The study, measurement, and description of depths and currents in open seas, lakes, estuaries, and rivers.
A term denoting the water portion of the Earth's surface.
An instrument that records the hygrometer's measure of water vapor.
Imaging Atmospheric Cherenkov Technique (IACT)
tašnik-e tasvirgiri-ye Čerenkov-e javvi
Fr.: téchnique d'imagerie Čerenkov atmosphérique
The method used to detect very brief flashes of → Cherenkov radiation generated by the → cascade shower of → relativistic charged particles produced when a very high-energy → gamma ray (in the range 50 GeV to 50 TeV) strikes the atmosphere at a typical altitude of 10 km. Owing to this technique, it possible to discriminate cosmic gamma rays from the cosmic ray background and to determine their energy and source direction. More specifically, the incoming gamma-ray photon undergoes → pair production in the vicinity of the nucleus of an atmospheric molecule. The electron-positron pairs produced are of extremely high energy and immediately radiate in a → bremsstrahlung process. This radiation is itself extremely energetic, with many of the photons undergoing further pair production. A cascade of charged particles ensues which, due to its extreme energy, produces a flash of Cherenkov radiation lasting between 5 and 20 nano-seconds. The total area on the ground illuminated by this flash corresponds to many hundreds of square meters, which is why the effective area of IACT telescopes should be large.
Fr.: en phase
The condition which exists when two waves of the same frequency pass through their maximum and minimum values in a correlated or synchronized way.
The global network of all the world's communications, databases, and sources of information.
initial phase angle
zâviye-ye fâz-e âqâzin
Fr.: angle de phase initial
The value of the phase corresponding to the origin of time. Same as the → epoch angle.
Fr.: éphémérides INPOP
A dynamical model developed in France since 2003 which calculates the motion of → Solar System bodies with the highest accuracy. It integrates data obtained by NASA and ESA space missions. See, for example, A. Fienga et al. 2011, arXiv:1108.5546.
INPOP, short for Intégration Numérique Planétaire de l'Observatoire de Paris; → ephemerides.
internal photoelectric effect
oskar-e šid-barqi-ye daruni
Fr.: effet photoélectrique interne
The → photoelectric effect whereby photons absorbed by a solid (→ semiconductor) raise electrons from a lower to a higher → energy level (from → valence band to → conduction band). See also → external photoelectric effect.
The region of the Earth's upper atmosphere containing a small percentage of free electrons and ions produced by photoionization of the constituents of the atmosphere by solar ultraviolet radiation.
miyânband-e titaki, ~ titakvâr
Fr.: diaphragme iris
A mechanical device, consisting of thin overlapping plates, designed to smoothly vary the effective diameter of a lens, thereby controlling the amount of light allowed through.
A line drawn through all points on a weather map having the same amount of → cloud cover.
From Gk. → iso- + nephos "cloud," cognate with Pers. nam "humidity, moisture;" Av. napta- "moist," nabās-câ- "cloud," nabah- "sky;" Skt. nábhas- "moisture, cloud, mist;" L. nebula "mist," nimbus "rainstorm, rain cloud;" O.H.G. nebul; Ger. Nebel "fog;" O.E. nifol "dark;" from PIE *nebh- "cloud, vapor, fog, moist, sky."
Of or relating to → isophotes.
Fr.: rayon isophotal
The size attributed to a galaxy corresponding to a particular level of → surface brightness. The reason is that galaxies do not have sharp edges.
A line joining points with the same surface brightness on a plot or in image of a celestial object such as a nebula or galaxy.
Isophote, from → iso- + a combining form of Gk. phos (gen. photos) "light."
Izošid, from izo-, → iso-, + šid "light, sunlight," from Mid.Pers. šêt "shining, radiant, bright;" Av. xšaēta- "shining, brilliant, splendid, excellent."
Fr.: effet Josephson
Named after the British physicist Brian David Josephson, who predicted the existence of the effect in 1962; → effect.
juhe-ye Josephson (#)
Fr.: jonction Josephson
javv-e Hormoz, havâsepehr-e ~
Fr.: atmosphère de Jupiter
The gaseous envelope surrounding Jupiter. It is about 90% → hydrogen and 10% → helium (by numbers of atoms, 75/25% by mass) with traces of → methane, → water, and → ammonia. This is very close to the composition of the primordial → solar nebula from which the entire solar system was formed. Saturn has a similar composition, but Uranus and Neptune have much less hydrogen and helium. The outermost layer is composed primarily of ordinary → molecular hydrogen and helium. Visually, Jupiter is dominated by two atmospheric features; a series of ever-changing atmospheric cloud bands arranged parallel to the equator and an oval atmospheric blob called the → Great Red Spot.
A branch of → linguistics that deals with the principle and methods of writing dictionaries.