Five-hundred-meter Aperture Spherical radio Telescope (FAST)
The 500 m diameter → radio telescope which is the largest → single-dish antenna in the world. It is an Arecibo type telescope nestled within a natural basin in China's remote and mountainous Dawodang, Kedu Town, in southeastern China's Guizhou Province. The → reflector consists of 4,450 triangular panels, each with a side length of 11 m. More than 2,000 → actuators are used, according to the feedback from the measuring system, to deform the whole reflector surface and directly correct for → spherical aberration. Several detectors are used to cover a frequency range of 70 MHz to 3 GHz.
Having the form of a sphere; of or pertaining to a sphere or spheres.
Fr.: aberration sphérique, ~ de sphéricité
An aberration of a spherical lens or spherical mirror in which light rays converge not to a single point but to a series of points with different distances from the lens or mirror. Spherical aberration is corrected by using parabolic reflecting and refracting surface.
Fr.: angle sphérique
An angle formed on the surface of a sphere by the intersection of two great circles of the sphere.
ostorlâb-e sepehri, ~ kore-yi
Fr.: astrolabe sphérique
A type of → astrolabe in which the observer's horizon is drawn on the surface of a globe, mounted with a freely rotating spherical lattice work or 'spider' representing the celestial sphere. The earliest description of the spherical astrolabe dates back to the Iranian astronomer Nayrizi (865-922).
Fr.: astronomie sphérique
The branch of astronomy that is concerned with determining the apparent positions and motions of celestial bodies on the celestial sphere. Same as → positional astronomy.
Fr.: coordonnées sphériques
A coordinate system using an origin (O) and three perpendicular axes (Ox, Oy, Oz), in which the position of a point (P) is given by three numbers (r, θ, φ). The coordinate r is the distance from the origin, θ the angle between the z-axis and the r direction, and φ the angle between the projection of r on the xy-plane and the Ox-axis. The coordinate φ is also called the → azimuthal angle.
fozuni-ye sepehri, ~ kore-yi
Fr.: excès sphérique
The difference between the sum of the three angles of a → spherical triangle and 180° (π radians).
Fr.: géométrie sphérique
The branch of geometry that deals with figures on the surface of a sphere (such as the spherical triangle and spherical polygon). It is an example of a non-Euclidean geometry.
Fr.: fonction harmonique sphérique
A solution of some mathematical equations when → spherical polar coordinates are used in investigating physical problems in three dimensions. For example, solutions of → Laplace's equation treated in spherical polar coordinates. Spherical harmonics are ubiquitous in atomic and molecular physics and appear in quantum mechanics as → eigenfunctions of → orbital angular momentum. They are also important in the representation of the gravitational and magnetic fields of planetary bodies, the characterization of the → cosmic microwave background anisotropy, the description of electrical potentials due to charge distributions, and in certain types of fluid motion.
varunâ-ye kore-yi, ~ sepehri
Fr.: latitude sphérique
Fr.: lentille sphérique
A lens with a refractng surface which is a portion of a sphere. Spherical lenses can be of various types: → biconvex, → biconcave, → plano-convex, → plano-concave, → concavo-convex, and → convexo-concave.
Fr.: miroir sphérique
spherical polar coordinate
hamârâhâ-ye kore-yi-ye qotbi
Fr.: coordonnées sphériques polaires
Same as → spherical coordinates.
Fr.: symétrie sphérique
A configuration in which the constituting parts are arranged concentrically around the center of a sphere.
Fr.: triangle sphérique
A triangle drawn on the → surface of a → sphere. A spherical triangle, like a plane triangle, may be right, obtuse, acute, equilateral, isosceles, or scalene. The sum of the angles of a spherical triangle is greater than 180° (π) and less than 540° (3π). See also → spherical excess.