An Etymological Dictionary of Astronomy and Astrophysics

A → binary system that has very short orbital period (less than one hour) and helium dominated spectrum. The prototype, AM Canum Venaticorum, with a period of 17 minutes, was discovered in 1967.
AM CVn stars are → semidetached binary systems in which → accretion is going on. The → donor star is hydrogen deficient and the → accretor is usually a → white dwarf.
To fit within their → Roche lobes, the donor stars must be dense, suggesting they may be → degenerate too. It is at present thought that AM CVn stars represent three possible evolutionary phases in 1) → double white dwarf systems, 2) white dwarf and → helium star binaries, and 3) → cataclysmic variables with evolved donors.
For a review see G. Nelemans 2005, astro-ph/0409676.

See also: AM, letters of alphabet used in variable star designations; CVn, abbreviation of → Canes Venatici; → star.

A → binary system that has very short orbital period (less than one hour) and helium dominated spectrum. The prototype, AM Canum Venaticorum, with a period of 17 minutes, was discovered in 1967.
AM CVn stars are → semidetached binary systems in which → accretion is going on. The → donor star is hydrogen deficient and the → accretor is usually a → white dwarf.
To fit within their → Roche lobes, the donor stars must be dense, suggesting they may be → degenerate too. It is at present thought that AM CVn stars represent three possible evolutionary phases in 1) → double white dwarf systems, 2) white dwarf and → helium star binaries, and 3) → cataclysmic variables with evolved donors.
For a review see G. Nelemans 2005, astro-ph/0409676.

See also: AM, letters of alphabet used in variable star designations; CVn, abbreviation of → Canes Venatici; → star.

A → red dwarf variable star located in the constellation → Hercules. AM Herculis usually remains in its “high” state (V ~ 13 mag), but from time to time it drops into a “low” state (V> 15 mag) that may last weeks or months. Originally classified as an irregular variable and associated with the X-ray source 3U 1809+50, AM Her was discovered in 1976 to be a short-period → binary system (3.1 hour orbital period) related to the → cataclysmic variables. It is in fact an → interacting binary in which a red dwarf (M4 V) loses mass to a → white dwarf primary star. The white dwarf has a very strong magnetic field (B ~ 2 × 10⁸ G) and rotates synchronously with the orbit. The magnetic field constrains the → mass loss from the secondary star to flow along a stream directly onto the white dwarf rather than into an → accretion disk as in the nonmagnetic cataclysmic variables. The optical spectrum shows strong emission lines of H, He I, and He II, along with weaker lines of other ions such as N III, C III, C II, and Ca II, all showing large velocity variations. → TiO bands from the M4 V secondary star are detected when the system is in its “low” state. AM Her is the class prototype of the → polars (see, e.g., Hutchings et al. 2002, AJ 123, 2841).

See also: AM, letters of alphabet used in variable star designations; → Hercules.

A → red dwarf variable star located in the constellation → Hercules. AM Herculis usually remains in its “high” state (V ~ 13 mag), but from time to time it drops into a “low” state (V> 15 mag) that may last weeks or months. Originally classified as an irregular variable and associated with the X-ray source 3U 1809+50, AM Her was discovered in 1976 to be a short-period → binary system (3.1 hour orbital period) related to the → cataclysmic variables. It is in fact an → interacting binary in which a red dwarf (M4 V) loses mass to a → white dwarf primary star. The white dwarf has a very strong magnetic field (B ~ 2 × 10⁸ G) and rotates synchronously with the orbit. The magnetic field constrains the → mass loss from the secondary star to flow along a stream directly onto the white dwarf rather than into an → accretion disk as in the nonmagnetic cataclysmic variables. The optical spectrum shows strong emission lines of H, He I, and He II, along with weaker lines of other ions such as N III, C III, C II, and Ca II, all showing large velocity variations. → TiO bands from the M4 V secondary star are detected when the system is in its “low” state. AM Her is the class prototype of the → polars (see, e.g., Hutchings et al. 2002, AJ 123, 2841).

See also: AM, letters of alphabet used in variable star designations; → Hercules.

A chemically peculiar A- or early F-type star showing an overabundance of → heavy elements and an underabundance of calcium and scandium. An Am star cannot receive a unique spectral type, as different methods (using the metallic lines, the hydrogen Balmer lines, and the calcium Ca II K-lines) yield three different spectral types. Contrarily to Ap stars, Am stars do not have significant external magnetic fields. Their rotational velocities are about 100-120 km s^-1 smaller than those of → Ap stars.

See also: A for the spectral type, m for → metal; → star.

A chemically peculiar A- or early F-type star showing an overabundance of → heavy elements and an underabundance of calcium and scandium. An Am star cannot receive a unique spectral type, as different methods (using the metallic lines, the hydrogen Balmer lines, and the calcium Ca II K-lines) yield three different spectral types. Contrarily to Ap stars, Am stars do not have significant external magnetic fields. Their rotational velocities are about 100-120 km s^-1 smaller than those of → Ap stars.

See also: A for the spectral type, m for → metal; → star.

The third of Jupiter’s known satellites orbiting at about 181,300 km from Jupiter with a period of about 12h. A mean diameter of 189 km makes it the fifth largest satellite of Jupiter. Amalthea was discovered by E. Barnard in 1892.

Etymology (EN): Amalthea, in Gk. mythology, the goat that suckled Zeus after his mother had him sent to Crete so his father would not eat him.

The third of Jupiter’s known satellites orbiting at about 181,300 km from Jupiter with a period of about 12h. A mean diameter of 189 km makes it the fifth largest satellite of Jupiter. Amalthea was discovered by E. Barnard in 1892.

Etymology (EN): Amalthea, in Gk. mythology, the goat that suckled Zeus after his mother had him sent to Crete so his father would not eat him.

1. To collect into a mass or pile; → accumulate.
   

2. To gather for oneself; collect as one’s own (Dictionary.com).

Etymology (EN): M.E., from O.Fr. amasser, from à “to,” → ad-, + masser “to gather in mass,” → mass.

Etymology (PE): Anbâštan, anbârdan “to fill, to replete,” from Mid.Pers. hambāridan “to fill;” from Proto-Iranian *ham-par-, from prefix ham-, → com-, + par- “to fill;” cf. Av. par- “to fill,” parav-, pauru-, pouru- “full, much, many;” O.Pers. paru- “much, many;” Mid.Pers. purr “full;” Mod.Pers. por “full, much, very;” PIE base *pelu- “full,” from *pel- “to be full;” cf. Skt. puru- “much, abundant;” Gk. polus “many,” plethos “great number, multitude;” O.E. full.

1. To collect into a mass or pile; → accumulate.
   

2. To gather for oneself; collect as one’s own (Dictionary.com).

Etymology (EN): M.E., from O.Fr. amasser, from à “to,” → ad-, + masser “to gather in mass,” → mass.

Etymology (PE): Anbâštan, anbârdan “to fill, to replete,” from Mid.Pers. hambāridan “to fill;” from Proto-Iranian *ham-par-, from prefix ham-, → com-, + par- “to fill;” cf. Av. par- “to fill,” parav-, pauru-, pouru- “full, much, many;” O.Pers. paru- “much, many;” Mid.Pers. purr “full;” Mod.Pers. por “full, much, very;” PIE base *pelu- “full,” from *pel- “to be full;” cf. Skt. puru- “much, abundant;” Gk. polus “many,” plethos “great number, multitude;” O.E. full.

One who engages in an activity (study, science, or sport) as a pastime rather than as a profession. → amateur astronomer, → amateur astronomy.

Etymology (EN): From Fr. amateur “lover of, one who has a taste for (something),” from L. amator “lover,” from amare “to love.”

Etymology (PE): Dustkâr, a variant of dustâr, dustdâr “he who likes, lover, supporter,” from dust “friend, lover” + kâr “occupation, → work.”

One who engages in an activity (study, science, or sport) as a pastime rather than as a profession. → amateur astronomer, → amateur astronomy.

Etymology (EN): From Fr. amateur “lover of, one who has a taste for (something),” from L. amator “lover,” from amare “to love.”

Etymology (PE): Dustkâr, a variant of dustâr, dustdâr “he who likes, lover, supporter,” from dust “friend, lover” + kâr “occupation, → work.”

A person who engages in astronomy as a pastime rather than as a profession. → amateur astronomy. See also → professional astronomer.

See also: → amateur; → astronomer.

A person who engages in astronomy as a pastime rather than as a profession. → amateur astronomy. See also → professional astronomer.

See also: → amateur; → astronomer.

The astronomical activities carried out by → amateur astronomers.

See also: → amateur; → astronomy.

The astronomical activities carried out by → amateur astronomers.

See also: → amateur; → astronomy.

The current geologic era on Mars that began around 2 billion to 3 billion years ago. It is characterized by lower geologic activity such as volcanism and only occasional releases of underground water. A dry environment with a very thin atmosphere in which water can only exist as a solid or a gas, not as a liquid. → Noachian era; → Hesperian era.

Etymology (EN): Named for the young lava-covered plains called Amazonia Planitia. → era.

The current geologic era on Mars that began around 2 billion to 3 billion years ago. It is characterized by lower geologic activity such as volcanism and only occasional releases of underground water. A dry environment with a very thin atmosphere in which water can only exist as a solid or a gas, not as a liquid. → Noachian era; → Hesperian era.

Etymology (EN): Named for the young lava-covered plains called Amazonia Planitia. → era.

A hard translucent yellow, orange, or brownish-yellow fossil resin. Amber becomes negatively charged when rubbed with wool, because it attracts negative charges (electrons) and will take them from wool.

Etymology (EN): M.E. ambre, from O.Fr., from L. ambra, ambar, from Ar. ‘anbar “ambergris, amber,” from Mid.Pers. ambar, → ambergris.

Etymology (PE): Kahrobâ, from kah “straw” + robâ “attractor.” The first component kah, kâh
“straw, hay,” from Mid.Pers. kâh “chaff, straw;” cf. Pali kattha- “a piece of wood;” Skt. kastha- “stick;” Gk. klados “twig;”
O.Ir. caill “wood;” P.Gmc. *khulto-; Ger. Holz “wood;” E. holt; PIE *kldo-. The second component robâ, from robudan “to attract, to grab, rob;” Av. urūpaiieinti “to cause racking pain(?);” cf. Skt. rup- “to suffer from abdominal pain,” rurupas “to cause violent pain,” ropaná- “causing racking pain,” rópi- “racking pain;” L. rumpere “to break;” O.E. reofan “to break, tear.”
In Arabic kahrobâ, a loanword from Persian, is used as equivalent for electricity.

A hard translucent yellow, orange, or brownish-yellow fossil resin. Amber becomes negatively charged when rubbed with wool, because it attracts negative charges (electrons) and will take them from wool.

Etymology (EN): M.E. ambre, from O.Fr., from L. ambra, ambar, from Ar. ‘anbar “ambergris, amber,” from Mid.Pers. ambar, → ambergris.

Etymology (PE): Kahrobâ, from kah “straw” + robâ “attractor.” The first component kah, kâh
“straw, hay,” from Mid.Pers. kâh “chaff, straw;” cf. Pali kattha- “a piece of wood;” Skt. kastha- “stick;” Gk. klados “twig;”
O.Ir. caill “wood;” P.Gmc. *khulto-; Ger. Holz “wood;” E. holt; PIE *kldo-. The second component robâ, from robudan “to attract, to grab, rob;” Av. urūpaiieinti “to cause racking pain(?);” cf. Skt. rup- “to suffer from abdominal pain,” rurupas “to cause violent pain,” ropaná- “causing racking pain,” rópi- “racking pain;” L. rumpere “to break;” O.E. reofan “to break, tear.”
In Arabic kahrobâ, a loanword from Persian, is used as equivalent for electricity.

A wax-like, ash-colored, strongly scent substance present in the intestines of → whales and found in seas or cast ashore. Used in perfumery.

Etymology (EN): From M.Fr. ambre gris “gray amber,” → gray;
→ amber.

Etymology (PE): Anbar “ambergris,” from Mid.Pers. ambar.

A wax-like, ash-colored, strongly scent substance present in the intestines of → whales and found in seas or cast ashore. Used in perfumery.

Etymology (EN): From M.Fr. ambre gris “gray amber,” → gray;
→ amber.

Etymology (PE): Anbar “ambergris,” from Mid.Pers. ambar.

Both, on both sides.

Etymology (EN): L. ambi “around, about,” akin to Gk. amphi “around, about,” Skt. abhi “on both sides,”
Av. aibi, aiwi, O.Pers. aiby “to, against, in addition to,” Mid.Pers. aw-, ab-, Mod.Pers. af- (as in afzudan “to increase, add,” afruxtan “to inflame, kindle, blaze,” afqân “lamentation, groaning, cires for help”); O.H.G. umbi, O.E. ymb(e); PIE *ambhi- “around”.

Etymology (PE): Ubâ- from O.Pers./Av. uba- (variants uva-, ava-, va-) “both,” Skt. ubha “both,” PIE *ubho(u); cf. Gk. ampho, L. ambo, Goth. bai, O.H.G. beide, Slav. oba, Lith. abhu.

Both, on both sides.

Etymology (EN): L. ambi “around, about,” akin to Gk. amphi “around, about,” Skt. abhi “on both sides,”
Av. aibi, aiwi, O.Pers. aiby “to, against, in addition to,” Mid.Pers. aw-, ab-, Mod.Pers. af- (as in afzudan “to increase, add,” afruxtan “to inflame, kindle, blaze,” afqân “lamentation, groaning, cires for help”); O.H.G. umbi, O.E. ymb(e); PIE *ambhi- “around”.

Etymology (PE): Ubâ- from O.Pers./Av. uba- (variants uva-, ava-, va-) “both,” Skt. ubha “both,” PIE *ubho(u); cf. Gk. ampho, L. ambo, Goth. bai, O.H.G. beide, Slav. oba, Lith. abhu.

The quality of state of being → ambiguous.

See also: → ambiguous; → -ity.

The quality of state of being → ambiguous.

See also: → ambiguous; → -ity.

Having more than one possible interpretation or meaning.

Etymology (EN): From L. ambiguus “having double meaning; doubtful,” from ambigere “to be uncertain,” from → ambi- “both; around” + agere “to drive, lead,” → act; cf. Av. az- “to drive, lead;” Pers. niyâz “need, want, misery,”

Etymology (PE): Ubâznâk, from ubâz, literally “having double directions,” from ubâ, → ambi-, + âz, from Av. az- “to lead, direct, drive,” → act, + -nâk adj. suffix.

Having more than one possible interpretation or meaning.

Etymology (EN): From L. ambiguus “having double meaning; doubtful,” from ambigere “to be uncertain,” from → ambi- “both; around” + agere “to drive, lead,” → act; cf. Av. az- “to drive, lead;” Pers. niyâz “need, want, misery,”

Etymology (PE): Ubâznâk, from ubâz, literally “having double directions,” from ubâ, → ambi-, + âz, from Av. az- “to lead, direct, drive,” → act, + -nâk adj. suffix.

1. Applying equally to both positive and negative ions.
   

2. Operating in two opposite directions simultaneously. → bipolar.

See also: Ambipolar, from → ambi- + → polar.

1. Applying equally to both positive and negative ions.
   

2. Operating in two opposite directions simultaneously. → bipolar.

See also: Ambipolar, from → ambi- + → polar.

A physical process which allows a → molecular cloud to decouple from → interstellar magnetic field in order to undergo → gravitational collapse. A cloud of pure molecular gas would form stars very fast through collapse
since neutral matter does not respond to the magnetic field. However, the magnetic
field holds up a collapse because the ions present in the cloud collide with the
neutrals and tie them to the field. The collapse can then only proceed if the
magnetic field can be separated from the gas. In denser molecular cores the ionization degree decreases substantially and therefore neutrals and ions decouple.

See also: → ambipolar; → diffusion.

A physical process which allows a → molecular cloud to decouple from → interstellar magnetic field in order to undergo → gravitational collapse. A cloud of pure molecular gas would form stars very fast through collapse
since neutral matter does not respond to the magnetic field. However, the magnetic
field holds up a collapse because the ions present in the cloud collide with the
neutrals and tie them to the field. The collapse can then only proceed if the
magnetic field can be separated from the gas. In denser molecular cores the ionization degree decreases substantially and therefore neutrals and ions decouple.

See also: → ambipolar; → diffusion.

A defect of vision due to abnormal development, without detectable organic lesion of the eye.

Etymology (EN): From Gk. amblyopia “dim-sightedness,” from amblys “dulled, blunt” + ops, → eye.

Etymology (PE): Tambalcašmi, literally “eye laziness,” from tambal “lazy” + cašm, → eye.

A defect of vision due to abnormal development, without detectable organic lesion of the eye.

Etymology (EN): From Gk. amblyopia “dim-sightedness,” from amblys “dulled, blunt” + ops, → eye.

Etymology (PE): Tambalcašmi, literally “eye laziness,” from tambal “lazy” + cašm, → eye.

An artificially produced → radioactive→ chemical element; symbol Am. → Atomic number 95; → atomic weight of most stable → isotope 243; → melting point about 1,175°C; → boiling point about 2,600°C; → specific gravity 13.67 at 20°C; → valence +2, +3, +4, +5, or +6. Its most stable isotope, ²⁴³Am, has → half-life
of 7.4 x 10³ years.

See also: From America, where it was first synthesized in 1944 by Glenn T. Seaborg, Ralph A. James, Leon O. Morgan, and Albert Ghiorso, who bombarded plutonium-239 with neutrons to form plutonium-241, which decays to form americium-241.

An artificially produced → radioactive→ chemical element; symbol Am. → Atomic number 95; → atomic weight of most stable → isotope 243; → melting point about 1,175°C; → boiling point about 2,600°C; → specific gravity 13.67 at 20°C; → valence +2, +3, +4, +5, or +6. Its most stable isotope, ²⁴³Am, has → half-life
of 7.4 x 10³ years.

See also: From America, where it was first synthesized in 1944 by Glenn T. Seaborg, Ralph A. James, Leon O. Morgan, and Albert Ghiorso, who bombarded plutonium-239 with neutrons to form plutonium-241, which decays to form americium-241.

An irritating, colorless, gaseous compound of → nitrogen and → hydrogen (NH₃), which is lighter than air and readily soluble in water. It is formed in nature as a by-product of protein metabolism in animals. Ammonia is used in the preparation of many substances containing nitrogen, such as fertilizers, explosives, refrigerants, and so on.

Etymology (EN): Coined in 1782 by Swedish chemist Torbern Bergman (1735-1784) for gas obtained from ammoniac, a salt and a gum resin containing ammonium chloride found near temple of Jupiter Ammon in Libya, from Gk. ammoniakos “belonging to Ammon” (Egyptian God).

Etymology (PE): Âmoniyâk, loan from Fr.

An irritating, colorless, gaseous compound of → nitrogen and → hydrogen (NH₃), which is lighter than air and readily soluble in water. It is formed in nature as a by-product of protein metabolism in animals. Ammonia is used in the preparation of many substances containing nitrogen, such as fertilizers, explosives, refrigerants, and so on.

Etymology (EN): Coined in 1782 by Swedish chemist Torbern Bergman (1735-1784) for gas obtained from ammoniac, a salt and a gum resin containing ammonium chloride found near temple of Jupiter Ammon in Libya, from Gk. ammoniakos “belonging to Ammon” (Egyptian God).

Etymology (PE): Âmoniyâk, loan from Fr.

A maser source in which excited → ammonia molecules (NH₃) produce → maser emission. The first device to demonstrate the principle of
→ stimulated emission of radiation used ammonia molecules (Gordon et al. 1954).
The hydrogen atoms of ammonia molecules have a rotation motion whereas the nitrogen atom oscillates between two positions, above and below the plane of the hydrogen atoms. These arrangements do not represent exactly the same energy, and therefore the molecule exists in two energy states. The difference in energy between the states corresponds to a frequency of 23.87 GHz, or 1.25 cm. In astrophysics, ammonia maser emission has been detected toward active star formation regions, such as W51. → interstellar masers.

See also: → ammonia; → maser.

A maser source in which excited → ammonia molecules (NH₃) produce → maser emission. The first device to demonstrate the principle of
→ stimulated emission of radiation used ammonia molecules (Gordon et al. 1954).
The hydrogen atoms of ammonia molecules have a rotation motion whereas the nitrogen atom oscillates between two positions, above and below the plane of the hydrogen atoms. These arrangements do not represent exactly the same energy, and therefore the molecule exists in two energy states. The difference in energy between the states corresponds to a frequency of 23.87 GHz, or 1.25 cm. In astrophysics, ammonia maser emission has been detected toward active star formation regions, such as W51. → interstellar masers.

See also: → ammonia; → maser.

A → near-Earth asteroid (NEA) with → perihelion distances between 1.017 and 1.3 → astronomical units. The Amor asteroids approach the orbit of the Earth from beyond, but do not intersect it. Most Amors do cross the orbit of Mars. It is estimated that 32% of the total number of NEAs are Amors. One of the larger Amors is → Eros.

See also: → Amor; → asteroid.

A → near-Earth asteroid (NEA) with → perihelion distances between 1.017 and 1.3 → astronomical units. The Amor asteroids approach the orbit of the Earth from beyond, but do not intersect it. Most Amors do cross the orbit of Mars. It is estimated that 32% of the total number of NEAs are Amors. One of the larger Amors is → Eros.

See also: → Amor; → asteroid.

Quantity; measure; the sum total of two or more quantities or sums.

Etymology (EN): From M.E. amounten “to ascend,” from O.Fr. amonter, from amont “upward,” from L. ad montem “to the hill,”
from ad “to” + mons, mont “hill,” → mountain.

Etymology (PE): Masâk, from Mid.Pers. masâk “size, amount, magnitude,” from mas “great, large,” Av. masan “greatness, importance,” from mas-; maz- “long, large; great”; cp. Skt. maha “great, mighty” (Mod.Pers. meh “great, large”),
Gk. megas “great, large” L. magnus “great,” PIE *meg- “great”.

Quantity; measure; the sum total of two or more quantities or sums.

Etymology (EN): From M.E. amounten “to ascend,” from O.Fr. amonter, from amont “upward,” from L. ad montem “to the hill,”
from ad “to” + mons, mont “hill,” → mountain.

Etymology (PE): Masâk, from Mid.Pers. masâk “size, amount, magnitude,” from mas “great, large,” Av. masan “greatness, importance,” from mas-; maz- “long, large; great”; cp. Skt. maha “great, mighty” (Mod.Pers. meh “great, large”),
Gk. megas “great, large” L. magnus “great,” PIE *meg- “great”.

The → SI unit of → electric current; symbol A. It is defined by taking the fixed numerical value of the → elementary charge, e, to be 1.602 176 634 × 10^-19 when expressed in the unit → coulomb (C), which is equal to A s, where the → second (s) is defined in terms of Δν_Cs.

See also: Named after the French physicist and mathematician André-Marie Ampère (1775-1836), one of the pioneers in studying electricity, who laid the foundation of electromagnetic theory.

The → SI unit of → electric current; symbol A. It is defined by taking the fixed numerical value of the → elementary charge, e, to be 1.602 176 634 × 10^-19 when expressed in the unit → coulomb (C), which is equal to A s, where the → second (s) is defined in terms of Δν_Cs.

See also: Named after the French physicist and mathematician André-Marie Ampère (1775-1836), one of the pioneers in studying electricity, who laid the foundation of electromagnetic theory.

One of the basic relations between → electricity and → magnetism, stating quantitatively the relation of a → magnetic field to the → electric current or changing electric field that produces it. Ampere’s law states that the line integral of the magnetic field around an arbitrarily chosen path is proportional to the net electric current enclosed by the path. Also known as Ampère’s theorem, Ampère’s circuital law.

See also: → ampere; → law.

One of the basic relations between → electricity and → magnetism, stating quantitatively the relation of a → magnetic field to the → electric current or changing electric field that produces it. Ampere’s law states that the line integral of the magnetic field around an arbitrarily chosen path is proportional to the net electric current enclosed by the path. Also known as Ampère’s theorem, Ampère’s circuital law.

See also: → ampere; → law.

1. General: The act or result of amplifying, enlarging, or extending.
   

2. Physics: The process of increasing the magnitude of a variable quantity, especially the magnitude of voltage, power, or current, without altering any other quantity.

See also: Verbal noun of → amplify.

1. General: The act or result of amplifying, enlarging, or extending.
   

2. Physics: The process of increasing the magnitude of a variable quantity, especially the magnitude of voltage, power, or current, without altering any other quantity.

See also: Verbal noun of → amplify.

1. Electronics: The extent to which an → analogue → amplifier boosts the strength of a → signal. Also called
   → gain.
   

2. In → gravitational lensing, the ratio of the lensed brightness to unlensed brightness. This factor depends on the mass of the → lensing object and the
   closeness of the alignment between observer, lens, and source (→ impact parameter).

See also: → amplification; → factor.

1. Electronics: The extent to which an → analogue → amplifier boosts the strength of a → signal. Also called
   → gain.
   

2. In → gravitational lensing, the ratio of the lensed brightness to unlensed brightness. This factor depends on the mass of the → lensing object and the
   closeness of the alignment between observer, lens, and source (→ impact parameter).

See also: → amplification; → factor.

Device for reproducing an electrical input at increased intensity.

See also: Agent noun of → amplify.

Device for reproducing an electrical input at increased intensity.

See also: Agent noun of → amplify.

General:To make larger, greater, or more powerful.
Physics:To increase the amplitude of an input signal.

Etymology (EN): From M.F. amplifier, from L. amplificare “to increase, augmant,” from L. amplus “wide, large.”

Etymology (PE): Dâmané, → amplitude; dâdan “to give” (Mid.Pers. dâdan “to give,” O.Pers./Av. dā- “to give, grant, yield,” dadāiti “he gives;” Skt. dadáti “he gives,” Gk. didomi “I give,” tithenai “to put, set, place;” L. dare “to give, offer;” Rus. delat “to do;” O.H.G. tuon, Ger. tun, O.E. don “to do”); gereftan
“to take, seize, catch,” (Mid.Pers. griftan, Av./O.Pers. grab- “to take, seize,” cf.
Skt. grah-, grabh- “to seize, take,” graha “seizing, holding, perceiving,” M.L.G. grabben “to grab,” from P.Gmc. *grab, E. grab “to take or grasp suddenly;” PIE base *ghrebh- “to seize”).

General:To make larger, greater, or more powerful.
Physics:To increase the amplitude of an input signal.

Etymology (EN): From M.F. amplifier, from L. amplificare “to increase, augmant,” from L. amplus “wide, large.”

Etymology (PE): Dâmané, → amplitude; dâdan “to give” (Mid.Pers. dâdan “to give,” O.Pers./Av. dā- “to give, grant, yield,” dadāiti “he gives;” Skt. dadáti “he gives,” Gk. didomi “I give,” tithenai “to put, set, place;” L. dare “to give, offer;” Rus. delat “to do;” O.H.G. tuon, Ger. tun, O.E. don “to do”); gereftan
“to take, seize, catch,” (Mid.Pers. griftan, Av./O.Pers. grab- “to take, seize,” cf.
Skt. grah-, grabh- “to seize, take,” graha “seizing, holding, perceiving,” M.L.G. grabben “to grab,” from P.Gmc. *grab, E. grab “to take or grasp suddenly;” PIE base *ghrebh- “to seize”).

General:The greatness, size, or extent of something.
In any periodically varying function, the maximum absolute value of the quantity.
The magnitude range of a variable star.

Etymology (EN): L. amplitudo “wide extent, width,” from amplus “large”.

Etymology (PE): Dâmané “the foot or skirt of a mountain,” from dâman “skirt.”

General:The greatness, size, or extent of something.
In any periodically varying function, the maximum absolute value of the quantity.
The magnitude range of a variable star.

Etymology (EN): L. amplitudo “wide extent, width,” from amplus “large”.

Etymology (PE): Dâmané “the foot or skirt of a mountain,” from dâman “skirt.”