It corresponds to the energy (13.6 eV) required for an electron in the hydrogen ground state to jump completely out of the atom, leaving the atom ionized.

Lyman; → limit.

Lyman series
  سری ِ لایمن   
seri-ye Lyman (#)

Fr.: séries de Lyman   

A series of lines in the spectrum of hydrogen, emitted when electrons jump from outer orbits to the first orbit. The Lyman series lies entirely within the ultraviolet region. The brightest lines are Lyman-alpha at 1216 Å, Lyman-beta at 1026 Å, and Lyman-gamma at 972 Å.

Lyman; → series.

Lyman-Werner photon
  فوتون ِ لایمن-ورنر   
foton-e Lyman-Werner

Fr.: photon de Lyman-Werner   

An → ultraviolet photon with an energy between 11.2 and 13.6 eV, corresponding to the energy range in which the Lyman and Werner absorption bands of → molecular hydrogen (H2) are found (→ Lyman band, → Werner band). The first generation of stars produces a background of Lyman-Werner radiation which can → photodissociate molecular hydrogen, the key → cooling agent in metal free gas below 104 K. In doing so, the Lyman-Werner radiation field delays the collapse of gaseous clouds, and thus star formation. After more massive → dark matter clouds are assembled, atomic line cooling becomes effective and H2 can begin to shield itself from Lyman-Werner radiation.

Lyman; → Werner band; → photon.

Lynx
  سیاهگوش   
Siyâhguš (#)

Fr.: Lynx   

The Lynx. A faint → constellation in the northern hemisphere that lies between → Auriga to the west and → Ursa Major to the east, at about 8h right ascension, 45° north declination. Abbreviation: Lyn; genitive: Lyncis.

From L. lynx, from Gk. lynx, probably from PIE *leuk-, → light, in reference to its gleaming eyes or its ability to see in the dark (cf. Lith. luzzis, O.H.G. luhs, Ger. Luchs, O.E. lox, Du. los, Swed. lo "lynx").

Siyâhguš "lynx," literally "black ear," from siyâh "black," from Mid.Pers. siyâ, siyâk, siyâvah "black," Av. sâma-, sayâva- "black, dark," cf. Skt. syama-, syava- "black, brown," Gk. skia "shadow" + guš, → ear.

Lyot division
  شکاف ِ لی‌یو   
šekâf-e Liyot (#)

Fr.: division de Lyot   

In Saturn's rings, the gap between rings B and C.

Named after Bernard Lyot (1897-1952), French astronomer who discovered the division. He was also a distinguished solar observer and invented (1930) the → coronagraph; → division.

Lyot filter
  پالایه‌ی ِ لی‌یو   
pâlâye-ye Lyot (#)

Fr.: filtre de Lyot   

A type of narrow-band filter consisting of a series of birefringent crystals and polarizers invented by the French astronomer Bernard Lyot (1897-1952) for isolating and observing significant wavelengths of solar light.

Lyot division; → filter.

Lyra
  چنگ   
Cang (#)

Fr.: Lyre   

The Lyre. A small, bright constellation in the northern hemisphere at about 19h right ascension, 40° declination. The brightest star in Lyra is → Vega.

L. lyra, from Gk. lyra, a foreign word of uncertain origin.

Cang "harp," frpm Mid.Pers. cang "harp."

Lyrids
  چنگیان   
Cangiyân (#)

Fr.: Lyrides   

A meteor shower that occurs between 18 and 24 April. Its radiant is in the constellation → Lyra.

Lyra + → -ids.

Lysithea (Jupiter X)
  لوسیته‌آ   
Lusitea (#)

Fr.: Lysithéa   

The eleventh of Jupiter's known satellites; it is 36 km across and orbits Jupiter at a distance of about 11,720,000 km with a period of 259 days. It was discovered by S. Nicholson in 1938.

Lysithea was a daughter of Oceanus and one of Zeus' lovers.

M dwarf
  کوتوله‌ی ِ M   
kutule-ye M

Fr.: naine M   

A star whose spectrum is dominated by the absorption bands of → titanium oxide (TiO) and → vanadium oxide (VO) and has many neutral metal lines. The → effective temperature of M dwarfs ranges from about 3850 to 2600 K. They are low mass stars with masses ranging from 0.6 times that of the Sun at spectral type M0 to less than 0.1 → solar masses. M dwarfs are very abundant, they account for about 70-80% of stars in the → Galactic disk. The nearest star to the Sun, → Proxima Centauri, is an M dwarf.

M, letter of alphabet in the → Harvard classification; → dwarf.

M star
  ستاره‌ی ِ M   
setâre-ye M (#)

Fr.: étoile de type M   

A cool, red star of spectral type M with a surface temperatures of less than 3600 K. The spectra of M stars are dominated by molecular bands, especially those of TiO. Naked-eye examples are Betelgeuse and Antares.

M, letter of alphabet, → star.

M-type asteroid
  سیارک ِ گونه‌ی ِ M   
sayârak-e gune-ye M

Fr.: astéroïde de type M   

A type of → asteroid that consists of metallic → iron and displays high → albedo (0.10-0.18). M-type asteroids inhabit the middle part of the → asteroid belt.

M for → metallic; → type; → asteroid.

M16
     
M16

Fr.: M16   

An → open cluster in the constellation → Serpens associated with the → Eagle Nebula. It is usually mistakenly stated as being that nebula. Also called NGC 6611. First discovered by Philippe Loys de Chéseaux in 1745-6.

Object bearing the number 16 in the → Messier catalog.

Mach angle
  زاویه‌ی ِ ماخ   
zâviye-ye Mach

Fr.: angle de Mach   

Half of the vertex angle of the → Mach cone generated by a body in → supersonic flight. It is given by sin μ = (a/v), where a is the speed of the sound waves and v the velocity of the object. In terms of Mach number: μ = asin (1/M). The Mach angle diminishes with the object velocity. For M = 1 it is 90°, for M = 2, it is 30°, and for M = 5, its is 11.5°.

Mach number; → angle.

Mach cone
  مخروط ِ ماخ   
maxrut-e Mach

Fr.: cône de Mach   

The cone that confines the pressure disturbance created by a → supersonic object moving in a → compressible medium.

Mach number; → cone.

Mach disk
  گرده‌ی ِ ماخ، دیسک ِ ~   
gerde-ye Mach, disk-e ~

Fr.: disque de Mach   

Same as → shock diamond.

So named because Ernst Mach (1838-1916) was the first to record its existence.

Mach number
  عدد ِ ماخ   
adad-e Mach (#)

Fr.: nombre de Mach   

The ratio of the speed of a moving object to the → sound speed in the medium through which the object is traveling.

Named after the Austrian physicist Ernst Mach (1838-1916); → number.

<< < -es -it -sc 201 951 abe abs abs aca acc acc aco act ada adh ado aer aft air Alf alg alk alp Alt alt amb ana And ang ani ann ant ant ant apo app app Apu arc arg Arn art ass ast ast ast atm ato att aur aut avo azi bac bal bar bar bat Bea Bel bet bia big bin bio Bir bla bla blo Blu bol Boo bou box bre Bri bro bur cal cal Can cap car Car cat cau cel cen cen cha Cha cha che Chi chr cir cir civ cla clo clo CMB coa coe 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 cri cro cry cul cur cyc D l dar dat day dea dec dec dec def def deg Del Den dep der det deu dew dic dif dif dil dip dir dis dis dis dis dis diu dog Dop dou Dra Dsc dus dwa dyn Dys Ear ecc eco edg egg Ein Ela ele ele ele ele ell eme emp enc eng ent epi equ equ equ eru eth Eur eve exa exc exe exi exo exp ext ext ext fab fai Fan fea fem fer fie fil fir fir fla fli flu foc for for for fra fre fre fri fun fuz gal gal gal Gam gau Gau gen geo geo geo geo Gib glo gov gra gra gra gra gre gro Gui H-a hal Ham har Hay hea hei hel Hel her het hie hig hoa hom hor hot Hub Hug hur hyd hyd hyl hyp ice ide ima ima imp imp inc inc ind ine inf inf inf ing inn ins ins int int int int int int int int inv inv ion iro Isl iso iso Jab jet Jov Jup Kar Kep kil Kip Kra Lag Lam Lan Lar las law lea Leg Leo lev lig lim lin lin lin lit loc loc log Lor low lum lun lun Lym Mac mag mag mag mag mag mai Mal map mas mas mat Mau mea mea med Men mer Mes Met met mic mic Mie mil min Mir mix mod mol mom Moo mor mov mul mur n-b nan nat nea neg Ner neu new New NGC noc nom non non nor nor nuc nuc nul nut obj obl obs occ oct off old one ope opp opt opt orb ord org Ori osc oth ove Owl P-s Pal par par par par Pas pat pec pen per per per per per Pha pha pho pho pho phy pie pix Pla pla pla pla Pli Poi pol pol pol pol por pos pos pow pre pre pre pre pri pri pri pro pro pro pro pro pro pro pub pul pyc qua qua qua qua qui rad rad rad rad rad rad rai ran rar Ray rea Rea rec rec red red ref ref reg rel rel rel ren res res res res ret rev Ric rig rin roc roo rot rot rur S5- Sal sat sca sca Sch sci Scu sec sec sed sel sel sem seq set sha she sho sid sie sil sim sin sit sky slo sno sod sol sol sol sol son sou spa spa spe spe spe spe sph spi spo squ sta sta sta sta ste ste ste Sti sto str str sub sub sub sul sup sup sup sup sur sur syl syn sys tal Tay tel ten ter tex the the the the Tho thr tid tim Tit too Tor tra tra Tra tra Tra tri Tri tru tub tur two Typ ult ult unc uni uni uni upl 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 > >>