Fr.: opérateur d'annihilation
Fr.: température d'antenne
In radio astronomy, a measure of the power absorbed by the antenna. In an ideal, loss-free radio telescope, the antenna temperature is equal to the brightness temperature if the intensity of the received radiation is constant within the main lobe. → antenna; → temperature.
antenna; → temperature.
Fr.: machine d'Anticythère
A unique Greek geared device, constructed around the end of the second century BC to display the movement of the Sun, the Moon, and possibly the planets around the Earth, and predict the dates of future eclipses. It measures about 32 by 16 by 10 cm and contains at least 30 interlocking gear-wheels, all of them having triangular teeth, from 15 to 223 in number. This device is one of the most stunning artefacts remained from antiquity, revealing an unexpected degree of technical creativity for the period. Nothing close to its technological sophistication appears again for well over a millennium, when astronomical clocks appear in the medieval Europe. It was discovered in 1901 in a sunken ship just off the coast of Antikythera, an island between Crete and the Greek mainland. Its significance and complexity were not understood until decades later. After lots of study involving several research fields, a copy of the device has recently been constructed. See, e.g., Freeth et al. 2006, Nature 444, 587.
Named after the Greek island in the Ionia Sea from which the fragments of the device were discovered in 1901 by sponge divers, who found a sunken Roman ship. Several pieces of evidence indicate that the Roman ship carrying the device wrecked sometime shortly after 85 BC. The ship also contained an enormous booty of bronzes, glassware, jewelry and pottery; → mechanism.
A number representing a group of quantities, obtained by adding each quantity of the group and dividing the total by the number of quantities. Same as → arithmetic mean.
From O.Fr. avarie "damage to ship," from It. avaria or maybe avere, O.Fr. aveir "property, goods," from L. habere "to have." Meaning shifted to "equal sharing of such loss by the interested parties."
Miyângin "the middle; middle-sized; the middle pearl in a string," from miyân, → middle, + -gin a suffix forming adjectives of possession.
Fr.: accélération moyenne
Of a body traveling from A to B, the change of → velocity divided by the time interval: ā = (v2 - v1) / (t2 - t1).
Fr.: vitesse moyenne
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.
Bayesian model averaging (BMA)
miyângin-giri-ye Bayesi-e model
An approach to model selection in which one bases inference on an average of all possible models instead of a single best model. The BMA is largely used in various branches of knowledge to properly account for model uncertainty in performing predictions.
Fr.: opération binaire
A mathematical operation that combines two numbers, quantities, sets, etc.,
to give a third. For example, multiplication of two numbers is a binary operation.
damâ-ye siyah-jesm (#)
Fr.: température de corps noir
The temperature at which a blackbody would emit the same radiation per unit area as that emitted by a given body at a given temperature.
Fr.: nébuleuse du Boomerang
A → nebula displaying two nearly symmetric lobes of matter that are being ejected from a central star at a speed of about 600,000 km per hour (each lobe nearly one light-year in length). The Boomerang Nebula resides 5,000 → light-years from Earth in the direction of the Southern constellation → Centaurus.
Boomerang, adapted from wo-mur-rang, boo-mer-rit, in the language of Australian aborigines; → nebula.
Fr.: température de brillance
In radio astronomy, the temperature of a source calculated on the assumption that it is a blackbody emitting radiation of the observed intensity at a given wavelength. → antenna temperature.
A large, roughly circular, → crater with diameter at least three or four times depth on the summit or in the side of a → volcano. A caldera can form from a volcanic blast or the collapse of a volcanic cone into an emptied → magma chamber.
From Sp. caldera "cauldron, kettle," also name of a crater on Canary Islands, from L. caldarius "of warming," from calidus "warm, hot," → calorie.
Tiyân "large cauldron; cauldron used for warming water in a communal bathhouse," of unknown origin.
Fr.: appareil photo, caméra
1) An apparatus for recording the light from an object
onto a sensitive material, such as film or CCD detector.
Mod.L. camera obscura "dark chamber" from L. camera "vaulted room," from Gk. kamara "vault," cf. Av. kamarâ- "waist; vault" Mod.Pers. kamar "waist," Skt. kamarati "is vaulted;" PIE base *kam- "to arch."
Kadak "small room," from kad, kadé "room, chamber, habitation, vault, cell, cavern," Mid.Pers. katak, Av. kata- "(small) room, closet, (small) house," cf. Goth. hethjo "small room" O.S. kotici "cavern, nest," PIE *kot(os).
šetâb-e markaz-goriz (#)
Fr.: accélération centrifuge
Of a point rotating in a circle round a central point, the outward acceleration away from the rotation axis. It corresponds to → centrifugal force. The centrifugal acceleration is given by ω x ω x r, or v2/r, where ω is → angular velocity, r the distance to the rotating axis, and v the → tangential velocity. The centrifugal and → centripetal accelerations are equal and opposite.
šetâb-e markaz-gerâ (#)
Fr.: accélération centripète
The rate of change of the → tangential velocity of a body moving along a circular path. The direction of centripetal acceleration is always inward along the → radius vector of the → circular motion. The magnitude of the centripetal acceleration is related to the → tangential velocity (v) and → angular velocity (ω) as follows: ac = v2/r = rω2. According to → Newton's second law, an object undergoing centripetal acceleration is experiencing a → centripetal force.
šetâbgar bâ tâbe-ye hamkubandé
Fr.: accélérateur à faisceau de collision
Same as → collider.
Fr.: température de couleur
The temperature of that black-body which has the same spectral energy distribution in a limited spectral region, as the object under study has.
donbâledâr 67P Churyumov-Gerasimenko
Fr.: comète Churyumov-Gerasimenko
A → comet with an irregular → nucleus of roughly 3 × 5 km across orbiting the Sun between → Jupiter and → Earth with a period of 6.45 years. The comet has been observed from Earth on seven approaches to the Sun: in 1969, 1976, 1982, 1989, 1996, 2002, and 2009. It was also imaged by the → Hubble Space Telescope in 2003, which allowed estimates of its size and shape. It arrived at → perihelion on 13 August 2015. In 2014 the → European Space Agency probe → Rosetta, launched in 2004, was placed on an orbit around 67P/Churyumov-Gerasimenko. Over an entire year, as it approached the Sun, Rosetta mapped the comet's surface and studied changes in its activity.
→ comet; Named after its discoverers, Klim Churyumov and Svetlana Gerasimenko, Ukrainian astronomers, who first noticed the comet in 1969.
Fr.: ère de Compton
A period in the early evolution of the Universe, before t = 10-23 sec when the radius of curvature of the Universe was less than the → Compton wavelength of typical particles.
A body comprising independent organizations that cooperate for a common purpose.