An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



Number of Results: 19 Search : surface
Alfven surface
  رویه‌ی ِ آلفون   
ruye-ye Alfvén

Fr.: surface d'Alfvén   

In a magnetized wind, the geometric loci of the points where the magnetic pressure equals the flow pressure. See also → Alfven point.

Alfven wave; → surface.

black hole surface gravity
  گرانی ِ رویه‌ی ِ سیه‌چال   
gerâni-ye ruye-ye siyah câl

Fr.: gravité de surface de trou noir   

The acceleration of gravity at the → event horizon of a → black hole. For a → Schwarzschild back hole it is given by κ = GM/RSch2 = c4/(4GM).

black; → hole; → surface; → gravity.

caustic surface
  رویه‌ی ِ سوچان   
ruye-ye sucân

Fr.: surface cuastique   

In an → optical system, the → envelope of all the → reflected or → refracted rays (by a → mirror or a → lens respectively) which do not come to a common focal point because of geometrical → aberration. This occurs when parallel rays of light fall on a → concave mirror or when a → convex lens receives parallel light. In the case of → spherical aberration, the caustic surface has an axis of symmetry.

caustic; → surface.

equipotential surface
  رویه‌ی ِ هموگ-توند   
ruye-ye hamugtavand

Fr.: surface équipotentielle   

An imaginary surface surrounding a body, or group of bodies, over which the gravitational field is of constant strength and, at all points, is directed perpendicular to the surface. For a single star the surface is spherical. In a close binary system the equipotential surface of the components interact to become hourglass-shaped. → Roche lobe; → Lagrangian points.

From → equi-; → potential; → surface.

fault surface
  رویه‌ی ِ گسله   
ruye-ye gosalé

Fr.: surface de faille   

Geology: The surface of a fracture along which dislocation of adjacent rocks has taken place.

falt; → surface.

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.

last scattering surface
  رویه‌ی ِ واپسین پراکنش   
ruye-ye vâpasin parâkaneš

Fr.: surface de dernière diffusion   

The set of locations in space corresponding to the → last scattering epoch in the early Universe. It is a spherical surface around the present-day observer from which the → cosmic microwave background radiation appears to emanate.

last; → scattering; → surface.

low surface brightness galaxy (LSBG)
  کهکشان با درخشندگی ِ رویه‌ای ِ کم   
kahkešân bâ deraxšandegi-ye ruye-yi-ye kam

Fr.: galaxie à faible brillance de surface   

A member of a particularly faint population of galaxies with a central → surface brightness below the brightness of the background sky. The central regions of many of them resemble a → dwarf galaxy, but most of the mass is contained in a large gaseous disk of low density that is observable only with long-exposure optical images or at radio wavelengths. Some are as massive as a large → spiral galaxy, for example Malin 1. The proportion of LSBGs relative to normal galaxies is unknown. They may however represent a significant fraction of mass in the Universe. LSBGs are thought to be primitive systems because they have total masses similar to normal galaxies, but have typically converted less than 10% of their gas into stars. Spiral LSBGs do not obey → Freeman's law.

low; → surface; → brightness; → galaxy.

ruled surface
  رویه‌ی ِ خط‌ساخته   
ruye-ye xatt sâxté

Fr.: surface réglée   

A surface, such as a cylinder or cone, that can be generated by moving a straight line.

Ruled, p.p. of rule; → surface.

Ruyé, → surface; xatt sâxté "built, formed by a line," from xattline; sâxté, p.p. of sâxtan "to build, make, fashion; to adapt, adjust, be fit" (from Mid.Pers. sâxtan, sâz-, Manichean Parthian s'c'dn "to prepare, to form;" Av. sak- "to understand, to mark," sâcaya- (causative) "to teach").

stationary limit surface
  رویه‌ی ِ حدّ ِ ایست‌ور   
ruye-ye hadd-e istvar

Fr.: surface limite stationnaire   

A property of → space-time outside a → rotating black hole, which consists of a surface which geometrically bounds the → ergosphere outward. At the stationary limit a particle would have to move with the local light velocity in order to appear stationary to a distant observer. This is because the space here is being dragged at exactly the speed of light relative to the rest of space. Outside this limit space is still dragged, but at a rate less than the speed of light. Also known as → static limit.

stationary; → limit; → surface.

ruyé (#)

Fr.: surface   

1) The outer face, outside, or exterior boundary of a thing; outermost or uppermost layer or area.
2) Math.: An infinite aggregate of points constituting space of two dimensions; part or all of the boundary of a solid.

sur-; → face.

surface brightness
  درخشندگی ِ رویه، ~ رویه‌ای   
deraxandegi-ye ruyé, ~ ruye-yi

Fr.: brillance de surface   

The brightness of an extended object, such as a planet, nebula, galaxy, or the sky background, expressed as magnitudes per unit area (usually square arc second). Surface brightness is calculated by dividing the object's magnitude by its size (→ isophotal radius).

surface; → brightness.

surface current
  جریان ِ رویه‌ای   
jarayân-e ruye-yi

Fr.: courant de surface   

A current whose core of maximum velocity is near the surface.

surface; → current.

surface density
  چگالی ِ رویه‌ای   
cagâli-ye ruye-yi

Fr.: densité de surface   

The amount of a quantity distributed over a surface area divided by the area, such as a surface-charge density.

surface; → density.

surface gravity
  گرانی ِ رویه، ~ رویه‌ای   
gerâni-ye ruyé, ~ ruye-yi

Fr.: gravité de surface   

1) The rate at which a small object in free fall near the surface of a body is accelerated by the gravitational force of the body: g = GM / R2, where G is the gravitational constant, and M and R are the mass and radius of the object. The surface gravity of Earth is equal to 980 cm s-2.
2) → black hole surface gravity.

surface; → gravity.

surface of last scattering
  رویه‌ی ِ واپسین پراکنش   
ruye-ye vâpasin parâkaneš

Fr.: surface de dernière diffusion   

Same as → last scattering surface.

surface; → last; → scattering.

surface temperature
  دما‌ی ِ رویه، ~ رویه‌ای   
damâ-ye ruyé, ~ ruye-yi

Fr.: température de surface   

1) For a star, same as → effective temperature.
2) Meteo.: The air temperature at or near the earth's surface.

surface; → temperature.

surface tension
  تنش ِ رویه‌ای   
taeš-e ruye-yi

Fr.: tension superficielle   

The inward → attraction of the → molecules at the → surface of a → liquid. The reason is that the molecules at the surface do not have other like molecules on all sides of them and consequently they cohere more strongly to those directly associated with them on the surface. Also called surface energy and capillary forces.

surface; → tension.

working surface
  زنار ِ اندر-آژیرش   
zonâr-e andar-âžireš

Fr.: zone d'interaction   

The double shock structure formed in any two fluids that collide supersonically. A working surface consists of two → shocks, a → bow shock where the ambient material is shocked and accelerated, and a jet shock or → Mach disk, where the → jet material is decelerated. It is common to find multiple working surfaces along the axis of an → Herbig-Haro jet, testifying to recurrent eruptions of the underlying source.

work; → -ing; → surface.