An Etymological Dictionary of Astronomy and Astrophysics

Of, pertaining to, characterized by, or forming an axis.

See also: → axis; → -al.

Of, pertaining to, characterized by, or forming an axis.

See also: → axis; → -al.

The angle at which a planet’s axis of rotation is tilted, with respect to that of the planet’s orbit.

See also: → axial; → inclination.

The angle at which a planet’s axis of rotation is tilted, with respect to that of the planet’s orbit.

See also: → axial; → inclination.

1. A change in the orientation of the → rotation axis of a non-spherical, spinning body caused by → gravity. A rotating top will precess in a direction determined by the → torque exerted by its → weight. The precession → angular velocity is inversely proportional to the spin angular velocity, so that the precession is faster and more pronounced as the top slows down.
   

   2. In particular, the gradual shift in the orientation of Earth’s rotation axis which traces out a conical path once every ~ 26,000 years. The cause of the Earth’s precession is the → equatorial bulge of the Earth, brought about by the → centrifugal force of the → rotation, which has changed the Earth from a perfect sphere to a slightly flattened one, thicker across the equator. The attraction of the Moon and Sun on the bulge is the reason which makes the Earth precess.

See also: → axial; → precession.

1. A change in the orientation of the → rotation axis of a non-spherical, spinning body caused by → gravity. A rotating top will precess in a direction determined by the → torque exerted by its → weight. The precession → angular velocity is inversely proportional to the spin angular velocity, so that the precession is faster and more pronounced as the top slows down.
   

   2. In particular, the gradual shift in the orientation of Earth’s rotation axis which traces out a conical path once every ~ 26,000 years. The cause of the Earth’s precession is the → equatorial bulge of the Earth, brought about by the → centrifugal force of the → rotation, which has changed the Earth from a perfect sphere to a slightly flattened one, thicker across the equator. The attraction of the Moon and Sun on the bulge is the reason which makes the Earth precess.

See also: → axial; → precession.

A symmetry with respect to a line. A geometric configuration is said to have axial symmetry if it remains unchanged when rotated about a given line.

See also: → axial; → symmetry.

A symmetry with respect to a line. A geometric configuration is said to have axial symmetry if it remains unchanged when rotated about a given line.

See also: → axial; → symmetry.

The angle between an object’s → rotation axis and its → orbital axis. In other words,
the angle between its → equatorial plane and → orbital plane.
Same as → axial inclination and
→ obliquity, but not to be confounded with → orbital inclination.

See also: → axial; → tilt.

The angle between an object’s → rotation axis and its → orbital axis. In other words,
the angle between its → equatorial plane and → orbital plane.
Same as → axial inclination and
→ obliquity, but not to be confounded with → orbital inclination.

See also: → axial; → tilt.

In any system of mathematics or logic, a statement or proposition from which secondary statements or propositions are derived. The truth of an axiom is either taken for granted or assumed. Axioms serve as the starting point of other mathematical statements called → theorems. In modern practice, axiom and → postulate have the same meaning.

Etymology (EN): M.Fr. axiome, from L. axioma, from Gk. axioma “authority,” literally “something worthy,” from axioun “to think worthy,” from axios “worthy,” from PIE adj. *ag-ty-o- “weighty,” from base *ag- “to drive, draw, move.”

Etymology (PE): Bondâšt, literally “taking as the base,” from bon “root, origin, base” + dâšt “held,” from dâštan “to have, to hold, to maintain, to consider.”
Arzâqâzé, from arz “value” + âqâzé “beginning, principle,” from âqâz “beginning.”

In any system of mathematics or logic, a statement or proposition from which secondary statements or propositions are derived. The truth of an axiom is either taken for granted or assumed. Axioms serve as the starting point of other mathematical statements called → theorems. In modern practice, axiom and → postulate have the same meaning.

Etymology (EN): M.Fr. axiome, from L. axioma, from Gk. axioma “authority,” literally “something worthy,” from axioun “to think worthy,” from axios “worthy,” from PIE adj. *ag-ty-o- “weighty,” from base *ag- “to drive, draw, move.”

Etymology (PE): Bondâšt, literally “taking as the base,” from bon “root, origin, base” + dâšt “held,” from dâštan “to have, to hold, to maintain, to consider.”
Arzâqâzé, from arz “value” + âqâzé “beginning, principle,” from âqâz “beginning.”

An axiom in → statics, stating that any → constrained body can be treated as a → free body detached from its → constraints, provided the latter are represented by their → reactions.

See also: → axiom; → constraint.

An axiom in → statics, stating that any → constrained body can be treated as a → free body detached from its → constraints, provided the latter are represented by their → reactions.

See also: → axiom; → constraint.

Of, relating to, or resembling an → axiom.

See also: → axiom; → -ic.

Of, relating to, or resembling an → axiom.

See also: → axiom; → -ic.

Any system of → logic which explicitly states → axioms from which → theorems can be → deduced.

See also: → axiomatic; → system.

Any system of → logic which explicitly states → axioms from which → theorems can be → deduced.

See also: → axiomatic; → system.

A hypothetical weakly-interacting → boson of small mass required by models of → particle physics in order to solve the strong CP problem and explain a number of observed astrophysical/cosmological phenomena, including → dark matter, and the dimming of → type Ia → supernovae (→ accelerating Universe). Photons traveling in the → intergalactic medium would in part turn into axions in the presence of magnetic fields. The transformed photons are not detected on Earth and therefore
supernovae would appear fainter even if the Universe is not accelerating.

Etymology (EN): Axion, first coined by Frank Wilczek (2004 Nobel Prize in Physics) apparently after a brand of washing detergent! The reason seems to be the idea that the particle will iron out a wrinkle in the → standard model of fundamental particles and forces while solving the problem of the Universe’s → missing mass.

A hypothetical weakly-interacting → boson of small mass required by models of → particle physics in order to solve the strong CP problem and explain a number of observed astrophysical/cosmological phenomena, including → dark matter, and the dimming of → type Ia → supernovae (→ accelerating Universe). Photons traveling in the → intergalactic medium would in part turn into axions in the presence of magnetic fields. The transformed photons are not detected on Earth and therefore
supernovae would appear fainter even if the Universe is not accelerating.

Etymology (EN): Axion, first coined by Frank Wilczek (2004 Nobel Prize in Physics) apparently after a brand of washing detergent! The reason seems to be the idea that the particle will iron out a wrinkle in the → standard model of fundamental particles and forces while solving the problem of the Universe’s → missing mass.

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.

Etymology (EN): 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.”

Etymology (PE): 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.”

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.

Etymology (EN): 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.”

Etymology (PE): 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.

See also: → axis; → rotation.

Same as → rotation axis and → rotational axis.

See also: → axis; → rotation.

Having → axisymmetry.

Having → axisymmetry.

Same as → axial symmetry.

Same as → axial symmetry.