An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



Number of Results: 13 Search : lamb
barré, baré (#)

Fr.: agneau   

A young sheep; the meat of a young sheep.

M.E., O.E.; cognate with Du. lam, Ger. Lamm, Goth. lamb; akin to Gk. elaphos "deer."

Mid.Pers. warrag "lamb; sheep;" warân "ram;" Av. varən-; cf. Skt. uaran-; L. vervex (Fr. brebis); Arm. garn; Baluci garând "ram;" Lori, Laki veran "ram;" PIE *wrhen- "lamb."

Lamb shift
  کیب ِ لمب   
kib-e Lamb

Fr.: décalage de Lamb   

A tiny change in the → energy levels of the → hydrogen atom between the states 2S1/2 and 2P1/2, which creates a shift in the corresponding → spectral lines. The 2P1/2 state is slightly lower than the 2S1/2 state, contrarily to the Schrodinger's solution. The difference is explained by the interaction between → vacuum energy fluctuations and the hydrogen electron in different orbitals.

Named after Willis Eugene Lamb, Jr. (1913-2008), an American physicist who discovered this effect in 1951, and won the Nobel Prize in physics in 1955 "for his discoveries concerning the fine structure of the hydrogen spectrum;" → shift.


Fr.: lambda   

The eleventh letter of the Greek alphabet. In lower case, λ, it denotes → wavelength. It is also used in the → Bayer designation system to identify a specific star in a → constellation. See also → lambda point.
In upper case, Λ, it represents the → cosmological constant or → dark energy.

From Phoenician lamedh.

Lambda Bootis star
  ستاره‌ی ِ لامبدا گاوران   
setâre-ye lâmbda Gâvrân

Fr.: étoile lambda du Bouvier   

The prototype of a small class of stars (A-F types) which have weak metallic lines (indicating that they are depleted in metals heavier than Si, but with solar abundances of C, N, O, and S). Moreover, they have moderately large rotational velocities and small space velocities. Lambda Boo stars may be pre-main-sequence objects, or they may be main sequence stars that formed from gas whose metal atoms had been absorbed by interstellar dust.

Named after the prototype, the star → Lambda (λ) of constellation → Bootes; → star.

lambda cold dark matter model
  مدل ِ لامبدا-ماده‌ی-سرد ِ- تاریک   
model-e lâmbdâ-mâde-ye-sard-e-târik

Fr.: modèle ΛCDM   

The → standard model of → Big Bang that incorporates both → dark matter and → dark energy. See also → cold dark matter (CDM).

lambda, → cosmological constant; → cold; → dark; → matter; → model.

Lambda Orionis
  لامبدا-شکارگر، ~-اریون   
Lâmbdâ-Šekârgar, ~-Oryon

Fr.: Lambda (λ) Orionis   

Same as → Meissa.

Lambda (λ), a Greek letter used in the → Bayer designation of star names.

lambda point
  نقطه‌ی ِ لامبدا   
noqte-ye lâmbdâ

Fr.: point lambda   

The temperature (roughly 2.17 K) at which → liquid helium (→ helium I) becomes → superfluid (→ helium II).

The name was given by the Dutch physicist Willem Hendrik Keesom (1876-1956), who discovered the behavior of helium near this transition point and successfully solidified helium in 1926 (under an external pressure of 25 atmospheres). The name was originally suggested by Paul Ehrenfest (1880-1933), who was inspired by the shape of the → specific heat curve, which resembles the Gk. letter → lambda; → point.


Fr.: lambert   

A centimeter-gram-second (cgs) unit of luminance (or brightness) equal to 1/π candle per square centimeter. Physically, the lambert is the luminance of a perfectly diffusing white surface receiving an illuminance of 1 lumen per square centimeter.

Johann Heinrich Lambert (1728-1777), German scientist and mathematician; → law.

Lambert's cosine law
  قانون ِ کوسینوس ِ لامبرت   
qânun-e cosinus-e Lambert

Fr.: loi en cosinus de Lambert   

The intensity of the light emanating in any given direction from a perfectly diffusing surface is proportional to the cosine of the angle between the direction and the normal to the surface. Also called → Lambert's law.

lambert; → cosine; → law.

Lambert's law
  قانون ِ لامبرت   
qânun-e Lambert

Fr.: loi de Lambert   

Same as → Lambert's cosine law.

lambert; → law.

Lambertian disk
  گرده‌ی ِ لامبرتی، دیسک ِ ~   
gerde-ye Lamberti, disk-e ~

Fr.: disque lambertien   

A → planetary or → satellite disk with → Lambertian surface. Such a disk has the same → surface brightness at all angles.

lambert; → disk.

Lambertian surface
  رویه‌ی ِ لامبرتی   
ruye-ye Lamberti

Fr.: surface lambertienne   

A surface whose → luminous intensity obeys → Lambert's cosine law. Such a source has a → reflectance that is uniform across its surface and uniformly emits in all directions from all its points. It appears equally bright from all viewing directions. Lambertian surface is a very useful concept for the approximation of radiant power transfer.

lambert; → surface.

Shaula (Lambda Scorpii)
Shulé (#)

Fr.: Shaula, λ Scorpii   

The second brightest star in the constellation → Scorpius, lying at a distance of 570 → light-years. With → Lesath (Upsilon Scorpii) both stars make up the Scorpion's stinger. Shaula is a → multiple star with three visible → components. The first one, Lambda Scorpii A, is classified as a B2 IV → subgiant. The 15th magnitude Lambda Scorpii B has a separation of 42 arcseconds from component A, while the 12th magnitude Lambda Scorpii C is 95 arcseconds from A. It is not known whether or not these components are physically associated with component A. The component A is actually a → triple system consisting of two → B-type stars and a → pre-main sequence star.

Shaula, from Ar. ash-shaulah (الشولاء) the "raised tail" of Scorpion.