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

The angle tilt required by the → stellar aberration phenomenon in order that a moving telescope points directly to a star.

→ aberration; → angle.

The figure formed by two lines extending from a common point; the figure formed by two intersecting planes (dihedral angle).

L. angulum (nominative angulus) "corner," a dim. form from PIE *ang-/*ank- "to bend;" cf. Skt. ankah "hook, bent," Gk. angkon "elbow," angkura "anchor," Lith. anka "loop," O.E. ancleo "ankle," O.H.G. ango "hook," Av. ank- "curved, crooked," Av. angušta- "toe," Mod.Pers. angošt, angol, angul "finger".

Zâviyé from Ar. zâwiyat "corner, angle".
Gušé "corner, angle," Mid.Pers. gošak "corner."
Konj, "angle, corner," → diagonal.

The angle between the → incident ray of light entering an → optical system (such as a prism) and the → refracted ray that emerges from the system. Because of the different indices of refraction for the different wavelengths of visible light, the angle of deviation varies with wavelength.

→ angle; → deviation.

The angle of the light coming out of a medium. For a medium with parallel sides (such as a glass slab) it is equal to the angle of incidence.

→ angle; → emergence.

The angle formed between a ray of light striking a surface and the normal to that surface at the point of incidence. Also called → incidence angle.

→ angle; → incidence.

1) General: The angle between one plane and another, or the angle formed by a reference axis and a given line.
2) Binary systems: The angle between the plane of the orbit and the → plane of the sky.
3) Rotating stars: The angle between the → equatorial plane and the → plane of the sky.

→ angle; → inclination.

The angle between the light entering and exiting the prism when the light passing through the prism is parallel to the prism's base. Angle of minimum deviation (D) is used to measure the → index of refraction (n) of the prism glass, because: n = sin [(A + D)/2]/sin (A/2), where A is the → prism angle.

→ angle; → minimum; → deviation.

→ prism angle.

→ angle; → prism.

The angle between the reflected ray and the normal to the reflecting surface.

→ angle; → reflection.

The angle between the direction in which a ray is refracted and the normal to the refracting surface.

→ angle; → refraction.

In → spherical coordinates, an angle measured from the x-axis in the xy-plane.

Azimuthal, adj. from azimuth; → angle.

The angle between the operating facet of the grooves and the overall plane of a diffraction grating.

→ blaze; → angle.

Angâl, zâviyée, → angle; beliz→ blaze.

The grazing angle between an incident beam of X-rays and a given set of crystal planes for which the secondary X-rays from the planes combine to give a single beam.

→ Bragg's law; → angle.

The → angle of incidence for which the sum of the incident angle and the → angle of refraction is 90°. The value of Brewster's angle for glass is 57° and for water is 53°. Same as → polarizing angle.

→ Brewster's law; → angle.

Any angle that when added to another one creates a 90° angle.

→ complementary; → angle.

An angle that results from the combination of two other angles. These angles are expressed by → compound angle formulae.

→ compound; → angle.

One of eight equations that give the → trigonometric functions of → compound angles.
sin(A± B) = sinA.cosnd angleB± cosA.sinB
cos(A + B) = cosA.cosB - sinA.sinB
cos(A - B) = cosA.cosB + sinA.sinB
tan(A + B) = (tanA + tanB)/(1 - tanA.tanB)
tan(A - B) = (tanA - tanB)/(1 + tanA.tanB).

→ compound; → angle; → formula.

Two angles if they have the same measure. Congruent angles may lie in different orientations or positions.

→ congruent; → angle.

Two triangles when all corresponding sides and interior angles have the same measure. The triangles will have the same shape and size, but one may be a mirror image of the other.

→ congruent; → triangle.

Two angles whose sum is 360° or 2π radians.

→ conjugate; → angle.