An Etymological Dictionary of Astronomy and Astrophysics
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Matter composed entirely of → antiparticles. See also → antihydrogen.

Antimatter from Gk. → anti- "opposite, opposing, against" + → matter.

Pâdmâddé from pâd-, → anti-, + mâddé, → matter.

A silver white metallic element of a flaky nature, extremely brittle, occurring in nature free or combined, symbol Sb. → Atomic number 51; → atomic weight 121.75; → meting point 630.74°C; → boiling point 1,750°C; → specific gravity (metallic form) 6.69 at 20°C. Antimony is recognized in compounds from antiquity, and as a metal since the 17th century. The minerals stibnite (Sb₂S₃) and stibine (SbH₃) are two of a multitude of mineral species which were known in the ancient world. Antimony is a poor conductor of heat and electricity. It greatly increases the hardness of metals with which it makes → alloys. Its various unstable isotopes have a half-life of 16 min (Sb¹²⁰) to 2.7 years (Sb¹²⁵).

From M.E. antimonie, from M.L. antimonium, an alchemist's term, of obscure origin, maybe a Latinization of Gk. stimmi or stibi, probably ultimately from Egyptian stm "cosmetic powder" used to paint the eyelids. The chemical symbol, Sb, comes from the original name, stibium, which is derived from Gk. stibi for "mark," since it was used for blackening eyebrows and eyelashes. The name was changed from stibium to antimonium to antimony.

Ântimuân, loan from Fr. antimoine.

The → antiparticle counterpart of the → neutrino.

→ anti-; → neutrino.

The → antiparticle of the → neutron. It has the same mass, → spin, and → electric charge (zero) as the neutron but has opposite → baryon number (+1 for neutron, -1 for the antineutron). This is because the antineutron is composed of → antiquarks, while neutrons are composed of → quarks. The antineutron consists of one up antiquark and two down antiquarks.

→ anti-; → neutron.

The position of maximum → amplitude midway between two adjacent → nodes in a → standing wave.

→ anti-; → node.

A unique → binary asteroid (90) which has two similar-sized components. The components, 91 and 86 km in diameter respectively, are separated by 171 km, and circle each other every 16.5 hours. Belonging to the main → asteroid belt, Antiope was discovered in 1866 by the German Robert Luther. Its binarity was discovered in 2000 by W. Merline and collaborators.

Antiope, from Gk. mythology, but it is not clear whether Antiope the Amazon or Antiope the mother of Amphion and Zethus.

A → pair of → vectors whose directions are parallel but having the opposite sense.

→ anti-; → parallel.

Any → elementary particle with a → charge of opposite sign to the same particle in normal matter.

→ anti- "opposite, opposing, against" + → particle.

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.

The Air Pump. A faint → constellation in the → southern hemisphere, at → right ascensionα ~ 10h, → declinationδ ~ -35 deg. Abbreviation: Ant; genitive form: Antliae. Antlia is one of the smaller constellations in the sky, occupying an area of 239 square degrees. It is located in the second quadrant of the southern hemisphere and can be seen at latitudes between +45° and -90°. The neighboring constellations are → Centaurus, → Hydra, → Pyxis, and → Vela. Antlia does not have any stars brighter than magnitude 3.00. It contains two stars located within 10 → parsecs of Earth. The brightest star in Antlia is Alpha Antliae. The nearest star in Antlia, DEN 1048-3956, is a → brown dwarf brown dwarf only ~ 4 parsecs, 13.15 → light-years distant from Earth. Notable deep sky objects in Antlia include the → Antlia dwarf Galaxy, → Antlia 2, the Antlia Cluster of Galaxies, and the unbarred → spiral galaxy NGC 2997.

L. antlia "pump," from Gk. antlia "ship's hold, bilge water," from antlos.

Tolombé "pump," from Turkish tulumba "pump," from It. tromba.

A Milky-Way satellite in the constellation → Antlia. Antlia. It was originally detected in Gaia DR2 data using a combination of → RR Lyrae, → proper motions, → parallaxes and shallow → broad-band photometry. Antlia 2 is located behind the → Galactic disk at a latitude of b ~ 11° and spans 1.26 degrees, which corresponds to ~ 2.9 kpc at its distance of 130 kpc. While similar in extent to the → Large Magellanic Cloud, Antlia 2 is orders of magnitude fainter with M_V = -8.5 mag, making it by far the lowest surface brightness system known (at 32.3 mag/arcsec²), ~ 100 times more diffuse than the so-called ultra diffuse galaxies. The dwarf's systemic velocity is 290.9 ± 0.5 km s^-1, its velocity dispersion, 5.7 ± 1.1 km s^-1, and mean → metallicity, [Fe/H]= -1.4 (Torrealba et al., 2018, arXiv:1811.04082).

→ Antlia.

A → dwarf spheroidal galaxy located about 4.3 million → light-years from. Earth. It is a very faint object, with an apparent magnitude of 16.2. The galaxy was not discovered until 1997. (PGC 29194) The Antlia Dwarf lies on the outer rim of the Local Group of galaxies, possibly even beyond it, and there is evidence suggesting that it is tidally interacting with another small galaxy, NGC 3109, in the → Hydra constellation.

→ Antlia; → dwarf.

A mathematical expression, derived from the → Clausius-Clapeyron equation, of the relation between the vapor pressure and the temperature of pure substances. It shows that the logarithm of vapor pressure is linearly dependent on the reciprocal of → absolute temperature.

Named after Louis Charles Antoine (1825-?), a French marine engineer, who derived the equation; → equation.