An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

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.

→ five; → hundred; → meter; → aperture; → spherical; → radio; → telescope.

Having the form of a sphere; of or pertaining to a sphere or spheres.

From → sphere + → -ic + → -al.

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.

→ spherical; → aberration.

An angle formed on the surface of a sphere by the intersection of two great circles of the sphere.

→ spherical; → angle.

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).

→ spherical; → astrolabe.

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.

→ spherical; → astronomy.

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.

→ spherical; → coordinate.

The difference between the sum of the three angles of a → spherical triangle and 180° (π radians).

→ spherical; → excess.

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.

→ spherical; → geometry.

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.

The term spherical harmonics was first used by William Thomson (Lord Kelvin) and Peter Guthrie Tait in their 1867 Treatise on Natural Philosophy; → spherical; → harmonic.

The angle between the → normal to a spherical reference surface and the → equatorial plane.

→ spherical; → latitude.

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.

→ spherical; → lens.

A mirror whose reflecting surface is a portion of a sphere. Spherical mirrors can be of two types: → concave mirror and → convex mirror.

→ spherical; → mirror.

Same as → spherical coordinates.

→ spherical; → polar; → coordinate

A configuration in which the constituting parts are arranged concentrically around the center of a sphere.

→ spherical; → symmetry.

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.

→ spherical; → triangle.