An Etymological Dictionary of Astronomy and Astrophysics

Prefix same as → a- “not, without” occurring before a vowel or h in loanwords from Greek.

See also: → a-.

Prefix same as → a- “not, without” occurring before a vowel or h in loanwords from Greek.

See also: → a-.

Prefix meaning: 1) up, upward (anode); 2) back, backward (ananym); 3) again, anew (anagenesis); 4) exceedingly (anamorphism).

Etymology (EN): From Gk. ana- “up, on, upon, throughout, again,”
cognate with Av. ana “on, over, along,” O.Pers. anâ “throughout,” O.E. on; PIE base *ano- “on, upon, above”.

Etymology (PE): Ânâ-, from ana, anâ, Av. and O.Pers. counterparts of Gk. ana-, as above.

Prefix meaning: 1) up, upward (anode); 2) back, backward (ananym); 3) again, anew (anagenesis); 4) exceedingly (anamorphism).

Etymology (EN): From Gk. ana- “up, on, upon, throughout, again,”
cognate with Av. ana “on, over, along,” O.Pers. anâ “throughout,” O.E. on; PIE base *ano- “on, upon, above”.

Etymology (PE): Ânâ-, from ana, anâ, Av. and O.Pers. counterparts of Gk. ana-, as above.

The shape resembling a figure of 8 obtained by following the Sun’s position in the sky at the same time of day throughout the year. It is a graphical presentation of the → equation of time.

Because the Earth’s orbit around the Sun is elliptical, the two loops of analemma have different sizes. Analemma figures for different latitudes or different times of day would appear slightly different. The analemma is widest in the period when the Earth is closest to the Sun
(December). This is because in this situation the Earth advances in its orbit faster due to the stronger gravitational attraction of the Sun. On the other hand, since the Earth rotates at a constant rate, the Sun appears to rise earlier than average because the Earth advances further in its orbit in one day when the Earth is close to the Sun. The opposite occurs in June when the Earth is further from the Sun.

Etymology (EN): From L. analemma “the pedestal of a sundial,” hence the sundial itself, from Gk. analemma “prop, support,” from analambanein, from → ana- “up” + lambanein “to take”.

Etymology (PE): Hurspicak from hur “Sun;” Av. hvar- “sun” (cf. Skt. surya; Gk. hlios; L. sol; O.H.G. sunna; Ger. Sonne; E. sun; PIE *sawel- “sun”) + picak “a curled, a twisted figure or object,” from picidan “to twist, invove, enttwine, coil.”

The shape resembling a figure of 8 obtained by following the Sun’s position in the sky at the same time of day throughout the year. It is a graphical presentation of the → equation of time.

Because the Earth’s orbit around the Sun is elliptical, the two loops of analemma have different sizes. Analemma figures for different latitudes or different times of day would appear slightly different. The analemma is widest in the period when the Earth is closest to the Sun
(December). This is because in this situation the Earth advances in its orbit faster due to the stronger gravitational attraction of the Sun. On the other hand, since the Earth rotates at a constant rate, the Sun appears to rise earlier than average because the Earth advances further in its orbit in one day when the Earth is close to the Sun. The opposite occurs in June when the Earth is further from the Sun.

Etymology (EN): From L. analemma “the pedestal of a sundial,” hence the sundial itself, from Gk. analemma “prop, support,” from analambanein, from → ana- “up” + lambanein “to take”.

Etymology (PE): Hurspicak from hur “Sun;” Av. hvar- “sun” (cf. Skt. surya; Gk. hlios; L. sol; O.H.G. sunna; Ger. Sonne; E. sun; PIE *sawel- “sun”) + picak “a curled, a twisted figure or object,” from picidan “to twist, invove, enttwine, coil.”

In electronics, a device that converts the analog signal to → analog-to-digital units or counts.

See also: → analogue; → digital; → converter.

In electronics, a device that converts the analog signal to → analog-to-digital units or counts.

See also: → analogue; → digital; → converter.

A number that represents a → charge-coupled device (CCD)’s output and is proportional to the → electron charge created by the → photons, plus the constant → bias offset. The relationship between the ADUs generated and the number of electrons acquired on the CCD is defined by the → CCD gain. Intensities given in ADUs provide a convenient method for comparing images and data generated by different cameras. Also referred to as → count and digital number.

In most cases, the analog signal is digitalized by an analog-to-digital (A/D) converter and fed into a computer where further manipulation and analysis are done on what the detector originally produced from the star’s photons (Howell, S.B., Handbook of CCD Astronomy, Cambridge Univ. Press, 2000).

See also: → analogue; → digital; → unit.

A number that represents a → charge-coupled device (CCD)’s output and is proportional to the → electron charge created by the → photons, plus the constant → bias offset. The relationship between the ADUs generated and the number of electrons acquired on the CCD is defined by the → CCD gain. Intensities given in ADUs provide a convenient method for comparing images and data generated by different cameras. Also referred to as → count and digital number.

In most cases, the analog signal is digitalized by an analog-to-digital (A/D) converter and fed into a computer where further manipulation and analysis are done on what the detector originally produced from the star’s photons (Howell, S.B., Handbook of CCD Astronomy, Cambridge Univ. Press, 2000).

See also: → analogue; → digital; → unit.

Of, relating to, or based on analogy; expressing or implying analogy.

See also: → analogy + -i + → -al.

Of, relating to, or based on analogy; expressing or implying analogy.

See also: → analogy + -i + → -al.

1. Similar or corresponding in some respect; having → analogy.
   

2. Biology: Similar in function but having different evolutionary origins, as the wings of birds and insects.
   

3. Chemistry: Similar in chemical properties and differing in chemical structure only with respect to one element or group.

See also: L. analogus, from Gk. analogos “proportionate,” → analogy.

1. Similar or corresponding in some respect; having → analogy.
   

2. Biology: Similar in function but having different evolutionary origins, as the wings of birds and insects.
   

3. Chemistry: Similar in chemical properties and differing in chemical structure only with respect to one element or group.

See also: L. analogus, from Gk. analogos “proportionate,” → analogy.

1. (n.) Something that has → analogy to something else.
   

2. Chemistry: (n.) A chemical compound whose molecular structure is closely similar to that of another.
   

3. Relating to or using signals or information represented by a continuous variable physical quantity such as spatial position or voltage. Often contrasted with → digital.

See also: From Fr. analogue, from Gk. analogon, → analogy.

1. (n.) Something that has → analogy to something else.
   

2. Chemistry: (n.) A chemical compound whose molecular structure is closely similar to that of another.
   

3. Relating to or using signals or information represented by a continuous variable physical quantity such as spatial position or voltage. Often contrasted with → digital.

See also: From Fr. analogue, from Gk. analogon, → analogy.

A computer in which data is stored and processed in the form of continually varying signals representing a physical quantity rather than in the form of individual numerical values. The simplest analogue computers are side rules, thermometers, voltmeters, and speedometers.

See also: → analogue; → computer.

A computer in which data is stored and processed in the form of continually varying signals representing a physical quantity rather than in the form of individual numerical values. The simplest analogue computers are side rules, thermometers, voltmeters, and speedometers.

See also: → analogue; → computer.

1. A similarity or comparability between two things.
   

2. Math.: A general similarity between two problems or methods. Analogy is used to infer new theorems from existing ones. Hypotheses based on analogy must still be proved.
   

3. Logic: A form of reasoning which asserts that if two or more entities are similar in one or more respects, then they would be similar in other respects.
   

4. Biology: An analogous relationship.
   

5. Linguistics: The process by which a word or form is either created or changed according to existing patterns in the language.

See also: M.E., from O.Fr. analogie or directly from L. analogia, from Gk. analogia “proportion,” from → ana- “upon, according to” + logos “ratio; word, speech, reckoning,” → -logy.

1. A similarity or comparability between two things.
   

2. Math.: A general similarity between two problems or methods. Analogy is used to infer new theorems from existing ones. Hypotheses based on analogy must still be proved.
   

3. Logic: A form of reasoning which asserts that if two or more entities are similar in one or more respects, then they would be similar in other respects.
   

4. Biology: An analogous relationship.
   

5. Linguistics: The process by which a word or form is either created or changed according to existing patterns in the language.

See also: M.E., from O.Fr. analogie or directly from L. analogia, from Gk. analogia “proportion,” from → ana- “upon, according to” + logos “ratio; word, speech, reckoning,” → -logy.

1. General: The separation of an intellectual or material whole into its constituent parts for individual study. The study of such constituent parts and their interrelationships in making up a whole (opposite of → synthesis).
   

2. Chemistry: The separation of a substance into its constituent elements to determine either their nature (qualitative analysis) or their proportions (quantitative analysis).
   

3. Mathematics: A branch of mathematics principally involving → differential and integral calculus, → sequences, and → series and concerned with → limits and → convergence.

Etymology (EN): From M.L. analysis, from Gk. analysis “a breaking up,”
from analyein “unloose,” from ana- “up, throughout” + lysis “a loosening,” from lyein “to loosen, release, untie”. The L. cognate and counterpart of this Gk. word, i.e. luere has formed the words solve, dissolve, solution. The Skt. cognate lu, lunoti “to cut, sever, mow, pluck, tear asunder, destroy,” lava “cutting, plucking; what is cut; fragment, piece;” PIE *leu- “to loosen, divide, cut apart”.
The Eng. lose, loose and Ger. los derive from this root.

Etymology (PE): Ânâlas, from ânâ-, → ana-, + las “loose” ([Mo’in], Gilaki, Tabari, Tâleši, Aftari). We do not know the Av./O.Pers. counterparts of these Gk. las, lysis, lyein, but we believe that las and the following words probably derive from the above-mentioned PIE *leu-:
lâ “slit, cut” (Tabari),
lâb, lâp, lib “slit, cut, piece, half” (Tabari),
lâpé “a cut piece of wood” [Mo’in],
lâpé kardan “to cut a timber along its length” [Mo’in],
lap “piece, big piece, big cut” [Mo’in]. This word was chosen by Farhangestân I for “lobe of the lung”.
lâc “open, wide-open” (Tabari),
luš “torn” [Mo’in], also luš luš [Mo’in] “in pieces,"
lat “torn, piece” [Mo’in]. Compare with luta “cut, cut off” in Pali. Lat may also be a contraction of laxt.
lok “torn, piece” (Qâyeni),
lâš “slit” (Tabari),
lâš kardan “to pick, to pluck” [Mo’in],
latu “plough” (Tabari).
Ânâkâvidan, from ânâ- + kâvidan (kâftan) “to examine, investigate, search; dig," from kâv + infinitive suffix -idan; compare with Mod.Pres. kâvâk “hollow, empty,” L. cavus “hollow” (E. derivatives: cavity, concave, cave, excavate), Gk. koilos “hollow.”

1. General: The separation of an intellectual or material whole into its constituent parts for individual study. The study of such constituent parts and their interrelationships in making up a whole (opposite of → synthesis).
   

2. Chemistry: The separation of a substance into its constituent elements to determine either their nature (qualitative analysis) or their proportions (quantitative analysis).
   

3. Mathematics: A branch of mathematics principally involving → differential and integral calculus, → sequences, and → series and concerned with → limits and → convergence.

Etymology (EN): From M.L. analysis, from Gk. analysis “a breaking up,”
from analyein “unloose,” from ana- “up, throughout” + lysis “a loosening,” from lyein “to loosen, release, untie”. The L. cognate and counterpart of this Gk. word, i.e. luere has formed the words solve, dissolve, solution. The Skt. cognate lu, lunoti “to cut, sever, mow, pluck, tear asunder, destroy,” lava “cutting, plucking; what is cut; fragment, piece;” PIE *leu- “to loosen, divide, cut apart”.
The Eng. lose, loose and Ger. los derive from this root.

Etymology (PE): Ânâlas, from ânâ-, → ana-, + las “loose” ([Mo’in], Gilaki, Tabari, Tâleši, Aftari). We do not know the Av./O.Pers. counterparts of these Gk. las, lysis, lyein, but we believe that las and the following words probably derive from the above-mentioned PIE *leu-:
lâ “slit, cut” (Tabari),
lâb, lâp, lib “slit, cut, piece, half” (Tabari),
lâpé “a cut piece of wood” [Mo’in],
lâpé kardan “to cut a timber along its length” [Mo’in],
lap “piece, big piece, big cut” [Mo’in]. This word was chosen by Farhangestân I for “lobe of the lung”.
lâc “open, wide-open” (Tabari),
luš “torn” [Mo’in], also luš luš [Mo’in] “in pieces,"
lat “torn, piece” [Mo’in]. Compare with luta “cut, cut off” in Pali. Lat may also be a contraction of laxt.
lok “torn, piece” (Qâyeni),
lâš “slit” (Tabari),
lâš kardan “to pick, to pluck” [Mo’in],
latu “plough” (Tabari).
Ânâkâvidan, from ânâ- + kâvidan (kâftan) “to examine, investigate, search; dig," from kâv + infinitive suffix -idan; compare with Mod.Pres. kâvâk “hollow, empty,” L. cavus “hollow” (E. derivatives: cavity, concave, cave, excavate), Gk. koilos “hollow.”

Of or relating to analysis, in contrast with → synthetic. Also analytical.

Etymology (EN): M.L. analyticus, from Gk. analytikos, from analy-, → analysis, + -tikos, -tic, equivalent to → -ic.

Etymology (PE): Pertaining to ânâlas, → analysis.

Of or relating to analysis, in contrast with → synthetic. Also analytical.

Etymology (EN): M.L. analyticus, from Gk. analytikos, from analy-, → analysis, + -tikos, -tic, equivalent to → -ic.

Etymology (PE): Pertaining to ânâlas, → analysis.

A curve whose parametric equations are real → analytic functions of a single
real variable.

See also: → analytic; → curve.

A curve whose parametric equations are real → analytic functions of a single
real variable.

See also: → analytic; → curve.

A function which can be represented by a convergent → power series.

See also: → analytic; → function.

A function which can be represented by a convergent → power series.

See also: → analytic; → function.

The study of the geometry of figures by algebraic representation and manipulation of equations describing their positions, configurations, and separations.

See also: → analytic; → geometry.

The study of the geometry of figures by algebraic representation and manipulation of equations describing their positions, configurations, and separations.

See also: → analytic; → geometry.

A language that is characterized largely by the fact that it depends on word order, rather than on inflections (grammatical endings), to convey sentence meanings. In an analytic language relations between nouns and adjectives are expressed using prepositions. English and (to a lesser extent) French, and Persian are considered analytic languages, while German and Russian are → synthetic languages.

See also: → analytic; → language.

A language that is characterized largely by the fact that it depends on word order, rather than on inflections (grammatical endings), to convey sentence meanings. In an analytic language relations between nouns and adjectives are expressed using prepositions. English and (to a lesser extent) French, and Persian are considered analytic languages, while German and Russian are → synthetic languages.

See also: → analytic; → language.

Same as → analytic.

See also: → analysis; → -al.

Same as → analytic.

See also: → analysis; → -al.

A branch of → mechanics based on → variational principle that describes systems by their → Lagrangian or → Hamiltonian. Analytical mechanics provides a formalism that is different from that of Newton and does not use the concept of force. Among other things, analytical mechanics gives a more simple description of continuous and constrained systems. Moreover, its mathematical structure allows it an easier transition to quantum mechanical topics.

See also: → analytical; → mechanics.

A branch of → mechanics based on → variational principle that describes systems by their → Lagrangian or → Hamiltonian. Analytical mechanics provides a formalism that is different from that of Newton and does not use the concept of force. Among other things, analytical mechanics gives a more simple description of continuous and constrained systems. Moreover, its mathematical structure allows it an easier transition to quantum mechanical topics.

See also: → analytical; → mechanics.

Infinitive of → analysis.

Infinitive of → analysis.

An optical device by which the direction of → polarization of a beam of light can be detected. Usually the light has been passed through a → polarizer before arriving at the analyzer.

See also: Agent noun, from → analyze + → -er.

An optical device by which the direction of → polarization of a beam of light can be detected. Usually the light has been passed through a → polarizer before arriving at the analyzer.

See also: Agent noun, from → analyze + → -er.

The quality of an → anamorphic system.

See also: → ana- “up,” + morphe “form,” → morphology + → -ic.

The quality of an → anamorphic system.

See also: → ana- “up,” + morphe “form,” → morphology + → -ic.

An optical system whose optical power, and imaging scale, differs in the two principal directions. See also → anamorphosis.

See also: → anamorphic; → system.

An optical system whose optical power, and imaging scale, differs in the two principal directions. See also → anamorphosis.

See also: → anamorphic; → system.

1. Optics: The formation of a distorted image by an → anamorphic system.
   

2. Biology: The evolution from one type to another through a gradual and steady process of changes.
   

3. Art: A distorted image that appears in proportion when it is viewed from a specific point of view or reflected in a curved mirror, or with some other optical device.

Etymology (EN): From Gk. anamorphosis “transformation,” noun of action from anamorphoein “to transform,” from → ana- “up,” + morphe “form” + -sis a suffix forming abstract nouns of action, process, state, condition, etc.

Etymology (PE): Ânârixtmandi, from ânâ- “up,” + rixt “morphe,” → morphology, + mand, → -ist

• noun suffix -i.

1. Optics: The formation of a distorted image by an → anamorphic system.
   

2. Biology: The evolution from one type to another through a gradual and steady process of changes.
   

3. Art: A distorted image that appears in proportion when it is viewed from a specific point of view or reflected in a curved mirror, or with some other optical device.

Etymology (EN): From Gk. anamorphosis “transformation,” noun of action from anamorphoein “to transform,” from → ana- “up,” + morphe “form” + -sis a suffix forming abstract nouns of action, process, state, condition, etc.

Etymology (PE): Ânârixtmandi, from ânâ- “up,” + rixt “morphe,” → morphology, + mand, → -ist

• noun suffix -i.

The thirteenth of Jupiter’s known satellites discovered by S.B. Nicholson in 1951. It orbits the planet at a mean distance of 21,200,000 km, and has a diameter of about 30 km.

Etymology (EN): In Gk. mythology, Ananke is the personification of destiny, unalterable necessity and fate; she is also the mother of Adrastea,

The thirteenth of Jupiter’s known satellites discovered by S.B. Nicholson in 1951. It orbits the planet at a mean distance of 21,200,000 km, and has a diameter of about 30 km.

Etymology (EN): In Gk. mythology, Ananke is the personification of destiny, unalterable necessity and fate; she is also the mother of Adrastea,

A lens designed to correct → astigmatism.

See also: → astigmatism; → lens.

A lens designed to correct → astigmatism.

See also: → astigmatism; → lens.

One from whom a person is descendant; a forefather.

Etymology (EN): M.E. ancestre, from O.Fr. ancestre, ancessor “ancestor, forebear, forefather,” from L.L. antecessor “predecessor,” literally “fore-goer,” agent noun from p.p. stem of L. antecedere “to precede,” from ante “before” + cedere “to go,” → process.

Etymology (PE): Niyâ, from Mid.Pers. niyâg “forefather, ancestor;” O.Pers. niyāka-, Av. nyāka-

One from whom a person is descendant; a forefather.

Etymology (EN): M.E. ancestre, from O.Fr. ancestre, ancessor “ancestor, forebear, forefather,” from L.L. antecessor “predecessor,” literally “fore-goer,” agent noun from p.p. stem of L. antecedere “to precede,” from ante “before” + cedere “to go,” → process.

Etymology (PE): Niyâ, from Mid.Pers. niyâg “forefather, ancestor;” O.Pers. niyāka-, Av. nyāka-

1. (Conjunction, used to connect grammatically coordinate words, phrases, or clauses) Along or together with; as well as; in addition to; besides; also; moreover. → if and only if.
   

2. (Conjunction) Added to; plus (Dictionary.com).

Etymology (EN): From M.E., from O.E., akin to O.H.G. unti “and.”

Etymology (PE): Va “and,” graphical corruption of o “and;” Mid.Pers. ut, u- “and;” O.Pers. utā; Av. uta- “and;” cf. Skt. utá; maybe also influenced by Av. vā a disjunctive particle (Skt. vā) “or,” occasionally used in the sense of “and;” vā … vā “either, or;” cf. Sogd. βa, fa “and, or,” fā “or.”

1. (Conjunction, used to connect grammatically coordinate words, phrases, or clauses) Along or together with; as well as; in addition to; besides; also; moreover. → if and only if.
   

2. (Conjunction) Added to; plus (Dictionary.com).

Etymology (EN): From M.E., from O.E., akin to O.H.G. unti “and.”

Etymology (PE): Va “and,” graphical corruption of o “and;” Mid.Pers. ut, u- “and;” O.Pers. utā; Av. uta- “and;” cf. Skt. utá; maybe also influenced by Av. vā a disjunctive particle (Skt. vā) “or,” occasionally used in the sense of “and;” vā … vā “either, or;” cf. Sogd. βa, fa “and, or,” fā “or.”

A six-branch modification of the → Maxwell bridge that measures → inductance in terms of → resistance and → capacitance.

See also: A. Anderson (1891, Phil. Mag. (5) 31, 329); → bridge.

A six-branch modification of the → Maxwell bridge that measures → inductance in terms of → resistance and → capacitance.

See also: A. Anderson (1891, Phil. Mag. (5) 31, 329); → bridge.

Being neither distinguishably → masculine nor → feminine, as in dress, appearance, or behavior (TheFreeDictionary.com).

Etymology (EN): From L. androgynus, from Gk. androgynos “male and female in one; womanish man; hermaphrodite,” from andros, genitive of aner “male,” from PIE root *ner-, Pers. nar, → male,

• gyne “woman,” from PIE root *gwen- “woman,” Pers. zan, → woman.

Etymology (PE): Merâcen, literally “man-woman,” from merâ, from Ardestâni, Nâini, Tarqi (Natanz) mera “man,” cf. Tâti malle “man,” Pers. mir “master,” Mid.Pers. mêrak “(young) man” + Gorgâni cen “woman,” variant Pers. zan, → woman.

Being neither distinguishably → masculine nor → feminine, as in dress, appearance, or behavior (TheFreeDictionary.com).

Etymology (EN): From L. androgynus, from Gk. androgynos “male and female in one; womanish man; hermaphrodite,” from andros, genitive of aner “male,” from PIE root *ner-, Pers. nar, → male,

• gyne “woman,” from PIE root *gwen- “woman,” Pers. zan, → woman.

Etymology (PE): Merâcen, literally “man-woman,” from merâ, from Ardestâni, Nâini, Tarqi (Natanz) mera “man,” cf. Tâti malle “man,” Pers. mir “master,” Mid.Pers. mêrak “(young) man” + Gorgâni cen “woman,” variant Pers. zan, → woman.

The state of appearing to be neither feminine nor masculine.

See also: Noun from → androgynous.

The state of appearing to be neither feminine nor masculine.

See also: Noun from → androgynous.

A northern constellation between → Perseus and → Pegasus located at approximately R.A. 1h, Dec. +40 deg. Abbreviation And, Genitive form Andromedae.

Etymology (EN): In Gk. mythology, Andromeda was the princess of Ethiopia, daughter of → Cepheus and → Cassiopeia. The queen Cassiopeia angered Poseidon by saying that Andromeda (or possibly Cassiopeia herself) was more beautiful than the Nereids. Poseidon sent a sea monster to prey upon the country; he could be appeased only by the sacrifice of the king’s daughter. Andromeda in sacrifice was chained to a rock by the sea; but she was rescued by → Perseus, who killed the monster and later married her. Cassiopeia, Cepheus, and Andromeda were all set among the stars as constellations.

Etymology (PE): Zan-e bé Zanjir Basté “the chained woman,” coined by the 11th century astronomer Biruni, from Ar. Emra’at al-mosalsalah “the chained woman,” from the Gk. mythology.

A northern constellation between → Perseus and → Pegasus located at approximately R.A. 1h, Dec. +40 deg. Abbreviation And, Genitive form Andromedae.

Etymology (EN): In Gk. mythology, Andromeda was the princess of Ethiopia, daughter of → Cepheus and → Cassiopeia. The queen Cassiopeia angered Poseidon by saying that Andromeda (or possibly Cassiopeia herself) was more beautiful than the Nereids. Poseidon sent a sea monster to prey upon the country; he could be appeased only by the sacrifice of the king’s daughter. Andromeda in sacrifice was chained to a rock by the sea; but she was rescued by → Perseus, who killed the monster and later married her. Cassiopeia, Cepheus, and Andromeda were all set among the stars as constellations.

Etymology (PE): Zan-e bé Zanjir Basté “the chained woman,” coined by the 11th century astronomer Biruni, from Ar. Emra’at al-mosalsalah “the chained woman,” from the Gk. mythology.

The nearest → spiral galaxy to our own and a major member of the → Local Group. It lies in the constellation → Andromeda and is the most remote object normally visible to the naked eye. The earliest known reference to this galaxy is by the Iranian astronomer Sufi who called it “the little cloud” in his Book of Fixed Stars (A.D. 964).

See also: → Andromeda; → galaxy.

The nearest → spiral galaxy to our own and a major member of the → Local Group. It lies in the constellation → Andromeda and is the most remote object normally visible to the naked eye. The earliest known reference to this galaxy is by the Iranian astronomer Sufi who called it “the little cloud” in his Book of Fixed Stars (A.D. 964).

See also: → Andromeda; → galaxy.

A meteor shower which appears about 25 November with its → radiant located in the constellation → Andromeda. The Andromedids are the debris of → Biela’s comet. The short-period comet, discovered in 1826, split into two parts in the middle of the 19th century and later vanished. Hence their alternative name Bielids.

Etymology (EN): Andromedids, from Andromeda constellation + → -ids suffix denoting “descendant of, belonging to the family of.”

Etymology (PE): Ândromedâiyân, from Ândromedâ + -iyân, → -ids.

A meteor shower which appears about 25 November with its → radiant located in the constellation → Andromeda. The Andromedids are the debris of → Biela’s comet. The short-period comet, discovered in 1826, split into two parts in the middle of the 19th century and later vanished. Hence their alternative name Bielids.

Etymology (EN): Andromedids, from Andromeda constellation + → -ids suffix denoting “descendant of, belonging to the family of.”

Etymology (PE): Ândromedâiyân, from Ândromedâ + -iyân, → -ids.

An instrument for measuring and indicating the force or speed of the wind.

Etymology (EN): From Gk. anemos “wind” + → -meter.

Etymology (PE): Bâdsanj, from bâd “wind” + -sanj, → -meter.

An instrument for measuring and indicating the force or speed of the wind.

Etymology (EN): From Gk. anemos “wind” + → -meter.

Etymology (PE): Bâdsanj, from bâd “wind” + -sanj, → -meter.

The figure formed by two lines extending from a common point; the figure formed by two intersecting planes (dihedral angle).

Etymology (EN): L. angulum (nominative angulus) “corner,” a dim. form from PIE *ang-/*ank- “to bend;” cf. Skt. ankah “hook, bent,” Gk. angkon “elbow,” angkura “anchor,” Lith. anka “loop,” O.E. ancleo “ankle,” O.H.G. ango “hook,” Av. ank- “curved, crooked,” Av. angušta- “toe,” Mod.Pers. angošt, angol, angul “finger”.

Etymology (PE): Zâviyé from Ar. zâwiyat “corner, angle”.
Gušé “corner, angle,” Mid.Pers. gošak “corner.”
Konj, “angle, corner,” → diagonal.

The figure formed by two lines extending from a common point; the figure formed by two intersecting planes (dihedral angle).

Etymology (EN): L. angulum (nominative angulus) “corner,” a dim. form from PIE *ang-/*ank- “to bend;” cf. Skt. ankah “hook, bent,” Gk. angkon “elbow,” angkura “anchor,” Lith. anka “loop,” O.E. ancleo “ankle,” O.H.G. ango “hook,” Av. ank- “curved, crooked,” Av. angušta- “toe,” Mod.Pers. angošt, angol, angul “finger”.

Etymology (PE): Zâviyé from Ar. zâwiyat “corner, angle”.
Gušé “corner, angle,” Mid.Pers. gošak “corner.”
Konj, “angle, corner,” → diagonal.

The angle between the → incident ray of light entering an → optical system (such as a prism) and the → refracted ray that emerges from the system. Because of the different indices of refraction for the different wavelengths of visible light, the angle of deviation varies with wavelength.

See also: → angle; → deviation.

The angle between the → incident ray of light entering an → optical system (such as a prism) and the → refracted ray that emerges from the system. Because of the different indices of refraction for the different wavelengths of visible light, the angle of deviation varies with wavelength.

See also: → angle; → deviation.

The angle of the light coming out of a medium. For a medium with parallel sides (such as a glass slab) it is equal to the angle of incidence.

See also: → angle; → emergence.

The angle of the light coming out of a medium. For a medium with parallel sides (such as a glass slab) it is equal to the angle of incidence.

See also: → angle; → emergence.

The angle formed between a ray of light striking a surface and the normal to that surface at the point of incidence. Also called → incidence angle.

See also: → angle; → incidence.

The angle formed between a ray of light striking a surface and the normal to that surface at the point of incidence. Also called → incidence angle.

See also: → angle; → incidence.

1. General: The angle between one plane and another, or the angle formed by a reference axis and a given line.
   

2. Binary systems: The angle between the plane of the orbit and the → plane of the sky.
   

3. Rotating stars: The angle between the → equatorial plane and the → plane of the sky.

See also: → angle; → inclination.

1. General: The angle between one plane and another, or the angle formed by a reference axis and a given line.
   

2. Binary systems: The angle between the plane of the orbit and the → plane of the sky.
   

3. Rotating stars: The angle between the → equatorial plane and the → plane of the sky.

See also: → angle; → inclination.

The angle between the light entering and exiting the prism when the light passing through the prism is parallel to the prism’s base. Angle of minimum deviation (D) is used to measure the → index of refraction (n) of the prism glass, because:

n = sin [(A + D)/2]/sin (A/2), where A is the → prism angle.

See also: → angle; → minimum; → deviation.

The angle between the light entering and exiting the prism when the light passing through the prism is parallel to the prism’s base. Angle of minimum deviation (D) is used to measure the → index of refraction (n) of the prism glass, because:

n = sin [(A + D)/2]/sin (A/2), where A is the → prism angle.

See also: → angle; → minimum; → deviation.

→ prism angle.

See also: → angle; → prism.

→ prism angle.

See also: → angle; → prism.

The angle between the reflected ray and the normal to the reflecting surface.

See also: → angle; → reflection.

The angle between the reflected ray and the normal to the reflecting surface.

See also: → angle; → reflection.

The angle between the direction in which a ray is refracted and the normal to the refracting surface.

See also: → angle; → refraction.

The angle between the direction in which a ray is refracted and the normal to the refracting surface.

See also: → angle; → refraction.

Unit of length used to describe wavelengths and interatomic distances. 1 Å = 10^-10 m.

See also: Named after Anders Jonas Ångström, Swedish physicist and astronomer who founded the science of spectroscopy and discovered by studying the solar spectrum that there is hydrogen in the Sun’s atmosphere; → unit.

Unit of length used to describe wavelengths and interatomic distances. 1 Å = 10^-10 m.

See also: Named after Anders Jonas Ångström, Swedish physicist and astronomer who founded the science of spectroscopy and discovered by studying the solar spectrum that there is hydrogen in the Sun’s atmosphere; → unit.

Having, forming, or consisting of an → angle or angles.

Etymology (EN): From L. angularis “having corners or angles,” from angulus→ angle.

Etymology (PE): Zâviye-yi, adj. from zâviyé, → angle.

Having, forming, or consisting of an → angle or angles.

Etymology (EN): From L. angularis “having corners or angles,” from angulus→ angle.

Etymology (PE): Zâviye-yi, adj. from zâviyé, → angle.

The rate of change of → angular velocity. It is equal to the → first derivative of the → angular velocity: α = dω/dt =d²θ/dt² = a_t/r, where θ is the angle rotated, a_t is the linear tangential acceleration, and r is the radius of circular path.

See also: → angular; → acceleration.

The rate of change of → angular velocity. It is equal to the → first derivative of the → angular velocity: α = dω/dt =d²θ/dt² = a_t/r, where θ is the angle rotated, a_t is the linear tangential acceleration, and r is the radius of circular path.

See also: → angular; → acceleration.

The apparent diameter of an object in angular measure.

See also: → angular; → diameter.

The apparent diameter of an object in angular measure.

See also: → angular; → diameter.

1. The ratio of an object’s → linear size (l)
   to its → angular size (δθ, in → radians), that is D_A = l/δθ. It is used to convert observed angular separations into proper separations at the source.
   
   

2. In cosmology, a distance defined as the ratio of an object’s physical transverse size (l) to its angular size (δθ). It is used to convert angular separations in telescope images into proper separations at the source. The angular diameter distance is defined by: D_A = l / δθ.

Consider a light source of size l at r = r₁ and t = t₁ subtending an angle δθ at the origin (r = 0, t = t₀). The proper distance between the two ends of the object is related to δθ by:

δθ = l / [a(t₁). r₁], where a(t₁) is the → scale factor at the present epoch. Therefore, D_A = r₁ / (1 + z).

The angular diameter distance has the particularity that it does not increase infinitely with z→ ∞. It gets its maximum value at a → redshift of ~ 1 and then decreases for higher z. Therefore, more distant objects appear larger in angular size. This is explained by considering the size of the Universe when the light of the object was emitted. At that time the Universe was smaller and therefore the object occupied a larger fraction of the size of the Universe. In other words, objects appear larger because the entire Universe acts
as a → gravitational lense.

See also: → angular; → diameter; → distance.

1. The ratio of an object’s → linear size (l)
   to its → angular size (δθ, in → radians), that is D_A = l/δθ. It is used to convert observed angular separations into proper separations at the source.
   
   

2. In cosmology, a distance defined as the ratio of an object’s physical transverse size (l) to its angular size (δθ). It is used to convert angular separations in telescope images into proper separations at the source. The angular diameter distance is defined by: D_A = l / δθ.

Consider a light source of size l at r = r₁ and t = t₁ subtending an angle δθ at the origin (r = 0, t = t₀). The proper distance between the two ends of the object is related to δθ by:

δθ = l / [a(t₁). r₁], where a(t₁) is the → scale factor at the present epoch. Therefore, D_A = r₁ / (1 + z).

The angular diameter distance has the particularity that it does not increase infinitely with z→ ∞. It gets its maximum value at a → redshift of ~ 1 and then decreases for higher z. Therefore, more distant objects appear larger in angular size. This is explained by considering the size of the Universe when the light of the object was emitted. At that time the Universe was smaller and therefore the object occupied a larger fraction of the size of the Universe. In other words, objects appear larger because the entire Universe acts
as a → gravitational lense.

See also: → angular; → diameter; → distance.

A high-contrast imaging technique that reduces minute temporal and spatial → seeing fluctuations and facilitates the detection of faint point sources, in close separation from their stars. It consists of the acquisition of a sequence of images with an → altazimuth mounting telescope while the instrument field derotator is switched off. This keeps the instrument and telescope optics aligned and allows the field of view to rotate with respect to the instrument. For each image, a reference → point spread function (PSF) is constructed from other appropriately selected images of the same sequence and subtracted to remove quasistatic PSF structure (Marois et al. 2006, ApJ 641, 556).

See also: → angular; → differential; → imaging.

A high-contrast imaging technique that reduces minute temporal and spatial → seeing fluctuations and facilitates the detection of faint point sources, in close separation from their stars. It consists of the acquisition of a sequence of images with an → altazimuth mounting telescope while the instrument field derotator is switched off. This keeps the instrument and telescope optics aligned and allows the field of view to rotate with respect to the instrument. For each image, a reference → point spread function (PSF) is constructed from other appropriately selected images of the same sequence and subtracted to remove quasistatic PSF structure (Marois et al. 2006, ApJ 641, 556).

See also: → angular; → differential; → imaging.

The rate of change of the angles of emergence θ of various wavelengths from a dispersing prism: dθ/dλ.

See also: → angular; → dispersion.

The rate of change of the angles of emergence θ of various wavelengths from a dispersing prism: dθ/dλ.

See also: → angular; → dispersion.

Between two points A and B, the angle → subtended by lines drawn from an observing point O to A and B. Same as → angular separation.

See also: → angular; → distance.

Between two points A and B, the angle → subtended by lines drawn from an observing point O to A and B. Same as → angular separation.

See also: → angular; → distance.

The number of complete rotations per unit time, expressed in radian per second: ω = 2πν, where ν is the frequency (cycles per second).

See also: → angular; → frequency.

The number of complete rotations per unit time, expressed in radian per second: ω = 2πν, where ν is the frequency (cycles per second).

See also: → angular; → frequency.

Same as → rotational energy.

See also: → angular; → kinetic; → energy.

Same as → rotational energy.

See also: → angular; → kinetic; → energy.

The product of → moment of inertia and
→ angular velocity; synonymous with moment of momentum about an axis. Angular momentum is a vector quantity; it is conserved in an isolated system.

See also: → angular; → momentum.

The product of → moment of inertia and
→ angular velocity; synonymous with moment of momentum about an axis. Angular momentum is a vector quantity; it is conserved in an isolated system.

See also: → angular; → momentum.

A problem encountered by the → cold dark matter model of galaxy formation. The model predicts too small systems lacking → angular momentum, in contrast to real, observed galaxies. → cusp problem; → missing dwarfs.

See also: → angular; → momentum;
→ catastrophe

A problem encountered by the → cold dark matter model of galaxy formation. The model predicts too small systems lacking → angular momentum, in contrast to real, observed galaxies. → cusp problem; → missing dwarfs.

See also: → angular; → momentum;
→ catastrophe

The ratio J/M, where J is the → angular momentum of a → rotating black hole and M the mass of the black hole.

See also: → angular; → momentum; → parameter.

The ratio J/M, where J is the → angular momentum of a → rotating black hole and M the mass of the black hole.

See also: → angular; → momentum; → parameter.

1. The fact that the Sun, which contains 99.9% of the mass of the → solar system, accounts for about 2% of the total → angular momentum of the solar system. The problem of outward → angular momentum transfer has been a main topic of interest for models attempting to explain the origin of the solar system.
   

2. More generally, in star formation studies, the question of the origin of the angular momentum of a star and the evolution of its distribution during the early history of a star. Consider a filamentary molecular cloud with a length of 10 pc and a radius of 0.2 pc, rotating about its long axis with a typical → angular velocity of Ω = 10^-15 s^-1. At a matter density of 20 cm^-3, the cloud is about 1 → solar mass. The cloud collapses to form a star with radius of 6 x 10¹⁰ cm. The conservation of angular momentum (∝ ΩR²) requires that as the radius decreases from 0.2 pc to the stellar value, a factor of 10⁷, the value of Ω must increase by 14 orders of magnitude to 10^-1 s^-1. The star’s rotational velocity will be 20% the speed of light and the ratio of → centrifugal force to gravity at the equator will be about 10⁴. Observational data, however, indicate that the youngest stars are in fact rotating quite slowly, with rotational velocities of 10% of the → break-up velocity. The angular momentum problem was first studied in the context of single stars forming in isolation (L. Mestel,
   1965, Quart. J. R. Astron. Soc. 6, 161). For more information see,
   e.g., P. Bodenheimer, 1995, ARAA 33, 199; H. Zinnecker, 2004, RevMexAA 22, 77; R. B. Larson, 2010, Rep. Prog. Phys. 73, 014901, and references therein.

See also: → angular; → momentum; → problem.

1. The fact that the Sun, which contains 99.9% of the mass of the → solar system, accounts for about 2% of the total → angular momentum of the solar system. The problem of outward → angular momentum transfer has been a main topic of interest for models attempting to explain the origin of the solar system.
   

2. More generally, in star formation studies, the question of the origin of the angular momentum of a star and the evolution of its distribution during the early history of a star. Consider a filamentary molecular cloud with a length of 10 pc and a radius of 0.2 pc, rotating about its long axis with a typical → angular velocity of Ω = 10^-15 s^-1. At a matter density of 20 cm^-3, the cloud is about 1 → solar mass. The cloud collapses to form a star with radius of 6 x 10¹⁰ cm. The conservation of angular momentum (∝ ΩR²) requires that as the radius decreases from 0.2 pc to the stellar value, a factor of 10⁷, the value of Ω must increase by 14 orders of magnitude to 10^-1 s^-1. The star’s rotational velocity will be 20% the speed of light and the ratio of → centrifugal force to gravity at the equator will be about 10⁴. Observational data, however, indicate that the youngest stars are in fact rotating quite slowly, with rotational velocities of 10% of the → break-up velocity. The angular momentum problem was first studied in the context of single stars forming in isolation (L. Mestel,
   1965, Quart. J. R. Astron. Soc. 6, 161). For more information see,
   e.g., P. Bodenheimer, 1995, ARAA 33, 199; H. Zinnecker, 2004, RevMexAA 22, 77; R. B. Larson, 2010, Rep. Prog. Phys. 73, 014901, and references therein.

See also: → angular; → momentum; → problem.

A process whereby in a rotating, non-solid system matter is displaced toward (→ accretion) or away from (→ mass loss) the rotation center. See also → magnetorotational instability.

See also: → angular; → momentum; → transfer.

A process whereby in a rotating, non-solid system matter is displaced toward (→ accretion) or away from (→ mass loss) the rotation center. See also → magnetorotational instability.

See also: → angular; → momentum; → transfer.

Same as → angular momentum transfer.

See also: → angular; → momentum; → transport.

Same as → angular momentum transfer.

See also: → angular; → momentum; → transport.

Of the → cosmic microwave background radiation, a plot of how much the temperature varies from point to point on the sky versus the angular frequency. This spectrum answers fundamental questions about the nature of the Universe. → cosmic microwave background anisotropy; → dipole anisotropy.

See also: → angular; → power; → spectrum.

Of the → cosmic microwave background radiation, a plot of how much the temperature varies from point to point on the sky versus the angular frequency. This spectrum answers fundamental questions about the nature of the Universe. → cosmic microwave background anisotropy; → dipole anisotropy.

See also: → angular; → power; → spectrum.

Of a telescope, the smallest angle betwwen two → point sources that produces distinct images. It depends on both the wavelength at which observations are made and on the diameter of the telescope. Same as → spatial resolution.

See also: → angular; → resolution.

Of a telescope, the smallest angle betwwen two → point sources that produces distinct images. It depends on both the wavelength at which observations are made and on the diameter of the telescope. Same as → spatial resolution.

See also: → angular; → resolution.

Same as → angular distance.

See also: → angular; → separation.

Same as → angular distance.

See also: → angular; → separation.

Same as → angular diameter distance.

See also: → angular; → size; → distance.

Same as → angular diameter distance.

See also: → angular; → size; → distance.

A measure of the angular displacement per unit time. Of a particle traveling on a circular path or a rotating body, the ratio of the angle traversed to the amount of time it takes to traverse that angle: ω = dθ/dt. For a rigid body, all lines in it rotate through the same angle in the same time, and the angular velocity is the characteristic of the body as a whole. The angular velocity is related to the linear velocity by the equation v = rω, where r is the distance of the point from the rotation axis. → vector angular velocity.

See also: → angular; → velocity.

A measure of the angular displacement per unit time. Of a particle traveling on a circular path or a rotating body, the ratio of the angle traversed to the amount of time it takes to traverse that angle: ω = dθ/dt. For a rigid body, all lines in it rotate through the same angle in the same time, and the angular velocity is the characteristic of the body as a whole. The angular velocity is related to the linear velocity by the equation v = rω, where r is the distance of the point from the rotation axis. → vector angular velocity.

See also: → angular; → velocity.

Any living creature that is distinguished from plants by independent movement and responsive sense organs.

Etymology (EN): From L. animale “living being, being which breathes,” neuter of animalis “animate, living; of the air,” from anima “breath; soul; breeze,” cognate with Pers. jân, as below.

Etymology (PE): Jânevar, jânvar, Mid.Pers. gyânwar “animal; animate,” literally “living, alive; quick,” from jân, Mid.Pers. (+ prefix *ui-) gyân “(breathing) soul,” gyânig “spiritual, vital;” Av. viiānayā “spirit(ness)”; Proto-Iranian *HanH- “to breathe” cf. Skt. ani- “to breathe,” aniti “breathes;” Gk. anemos “wind;” L. animus “soul, spirit,” anima “breeze, breath, soul;” Goth. uz-anan “to exhale” (Cheung 2007)

• -e epenthesis + -var possession suffix; also hen o hen “to pant;” dialects, e.g. Lori, Kurd., henâs, henâsa “breath,” henowša “panting.”

Any living creature that is distinguished from plants by independent movement and responsive sense organs.

Etymology (EN): From L. animale “living being, being which breathes,” neuter of animalis “animate, living; of the air,” from anima “breath; soul; breeze,” cognate with Pers. jân, as below.

Etymology (PE): Jânevar, jânvar, Mid.Pers. gyânwar “animal; animate,” literally “living, alive; quick,” from jân, Mid.Pers. (+ prefix *ui-) gyân “(breathing) soul,” gyânig “spiritual, vital;” Av. viiānayā “spirit(ness)”; Proto-Iranian *HanH- “to breathe” cf. Skt. ani- “to breathe,” aniti “breathes;” Gk. anemos “wind;” L. animus “soul, spirit,” anima “breeze, breath, soul;” Goth. uz-anan “to exhale” (Cheung 2007)

• -e epenthesis + -var possession suffix; also hen o hen “to pant;” dialects, e.g. Lori, Kurd., henâs, henâsa “breath,” henowša “panting.”

1. To give life to; make alive; make lively or vigorous; give motion to.
   

2. To give an image or cartoon character the appearance of movement using animation techniques.

Etymology (EN): From L. animatus p.p. of animare “give breath to,” also “to endow with a particular spirit, to give courage to,” from anima “life, breath”  L. animus “soul, spirit,”
anima “breeze, breath, soul;” Goth. uz-anan “to exhale;” Gk. anemos “wind;” PIE root *ane- “to blow, to breathe;” cognate with Pers. jân “vital spirit, soul, mind,” as below.

Etymology (PE): Farhanidan, from far- perfection prefix + han
variant of jân “vital spirit, soul;” hen o hen “to pant;” Lori, Kurd., henâs, henâsa “breath,” henowša “panting;” Mid.Pers. (+ prefix *ui-) gyân “(breathing) soul,” gyânig “spiritual, vital;” Av. viiānayā “spirit(ness);” Proto-Iranian *HanH- “to breathe” cf. Skt. ani- “to breathe,” aniti “breathes;” Gk. and L., as above, + -idan infinitive suffix.

1. To give life to; make alive; make lively or vigorous; give motion to.
   

2. To give an image or cartoon character the appearance of movement using animation techniques.

Etymology (EN): From L. animatus p.p. of animare “give breath to,” also “to endow with a particular spirit, to give courage to,” from anima “life, breath”  L. animus “soul, spirit,”
anima “breeze, breath, soul;” Goth. uz-anan “to exhale;” Gk. anemos “wind;” PIE root *ane- “to blow, to breathe;” cognate with Pers. jân “vital spirit, soul, mind,” as below.

Etymology (PE): Farhanidan, from far- perfection prefix + han
variant of jân “vital spirit, soul;” hen o hen “to pant;” Lori, Kurd., henâs, henâsa “breath,” henowša “panting;” Mid.Pers. (+ prefix *ui-) gyân “(breathing) soul,” gyânig “spiritual, vital;” Av. viiānayā “spirit(ness);” Proto-Iranian *HanH- “to breathe” cf. Skt. ani- “to breathe,” aniti “breathes;” Gk. and L., as above, + -idan infinitive suffix.

1. An act or instance of animating or enlivening; the state or condition of being animated.
   

2. The technique of imaging successive drawings or positions of cartoons to create an illusion of movement when the film is shown as a sequence.

See also: → animate; → -tion.

1. An act or instance of animating or enlivening; the state or condition of being animated.
   

2. The technique of imaging successive drawings or positions of cartoons to create an illusion of movement when the film is shown as a sequence.

See also: → animate; → -tion.

A → negatively charged → ion or → radical. Anions in a liquid subjected to electric potential are attracted toward the → anode. See also → cation.

See also: From Gk. anienai “to go up,” from an-, from → ana- “up,” + -i-, from ire, eo “to go, walk,” cf. Pers. ây-, → assembly, + -on, as in → ion.

A → negatively charged → ion or → radical. Anions in a liquid subjected to electric potential are attracted toward the → anode. See also → cation.

See also: From Gk. anienai “to go up,” from an-, from → ana- “up,” + -i-, from ire, eo “to go, walk,” cf. Pers. ây-, → assembly, + -on, as in → ion.

In an imaging system, the dependence of its performance on field angle. In other words, the spatial variability of the → point spread function for off-axis sources.

See also: → an- + → isoplanatism.

In an imaging system, the dependence of its performance on field angle. In other words, the spatial variability of the → point spread function for off-axis sources.

See also: → an- + → isoplanatism.

The departure from → isoplanicity.

See also: → an-; → isoplanicity.

The departure from → isoplanicity.

See also: → an-; → isoplanicity.

Describing a medium in which certain physical properties are different in different directions.

See also: → anisotropy; → -ic.

Describing a medium in which certain physical properties are different in different directions.

See also: → anisotropy; → -ic.

A solution to Einstein’s theory of → general relativity that is spatially homogeneous but allows for rotation and/or shear. See also → Bianchi cosmological model.

See also: → anisotropic; → homogeneous; → cosmological; → model.

A solution to Einstein’s theory of → general relativity that is spatially homogeneous but allows for rotation and/or shear. See also → Bianchi cosmological model.

See also: → anisotropic; → homogeneous; → cosmological; → model.

A variation in a property with direction, e.g. → cosmic microwave background anisotropy, → dipole anisotropy.

See also: From → an-, privative prefix, + → isotropy.

A variation in a property with direction, e.g. → cosmic microwave background anisotropy, → dipole anisotropy.

See also: From → an-, privative prefix, + → isotropy.

1. (in humans) The joint between the foot and the leg, in which movement occurs in two planes.
   

   2. The corresponding joint in a quadruped or bird; hock (Dictionary.com).

Etymology (EN): M.E. ankel, enkel, cognate with M.L.G., Du. enkel, O.H.G. anchal, enchil, O.Norse okkul.

Etymology (PE): Quzak, from quz, variant of kuž “humped,” → convex.

1. (in humans) The joint between the foot and the leg, in which movement occurs in two planes.
   

   2. The corresponding joint in a quadruped or bird; hock (Dictionary.com).

Etymology (EN): M.E. ankel, enkel, cognate with M.L.G., Du. enkel, O.H.G. anchal, enchil, O.Norse okkul.

Etymology (PE): Quzak, from quz, variant of kuž “humped,” → convex.

The process in which the entire → mass of → two colliding → particles, one of → matter and one of → antimatter, is → converted into → radiant energy in the form of → gamma rays. See also → annihilation operator.

Etymology (EN): L. annihilatus, p.p. of annihilare “to reduce to nothing,” from ad- “to” + nihil “nothing,” from ne- “not” + hilum “small thing, trifle”

Etymology (PE): Nâbudi, from nâ- “not” + bud “to be, exist,” from budan “to be, exist” + -i noun forming suffix.

The process in which the entire → mass of → two colliding → particles, one of → matter and one of → antimatter, is → converted into → radiant energy in the form of → gamma rays. See also → annihilation operator.

Etymology (EN): L. annihilatus, p.p. of annihilare “to reduce to nothing,” from ad- “to” + nihil “nothing,” from ne- “not” + hilum “small thing, trifle”

Etymology (PE): Nâbudi, from nâ- “not” + bud “to be, exist,” from budan “to be, exist” + -i noun forming suffix.

In → quantum field theory, the operator that lowers → eigenstates one → energy level, contrarily to the → creation operator.

See also: → annihilation; → operator.

In → quantum field theory, the operator that lowers → eigenstates one → energy level, contrarily to the → creation operator.

See also: → annihilation; → operator.

To make known publicly or officially; proclaim; give notice of (Dictionary.com).

Etymology (EN): M.E., from M.Fr. anoncer, O.Fr. anoncier “announce, proclaim,” from L. annuntiare, adnuntiare “to announce, relate,” literally “to bring news,” from → ad- “to”

• nuntiare “relate, report,” from nuntius “messenger.”

Etymology (PE): žâyidan, from prefix â- + Sogd., Munji žây- “to speak, to say,” Yaghnobi žoy- “to read, sing,” Yazghulami γay- “to call,” Pers. (prefixed) afqân “lamentation, groaning;” Av. gā- “to sing,” pairi.gā.vacah- “who sings the words around,” bərəzi.gāθra- “singing high,” gāθə- “song, gāthā;” cf. Skt. gā- “to sing;” O.Russ. gajati “to croak (ravens)”; Lith. giedoti “to sing” (Cheung 2007).

To make known publicly or officially; proclaim; give notice of (Dictionary.com).

Etymology (EN): M.E., from M.Fr. anoncer, O.Fr. anoncier “announce, proclaim,” from L. annuntiare, adnuntiare “to announce, relate,” literally “to bring news,” from → ad- “to”

• nuntiare “relate, report,” from nuntius “messenger.”

Etymology (PE): žâyidan, from prefix â- + Sogd., Munji žây- “to speak, to say,” Yaghnobi žoy- “to read, sing,” Yazghulami γay- “to call,” Pers. (prefixed) afqân “lamentation, groaning;” Av. gā- “to sing,” pairi.gā.vacah- “who sings the words around,” bərəzi.gāθra- “singing high,” gāθə- “song, gāthā;” cf. Skt. gā- “to sing;” O.Russ. gajati “to croak (ravens)”; Lith. giedoti “to sing” (Cheung 2007).

Covering the period of a year; occurring or happening every year or once a year.

Etymology (EN): Annual, from M.Fr. annuel, from L.L. annualis,
blend of L. annuus “yearly,” from annus “year” and L. annalis “yearly,” from annus “year,” from PIE *atnos, from *at- “to go” (Skt. a’tati “he goes, wanders”).

Etymology (PE): Sâlâné, from sâl, → year,

• âné “-ly”.

Covering the period of a year; occurring or happening every year or once a year.

Etymology (EN): Annual, from M.Fr. annuel, from L.L. annualis,
blend of L. annuus “yearly,” from annus “year” and L. annalis “yearly,” from annus “year,” from PIE *atnos, from *at- “to go” (Skt. a’tati “he goes, wanders”).

Etymology (PE): Sâlâné, from sâl, → year,

• âné “-ly”.

The apparent, small displacement in position of a star during the year due to the → aberration of starlight. It depends on the → celestial latitude, and its maximum value is about 20’’.50. See also → constant of aberration; → aberration orbit.

See also: → annual; → aberration.

The apparent, small displacement in position of a star during the year due to the → aberration of starlight. It depends on the → celestial latitude, and its maximum value is about 20’’.50. See also → constant of aberration; → aberration orbit.

See also: → annual; → aberration.

→ annual motion.

See also: → annual; → apparent; → motion.

→ annual motion.

See also: → annual; → apparent; → motion.

An irregularity in the Moon’s orbit, which can amount to 11 degrees in a period of one year. It results from the Sun’s disturbing effect on the motion of the Moon due to varying distance between them.

See also: → annual; → equation.

An irregularity in the Moon’s orbit, which can amount to 11 degrees in a period of one year. It results from the Sun’s disturbing effect on the motion of the Moon due to varying distance between them.

See also: → annual; → equation.

The annual apparent motion of the → Sun in the sky with respect to → fixed stars along the path called → ecliptic. The apparent annual motion is due to the → Earth’s → revolution about the Sun. In the course of this motion, the Sun appears to shifts about 1° eastward per day.

See also: → annual; → motion.

The annual apparent motion of the → Sun in the sky with respect to → fixed stars along the path called → ecliptic. The apparent annual motion is due to the → Earth’s → revolution about the Sun. In the course of this motion, the Sun appears to shifts about 1° eastward per day.

See also: → annual; → motion.

The difference in position of a star as seen from the → Earth and → Sun, i.e. the angle subtended at a star by the mean → radius of the Earth’s orbit around the Sun. Same as → heliocentric parallax.

Because the Earth revolves around the Sun, we observe the sky from a constantly moving position in space. Therefore, we should expect to see an annual effect, in which the positions of nearby objects appear to oscillate back and forth in response to our motion around the Sun. This does in fact happen, but the distances to even the nearest stars are so great that we need to make careful observations with a telescope to detect it. The annual parallax of the nearest star, → Proxima Centauri, is 0.762 arcsec, which is too small for our → acuity of vision.

See also: → annual; → parallax.

The difference in position of a star as seen from the → Earth and → Sun, i.e. the angle subtended at a star by the mean → radius of the Earth’s orbit around the Sun. Same as → heliocentric parallax.

Because the Earth revolves around the Sun, we observe the sky from a constantly moving position in space. Therefore, we should expect to see an annual effect, in which the positions of nearby objects appear to oscillate back and forth in response to our motion around the Sun. This does in fact happen, but the distances to even the nearest stars are so great that we need to make careful observations with a telescope to detect it. The annual parallax of the nearest star, → Proxima Centauri, is 0.762 arcsec, which is too small for our → acuity of vision.

See also: → annual; → parallax.

Generally, the variation of a quantity over a year. In particular the yearly change in the right ascension or declination of a star, produced by the combined effects of the precession of the equinoxes and the proper motion of the star.

See also: → annual; → variation.

Generally, the variation of a quantity over a year. In particular the yearly change in the right ascension or declination of a star, produced by the combined effects of the precession of the equinoxes and the proper motion of the star.

See also: → annual; → variation.

(Especially of laws or other established rules, usages, etc.) to make void or null; abolish; cancel; invalidate (Dictionary.com).

Etymology (EN): M.E., from O.Fr. anuller, from L.L. annullare “to make to nothing,” from L. → ad- “to” + nullum, neuter of nullus “nothing,” → null.

Etymology (PE): Ânulidan, from prefix â- + nul, → null,

• -idan infinitive suffix.

(Especially of laws or other established rules, usages, etc.) to make void or null; abolish; cancel; invalidate (Dictionary.com).

Etymology (EN): M.E., from O.Fr. anuller, from L.L. annullare “to make to nothing,” from L. → ad- “to” + nullum, neuter of nullus “nothing,” → null.

Etymology (PE): Ânulidan, from prefix â- + nul, → null,

• -idan infinitive suffix.

Having the form of a → ring.

Etymology (EN): From Fr. annulaire or directly from L. annularis “pertaining to a ring,” from annulus, diminutive of anus “ring.”

Etymology (PE): Halge-yi, halqevâr, adj. from halqé, → ring.

Having the form of a → ring.

Etymology (EN): From Fr. annulaire or directly from L. annularis “pertaining to a ring,” from annulus, diminutive of anus “ring.”

Etymology (PE): Halge-yi, halqevâr, adj. from halqé, → ring.

A solar eclipse in which the Moon is close the → apogee and is, therefore, too small to cover the whole disk of the Sun, leaving a visible edge or ring of sunlight. An annular eclipse can last for 12m 30s at the most. See also → total eclipse.

See also: → annular; → eclipse.

A solar eclipse in which the Moon is close the → apogee and is, therefore, too small to cover the whole disk of the Sun, leaving a visible edge or ring of sunlight. An annular eclipse can last for 12m 30s at the most. See also → total eclipse.

See also: → annular; → eclipse.

A solar eclipse that has both annular and total phases. Same as → hybrid eclipse.

See also: → annular; → total; → eclipse.

A solar eclipse that has both annular and total phases. Same as → hybrid eclipse.

See also: → annular; → total; → eclipse.

The maximum phase of an → annular eclipse during which the Moon’s entire disk is seen silhouetted against the Sun. Annularity is the period between second and → third contact during an annular eclipse. It can last from a fraction of a second to a maximum of 12 minutes 29 seconds (F. Espenak, NASA).

See also: → annular; → -ity.

The maximum phase of an → annular eclipse during which the Moon’s entire disk is seen silhouetted against the Sun. Annularity is the period between second and → third contact during an annular eclipse. It can last from a fraction of a second to a maximum of 12 minutes 29 seconds (F. Espenak, NASA).

See also: → annular; → -ity.

An → electrode from which a stream of → electrons leaves, as in an electron tube or electrolytic cell. → cathode.

Etymology (EN): From Gk. anodos “way up,” from → ana- “up” + hodos “way.”

Etymology (PE): Ânod, loanword from anode as above.

An → electrode from which a stream of → electrons leaves, as in an electron tube or electrolytic cell. → cathode.

Etymology (EN): From Gk. anodos “way up,” from → ana- “up” + hodos “way.”

Etymology (PE): Ânod, loanword from anode as above.

The time interval of 27.554 551 days (27d 13h 18m 33.2s), on average, between two successive passages of the Moon through the → perigee of its orbit.

Etymology (EN): Anomalistic from → anomaly.

Etymology (PE): Pirâzamini from pirâzamin, → perigee.

The time interval of 27.554 551 days (27d 13h 18m 33.2s), on average, between two successive passages of the Moon through the → perigee of its orbit.

Etymology (EN): Anomalistic from → anomaly.

Etymology (PE): Pirâzamini from pirâzamin, → perigee.

Etymology (EN): Anomalistic from → anomaly.

Etymology (PE): Pirâhuri from pirâhur, → perihelion.

Etymology (EN): Anomalistic from → anomaly.

Etymology (PE): Pirâhuri from pirâhur, → perihelion.

Deviating from the normal or common order, form, or rule. → anomaly.

Etymology (EN): From Gk. anomalos “uneven, irregular,” from → an- “not” + homalos “even,” from homos “same”.

Etymology (PE): Nâsân, from Pers. nâ- “not” + sân “rule, custom, law, fashion,” literally “out of rule”.

Deviating from the normal or common order, form, or rule. → anomaly.

Etymology (EN): From Gk. anomalos “uneven, irregular,” from → an- “not” + homalos “even,” from homos “same”.

Etymology (PE): Nâsân, from Pers. nâ- “not” + sân “rule, custom, law, fashion,” literally “out of rule”.

The phenomenon whereby the → refractive index
of light in a medium changes rapidly with wavelength in the vicinity of an → absorption band. Hence the → dispersion curve of the substance shows marked deviations from → Cauchy’s equation, in contrast with the behavior of → normal dispersion. On the shorter λ side of the absorption band the refractive index falls off more rapidly than required by Cauchy’s equation representing values of n for visible light. On the long λ side of the absorption band the index is very high, decreasing at first rapidly and then more slowly as one goes beyond the absorption band.

See also: → anomalous; → dispersion.

The phenomenon whereby the → refractive index
of light in a medium changes rapidly with wavelength in the vicinity of an → absorption band. Hence the → dispersion curve of the substance shows marked deviations from → Cauchy’s equation, in contrast with the behavior of → normal dispersion. On the shorter λ side of the absorption band the refractive index falls off more rapidly than required by Cauchy’s equation representing values of n for visible light. On the long λ side of the absorption band the index is very high, decreasing at first rapidly and then more slowly as one goes beyond the absorption band.

See also: → anomalous; → dispersion.

Discrepant luminosity classes derived for the same → Am star when different criteria are used. Lore specifically, a luminosity criterion may indicate a → giant star, wheras another criterion indicates a → supergiant.

See also: → anomalous; → luminosity; → effect.

Discrepant luminosity classes derived for the same → Am star when different criteria are used. Lore specifically, a luminosity criterion may indicate a → giant star, wheras another criterion indicates a → supergiant.

See also: → anomalous; → luminosity; → effect.

The high redshift of a quasar which is seemingly physically associated with a galaxy of low redshift.

See also: → anomalous; → redshift.

The high redshift of a quasar which is seemingly physically associated with a galaxy of low redshift.

See also: → anomalous; → redshift.

A member of a small class of → X-ray pulsars with long rotation periods (6-12 seconds), short → spin-down times (~ 10³-10⁵ years), and
→ soft X-ray spectrum. AXPs show no evidence of being → X-ray binary systems.
Their magnetic fields, as deduced from their spin-down rate, are the highest known, reaching 10¹³-10¹⁵ → gauss. AXPs are generally believed to be → magnetars.

See also: → anomalous; → X-ray;
→ pulsar.

A member of a small class of → X-ray pulsars with long rotation periods (6-12 seconds), short → spin-down times (~ 10³-10⁵ years), and
→ soft X-ray spectrum. AXPs show no evidence of being → X-ray binary systems.
Their magnetic fields, as deduced from their spin-down rate, are the highest known, reaching 10¹³-10¹⁵ → gauss. AXPs are generally believed to be → magnetars.

See also: → anomalous; → X-ray;
→ pulsar.

The splitting of a spectral line into several components in the → Zeeman effect when the magnetic field is weak. The splitting is much more complex than in the normal effect. The number of components of the lines often considerably exceeds their number in the normal effect. Contrarily to the normal Zeeman effect, the anomalous effect cannot be explained by classical theory. The historically “anomalous” effect is accounted for by the inclusion of electron spin in the total angular moment. In fact the idea of electron spin was put forward (Uhlenbeck and Goudsmit, 1926) to explain the anomalous Zeeman effect.

See also: → anomalous; → Zeeman effect.

The splitting of a spectral line into several components in the → Zeeman effect when the magnetic field is weak. The splitting is much more complex than in the normal effect. The number of components of the lines often considerably exceeds their number in the normal effect. Contrarily to the normal Zeeman effect, the anomalous effect cannot be explained by classical theory. The historically “anomalous” effect is accounted for by the inclusion of electron spin in the total angular moment. In fact the idea of electron spin was put forward (Uhlenbeck and Goudsmit, 1926) to explain the anomalous Zeeman effect.

See also: → anomalous; → Zeeman effect.

In general, a deviation from the norm.
An angle that gives the position of an object in an elliptical orbit at any given time with respect to its primary. The true anomaly is the angle between the periapsis of an orbit and the object’s current orbital position, measured from the body being orbited and in the direction of orbital motion. The mean anomaly is what the true anomaly would be if the object orbited in a perfect circle at constant speed.

Etymology (EN): Anomaly from → anomalous

Etymology (PE): Nâsâni, from nâ- negation suffix + sân “rule, law, custom” + -i noun maker suffix.

In general, a deviation from the norm.
An angle that gives the position of an object in an elliptical orbit at any given time with respect to its primary. The true anomaly is the angle between the periapsis of an orbit and the object’s current orbital position, measured from the body being orbited and in the direction of orbital motion. The mean anomaly is what the true anomaly would be if the object orbited in a perfect circle at constant speed.

Etymology (EN): Anomaly from → anomalous

Etymology (PE): Nâsâni, from nâ- negation suffix + sân “rule, law, custom” + -i noun maker suffix.

Having an unknown or unacknowledged name. → anonymous object.

Etymology (EN): L. annymus, from Gk. annumos “nameless,” from → an- “without” + onoma, onuma “name”. Compare with L. nomen, Skt. nama, Av. nama, Mod. Pers. nâm, PIE *nomen “name”.

Etymology (PE): Anâm, from Persian → a-, an- “without” + nâm “name,” as above. Binâm, from bi- “without”

• nâm.

Having an unknown or unacknowledged name. → anonymous object.

Etymology (EN): L. annymus, from Gk. annumos “nameless,” from → an- “without” + onoma, onuma “name”. Compare with L. nomen, Skt. nama, Av. nama, Mod. Pers. nâm, PIE *nomen “name”.

Etymology (PE): Anâm, from Persian → a-, an- “without” + nâm “name,” as above. Binâm, from bi- “without”

• nâm.

An → astronomical object which has not been catalogued.

See also: → anonymous; → object.

An → astronomical object which has not been catalogued.

See also: → anonymous; → object.

Plural form: ansae.

1. The “handles,” or extremities, of → Saturn’s rings as viewed from Earth.
   
2. The extremities of a → lenticular galaxy.

Etymology (EN): L. ansa “handle.”

Etymology (PE): Dastak “handle,” from dast “hand” (Mid.Pers. dast; O.Pers. dasta-; Av. zasta-; cf. Skt. hásta-; Gk. kheir; L. praesto “at hand;” Arm. jern “hand;” Lith. pa-žastis “arm-pit;” PIE *ghes-to-) + -ak suffix denoting relation, affinity, similarity.

Plural form: ansae.

1. The “handles,” or extremities, of → Saturn’s rings as viewed from Earth.
   
2. The extremities of a → lenticular galaxy.

Etymology (EN): L. ansa “handle.”

Etymology (PE): Dastak “handle,” from dast “hand” (Mid.Pers. dast; O.Pers. dasta-; Av. zasta-; cf. Skt. hásta-; Gk. kheir; L. praesto “at hand;” Arm. jern “hand;” Lith. pa-žastis “arm-pit;” PIE *ghes-to-) + -ak suffix denoting relation, affinity, similarity.

In physics and mathematics an a priori assumption that is used to establish
the form of an equation or a system of equations. The ansatz, which is verified later by the result, is meant to facilitate the solution. → Bethe ansatz.

See also: From Ger. Ansatz “attempt, approach, beginning.”

In physics and mathematics an a priori assumption that is used to establish
the form of an equation or a system of equations. The ansatz, which is verified later by the result, is meant to facilitate the solution. → Bethe ansatz.

See also: From Ger. Ansatz “attempt, approach, beginning.”

The direction in the sky (in → Columba) away from which the Sun seems to be moving (at a speed of 19.4 km/s) relative to general field stars in the Galaxy.

Etymology (EN): Antapex from L. ant-, → anti- “against, opposite,” + L. → apex “summit, peak, tip.”

Etymology (PE): Pâdcakâd from pâd-, → anti- + cakâd “summit of a mountain; top, crown of the head, top of the forehead,” from Mid.Pers. cakât “summit,” → apex.

The direction in the sky (in → Columba) away from which the Sun seems to be moving (at a speed of 19.4 km/s) relative to general field stars in the Galaxy.

Etymology (EN): Antapex from L. ant-, → anti- “against, opposite,” + L. → apex “summit, peak, tip.”

Etymology (PE): Pâdcakâd from pâd-, → anti- + cakâd “summit of a mountain; top, crown of the head, top of the forehead,” from Mid.Pers. cakât “summit,” → apex.

The south polar area, south of latitude 66° 33’ 8’’ S.

Etymology (EN): Antarctic, from O.Fr. antartique, from M.L. antarcticus, from Gk. antarktikos “opposite the north,” from → anti- “opposite” + arktikos, → arctic.

Etymology (PE): Daštargân, from daštar, → south, + -gân suffix indicating the direction.
Jonubgân, from jonub “south,” from Ar. janub “south,” + -gân, as above.

The south polar area, south of latitude 66° 33’ 8’’ S.

Etymology (EN): Antarctic, from O.Fr. antartique, from M.L. antarcticus, from Gk. antarktikos “opposite the north,” from → anti- “opposite” + arktikos, → arctic.

Etymology (PE): Daštargân, from daštar, → south, + -gân suffix indicating the direction.
Jonubgân, from jonub “south,” from Ar. janub “south,” + -gân, as above.

A → red supergiant star (→ spectral type M1 Ib) in the constellation → Scorpius, lying about 500 → light-years (170 (+35/-25) → parsecs) from Earth. It has a dwarf massive companion (B3 V), which is a → radio source.

Etymology (EN): Antares, in Gk. “rival of Mars,” from Gk. → anti + Ares “the Gk. god of War, called Mars by the Romans.” The comparison with the planet Mars is because they are both red in color and have the same brightness.

Etymology (PE): Každom-del “the heart of the Scorpion,” from každom “scorpion” + del, → heart. Qalb-ol-‘Aqrab “the heart of the Scorpion,” from Ar. Qalb “heart” + ‘aqrab “scorpion”.

A → red supergiant star (→ spectral type M1 Ib) in the constellation → Scorpius, lying about 500 → light-years (170 (+35/-25) → parsecs) from Earth. It has a dwarf massive companion (B3 V), which is a → radio source.

Etymology (EN): Antares, in Gk. “rival of Mars,” from Gk. → anti + Ares “the Gk. god of War, called Mars by the Romans.” The comparison with the planet Mars is because they are both red in color and have the same brightness.

Etymology (PE): Každom-del “the heart of the Scorpion,” from každom “scorpion” + del, → heart. Qalb-ol-‘Aqrab “the heart of the Scorpion,” from Ar. Qalb “heart” + ‘aqrab “scorpion”.

Logic: In a → conditional proposition, the → clause which follows if.

Etymology (EN): M.E., from from L. antecedentem, from antecedere “go before, precede,” from ante- “before” + cedere “to yield, to go,” → process.

Etymology (PE): Pišây, from piš “before,” → pre-,

• ây present stem of âmadan “to come,” → process.

Logic: In a → conditional proposition, the → clause which follows if.

Etymology (EN): M.E., from from L. antecedentem, from antecedere “go before, precede,” from ante- “before” + cedere “to yield, to go,” → process.

Etymology (PE): Pišây, from piš “before,” → pre-,

• ây present stem of âmadan “to come,” → process.

1. General: A device or a set of wires that receives or sends out radio signals.
   

2. In radio astronomy, the major dish-like component or wired structure used to collect radio signals.

Etymology (EN): L. antenna “sail yard,” the long yard that sticks up on some sails, of unknown origin, perhaps from PIE base *temp- “to stretch, extend.”
In this sense, it is a translation of Gk. keraiai “horns” (of insects).

Etymology (PE): Âten, from Fr. antenne, from L. as above.

1. General: A device or a set of wires that receives or sends out radio signals.
   

2. In radio astronomy, the major dish-like component or wired structure used to collect radio signals.

Etymology (EN): L. antenna “sail yard,” the long yard that sticks up on some sails, of unknown origin, perhaps from PIE base *temp- “to stretch, extend.”
In this sense, it is a translation of Gk. keraiai “horns” (of insects).

Etymology (PE): Âten, from Fr. antenne, from L. as above.

A measure of the directivity of a radio telescope. It is the ratio of the amount of power received in the direction the dish is pointing to the smaller amount of power from other directions in the sidelobes.

See also: → antenna; → gain.

A measure of the directivity of a radio telescope. It is the ratio of the amount of power received in the direction the dish is pointing to the smaller amount of power from other directions in the sidelobes.

See also: → antenna; → gain.

A three-dimensional section of the → radiation pattern ofa directional antenna, bounded by one or more cones of nulls or by regions of diminished irradiance.

See also: → antenna; → lobe.

A three-dimensional section of the → radiation pattern ofa directional antenna, bounded by one or more cones of nulls or by regions of diminished irradiance.

See also: → antenna; → lobe.

The response of an antenna to incident radiation as a function of the direction of incidence of the radiation. A generic antenna pattern consists of a → main lobe and a number of smaller → side lobes. Also called → radiation pattern.

See also: → antenna; → pattern.

The response of an antenna to incident radiation as a function of the direction of incidence of the radiation. A generic antenna pattern consists of a → main lobe and a number of smaller → side lobes. Also called → radiation pattern.

See also: → antenna; → pattern.

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.

See also: antenna; → temperature.

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.

See also: antenna; → temperature.

The pair of colliding galaxies NGC4038 and NGC4039 and the long arcing insect-like “antennae” of luminous matter revealed by optical telescopes. The “antennae” are believed to have been produced by the collision between the galaxies that began about 100 million years ago and is still occurring. The Antennae Galaxies, about 60 million → light-years from Earth, lie in the constellation → Corvus.

Etymology (EN): Antennae, plural of → antenna; → galaxy.

Etymology (PE): Kahkešânhâ, plural of kahkešân→ galaxy; šâxak “insect antenna,” from šâx “horn” (Mid.Pers šâk, cf. Skt. sakha- “a branch, a limb,” Arm. cax, Lit. šaka, O.S. soxa, PIE *kakhâ “branch”) + -ak
suffix denoting relation, affinity, similarity (as in dastak, pos(tak, pas(mak, xarak, nâxonak, mus(ak, eynak);

The pair of colliding galaxies NGC4038 and NGC4039 and the long arcing insect-like “antennae” of luminous matter revealed by optical telescopes. The “antennae” are believed to have been produced by the collision between the galaxies that began about 100 million years ago and is still occurring. The Antennae Galaxies, about 60 million → light-years from Earth, lie in the constellation → Corvus.

Etymology (EN): Antennae, plural of → antenna; → galaxy.

Etymology (PE): Kahkešânhâ, plural of kahkešân→ galaxy; šâxak “insect antenna,” from šâx “horn” (Mid.Pers šâk, cf. Skt. sakha- “a branch, a limb,” Arm. cax, Lit. šaka, O.S. soxa, PIE *kakhâ “branch”) + -ak
suffix denoting relation, affinity, similarity (as in dastak, pos(tak, pas(mak, xarak, nâxonak, mus(ak, eynak);

The idea that the existence of → life and, in particular, our presence as → intelligent  → observers, → constrains the nature of the → Universe.

It is an attempt to explain the observed fact that the → fundamental constants of nature are just right or fine-tuned to allow the Universe and life to exist. This is not however a “principle.” See also → weak anthropic principle, → strong anthropic principle. Compare → Copernican principle.

Etymology (EN): Anthropic, from Gk. anthropikos “human,” from anthropos “human being, man,” → anthropo-; → principle.

Etymology (PE): Parvaz, → principle; ensân-hasti, from ensân, → anthropo-,

• Mod.Pers. hasti “existence, being,” Mid.Pers. astih, O.Pers. astiy; Av. asti “is,” O.Pers./Av. root ah- “to be;” cf. Skt. as-; Gk. esti; L. est; PIE *es-.

The idea that the existence of → life and, in particular, our presence as → intelligent  → observers, → constrains the nature of the → Universe.

It is an attempt to explain the observed fact that the → fundamental constants of nature are just right or fine-tuned to allow the Universe and life to exist. This is not however a “principle.” See also → weak anthropic principle, → strong anthropic principle. Compare → Copernican principle.

Etymology (EN): Anthropic, from Gk. anthropikos “human,” from anthropos “human being, man,” → anthropo-; → principle.

Etymology (PE): Parvaz, → principle; ensân-hasti, from ensân, → anthropo-,

• Mod.Pers. hasti “existence, being,” Mid.Pers. astih, O.Pers. astiy; Av. asti “is,” O.Pers./Av. root ah- “to be;” cf. Skt. as-; Gk. esti; L. est; PIE *es-.

A prefix with the meaning of “pertaining to man or human beings.” Before a vowel, anthrop-. See also → man, → human. → anthropic principle.

Etymology (EN): Frpm Gk. anthropos “man, human being,” from aner “man” (as opposed to a woman, a god, or a boy), from PIE *hner “man;” cf. Pers. nar “male,” Skt. nara-, Welsh ner “man.”

Etymology (PE): Ensân-, from ensân “mankind,” loan from Ar. insân.

A prefix with the meaning of “pertaining to man or human beings.” Before a vowel, anthrop-. See also → man, → human. → anthropic principle.

Etymology (EN): Frpm Gk. anthropos “man, human being,” from aner “man” (as opposed to a woman, a god, or a boy), from PIE *hner “man;” cf. Pers. nar “male,” Skt. nara-, Welsh ner “man.”

Etymology (PE): Ensân-, from ensân “mankind,” loan from Ar. insân.

Prefix meaning “against, opposite of;” e.g. in
→ anticenter; → anticorrelation; → anticyclone; → antiparticle.

Etymology (EN): L. anti- from Gk. anti “against, opposite, instead of,” from PIE *anti “against”.

Etymology (PE): Pâd- “agaist, contrary to,” from Mid.Pers. pât- “to, at, for, in,” from O.Pers. paity “agaist, back, opposite to, toward, face to face, in front of;” Av. paiti; cf.
Skt. práti “toward, against, again, back, in return, opposite;” Pali pati-; Gk. proti, pros “face to face with, toward, in addition to, near;” PIE *proti.

Prefix meaning “against, opposite of;” e.g. in
→ anticenter; → anticorrelation; → anticyclone; → antiparticle.

Etymology (EN): L. anti- from Gk. anti “against, opposite, instead of,” from PIE *anti “against”.

Etymology (PE): Pâd- “agaist, contrary to,” from Mid.Pers. pât- “to, at, for, in,” from O.Pers. paity “agaist, back, opposite to, toward, face to face, in front of;” Av. paiti; cf.
Skt. práti “toward, against, again, back, in return, opposite;” Pali pati-; Gk. proti, pros “face to face with, toward, in addition to, near;” PIE *proti.

The → antiparticle of a → baryon.

See also: → anti-; → baryon.

The → antiparticle of a → baryon.

See also: → anti-; → baryon.

The point in the → Galactic plane that lies directly opposite the → Galactic center. It lies in → Auriga at approximately R.A. 5h 46m, Dec. +28° 56’; the nearest bright star to it is → Alnath in → Taurus.

Etymology (EN): Anticenter, from → anti- + → center.

Etymology (PE): Pâdmarkaz, from pâd-, → anti-, + markaz, → center.

The point in the → Galactic plane that lies directly opposite the → Galactic center. It lies in → Auriga at approximately R.A. 5h 46m, Dec. +28° 56’; the nearest bright star to it is → Alnath in → Taurus.

Etymology (EN): Anticenter, from → anti- + → center.

Etymology (PE): Pâdmarkaz, from pâd-, → anti-, + markaz, → center.

Meteorology: Small, faintly colored rings of light surrounding the → antisolar point, seen when looking down at a water cloud. Same as glory.

Etymology (EN): Anticorona, from → anti- + → corona.

Etymology (PE): Pâdafsar, from pâd-, → anti- + afsar “corona."
Šokuh “glory.”

Meteorology: Small, faintly colored rings of light surrounding the → antisolar point, seen when looking down at a water cloud. Same as glory.

Etymology (EN): Anticorona, from → anti- + → corona.

Etymology (PE): Pâdafsar, from pâd-, → anti- + afsar “corona."
Šokuh “glory.”

Statistics: The correlation coefficient of two random variables X and Y is in general defined as the ratio of the Cov(X,Y) to the two standard deviations of X and Y. It varies between 1 and -1 corresponding to complete correlation or anticorrelation.

Etymology (EN): Anticorrelation, from → anti- + → correlation.

Etymology (PE): Pâdhambâzâneš, from pâd-, → anti-, + hambâzâneš, → correlation.

Statistics: The correlation coefficient of two random variables X and Y is in general defined as the ratio of the Cov(X,Y) to the two standard deviations of X and Y. It varies between 1 and -1 corresponding to complete correlation or anticorrelation.

Etymology (EN): Anticorrelation, from → anti- + → correlation.

Etymology (PE): Pâdhambâzâneš, from pâd-, → anti-, + hambâzâneš, → correlation.

Rays of → sunlight that appear to converge at the → antisolar point. Like → crepuscular rays, they are parallel beams of sunlight from holes in the clouds, and their apparently odd directions are a perspective effect.

See also: → anti-; → crepuscular rays.

Rays of → sunlight that appear to converge at the → antisolar point. Like → crepuscular rays, they are parallel beams of sunlight from holes in the clouds, and their apparently odd directions are a perspective effect.

See also: → anti-; → crepuscular rays.

Meteo.: A weather phenomenon associated with atmospheric high pressure. In the Northern Hemisphere an anticyclone rotates in the clockwise direction. The rotation is caused by the movement of colder higher pressure air that is moving away from the poles toward the equator being affected by the rotation of the Earth.

See also: → anti-; → cyclone.

Meteo.: A weather phenomenon associated with atmospheric high pressure. In the Northern Hemisphere an anticyclone rotates in the clockwise direction. The rotation is caused by the movement of colder higher pressure air that is moving away from the poles toward the equator being affected by the rotation of the Earth.

See also: → anti-; → cyclone.

Having a sense of rotation about the local vertical opposite to that of the Earth’s rotation. In other words, → clockwise in the Northern Hemisphere, → counterclockwise in the Southern Hemisphere, and undefined at the equator. The opposite of → cyclonic (Meteorology Glossary, American Meteorological Society).

See also: → anticyclone; → -ic.

Having a sense of rotation about the local vertical opposite to that of the Earth’s rotation. In other words, → clockwise in the Northern Hemisphere, → counterclockwise in the Southern Hemisphere, and undefined at the equator. The opposite of → cyclonic (Meteorology Glossary, American Meteorological Society).

See also: → anticyclone; → -ic.

The function F(x) is called the antiderivative of the function f(x) on the interval [a,b] if at all points of this interval F’(x) = f(x). Same as primitive.

Etymology (EN): → anti- + → derivative.

Etymology (PE): Karyâ, → function; noxostin “primitive,” → first.

The function F(x) is called the antiderivative of the function f(x) on the interval [a,b] if at all points of this interval F’(x) = f(x). Same as primitive.

Etymology (EN): → anti- + → derivative.

Etymology (PE): Karyâ, → function; noxostin “primitive,” → first.

A property possessed by some → metals, → alloys, and salts of transition elements in which there is a lack of → magnetic moment due to the antiparallel or spiral arrangement of atomic → magnetic moments.

See also: → anti- + → ferromagnetism.

A property possessed by some → metals, → alloys, and salts of transition elements in which there is a lack of → magnetic moment due to the antiparallel or spiral arrangement of atomic → magnetic moments.

See also: → anti- + → ferromagnetism.

An atom made from an → antiproton and a → positron. In 2010 a research collaboration at CERN combined decelerated antiprotons with positrons to produce antihydrogen atoms. They managed 38 times to confine single antihydrogen atoms in a magnetic trap for more than 170 milliseconds (Andersen et al. 2010, Nature, 17 Nov.).

See also: → anti- + → hydrogen.

An atom made from an → antiproton and a → positron. In 2010 a research collaboration at CERN combined decelerated antiprotons with positrons to produce antihydrogen atoms. They managed 38 times to confine single antihydrogen atoms in a magnetic trap for more than 170 milliseconds (Andersen et al. 2010, Nature, 17 Nov.).

See also: → anti- + → hydrogen.

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.

See also: 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 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.

See also: 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.

Matter composed entirely of → antiparticles. See also → antihydrogen.

Etymology (EN): Antimatter from Gk. → anti- “opposite, opposing, against” + → matter.

Etymology (PE): Pâdmâddé from pâd-, → anti-,

• mâddé, → matter.

Matter composed entirely of → antiparticles. See also → antihydrogen.

Etymology (EN): Antimatter from Gk. → anti- “opposite, opposing, against” + → matter.

Etymology (PE): Pâdmâddé from pâd-, → anti-,

• mâddé, → matter.

A silver white metallic element of a flaky nature, extremely brittle, occurring in nature free or combined, symbol Sb.
→ Atomic number 51; → atomic weight 121.75; → meting point 630.74°C; → boiling point 1,750°C; → specific gravity (metallic form) 6.69 at 20°C. Antimony is recognized in compounds from antiquity, and as a metal since the 17th century. The minerals stibnite (Sb₂S₃) and stibine (SbH₃) are two of a multitude of mineral species
which were known in the ancient world. Antimony is a poor conductor of heat and electricity. It greatly increases the hardness of metals with which it makes → alloys. Its various unstable isotopes have a half-life of 16 min (Sb¹²⁰) to 2.7 years (Sb¹²⁵).

Etymology (EN): From M.E. antimonie, from M.L. antimonium, an alchemist’s term, of obscure origin, maybe a Latinization of Gk. stimmi or stibi,
probably ultimately from Egyptian stm “cosmetic powder” used to paint the eyelids.
The chemical symbol, Sb, comes from the original name, stibium, which is derived from Gk. stibi for “mark,” since it was used for blackening eyebrows and eyelashes.
The name was changed from stibium to antimonium to antimony.

Etymology (PE): Ântimuân, loan from Fr. antimoine.

A silver white metallic element of a flaky nature, extremely brittle, occurring in nature free or combined, symbol Sb.
→ Atomic number 51; → atomic weight 121.75; → meting point 630.74°C; → boiling point 1,750°C; → specific gravity (metallic form) 6.69 at 20°C. Antimony is recognized in compounds from antiquity, and as a metal since the 17th century. The minerals stibnite (Sb₂S₃) and stibine (SbH₃) are two of a multitude of mineral species
which were known in the ancient world. Antimony is a poor conductor of heat and electricity. It greatly increases the hardness of metals with which it makes → alloys. Its various unstable isotopes have a half-life of 16 min (Sb¹²⁰) to 2.7 years (Sb¹²⁵).

Etymology (EN): From M.E. antimonie, from M.L. antimonium, an alchemist’s term, of obscure origin, maybe a Latinization of Gk. stimmi or stibi,
probably ultimately from Egyptian stm “cosmetic powder” used to paint the eyelids.
The chemical symbol, Sb, comes from the original name, stibium, which is derived from Gk. stibi for “mark,” since it was used for blackening eyebrows and eyelashes.
The name was changed from stibium to antimonium to antimony.

Etymology (PE): Ântimuân, loan from Fr. antimoine.

The → antiparticle counterpart of the → neutrino.

See also: → anti-; → neutrino.

The → antiparticle counterpart of the → neutrino.

See also: → anti-; → neutrino.

The → antiparticle of the → neutron. It has the same mass, → spin, and → electric charge (zero) as the neutron but has opposite → baryon number (+1 for neutron, -1 for the antineutron). This is because the antineutron is composed of → antiquarks, while neutrons are composed of → quarks. The antineutron consists of one up antiquark and two down antiquarks.

See also: → anti-; → neutron.

The → antiparticle of the → neutron. It has the same mass, → spin, and → electric charge (zero) as the neutron but has opposite → baryon number (+1 for neutron, -1 for the antineutron). This is because the antineutron is composed of → antiquarks, while neutrons are composed of → quarks. The antineutron consists of one up antiquark and two down antiquarks.

See also: → anti-; → neutron.

The position of maximum → amplitude midway between two adjacent → nodes in a → standing wave.

See also: → anti-; → node.

The position of maximum → amplitude midway between two adjacent → nodes in a → standing wave.

See also: → anti-; → node.

A unique → binary asteroid (90) which has two similar-sized components. The components, 91 and 86 km in diameter respectively, are separated by 171 km, and circle each other every 16.5 hours. Belonging to the main → asteroid belt, Antiope was discovered in 1866 by the German Robert Luther. Its binarity was discovered in 2000 by W. Merline and collaborators.

See also: Antiope, from Gk. mythology, but it is not clear whether Antiope the Amazon or Antiope the mother of Amphion and Zethus.

A unique → binary asteroid (90) which has two similar-sized components. The components, 91 and 86 km in diameter respectively, are separated by 171 km, and circle each other every 16.5 hours. Belonging to the main → asteroid belt, Antiope was discovered in 1866 by the German Robert Luther. Its binarity was discovered in 2000 by W. Merline and collaborators.

See also: Antiope, from Gk. mythology, but it is not clear whether Antiope the Amazon or Antiope the mother of Amphion and Zethus.

A → pair of → vectors whose directions are parallel but having the opposite sense.

See also: → anti-; → parallel.

A → pair of → vectors whose directions are parallel but having the opposite sense.

See also: → anti-; → parallel.

Any → elementary particle with a → charge of opposite sign to the same particle in normal matter.

See also: → anti- “opposite, opposing, against” + → particle.

Any → elementary particle with a → charge of opposite sign to the same particle in normal matter.

See also: → anti- “opposite, opposing, against” + → particle.

1. Of or relating to the → antipodes.
   

2. Describing two points when a line drawn from one to the other does not pass through the geometric centre of the Earth.

See also: → antipode; → -al.

1. Of or relating to the → antipodes.
   

2. Describing two points when a line drawn from one to the other does not pass through the geometric centre of the Earth.

See also: → antipode; → -al.

1. The exact or direct opposite.
   

2. Either or both of two points, places, or regions that are situated diametrically opposite to one another on the Earth’s surface (Dictionary.com).

Etymology (EN): M.E., from L., from Gk. antipod-, antipous, literally “with feet opposite,” from → anti- “against,” + pod-, pous, → foot.

Etymology (PE): Pâdpây, from pâd-, → anti-, +
pây, → foot.

1. The exact or direct opposite.
   

2. Either or both of two points, places, or regions that are situated diametrically opposite to one another on the Earth’s surface (Dictionary.com).

Etymology (EN): M.E., from L., from Gk. antipod-, antipous, literally “with feet opposite,” from → anti- “against,” + pod-, pous, → foot.

Etymology (PE): Pâdpây, from pâd-, → anti-, +
pây, → foot.

The antiparticle of a proton, identical in mass and spin but of opposite (negative) charge.

Etymology (EN): From → anti- + → proton.

The antiparticle of a proton, identical in mass and spin but of opposite (negative) charge.

Etymology (EN): From → anti- + → proton.

The → antiparticle of a → quark.

See also: → anti-; → quark.

The → antiparticle of a → quark.

See also: → anti-; → quark.

Meteo.: The point on the → celestial sphere that lies directly opposite the Sun from the → observer, observer, that is, on the line from the Sun through the observer.

The antisolar point is the center of the rainbow, and can be easily found on a sunny day: it it located at the shadow of one’s head; it is 180° away from the Sun.

If the Sun is in the sky, the antisolar point is below the horizon. If the Sun has set, the antisolar point is above the horizon.

See also: → anti-; → solar; → point.

Meteo.: The point on the → celestial sphere that lies directly opposite the Sun from the → observer, observer, that is, on the line from the Sun through the observer.

The antisolar point is the center of the rainbow, and can be easily found on a sunny day: it it located at the shadow of one’s head; it is 180° away from the Sun.

If the Sun is in the sky, the antisolar point is below the horizon. If the Sun has set, the antisolar point is above the horizon.

See also: → anti-; → solar; → point.

A small tail-like structure on a comet that, unlike most comet tails, seems to point toward the Sun. This rare event is an optical
illusion due to larger dust particles left along the comet’s orbit. And typically occurs when the Earth crosses the plane of the comet’s orbit. It seen when the observer is in the plane of the cometary orbit.

Etymology (EN): Antitail, from → anti- “opposite, opposing, against” + → tail.

Etymology (PE): Pâddom, from pâd-, → anti-,

• dom “tail.”

A small tail-like structure on a comet that, unlike most comet tails, seems to point toward the Sun. This rare event is an optical
illusion due to larger dust particles left along the comet’s orbit. And typically occurs when the Earth crosses the plane of the comet’s orbit. It seen when the observer is in the plane of the cometary orbit.

Etymology (EN): Antitail, from → anti- “opposite, opposing, against” + → tail.

Etymology (PE): Pâddom, from pâd-, → anti-,

• dom “tail.”

Logical or verbal opposition.
Philo. The second of two opposed propositions in Hegelian dialectic, the first of which is the → thesis; → synthesis.

See also: → anti-; → thesis.

Logical or verbal opposition.
Philo. The second of two opposed propositions in Hegelian dialectic, the first of which is the → thesis; → synthesis.

See also: → anti-; → thesis.

1. Of the nature of or involving → antithesis.
   

2. Directly opposed or contrasted; opposite (Dictionary.com).

See also: → antithesis; → -ic.

1. Of the nature of or involving → antithesis.
   

2. Directly opposed or contrasted; opposite (Dictionary.com).

See also: → antithesis; → -ic.

The Air Pump. A faint → constellation in the → southern hemisphere, at → right ascensionα ~ 10h, → declinationδ ~ -35 deg. Abbreviation: Ant; genitive form: Antliae.