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

1) One of the principal lines through the center of a figure or a solid, especially, the line which divides the figure or solid symmetrically.
2) A fixed line along which distances are measured or to which position are referred.

L. axis "axle, pivot," akin to O.E. eax "axis, axle," Gk. axon "axle," Skt. aksa- "axle, axis, beam of a balance;" PIE base *aks- "axis."

Âsé, from Pers. dialects: Qâyeni asak "the shaft connecting the plough to the yoke," Lori esi "a pillar (used to put up a tribal tent)," variants hosi, hosin, Tabari âssen "the foot of a door on which it turns," cf. Skt. īṣā- "pole or shafts of a carriage or plough," Av. aêša "the two shafts," Mod.Pers. xiš "plough(share)," Gk. oiax "handle of rudder, tiller, helm," PIE base *ei-, *oi- "pole, thill."

Same as → rotation axis and → rotational axis.

→ axis; → rotation.

Having → axisymmetry.

Same as → axial symmetry.

The Earth's axis extended to the → celestial pole.

→ celestial; → axis.

One of the two diameters of a conic, so related that a tangent at the end of one is parallel to the other.

→ conjugate; → axis.

The axis to which the telescope tube is fastened in an → equatorial mounting.

→ declination; → axis.

The angle between the rotation axis of a planet and the normal to the ecliptic.

→ inclination; → axis.

The imaginary straight line joining the two → poles of a → magnet.

→ magnetic; → meridian.

The greatest diameter of an ellipse; it passes through the two foci.

→ major; → axis.

The axis of an ellipse that is perpendicular to the major axis at a point equidistant from the foci.

→ minor; → axis.

A → tumbling motion of an → asteroid. See also → tumbling asteroid.

→ non-; → principal axis; → rotational; → motion.

An → optical system in which the → optical axis of the → aperture is not coincident with the mechanical center of the aperture.

→ off; → axis; → optical; → system.

The direction in a doubly refracting crystal in which light is propagated without double refraction.

→ optic; → axis.

Line passing through the optical center and the center of curvature of a → spherical mirror or → lens. Same as → principal axis.

→ optical; → axis.

The → perpendicular to the → orbital plane.

→ orbital; → axis.

The → moment of inertia of a body about any given axis is the moment of inertia about a parallel axis through the center of mass, plus the moment of inertia about the given axis if the mass were located at the center of mass. same as → Steiner's theorem.

→ parallel; → axis; → theorem.

The → moment of inertia of a plane object (→ lamina) about an axis perpendicular to the plane is equal to the sum of the moments of inertia about any two perpendicular axes in the plane. Thus if x and y axes are in the plane, I_z = I_x + I_y.

→ perpendicular; → axis; → theorem.

The axis of an → equatorial mounting that is parallel to the Earth's axis, and consequently points to the celestial pole.

→ polar; → axis.

1) The practice and practical side of knowledge or skills, as opposed to the → theory.
2) Accepted practice or custom.

M.L. praxis "practice, action," from Gk. praxis "practice, action, doing," from stem of prassein "to do, to act."

Varzidâr, from varzid past stem of varzidan, → practice, + -âr prefix forming nouns of action, such as kerdâr, raftâr, didâr, goftâr, jostâr, etc.