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

1) Of or relating to the → antipodes.
2) Describing two points when a line drawn from one to the other does not pass through the geometric centre of the Earth.

→ antipode; → -al.

1) The exact or direct opposite.
2) Either or both of two points, places, or regions that are situated diametrically opposite to one another on the Earth's surface (Dictionary.com).

M.E., from L., from Gk. antipod-, antipous, literally "with feet opposite," from → anti- "against," + pod-, pous, → foot.

Pâdpây, from pâd-, → anti-, + pây, → foot.

The antiparticle of a proton, identical in mass and spin but of opposite (negative) charge.

From → anti- + → proton.

The → antiparticle of a → quark.

→ anti-; → quark.

Meteo.: The point on the → celestial sphere that lies directly opposite the Sun from the → observer, observer, that is, on the line from the Sun through the observer. The antisolar point is the center of the rainbow, and can be easily found on a sunny day: it it located at the shadow of one's head; it is 180° away from the Sun. If the Sun is in the sky, the antisolar point is below the horizon. If the Sun has set, the antisolar point is above the horizon.

→ anti-; → solar; → point.

A small tail-like structure on a comet that, unlike most comet tails, seems to point toward the Sun. This rare event is an optical illusion due to larger dust particles left along the comet's orbit. And typically occurs when the Earth crosses the plane of the comet's orbit. It seen when the observer is in the plane of the cometary orbit.

Antitail, from → anti- "opposite, opposing, against" + → tail.

Pâddom, from pâd-, → anti-, + dom "tail."

Logical or verbal opposition.
Philo. The second of two opposed propositions in Hegelian dialectic, the first of which is the → thesis; → synthesis.

→ anti-; → thesis.

1) Of the nature of or involving → antithesis.
2) Directly opposed or contrasted; opposite (Dictionary.com).

→ antithesis; → -ic.

Of or pertaining to the Atlantic Ocean.

M.E., from L. Atlanticum (mare) "the Atlantic (ocean)," from Gk. Atlantikos "of Atlas," adj. of → Atlas, in reference to Mount Atlas in NW Africa. So called because it lay beyond that mountain.

A → quantity that remains → constant when its corresponding → physical system undergoes a → transformation.

→ conserve→ quantity.

A quantity without an associated → physical dimension. Dimensionless quantities are defined as the ratio of two quantities with the same dimension. The magnitude of such quantities is independent of the system of units used. A dimensionless quantity is not always a ratio; for instance, the number of people in a room is a dimensionless quantity. Examples include the → Alfven Mach number, → Ekman number, → Froude number, → Mach number, → Prandtl number, → Rayleigh number, → Reynolds number, → Richardson number, → Rossby number, → Toomre parameter. See also → large number.

→ dimension; → quantity.

A symbol of → predicate logic which expresses that the statements within its scope are → true for at least one instance of something. The symbol ∃ is used as the existential quantifier. Existential quantifiers are normally used in logic in → conjunction with → predicate symbols, which say something about a → variable or → constant, in this case the variable being quantified (→ quantify, → quantification).

→ existential; → quantifier.

The point in the → Galactic plane that lies directly opposite the → Galactic center. It lies in the constellation → Auriga at approximately R.A. 05h 46m, Dec. +28° 56'.

→ galactic; → anticenter.

The fractional or the decimal part of a → common logarithm. For example, log₁₀ 4000 = 3.602, where the → characteristic is 3 and the mantissa 0.602.

From L. mantis "makeweight, addition," of unknown origin. Introduced by Henry Briggs (1561-1630).

→ makeweight.

An immense chain of underwater mountains that runs down the middle of the Atlantic Ocean. The MAR, approximately 500-1000 km wide, extends 16,000 km from Iceland to the Antarctic Circle. The MAR is so high that it actually rises above sea level in many places, forming volcanic islands. The Azores, Ascension, St. Helena, and Iceland all arise from this great Atlantic range. The chain results from the movement of the continental plates. As these plates slowly separate, they leave gaps in the → Earth's crust. This allows molten rock from beneath the Earth's crust to reach the surface and forms a ridge. The MAR is a part of the global → mid-ocean ridge system.

→ mid-; → Atlantic; → ridge.

1) Opposition to the spread of knowledge; a policy of withholding knowledge from the general public.
2) A style (as in literature or art) characterized by deliberate vagueness or abstruseness (Merriam-Webster.com).

From Fr. obscurantisme (1819), from obscurant, from obscure, from L. obscurus "dark, dusky," figuratively "unknown; unintelligible," from ob- "over" + -scurus "covered," from PIE *(s)keu- "to cover, conceal;" → -ism.

A physical → property that can be measured and/or calculated.

→ physical; → quantity.

The religion of → Protestants.

→ protestant; → -ism.

An annual → meteor shower reaching a peak about 3 January and having its → radiant in the constellation → Boötes.

From L. Quadrant-, from Quadrans Muralis , → mural quadrant.

The fact or process of quantifying.

Verbal noun of → quantify.