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 about alpha 10h, delta -35 deg. Abbreviation: Ant; genitive form: Antliae.
L. antlia "pump," from Gk. antlia "ship's hold, bilge water," from antlos.
Tolombé "pump," from Turkish tulumba "pump," from It. tromba.
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.
Fr.: étoile Ap
A star of spectral type A in which lines of ionized metals and → rare-earth elements are abnormally enhanced. Such stars have unusually strong magnetic fields, thousands of times stronger than the Sun's typical surface field. Ap stars are generally slow rotators because of magnetic braking.
Fr.: étoile Ap/Bp
A class of → intermediate-mass stars which possess anomalously strong → magnetic fields (about 100-10000 G). Ap/Bp stars typically show → overabundances of → iron peak elements, → rare earths, and → silicon, ranging up to ~2 dex above solar. These magnetic → chemically peculiar stars make up about 5% of the → main sequence A and B population (→ A star, → B star). Ap/Bp stars have predominantly → dipolar magnetic fields. The presence of strong, ordered magnetic fields in some main sequence A and B stars has been known for nearly one-half of a century (Babcock 1947). However the cause of the magnetic field is still a matter of debate. There are two competing theories: the contemporaneous → dynamo effect, and the → fossil magnetic field theory. Contemporaneous dynamo effect suggests that there is a dynamo effect currently working in the → convective core of the star. The fossil field theory assumes that the magnetic field is a remnant, produced by a dynamo effect operating at an earlier evolutionary phase, or swept up from the → interstellar medium during → star formation (Power et al., 2006, astro-ph/0612557).
A and B represent spectral types and p stands for → peculiar.
The point at which a binary star is furthest from its companion.
Apastron, from Gk. ap-, → apo- + astron "star."
Fr.: amortissement apériodique
A system in which the → damping is great enough to prevent oscillation.
The diameter of the main mirror in a reflecting telescope, the objective lens in a refracting telescope, the dish of a radio telescope, or the entry of an instrument such as spectrograph, photometer.
From L. apertura, from apertus, p.p. of aperire "to open, uncover," from PIE *ap-wer-yo- from *ap- "off, away" + base *wer- "to cover".
Ddahâné "an opening," from dahân "mouth," from Mid.Pers./Mod.Pers. zafar, Av. zafar, zafan "mouth," compare with Skt. jambha- "set of teeth, mouth, jaws," Ger. Kiefer "mouth".