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fizik-e setâre-yi (#)
Fr.: physique stellaire
Same as → stellar astrophysics.
Fr.: population stellaire
stellar population synthesis
handâyeš-e porinešhâ-ye setâre-yi
Fr.: synthèse de poupulations stellaires
A theoretical model that reconstructs the integrated spectrum of → stellar populations from an empirical library of stellar spectra containing the range of types expected to be present in the sample. The light received from a given galaxy is emitted by a large number of stars that may have different masses, ages, and metallicities. Stellar population synthesis models are tools for interpreting the integrated light that we observe from the galaxies.
tapeš-e setâré, ~ setâre-yi
Fr.: pulsation stellaire
The expansion of a star followed by contraction so that its → surface temperature and → luminosity undergo periodic variation. Pulsation starts with a loss of → hydrostatic equilibrium, when, for example, a layer contracts. This layer heats up and becomes more opaque to radiation. Therefore, radiative diffusion slows down through the layer because of its increased → opacity and heat increases beneath it. Hence pressure rises below the layer. Eventually this increase in pressure starts to push the layer out. The layer expands, cools and becomes more transparent to radiation. Energy now escapes from below the layer and the pressure beneath the layer drops. The layer falls inward and the cycle starts over. See also → kappa mechanism; → gamma mechanism; → partial ionization zone; → pulsating star; → valve mechanism.
carxeš-e setâré, é setêre-yi
Fr.: rotation stellaire
The spinning of a star about its axis, due to its angular momentum. Stars do not necessarily rotate as solid bodies, and their angular momentum may be distributed non-uniformly, depending on radius or latitude.Thus the equator of the star can rotate at a different angular velocity than the higher latitudes. These differences in the rate of rotation within a star may have a significant role in the generation of a stellar magnetic field.
sâxtâr-e setâré, ~ setêre-yi
Fr.: structure stellaire
A physical model that describes the internal arrangement of a star in detail and makes detailed predictions about the luminosity, the color, and the future evolution of the star.
stellar structure equation
hamugeš-e sâxtâr-e setâré
Fr.: équation de structure stellaire
A set of → differential equations describing the physical properties of stars based on two main assumptions: a star is a perfect sphere and the net force on a macroscopic mass element is zero. If the effects of rotation and magnetism are ignored, these assumptions lead to a set of five differential equations.
Fr.: système stellaire
Fr.: vent stellaire
The steady flow of gas away from a star resulting in → mass loss. They range from gentle solar wind (2 x 10-14 solar masses per year) to violent winds some 10 billions times stronger (10-4 solar masses per year) for hot, massive stars.
stellar-mass black hole
siyah câl bâ jerm-e setâre-y
Fr.: trou noir de masse stellaire
Same as → stellar black hole.
Fr.: fonction échelon
Math.: A function f of a real variable defined on an interval [a,b] so that [a,b] can be divided into a finite number of sub-intervals on each of which f is a constant. The graph of a step function is a series of line segments resembling a set of steps.
Step, from M.E. steppen, O.E. steppan; cf. Du. stap, O.H.G. stapfo, Ger. stapfe "footprint;" → function.
Fr.: Quintet de Stéphan
A group of five closely grouped galaxies (NGC 7317, 7318A, 7318B, 7319 and 7320) in the constellation → Pegasus. Four of the galaxies show essentially the same → redshift, suggesting that they are at the same distance from us. The fifth galaxy (NGC 7320) has a smaller redshift than the others, indicating it is much closer. This one is probably a foreground galaxy which happens to lie along the line of sight. The four distant galaxies seem to be colliding, showing serious distortions due to gravitational → tidal forces. The NASA → Spitzer Space Telescope has revealed the presence of a huge intergalactic → shock wave. Collisions play an important role in the life cycles of galaxies. → merging galaxies.
The solid angle subtended at the center of a sphere by an area on its surface numerically equal to the square of the radius. → square degree.
A combining form meaning "having and dealing with three dimensions of space; solid."
From stereo a shortening of stereotype, from Fr. stéréotype (adj.) "printing by means of a solid plate of type," from Gk. stereos "solid."
Loan from Fr., as above.
Fr.: stéréo comparateur
A device that allows two images of the sky taken at different times to be optically superimposed so that changes in star brightness or moving objects can be detected.
Of, relating to, or being a delineation of the form of a solid body on a plane.
Fr.: projection stéréographique
A graphical method of depicting three-dimensional geometrical objects in two dimensions. In a → planispheric astrolabe, it is the projection of a point of the celestial sphere onto the equatorial plane, as seen from one of the poles. The center of projection is the South pole for the northern hemisphere, and the North pole for the southern hemisphere. In this operation the projection of any circle of the sphere remains a circle on the projection plane and moreover the projection does not alter angles.
The process or art of depicting solid objects on a plane surface.
An optical instrument for viewing an overlapping pair of photographs (or perspective drawings) in order to see a three-dimensional image.
Incapable of producing offspring; not producing offspring (Dictionary.com).
M.Fr. stérile "not producing fruit," from L. sterilis "barren, unproductive, unfruitful," from PIE *ster- "stiff, rigid, firm, strong."
Satarvan, literally "mule-like, resembling a mule," from setar, variant of astar, → mule, + -van similarity and attribution suffix.