# An Etymological Dictionary of Astronomy and AstrophysicsEnglish-French-Persian

## فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

### M. Heydari-Malayeri    -    Paris Observatory

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 Fermat prime   نخست ِ فرما   naxost-e FermatFr.: nombre de Fermat premier   A → Fermat number, 22n + 1, that is a → prime number. The only known Fermat primes are: 3, 5, 17, 257, and 65537, corresponding to n = 0, 1, 2, 3, and 4. Fermat's last theorem   واپسین فربین ِ فرما   vâpasin farbin-e FermatFr.: dernier théorème de Fermat   In → number theory, the statement that for all → integers, the equation xn + yn = zn has no solution in → positive integer. After 358 years of effort by mathematicians to prove the theorem, a complete proof was found by Andrew Wiles in 1995.→ Fermat's principle; → last; → theorem. Fermat's principle   پروز ِ فرما   parvaz-e FermatFr.: principe de Fermat   The path taken by a ray of light going from one point to another through any set of media is such that the time taken is a minimum. This principle governs the light propagation and determines the geodesics of optical paths.Put forward by Pierre de Fermat (1601-1665), French mathematician, born at Beaumont-de-Lomagne; → principle fermi   فرمی   fermi (#)Fr.: fermi   A unit of length equal to 10-13 cm.After Enrico Fermi (1901-1954), the Italian-born American physicist who was a key figure in the development of nuclear physics. He was awarded the 1938 Nobel Prize for Physics. Fermi constant   پایای ِ فرمی   pâyâ-ye FermiFr.: constante de Fermi   The → coupling constant associated with the → weak interaction, which gives rise to → beta decay. CF = 1.167 x 10-5 GeV-2.→ Fermi; → constant. Fermi energy   کاروژ ِ فرمی   kâruž-e FermiFr.: énergie de Fermi   The energy of the highest occupied quantum state in a system of fermions at absolute zero temperature. See also → Fermi sea.→ fermi; → energy. Fermi Gamma-ray Space Telescope   دوربین ِ فضایی ِ پرتوهای ِ گاما فرمی   Durbin-e fazâyi-ye partowhâ-ye gâmâ FermiFr.: Télescope spatial à rayons gamma Fermi   A space observatory, formerly named GLAST, devoted to the study of → gamma rays emitted from astrophysical objects. Developed by NASA in collaboration with the U.S. Department of Energy, along with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden, and the United States, Fermi was launched on June 11, 2008. The main instrument, the Large Area Telescope (LAT), is an imaging → camera covering the energy range from about 20 → MeV to more than 300 → GeV. Such gamma rays are emitted only in the most extreme conditions, by particles moving very nearly at the → speed of light. The LAT's → field of view covers about 20% of the sky at any time, and it scans continuously, covering the whole sky every three hours. Another instrument, the Gamma-ray Burst Monitor (GBM) has a field of view several times larger than the LAT and provides → spectral coverage of → gamma-ray burst that extends from the lower limit of the LAT down to 10 → keV.→ Fermi; → gamma ray; → space; → telescope. Fermi interaction   اندرژیرش ِ فرمی   andaržirš-e FermiFr.: interaction de Fermi   An old explanation, proposed by Enrico Fermi, of the → weak interaction.→ fermi; → interaction. Fermi level   تراز ِ فرمی   tarâz-e FermiFr.: niveau de Fermi   A measure of the → energy of the least tightly held → electrons within a → solid at a → non-zero → temperature. The value of the Fermi level at → absolute zero (-273.15 °C) is called the → Fermi energy and is a constant for each solid. In other words, the Fermi level is any → energy level having the probability that it is exactly half filled with electrons in the → Fermi-Dirac statistics. Levels of lower energy than the Fermi level tend to be entirely filled with electrons, whereas energy levels higher than the Fermi tend to be empty.→ Fermi; → level. Fermi paradox   پارادخش ِ فرمی   pârâdaxš-e FermiFr.: paradoxe de Fermi   The apparent contradiction between the high probability of the existence of extraterrestrial civilizations and the lack of evidence of contact with such civilizations.→ fermi; → paradox. Fermi pressure   فشار ِ فرمی   fešâr-e FermiFr.: pression de Fermi   Same as → degeneracy pressure.→ fermi; → pressure. Fermi sea   دریای ِ فرمی   daryâ-ye FermiFr.: mer de Fermi   A large aggregate of single-state → fermions of lowest energy. When the temperature is lowered to absolute zero, all electrons in solids attempt to get into the lowest available energy level. However, electrons cannot all occupy the lowest energy, or ground state, in virtue of the → Pauli exclusion principle. They stack up in the lowest energy states, with two fermions in each state, one spin up and one spin down. Such assemblage of filled states is called the Fermi "sea," and this state of matter is called → degenerate. All states with energy less than the Fermi energy are filled, and all states above the Fermi energy are empty.→ fermi; → sea. Fermi-Dirac statistics   آمار ِ فرمی-دیراک   âmâr-e Fermi-Dirac (#)Fr.: distribution Fermi-Dirac   The statistical distribution of → fermions over the energy states for a system in → thermodynamic equilibrium. In other words, the probability that a given energy level be occupied by a fermion.→ fermi, → Dirac function; → statistics. Fermi-Pasta-Ulam problem   پراسه‌ی ِ فرمی-پستا-اولام   parâse-ye Fermi-Pasta-UlamFr.: expérience Fermi-Pasta-Ulam   A computer experiment that was aimed to study the → thermalization process of a → solid. In other words, the goal was to see whether there is an approximate → equipartition of energy in the system, which would mean that the motion is → chaotic. Using computer simulation, Fermi-Pasta-Ulam studied the behavior of a chain of 64 mass particles connected by → nonlinear springs. In fact, they were looking for a theoretical physics problem suitable for an investigation with one of the very first computers, the he MANIAC (Mathematical Analyzer, Numerical Integrator and Computer). They decided to study how a → crystal evolves toward → thermal equilibrium by simulating a chain of particles, linked by a quadratic interaction potential, but also by a weak nonlinear interaction. Fermi-Pasta-Ulam assumed that if the interaction in the chain were nonlinear, then an exchange of energy among the normal modes would occur, and this would bring forth the equipartition of energy, i.e. the thermalization. Contrary to expectations, the energy revealed no tendency toward equipartition. The system had a simple quasi-periodic behavior, and no → chaoticity was observed. This result, known as the Fermi-Pasta-Ulam paradox, shows that → nonlinearity is not enough to guarantee the equipartition of energy (see, e.g., Dauxois et al., 2005, Eur. J. Phys., 26, S3).E. Fermi, J. Pasta, S. Ulam, 1955, Los Alamos report LA-1940; → problem. fermion   فرمیون   fermion (#)Fr.: fermion   An elementary particle, such as → electron, → proton, or → neutron, having a half integral value of → spin. Fermions obey the → Pauli exclusion principle.From Fermi → fermi + → -on. ferric   فریک   ferrikFr.: ferrique   Of or containing → iron, especially in the trivalent state. More specifically, iron with an → oxidation number of +3; also denoted iron(III) or Fe3+.Ferric, from L. ferrum "iron," + → -ic. ferric iron   آهن ِ فریک   âhan-e ferrikFr.: fer ferrique, fer trivalent   Iron in a plus-3 → oxidation state. Ferric iron needs to share three electrons with an oxygen molecule to make the ion neutral.→ ferric; → iron. ferro-   آهن-، فرو-   âhan-, ferro-Fr.: ferro-   Indicating a property of → iron or the presence of iron.Ferro-, variant ferri-, combining form of L. ferrum "iron."Âhan-, → iron. ferroelectric   آهن‌برق‌مند   âhanbarqmandFr.: ferroélectrique   Characterized by the presence of a spontaneous → electric dipole while not exposed to an external electric field. → ferroelectricity.→ ferro-; → electric. ferroelectricity   آهن‌برق‌مندی   âhanbarqmandiFr.: ferroélectricité   A property observed in certain materials characterized by the presence of a spontaneous electric polarization even in the absence of an external electric field. In the ferroelectric state the center of positive charge of the material does not coincide with the center of negative charge. This phenomenon is explained by spontaneous alignment of these permanent moments along the same direction. The term comes from the similarity with → ferromagnetism, but iron is not a ferroelectric. Ferroelectricity disappears above a critical temperature. Ferroelectric materials have been a fertile field for the study of → phase transitions.→ ferro-; → electricity.