An Etymological Dictionary of Astronomy and Astrophysics

One of light appendages that grow from a bird’s skin and form its covering.

Etymology (EN): M.E., from O.E. fether; akin to Du. veder, Ger. Feder, O.N. fioþr, Sw. fjäder, from PIE root *pet- “to rush, to fly.”

Etymology (PE): Parr “feather,” variant bâl “wing,” Mid.Pers. parr “feather, wing,” bâl; Av. parəna- “feather,” Skt. parnam, cf.
O.H.G. farn “fern,” PIE pornom “feather.”

One of light appendages that grow from a bird’s skin and form its covering.

Etymology (EN): M.E., from O.E. fether; akin to Du. veder, Ger. Feder, O.N. fioþr, Sw. fjäder, from PIE root *pet- “to rush, to fly.”

Etymology (PE): Parr “feather,” variant bâl “wing,” Mid.Pers. parr “feather, wing,” bâl; Av. parəna- “feather,” Skt. parnam, cf.
O.H.G. farn “fern,” PIE pornom “feather.”

A prominent or conspicuous part or characteristic. → absorption feature; → coronal features;
→ dust feature; → emission feature.

Etymology (EN): From O.Fr. faiture “fashion, shape, form,” from L. facura “a formation,” from facere “to make, do, perform” (cf. Fr. faire, Sp. hacer), from PIE base *dhe- “to put, to do” (cf. Mod.Pers. dâdan “to give;” O.Pers./Av. dā- “to give, grant, yield,” dadāiti “he gives; puts;” Skt. dadáti “puts, places;” Hitt. dai- “to place;” Gk. tithenai “to put, set, place;” Lith. deti “to put;” Czech diti, Pol. dziac’, Rus. det’ “to hide,” delat’ “to do;” O.H.G. tuon, Ger. tun, O.E. don “to do”).

Etymology (PE): Ârang “color; mode, form, manner,” cf. Av. *iringa- “sign, mark” in haptôiringa- “with seven marks,” from hapto- “seven,” + iringa-; Mid.Pers. haptiring, Mod.Pers. haftowrang “the constellation of Great Bear;” cf. Skt. linga- “mark, token, sign.”

A prominent or conspicuous part or characteristic. → absorption feature; → coronal features;
→ dust feature; → emission feature.

Etymology (EN): From O.Fr. faiture “fashion, shape, form,” from L. facura “a formation,” from facere “to make, do, perform” (cf. Fr. faire, Sp. hacer), from PIE base *dhe- “to put, to do” (cf. Mod.Pers. dâdan “to give;” O.Pers./Av. dā- “to give, grant, yield,” dadāiti “he gives; puts;” Skt. dadáti “puts, places;” Hitt. dai- “to place;” Gk. tithenai “to put, set, place;” Lith. deti “to put;” Czech diti, Pol. dziac’, Rus. det’ “to hide,” delat’ “to do;” O.H.G. tuon, Ger. tun, O.E. don “to do”).

Etymology (PE): Ârang “color; mode, form, manner,” cf. Av. *iringa- “sign, mark” in haptôiringa- “with seven marks,” from hapto- “seven,” + iringa-; Mid.Pers. haptiring, Mod.Pers. haftowrang “the constellation of Great Bear;” cf. Skt. linga- “mark, token, sign.”

One of the most successful general methods for the numerical solution of the → radiative transfer equation.
This method has been primarily used to study → radiative transfer in the → photospheres of stars.

See also: P. Feautrier (1964), C.r. hebd. Séanc. Acad. Sci. Paris 258, 3198; → method.

One of the most successful general methods for the numerical solution of the → radiative transfer equation.
This method has been primarily used to study → radiative transfer in the → photospheres of stars.

See also: P. Feautrier (1964), C.r. hebd. Séanc. Acad. Sci. Paris 258, 3198; → method.

See → Weber-Fechner law.

See → Weber-Fechner law.

Biology: To impregnate, to fertilize.

Etymology (EN): L. fecundetus “made fruitful, fertilized,” p.p. of fcundare, from fecundus “fruitful, fertile, productive,” from L. root *fe-, corresponding to PIE *dhe(i)- “to suck, suckle;” cf. Skt. dhayati “sucks,” dhayah “nourishing;” Gk. thele “mother’s breast, nipple,” thelys “female, fruitful;” Mid.Pers. dâyag “(wet-)nurse;” Mod.Pers. dâyé “(wet-)nurse;” Proto-Iranian *daH- “to suck, suckle;” O.C.S. dojiti “to suckle,” dojilica “nurse;” Lith. dele “leech;” Goth. daddjan “to suckle;” O.H.G. tila “female breast.”

Etymology (PE): Gošnidan, from gošn “male,” Mid.Pers. gušn; cf. Av. varšni- “male;” Skt. vrsan-.

Biology: To impregnate, to fertilize.

Etymology (EN): L. fecundetus “made fruitful, fertilized,” p.p. of fcundare, from fecundus “fruitful, fertile, productive,” from L. root *fe-, corresponding to PIE *dhe(i)- “to suck, suckle;” cf. Skt. dhayati “sucks,” dhayah “nourishing;” Gk. thele “mother’s breast, nipple,” thelys “female, fruitful;” Mid.Pers. dâyag “(wet-)nurse;” Mod.Pers. dâyé “(wet-)nurse;” Proto-Iranian *daH- “to suck, suckle;” O.C.S. dojiti “to suckle,” dojilica “nurse;” Lith. dele “leech;” Goth. daddjan “to suckle;” O.H.G. tila “female breast.”

Etymology (PE): Gošnidan, from gošn “male,” Mid.Pers. gušn; cf. Av. varšni- “male;” Skt. vrsan-.

Biology: The act or process of fecundating.

See also: → fecundate; → -tion.

Biology: The act or process of fecundating.

See also: → fecundate; → -tion.

Relating to or characteristic of a unified body (e.g. a government) with constituent parts (states) that retain a measure of autonomy.

Etymology (EN): From Fr. fédéral, from L. foedus (genitive foederis) “league, treaty, alliance,” → federate, + → -al.

Etymology (PE): Hiyâvi, from hiyâvidan, → federate.

Relating to or characteristic of a unified body (e.g. a government) with constituent parts (states) that retain a measure of autonomy.

Etymology (EN): From Fr. fédéral, from L. foedus (genitive foederis) “league, treaty, alliance,” → federate, + → -al.

Etymology (PE): Hiyâvi, from hiyâvidan, → federate.

1. To join together in a → federation.
   
2. To organize on a → federal basis.

Etymology (EN): From L. foederatus “leagued together, allied,” p.p. of foederare “to establish by treaty,” from foedus
“league, treaty, alliance,” related to fides “faith.”

Etymology (PE): Hiyâvidan, from Tabari hiyâ “together, with each other,” probably related to Av. hi- “to chain, bind,” hiθav- “association, assemblage,”
hinav- “bond, chain,” hita- “fastened;”
O.P. vištāspa- literally “with unbound horses;” Av. hitāspa-; Pers. gošudan “to open,” → resolve; cf. Skt. sā-/say- “to bind, fasten, fetter.” Coined on the model of Ger. Bund “federation, alliance, band,” cognate with Pers. bastan “to bind,” → absolute.

1. To join together in a → federation.
   
2. To organize on a → federal basis.

Etymology (EN): From L. foederatus “leagued together, allied,” p.p. of foederare “to establish by treaty,” from foedus
“league, treaty, alliance,” related to fides “faith.”

Etymology (PE): Hiyâvidan, from Tabari hiyâ “together, with each other,” probably related to Av. hi- “to chain, bind,” hiθav- “association, assemblage,”
hinav- “bond, chain,” hita- “fastened;”
O.P. vištāspa- literally “with unbound horses;” Av. hitāspa-; Pers. gošudan “to open,” → resolve; cf. Skt. sā-/say- “to bind, fasten, fetter.” Coined on the model of Ger. Bund “federation, alliance, band,” cognate with Pers. bastan “to bind,” → absolute.

A composition of different databases which work in an integrated manner while preserving their autonomy.

See also: → federate; → database; → system.

A composition of different databases which work in an integrated manner while preserving their autonomy.

See also: → federate; → database; → system.

1. The act of federating or uniting in a league.
   

2. A political unit formed from smaller units on a → federal basis.

See also: Verbal noun of → federate.

1. The act of federating or uniting in a league.
   

2. A political unit formed from smaller units on a → federal basis.

See also: Verbal noun of → federate.

Pertaining to or of the nature of a → federation.

See also: → federate.

Pertaining to or of the nature of a → federation.

See also: → federate.

He who, or that which, federates.

See also: Agent noun of → federate + → -or.

He who, or that which, federates.

See also: Agent noun of → federate + → -or.

1. To give food to; supply with nourishment.
   

2. To furnish with necessary material.

Etymology (EN): M.E. feden, from O.E. fedan “to nourish;”
cf. O.S. fodjan, O.Fris. feda, Goth. fodjan “to feed.”

Etymology (PE): Xorândan, transitive form of xordan “to eat, consume,” Mid.Pers. xvardan “to eat, enjoy (food),” Av. x^var “to consume, eat;” Laki dialect hovârden “to eat;” Proto-Iranian *huar- “to consume, eat.”

1. To give food to; supply with nourishment.
   

2. To furnish with necessary material.

Etymology (EN): M.E. feden, from O.E. fedan “to nourish;”
cf. O.S. fodjan, O.Fris. feda, Goth. fodjan “to feed.”

Etymology (PE): Xorândan, transitive form of xordan “to eat, consume,” Mid.Pers. xvardan “to eat, enjoy (food),” Av. x^var “to consume, eat;” Laki dialect hovârden “to eat;” Proto-Iranian *huar- “to consume, eat.”

1. For any system that has an → input and → output, the return of a fraction of the output to the input for the next action. Feedback process allows a system to regulate itself by monitoring its own output. It is of prime importance to the working of all regulatory mechanisms found in living and non-living nature, as well as in social systems such as education and economy.
   

2. By extension, any response or information about the result of a process.
   

3. → stellar feedback.
   

See also: → feedback loop, → negative feedback, → positive feedback, → radiative feedback, → feedforward.

See also: → feed; → back.

1. For any system that has an → input and → output, the return of a fraction of the output to the input for the next action. Feedback process allows a system to regulate itself by monitoring its own output. It is of prime importance to the working of all regulatory mechanisms found in living and non-living nature, as well as in social systems such as education and economy.
   

2. By extension, any response or information about the result of a process.
   

3. → stellar feedback.
   

See also: → feedback loop, → negative feedback, → positive feedback, → radiative feedback, → feedforward.

See also: → feed; → back.

A closed transmission path in a → feedback process involving part of the → output as an → input for correction or control of the operation of a → system.

See also: → feedback; → loop.

A closed transmission path in a → feedback process involving part of the → output as an → input for correction or control of the operation of a → system.

See also: → feedback; → loop.

In a self-regulatory system, monitoring a disturbance before it enters the → system to apply corrections before the disturbance has influenced the system. See also → feedback.

See also: → feed; → forward.

In a self-regulatory system, monitoring a disturbance before it enters the → system to apply corrections before the disturbance has influenced the system. See also → feedback.

See also: → feed; → forward.

In a → radio telescope, a device located at the → focal point of the → antenna. It receives the → radio waves which the antenna collects and guides them to the → detector.

See also: → feed; → horn.

In a → radio telescope, a device located at the → focal point of the → antenna. It receives the → radio waves which the antenna collects and guides them to the → detector.

See also: → feed; → horn.

1. To perceive or examine by touch.
   

2. To have a sensation of (something), other than by sight, hearing, taste, or smell (Dictionary.com).

Etymology (EN): M.E. felen, from O.E. felan “to touch;” cf. O.S. gifolian, O.Fr.fela, Du. voelen, O.H.G. vuolen, Ger. fühlen “to feel;” from PIE root *pal- “to touch, feel, shake, strike softly” (cognates: Gk. psallein “to pluck (the harp),” L. palpare “to touch softly, stroke”).

Etymology (PE): Sohidan, from Mid.Pers. sôhistan “to feel, to touch,” sôhešn “feeling, sense,” of unknown origin. Note Pers. sahestan “to fear,” from Proto-Ir. *θrah- “to shake; to fear;” Pers. tars, harâs, sham “fear;” may be they are of different roots.

1. To perceive or examine by touch.
   

2. To have a sensation of (something), other than by sight, hearing, taste, or smell (Dictionary.com).

Etymology (EN): M.E. felen, from O.E. felan “to touch;” cf. O.S. gifolian, O.Fr.fela, Du. voelen, O.H.G. vuolen, Ger. fühlen “to feel;” from PIE root *pal- “to touch, feel, shake, strike softly” (cognates: Gk. psallein “to pluck (the harp),” L. palpare “to touch softly, stroke”).

Etymology (PE): Sohidan, from Mid.Pers. sôhistan “to feel, to touch,” sôhešn “feeling, sense,” of unknown origin. Note Pers. sahestan “to fear,” from Proto-Ir. *θrah- “to shake; to fear;” Pers. tars, harâs, sham “fear;” may be they are of different roots.

1. The function or the power of perceiving by touch.
   

2. Physical sensation not connected with sight, hearing, taste, or smell.
   

3. A particular sensation of this kind (Dictionary.com).

See also: Verbal noun of “to → feel.”

1. The function or the power of perceiving by touch.
   

2. Physical sensation not connected with sight, hearing, taste, or smell.
   

3. A particular sensation of this kind (Dictionary.com).

See also: Verbal noun of “to → feel.”

A group of rock-forming minerals whose members are the most abundant constituents of igneous rocks. They consist of aluminum silicates of potassium, sodium, and calcium and
typically occur as colorless or pale-colored crystals.

See also: Modification of obsolete Ger. Feldspath (now Feldspat), from Ger. Feld “field” + obsolete Ger. Spath (now Spat) “spar.”

A group of rock-forming minerals whose members are the most abundant constituents of igneous rocks. They consist of aluminum silicates of potassium, sodium, and calcium and
typically occur as colorless or pale-colored crystals.

See also: Modification of obsolete Ger. Feldspath (now Feldspat), from Ger. Feld “field” + obsolete Ger. Spath (now Spat) “spar.”

1. Of, relating to, or being the sex that typically has the capacity to bear offsprings or produce eggs.

   2. A female person, animal, or plant.

Etymology (EN): M.E., alteration of femel, femelle, from O.Fr. femelle “woman, female,” from M.L. femella “a female,” from L. femella “young female, girl,” diminutive of femina “woman, a female,” → feminine.

Etymology (PE): Mâdé “female,” from Mid.Pers. mâdag, “female,” from mâd, → mother.

1. Of, relating to, or being the sex that typically has the capacity to bear offsprings or produce eggs.

   2. A female person, animal, or plant.

Etymology (EN): M.E., alteration of femel, femelle, from O.Fr. femelle “woman, female,” from M.L. femella “a female,” from L. femella “young female, girl,” diminutive of femina “woman, a female,” → feminine.

Etymology (PE): Mâdé “female,” from Mid.Pers. mâdag, “female,” from mâd, → mother.

1. Characteristic of or appropriate or unique to women.
   

2. Of, relating to, or constituting the gender that ordinarily includes most words or grammatical forms referring to females (Merriam-Webster.com).

Etymology (EN): M.E. feminin, from O.Fr. femenin “feminine, female; with feminine qualities,” from L. femininus “feminine,” from femina “woman, female,” literally “she who suckles,” from root of felare “to suck, suckle;” cf. Gk. thele “mother’s breast, nipple,” thelys “female, fruitful;” Pers. dâyé, dâyah “(wet-nurse);” PIE root *d^he(i)- “to suck, suckle.”

Etymology (PE): Mâdin, from mâdé, → female.

1. Characteristic of or appropriate or unique to women.
   

2. Of, relating to, or constituting the gender that ordinarily includes most words or grammatical forms referring to females (Merriam-Webster.com).

Etymology (EN): M.E. feminin, from O.Fr. femenin “feminine, female; with feminine qualities,” from L. femininus “feminine,” from femina “woman, female,” literally “she who suckles,” from root of felare “to suck, suckle;” cf. Gk. thele “mother’s breast, nipple,” thelys “female, fruitful;” Pers. dâyé, dâyah “(wet-nurse);” PIE root *d^he(i)- “to suck, suckle.”

Etymology (PE): Mâdin, from mâdé, → female.

1. Belief in the social, political, and economic freedom of women and equality of the sexes. Feminism is closely tied to democracy and → secularism.
   

2. The movement organized around this belief.

Etymology (EN): From Fr. féminisme, from féminin “feminine, female,” from L. femininus “feminine” (originally in the grammatical sense), from femina “woman, female,” literally “she who suckles,”
cognates fecund “fruitful, fertile,” felix “happy,” fetus “offspring, pregnancy;” PIE base *d^heh(i)- “to suck, suckle;” cf. Gk. thele “mother’s breast;” Pers. dâyé “wet nurse.”

Etymology (PE): Zâd-zan-bâvari, from zâdzan “free woman” (on the model of zâdmard “free man, valiant man, generous man,” zâdsarv “tall and upright cypress tree”), from zâd, contraction of âzâd,
→ free,

• zan, → woman, + bâvari, → -ism.

1. Belief in the social, political, and economic freedom of women and equality of the sexes. Feminism is closely tied to democracy and → secularism.
   

2. The movement organized around this belief.

Etymology (EN): From Fr. féminisme, from féminin “feminine, female,” from L. femininus “feminine” (originally in the grammatical sense), from femina “woman, female,” literally “she who suckles,”
cognates fecund “fruitful, fertile,” felix “happy,” fetus “offspring, pregnancy;” PIE base *d^heh(i)- “to suck, suckle;” cf. Gk. thele “mother’s breast;” Pers. dâyé “wet nurse.”

Etymology (PE): Zâd-zan-bâvari, from zâdzan “free woman” (on the model of zâdmard “free man, valiant man, generous man,” zâdsarv “tall and upright cypress tree”), from zâd, contraction of âzâd,
→ free,

• zan, → woman, + bâvari, → -ism.

In the International System of Units, a prefix meaning 10^-15.

See also: From Danish and Norwegian femten “fifteen,” from O.N. fimmtān (Sw. femton, Du. vüftien, Ger. fünfzehn, E. fifteen, Pers. pânzdah), ultimately from
PIE base *penk^we “five” (cf. Mod.Pers. panj, Av. panca, Skt. pánca, Gk. pente, L. quinque) + PIE *dekm “ten” (cf. Mod.Pers. dah, Av. dasa, Skt. dáśa, Arm. tasn, Gk. deka, L. decem, Ger. zehn, E. ten, Fr. dix).

In the International System of Units, a prefix meaning 10^-15.

See also: From Danish and Norwegian femten “fifteen,” from O.N. fimmtān (Sw. femton, Du. vüftien, Ger. fünfzehn, E. fifteen, Pers. pânzdah), ultimately from
PIE base *penk^we “five” (cf. Mod.Pers. panj, Av. panca, Skt. pánca, Gk. pente, L. quinque) + PIE *dekm “ten” (cf. Mod.Pers. dah, Av. dasa, Skt. dáśa, Arm. tasn, Gk. deka, L. decem, Ger. zehn, E. ten, Fr. dix).

Any number of the form 2²ⁿ + 1, where n is a connective → integer. If Fermat number is → prime, it is called a → Fermat prime.

See also: → Fermat’s principle; → number.

Any number of the form 2²ⁿ + 1, where n is a connective → integer. If Fermat number is → prime, it is called a → Fermat prime.

See also: → Fermat’s principle; → number.

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.

See also: → Fermat’s principle; → prime.

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.

See also: → Fermat’s principle; → prime.

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.

See also: → Fermat’s principle; → last; → theorem.

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.

See also: → Fermat’s principle; → last; → theorem.

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.

See also: Put forward by Pierre de Fermat (1601-1665), French mathematician, born at Beaumont-de-Lomagne; → principle

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.

See also: Put forward by Pierre de Fermat (1601-1665), French mathematician, born at Beaumont-de-Lomagne; → principle

A unit of length equal to 10^-13 cm.

See also: 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.

A unit of length equal to 10^-13 cm.

See also: 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.

The → coupling constant associated with the → weak interaction, which gives rise to → beta decay. C_F = 1.167 x 10^-5 GeV^-2.

See also: → Fermi; → constant.

The → coupling constant associated with the → weak interaction, which gives rise to → beta decay. C_F = 1.167 x 10^-5 GeV^-2.

See also: → Fermi; → constant.

The energy of the highest occupied quantum state in a system of fermions at absolute zero temperature. See also → Fermi sea.

See also: → fermi; → energy.

The energy of the highest occupied quantum state in a system of fermions at absolute zero temperature. See also → Fermi sea.

See also: → fermi; → energy.

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.

See also: → Fermi; → gamma ray; → space; → telescope.

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.

See also: → Fermi; → gamma ray; → space; → telescope.

An old explanation, proposed by Enrico Fermi, of the → weak interaction.

See also: → fermi; → interaction.

An old explanation, proposed by Enrico Fermi, of the → weak interaction.

See also: → fermi; → interaction.

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.

See also: → Fermi; → level.

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.

See also: → Fermi; → level.

The apparent contradiction between the high probability of the existence of extraterrestrial civilizations and the lack of evidence of contact with such civilizations.

See also: → fermi; → paradox.

The apparent contradiction between the high probability of the existence of extraterrestrial civilizations and the lack of evidence of contact with such civilizations.

See also: → fermi; → paradox.

Same as → degeneracy pressure.

See also: → fermi; → pressure.

Same as → degeneracy pressure.

See also: → fermi; → pressure.

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.

See also: → fermi; → sea.

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.

See also: → fermi; → sea.

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.

See also: → fermi, → Dirac function; → statistics.

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.

See also: → fermi, → Dirac function; → statistics.

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).

See also: E. Fermi, J. Pasta, S. Ulam, 1955, Los Alamos report LA-1940; → problem.

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).

See also: E. Fermi, J. Pasta, S. Ulam, 1955, Los Alamos report LA-1940; → problem.

An elementary particle, such as → electron, → proton, or → neutron, having a half integral value of → spin. Fermions obey the → Pauli exclusion principle.

See also: From Fermi → fermi + → -on.

An elementary particle, such as → electron, → proton, or → neutron, having a half integral value of → spin. Fermions obey the → Pauli exclusion principle.

See also: From Fermi → fermi + → -on.

Of or containing → iron, especially in the trivalent state. More specifically, iron with an → oxidation number of +3; also denoted iron(III) or Fe³⁺.

See also: Ferric, from L. ferrum “iron,” + → -ic.

Of or containing → iron, especially in the trivalent state. More specifically, iron with an → oxidation number of +3; also denoted iron(III) or Fe³⁺.

See also: Ferric, from L. ferrum “iron,” + → -ic.

Iron in a plus-3 → oxidation state.
Ferric iron needs to share three electrons with an oxygen molecule to make the ion neutral.

See also: → ferric; → iron.

Iron in a plus-3 → oxidation state.
Ferric iron needs to share three electrons with an oxygen molecule to make the ion neutral.

See also: → ferric; → iron.

Indicating a property of → iron or the presence of iron.

Etymology (EN): Ferro-, variant ferri-, combining form of L. ferrum “iron.”

Etymology (PE): Âhan-, → iron.

Indicating a property of → iron or the presence of iron.

Etymology (EN): Ferro-, variant ferri-, combining form of L. ferrum “iron.”

Etymology (PE): Âhan-, → iron.

Characterized by the presence of a spontaneous → electric dipole while not exposed to an external electric field. → ferroelectricity.

See also: → ferro-; → electric.

Characterized by the presence of a spontaneous → electric dipole while not exposed to an external electric field. → ferroelectricity.

See also: → ferro-; → electric.

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.

See also: → ferro-; → electricity.

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.

See also: → ferro-; → electricity.

A ferroamagnetic substance, which possesses → ferromagnetism.

See also: → ferro-; → magnet.

A ferroamagnetic substance, which possesses → ferromagnetism.

See also: → ferro-; → magnet.

Relative to or characterized by → ferromagnetism.

See also: → ferro-; → magnetic.

Relative to or characterized by → ferromagnetism.

See also: → ferro-; → magnetic.

A property of certain substances which are enormously more magnetic than any other known substance. Ferromagnetic substances, such as the chemical elements iron, nickel, cobalt, some of the rare earths,
and ceratin alloys, achieve maximum → magnetization at relatively low magnetic field strengths. Their large → magnetic permeabilityies (greater than unity)
vary with the strength of the applied field. When the temperature of a ferromagnet
is increased the property vanishes gradually due to randomizing effects of thermal agitation. Beyond a definite temperature for each substance ( → Curie temperature) it ceases to behave as a ferromagnet and becomes a → paramagnet.
Ferromagnetism is due to the alignment of the → magnetic moments of uncompensated electrons in the crystal lattice. Under the influence of an external magnetizing field, all of the uncompensated electrons line up with their → spins in the direction of the field. In contrast with paramagnetic substances, in which spins interact only with an external magnetic field, in ferromagnets the spins interact with each others, each of them trying to align the others in its own direction. This coupling gives rise to a spontaneous alignment of the moments over macroscopic regions called domains. The domains undergo further alignment when the substance is subjected to an applied field. Ferromagnets retain their magnetisation even when the external magnetic field has been removed. See also → antiferromagnetism ; → diamagnetism; → magnetism.

See also: → ferro-; → magnetism.

A property of certain substances which are enormously more magnetic than any other known substance. Ferromagnetic substances, such as the chemical elements iron, nickel, cobalt, some of the rare earths,
and ceratin alloys, achieve maximum → magnetization at relatively low magnetic field strengths. Their large → magnetic permeabilityies (greater than unity)
vary with the strength of the applied field. When the temperature of a ferromagnet
is increased the property vanishes gradually due to randomizing effects of thermal agitation. Beyond a definite temperature for each substance ( → Curie temperature) it ceases to behave as a ferromagnet and becomes a → paramagnet.
Ferromagnetism is due to the alignment of the → magnetic moments of uncompensated electrons in the crystal lattice. Under the influence of an external magnetizing field, all of the uncompensated electrons line up with their → spins in the direction of the field. In contrast with paramagnetic substances, in which spins interact only with an external magnetic field, in ferromagnets the spins interact with each others, each of them trying to align the others in its own direction. This coupling gives rise to a spontaneous alignment of the moments over macroscopic regions called domains. The domains undergo further alignment when the substance is subjected to an applied field. Ferromagnets retain their magnetisation even when the external magnetic field has been removed. See also → antiferromagnetism ; → diamagnetism; → magnetism.

See also: → ferro-; → magnetism.

Of or containing → iron, especially in the bivalent state. More specifically, iron with → oxidation number of +2, denoted iron(II) or Fe2+.

Etymology (EN): From L. ferrum “iron,” + -ous a suffix forming adjectives that have the general sense “possessing, full of” a given quality.

Etymology (PE): Fervar, from fer, loan from Fr., + -var adj. suffix.

Of or containing → iron, especially in the bivalent state. More specifically, iron with → oxidation number of +2, denoted iron(II) or Fe2+.

Etymology (EN): From L. ferrum “iron,” + -ous a suffix forming adjectives that have the general sense “possessing, full of” a given quality.

Etymology (PE): Fervar, from fer, loan from Fr., + -var adj. suffix.

Iron in a plus-2 → oxidation state.

See also: → ferrous; → iron.

Iron in a plus-2 → oxidation state.

See also: → ferrous; → iron.

Physics: (of nuclear material) Able to become → fissile by → neutron capture.

Etymology (EN): M.E., from M.Fr. fertil, from L. fertilis “bearing in abundance, fruitful, productive,” from ferre “to bear,” from PIE root *bher- “to carry,” also “to bear children,” cognate with Pers. bordan “to carry, bear,” → refer.

Etymology (PE): Bârvar, literally “fruitful,” from bâr “fruit; flower; load; charge”

• possession suffix -var, related to bordan “to bear, carry,” as above.

Physics: (of nuclear material) Able to become → fissile by → neutron capture.

Etymology (EN): M.E., from M.Fr. fertil, from L. fertilis “bearing in abundance, fruitful, productive,” from ferre “to bear,” from PIE root *bher- “to carry,” also “to bear children,” cognate with Pers. bordan “to carry, bear,” → refer.

Etymology (PE): Bârvar, literally “fruitful,” from bâr “fruit; flower; load; charge”

• possession suffix -var, related to bordan “to bear, carry,” as above.

An → isotope not itself → fissile but that is converted into a fissile isotope, either directly or after a short → decay process following absorption of a → neutron. Example: U-238 can capture a neutron to give U-239. U-239 then decays to Np-239 which in turn decays to fissile Pu-239.

The most important fertile isotope is U-238. This is by far the most abundant isotope of natural uranium, making up 99.28%. The important transformation chain is: ₉₂U²³⁸ + ₀n¹→ ₉₃Np²³⁹ + β^- (23.5 minutes) → ₉₄Pu²³⁹ + β^- (2.36 days).

See also: → fertile; → isotope .

An → isotope not itself → fissile but that is converted into a fissile isotope, either directly or after a short → decay process following absorption of a → neutron. Example: U-238 can capture a neutron to give U-239. U-239 then decays to Np-239 which in turn decays to fissile Pu-239.

The most important fertile isotope is U-238. This is by far the most abundant isotope of natural uranium, making up 99.28%. The important transformation chain is: ₉₂U²³⁸ + ₀n¹→ ₉₃Np²³⁹ + β^- (23.5 minutes) → ₉₄Pu²³⁹ + β^- (2.36 days).

See also: → fertile; → isotope .

A schematic representation, in quantum electrodynamics and quantum chromodynamics,
of the way elementary particles like electrons and protons interact with each other by exchanging photons. Use of Feynman diagrams can greatly reduce the amount of computation involved in calculating a rate or cross section of a physical process.

See also: After the American physicist Richard P. Feynman (1918-1988), Nobel prize 1965; → diagram.

A schematic representation, in quantum electrodynamics and quantum chromodynamics,
of the way elementary particles like electrons and protons interact with each other by exchanging photons. Use of Feynman diagrams can greatly reduce the amount of computation involved in calculating a rate or cross section of a physical process.

See also: After the American physicist Richard P. Feynman (1918-1988), Nobel prize 1965; → diagram.