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

Of a body traveling from A to B, the change of → velocity divided by the time interval: ā = (v₂ - v₁) / (t₂ - t₁).

→ average; → acceleration.

The ratio of the displacement (Δx) of a particle, as it moves from point A to point B, to the corresponding time interval: v = Δx/Δt.

→ average; → velocity.

The technique of looking slightly to the side of a faint object being studied while continuing to concentrate on the object. The technique helps bring out details which otherwise would be missed by looking directly at an object. The reason is that the portion of the eye's retina that best detects dim light (fovea) is located all around the edges rather than the center.

Averted p.p. from avert, from O.Fr. avertir, from L. avertere "to turn away," from → ab- "from, away" + vertere "to turn" (cognate with Pers. gardidan "to turn"); → vision.

Negâh, → vision; kaž "averted."

The number of units in one → mole of any → substance (defined as its → molecular weight in grams), equal to 6.022 140 857 × 10²³. The units may be electrons, atoms, ions, or molecules, depending on the nature of the substance.

Named after Amedeo Avogadro (1776-1856), whose law allowed other physicists to calculate Avogadro's number; → number.

A statement according to which equal volumes of different gases contain an equal number of molecules under the same conditions of temperature and pressure.

After Amedeo Avogadro (1776-1856), Italian chemist and physicist, who advanced the hypothesis in 1811.

→ Avogadro constant.

Named after Amedeo Avogadro (1776-1856), whose law allowed other physicists to calculate Avogadro's number; → constant.

1) To keep away from; keep clear of; shun.
2) To prevent from happening (Dictionary.com). → abstain.

M.E. avoiden, from Anglo-French avoider "to clear out, withdraw (oneself)," from O.Fr. esvuidier "to empty out," from es- "out," → ex-, + vuidier "to be empty," from voide "empty, vast, waste," from L. vocivos "unoccupied, vacant," vacare "be empty," from PIE base *eue- "to leave, abandon, give out."

Tosnidan, from Baluci tôsênag "avoid," tusag "be quenched," tôsaq "quench;" related to Pers. tohi "empty, void;" Mid.Pers. tuhig "empty;" Parthian tôšênitan "to empty;" cf. Pashto taš; Ormuri tusk; Waxi töš, təš; Sariqoli tīs; Skt. tucchá-, tucchyá- "empty;" L. tesqua "deserts;" O.Slav tušti "empty;" Russ. tošcij "meager."

Able to be avoided or prevented.

→ avoid; → -ance.

The act of avoiding or keeping away from.

→ avoid; → -ance.

Having knowledge; conscious; informed; alert. → awareness.

M.E., variant of iwar, O.E. gewær; cf. O.S. giwar, M.Du. gheware, O.H.G. giwar, Ger. gewahr.

Âgâh "aware, knowing," related to negâh "look, attention;" Mid.Pers. âkâh; Av. ākas- "to look;" Proto-Iranian *kas- "to look, appear;" cf. Skt. kāś- "to become visible, appear;" Gk. tekmar, tekmor "sign, mark;"

The state or condition of being aware; having knowledge; consciousness (Dictionary.com).
See also: → Space Situational Awareness.

→ aware; → -ness.

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

→ axis; → -al.

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

→ 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.

→ 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.

→ 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.

→ 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.

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."

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.

→ axiom; → constraint.

Of, relating to, or resembling an → axiom.

→ axiom; → -ic.

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

→ axiomatic; → system.