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.
pâdgereh (#), šekam (#)
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.
1) Of or relating to the → antipodes.
1) The exact or direct opposite.
The antiparticle of a proton, identical in mass and spin but of opposite (negative) charge.
Fr.: direction antisolaire
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.
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.
Pâddom, from pâd-, → anti-, + dom "tail."
1) Of the nature of or involving → antithesis.
Fr.: Machine pneumatique
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.
Fr.: Antlia 2
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 MV = -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).
Fr.: naine d'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.
Fr.: équation d'Antoine
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.
Grammar: A word opposite in meaning to another.
That part of the Moon's shadow that extends beyond the → umbra. It is similar to the → penumbra in that the Sun is only partially blocked by the Moon. From within the antumbra, the Sun appears larger than the Moon which is seen in complete silhouette. An → annular eclipse is seen when an observer passes through the antumbra (F. Espenak, NASA).
Ap and Bp star
Fr.: étoile Ap/Bp
Same as → Ap/Bp star.
→ Ap/Bp star.