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

A mirror whose surface is curved inward and converges the light rays.

→ concave; → mirror.

A concave mirror that reflects a parallel beam into a convergent beam.

From → converge + → -ing; → mirror.

A → spherical mirror with a reflecting surface curved outward, that is toward the object.

→ convex; → mirror.

A very thin mirror whose shape can be changed by the force applied by many small pistons behind the mirror. Such a mirror is used in the → adaptive optics technique to correct the → wavefront affected by the → atmospheric turbulence. See also → tip-tilt mirror.

→ deformable; → mirror.

A pair of plane mirrors which are slightly inclined to one another. It is used for producing two coherent images in interference experiments.

→ Fresnel diffraction; → mirror.

Two plane mirrors, fitted side by side at a small angle, used to create two mutually → coherent sources in a famous → interference experiment first suggested by A. Fresnel. A point source reflected at the mirrors appears as a pair of → virtual light sources, positioned close together, which interfere with each other due to their → coherence. This arrangement removes the problem that two separate light sources do not produce observable interference on account of their incoherence. Same as Fresnel's double mirror. See also → Fresnel's biprism, → Lloyd's mirror.

→ Fresnel diffraction; → mirror.

A mirror composed of liquid, taking advantage of the parabolic shape of a spinning liquid and the fact that the mirror's focal length can be adjusted by altering the velocity at which the liquid's container spins.

→ liquid; → mirror.

An optical arrangement in which light from a source is allowed to fall on a plane mirror at → grazing incidence. The light directly coming from the source interferes with the light reflected from the mirror forming an → interference pattern. See also → Fresnel's biprism, → Fresnel's mirrors.

After the Irish physicist Humphry Lloyd (1800-1881); → mirror.

A smooth, highly polished surface, for reflecting light, that may be plane or curved. The actual reflecting surface is usually a thin coating of silver or aluminum on glass.

From O.Fr. mireor "a reflecting glass," earlier miradoir, from mirer "look at," from V.L. *mirare, from L. mirari "to wonder at, admire."

Âyene, from Mid.Pers. êwênag "mirror," from *âdênak, cf. Khotanese âyäna- "mirror," from Proto-Iranian *ādayana-, from prefix ā- + the root of Av. dā(y)- "to see," didāti "sees" (cf. Mod.Pers. didan "to see," Mid.Pers. ditan "to see, regard, catch sight of, contemplate, experience;" O.Pers. dī- "to see;" Skt. dhī- "to perceive, think, ponder; thought, reflection, meditation," dādhye; Gk. dedorka "have seen") + suffix -ak.

The material on which the reflecting coating is applied. It may be glass, quartz, or metal.

→ mirror; blank "a piece of metal ready to be drawn, pressed, or machined into a finished object," from M.E., from O.Fr. blanc (adj.) from Gmc; cf. O.E. blanca "white horse," O.H.G. blanch "bright, white."

Gerdé, → disk; âyené, → mirror.

Same as → mirror blank.

→ mirror; → disk.

The observation and measurement of the flatness of a mirror surface. The process generally is done before coating so as not to damage the delicate coated surface. For coated and curved surfaces, non-contact methods are often employed, generally using interference techniques.

→ mirror; → test.

A concave mirror that has the form of a paraboloid of revolution.

→ parabolic; → mirror.

A mirror whose reflective surface is neither concave nor convex.

→ plane; → mirror.

The point where the → principal axis passes through the mirror.

→ pole; → mirror.

In a → reflecting telescope, the first mirror that collects the light and focuses it to the → focal plane.

→ primary; → mirror.

The second reflecting surface in a → reflecting telescope. It directs the light either out a side opening of the tube (→ Newtonian telescope) or back toward a → focal point behind and through the → primary mirror (→ Cassegrain telescope). The secondary is usually suspended in the beam and therefore obstructs part of the primary.

→ secondary; → mirror.

A large telescope mirror consisting of smaller mirror segments designed to act as a single, larger reflecting surface. Because current monolithic mirrors cannot be constructed larger than about eight meters in diameter, the use of segmented mirrors is a key component for larger aperture telescopes.

Segmented, p.p. of → segment (v.); → mirror.

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.

A rapidly moving → mirror used in → adaptive optics to correct overall movements of the incoming → wavefront of light caused by → atmospheric turbulence. The simplest form of adaptive optics is tip-tilt correction, which corresponds to correction of the tilts of the wavefront in two dimensions. This is done by tipping and tilting the mirror rapidly in response to overall changes in position of a reference star. See also → deformable mirror.

From, tip noun from tip (v.) "to overturn, upset," from M.E. typen "to upset, overturn" + tilt noun from tilt (v.) "to cause to lean, incline, slope, or slant," → tilt; → mirror.

Âyené, → mirror; kaj "turned aside; crooked, bent" (cf. Skt. kubja- "hump-backed, crooked," Pali kujja- "bent," L. gibbus "hump, hunch," Lith. kupra "hump") + -o- "and" + râst→ right + -gar agent noun suffix → -or.