An Etymological Dictionary of Astronomy and Astrophysics

1. Capable of moving or being moved readily.
   

   2. A mobile phone.

Etymology (EN): From M.Fr. mobile, from L. mobilis “movable, easy to move; loose, not firm,” contraction of *movibilis, from movere “to → move.”

Etymology (PE): Miyâvâ verval adj. and agent noun from miyâvidan, → move.

1. Capable of moving or being moved readily.
   

   2. A mobile phone.

Etymology (EN): From M.Fr. mobile, from L. mobilis “movable, easy to move; loose, not firm,” contraction of *movibilis, from movere “to → move.”

Etymology (PE): Miyâvâ verval adj. and agent noun from miyâvidan, → move.

Of or relating to mode, manner, or form.

See also: → mode; → -al.

Of or relating to mode, manner, or form.

See also: → mode; → -al.

The quality or state of being → modal.

See also: → modal; → -ity.

The quality or state of being → modal.

See also: → modal; → -ity.

1. Physics: Any of the distinct patterns of oscillation that a given periodically varying system can have.
   

2. Math.: In a series of statistical data, the item or value which occurs most frequently. It is a measure of central tendency.

Etymology (EN): Mode, from Fr. mode, from L. modus “measure, rhythm, song, manner,” from PIE base *med- “to measure, limit, judge, advise;” cf. L. meditari “to think or reflect upon, consider;” Av. mad- “to measure out, apportion, allot;” Gk. medein “to rule;” O.E. metan “to measure out.”

Etymology (PE): Tarz “manner, mode,” Arabicized as طرز. Tarz may be related to Av. darəsa- “appearance, looking” (huuarə.darəsa- “having the appearance of the sun”), from Av. darəs- “to look;” cf. Skt. darś-, drś- “to see, appear, look, show” darśa- “apperance, look,” drśta- “apparent, visible.”
Mod, loan from Fr., cognate with Av. mad- “to measure out, apportion, allot,” as above.

1. Physics: Any of the distinct patterns of oscillation that a given periodically varying system can have.
   

2. Math.: In a series of statistical data, the item or value which occurs most frequently. It is a measure of central tendency.

Etymology (EN): Mode, from Fr. mode, from L. modus “measure, rhythm, song, manner,” from PIE base *med- “to measure, limit, judge, advise;” cf. L. meditari “to think or reflect upon, consider;” Av. mad- “to measure out, apportion, allot;” Gk. medein “to rule;” O.E. metan “to measure out.”

Etymology (PE): Tarz “manner, mode,” Arabicized as طرز. Tarz may be related to Av. darəsa- “appearance, looking” (huuarə.darəsa- “having the appearance of the sun”), from Av. darəs- “to look;” cf. Skt. darś-, drś- “to see, appear, look, show” darśa- “apperance, look,” drśta- “apparent, visible.”
Mod, loan from Fr., cognate with Av. mad- “to measure out, apportion, allot,” as above.

1a) A mathematical representation of a process, system, or object
developed to understand its behavior or to make predictions. The representation always involves certain simplifications and assumptions. See also → theory, → hypothesis.

1b) A mental image of a phenomenon using familiar terms (or images). For example, in the Bohr model the atom is visualized as a nucleus with electrons orbiting around it in a manner similar to the way that planets revolve around the Sun. While this model is use ul in understanding the atom, it is an over-simplified description of a real atom and does not describe/predict all of its attributes (G. Smooth, Lawrence Berkeley Lab website).

2. To make or construct a model of.

Etymology (EN): M.Fr. modelle (Fr. modèle), from It. modello “a model, mold,” from V.L. *modellus, from L. modulus “measure, standard,” from modus “manner, measure” (cf. Av. mad-, → mode), PIE *med- + -ulus, → -ula.

Etymology (PE): 1) Model, from Fr. modèle. Tarzâl, from tarz, → mode + -âl, → -al.
2) Model sâxtan, from model + sâxtan, sâzidan “to build, make, fashion; to adapt, adjust, be fit” (from
Mid.Pers. sâxtan, sâz-, Manichean Parthian s’c’dn “to prepare, to form;” Av. sak- “to understand, to mark,” sâcaya- (causative) “to teach”).
Tarzâlidan, from tarzâl + -idan infinitive suffix.

1a) A mathematical representation of a process, system, or object
developed to understand its behavior or to make predictions. The representation always involves certain simplifications and assumptions. See also → theory, → hypothesis.

1b) A mental image of a phenomenon using familiar terms (or images). For example, in the Bohr model the atom is visualized as a nucleus with electrons orbiting around it in a manner similar to the way that planets revolve around the Sun. While this model is use ul in understanding the atom, it is an over-simplified description of a real atom and does not describe/predict all of its attributes (G. Smooth, Lawrence Berkeley Lab website).

2. To make or construct a model of.

Etymology (EN): M.Fr. modelle (Fr. modèle), from It. modello “a model, mold,” from V.L. *modellus, from L. modulus “measure, standard,” from modus “manner, measure” (cf. Av. mad-, → mode), PIE *med- + -ulus, → -ula.

Etymology (PE): 1) Model, from Fr. modèle. Tarzâl, from tarz, → mode + -âl, → -al.
2) Model sâxtan, from model + sâxtan, sâzidan “to build, make, fashion; to adapt, adjust, be fit” (from
Mid.Pers. sâxtan, sâz-, Manichean Parthian s’c’dn “to prepare, to form;” Av. sak- “to understand, to mark,” sâcaya- (causative) “to teach”).
Tarzâlidan, from tarzâl + -idan infinitive suffix.

In a theoretical analysis, the solution that does not correctly treat the intervening parameters, or neglects some crucial factors.

See also: → model. dependence, noun of → dependent.

In a theoretical analysis, the solution that does not correctly treat the intervening parameters, or neglects some crucial factors.

See also: → model. dependence, noun of → dependent.

The simulation of a process, concept, or operation of a system often implemented by a computer program and making use of a mathematical treatment.

See also: Verbal noun of → model

The simulation of a process, concept, or operation of a system often implemented by a computer program and making use of a mathematical treatment.

See also: Verbal noun of → model

1. Relating or belonging to present and recent time. → modern physics.
   

2. Of or pertaining to the historical period following the Middle Ages.
   

3. Of the latest, most advanced kind, or using the most advanced equipment and techniques available.

Etymology (EN): From M.Fr. moderne, from L.L. modernus, from L. modo “lately, just now,” from modo “to the measure,” ablative of modus “manner, measure,” → mode.

Etymology (PE): Novin, from now, → new, + -in adj. suffix, as in dirin, pasin, barin, kehin, mehin, behin, zirin, zabarin, pâyin, bâlâyin.

1. Relating or belonging to present and recent time. → modern physics.
   

2. Of or pertaining to the historical period following the Middle Ages.
   

3. Of the latest, most advanced kind, or using the most advanced equipment and techniques available.

Etymology (EN): From M.Fr. moderne, from L.L. modernus, from L. modo “lately, just now,” from modo “to the measure,” ablative of modus “manner, measure,” → mode.

Etymology (PE): Novin, from now, → new, + -in adj. suffix, as in dirin, pasin, barin, kehin, mehin, behin, zirin, zabarin, pâyin, bâlâyin.

The physics developed since about 1900, which includes Einstein’s → relativity theory and → quantum mechanics, as distinguished from → classical physics. Much of modern physics is concerned with the behavior of matter and energy under extreme conditions or on the very small scale.

See also: → modern; → physics.

The physics developed since about 1900, which includes Einstein’s → relativity theory and → quantum mechanics, as distinguished from → classical physics. Much of modern physics is concerned with the behavior of matter and energy under extreme conditions or on the very small scale.

See also: → modern; → physics.

1. Modern spirit or character.
   

2. Modern usage, expression, or trait.
   

3. In early 20th century art, literature, and architecture, a movement characterized by the use of unconventional subject matter and style, experimental technique, etc.

See also: → modern + → -ism.

1. Modern spirit or character.
   

2. Modern usage, expression, or trait.
   

3. In early 20th century art, literature, and architecture, a movement characterized by the use of unconventional subject matter and style, experimental technique, etc.

See also: → modern + → -ism.

1. An admirer of modern ideas, ways, etc.
   
2. Someone who practises or advocates → Modernism.

See also: → modern + → -ist.

1. An admirer of modern ideas, ways, etc.
   
2. Someone who practises or advocates → Modernism.

See also: → modern + → -ist.

1. The quality of being → modern.
   

2. A rather diffuse term with many meanings depending on the disciplinary context. Generally, modernity refers to the cultural, intellectual, and economic consequences of the → Enlightenment and the epoch with which they are associated. Modernity is the end result of the → modernization process.

See also: → modern + → -ity.

1. The quality of being → modern.
   

2. A rather diffuse term with many meanings depending on the disciplinary context. Generally, modernity refers to the cultural, intellectual, and economic consequences of the → Enlightenment and the epoch with which they are associated. Modernity is the end result of the → modernization process.

See also: → modern + → -ity.

1. The act of modernizing; the state of being modernized; something modernized.
   

2. A pattern of social and economic change initiated in the 17th century in Western Europe and subsequently extended to many other parts of the world. Its characteristics include secularization, rationalization in political and economic life, industrialization, urbanization, and increased level of popular involvement in public affairs.

See also: Verbal noun of → modernize; → -tion.

1. The act of modernizing; the state of being modernized; something modernized.
   

2. A pattern of social and economic change initiated in the 17th century in Western Europe and subsequently extended to many other parts of the world. Its characteristics include secularization, rationalization in political and economic life, industrialization, urbanization, and increased level of popular involvement in public affairs.

See also: Verbal noun of → modernize; → -tion.

To bring something up to modern standards, or adapt it to modern style, conditions, etc.

See also: → modern + → -ize.

To bring something up to modern standards, or adapt it to modern style, conditions, etc.

See also: → modern + → -ize.

An act or instance of modifying; the state of being modified; partial alteration.

See also: Verbal noun of → modify.

An act or instance of modifying; the state of being modified; partial alteration.

See also: Verbal noun of → modify.

A modification of the Julian Date, representing the number of days that have elapsed since midnight (instead of noon) at the beginning of Wednesday November 17, 1858. MJD = JD - 2,400,000.5 The reason for adopting that date is the fact that
the Julian Day 2,400,000 just happens to be November 17, 1858.

See also: → modify; → Julian date.

A modification of the Julian Date, representing the number of days that have elapsed since midnight (instead of noon) at the beginning of Wednesday November 17, 1858. MJD = JD - 2,400,000.5 The reason for adopting that date is the fact that
the Julian Day 2,400,000 just happens to be November 17, 1858.

See also: → modify; → Julian date.

A modification of the Newton’s law of gravitation below a critical acceleration of about 1.2 x 10^-8 cm s^-2, where the gravitational force scales as 1/r instead of 1/r². Originally put forward to describe the rotation curves of galaxies with no need to assume any dark matter,
MOND is now tested at larger cosmological scales (Milgrom, M. 1983, ApJ, 270, 365).

Etymology (EN): → modify; → Newtonian dynamics.

A modification of the Newton’s law of gravitation below a critical acceleration of about 1.2 x 10^-8 cm s^-2, where the gravitational force scales as 1/r instead of 1/r². Originally put forward to describe the rotation curves of galaxies with no need to assume any dark matter,
MOND is now tested at larger cosmological scales (Milgrom, M. 1983, ApJ, 270, 365).

Etymology (EN): → modify; → Newtonian dynamics.

A quantity defined as Π = (dM/dt) v_∞ R^0.5 for a star with radius R having a wind with → terminal velocity v_∞ and a → mass loss rate dM/dt. There is a tight linear relation between the modified wind momenta and the stellar luminosities for → Population I→ O stars. See also → wind momentum.

See also: → modify; → wind; → momentum.

A quantity defined as Π = (dM/dt) v_∞ R^0.5 for a star with radius R having a wind with → terminal velocity v_∞ and a → mass loss rate dM/dt. There is a tight linear relation between the modified wind momenta and the stellar luminosities for → Population I→ O stars. See also → wind momentum.

See also: → modify; → wind; → momentum.

In data processing, a quantity used to alter an instruction in a prescribed way to produce the instruction actually obeyed.

See also: Agent noun of → modify.

In data processing, a quantity used to alter an instruction in a prescribed way to produce the instruction actually obeyed.

See also: Agent noun of → modify.

To change somewhat the form or qualities of; alter partially; amend.
To reduce or lessen in degree or extent; moderate; soften:

Etymology (EN): From O.Fr. modifier, from L. modificare “to impose a rule or pattern, regulate, restrain,” from modus “measure, rhythm, song, manner” PIE base *med-/*met- “to measure, limit, consider, advise, take appropriate measures”

• root of facere “to make”

Etymology (PE): Vâtarzidan, from vâ- prefix denoting “reversal, opposition; separation; repetition; open; off; away” (variant of bâz-, from Mid.Pers. abâz-, apâc-; O.Pers. apa- [pref.] “away, from;” Av. apa- [pref.] “away, from,”
apaš [adv.] “toward the back;” cf. Skt. ápāñc “situated behind”) + tarz “mode, manner” + -idan infinitive suffix.

To change somewhat the form or qualities of; alter partially; amend.
To reduce or lessen in degree or extent; moderate; soften:

Etymology (EN): From O.Fr. modifier, from L. modificare “to impose a rule or pattern, regulate, restrain,” from modus “measure, rhythm, song, manner” PIE base *med-/*met- “to measure, limit, consider, advise, take appropriate measures”

• root of facere “to make”

Etymology (PE): Vâtarzidan, from vâ- prefix denoting “reversal, opposition; separation; repetition; open; off; away” (variant of bâz-, from Mid.Pers. abâz-, apâc-; O.Pers. apa- [pref.] “away, from;” Av. apa- [pref.] “away, from,”
apaš [adv.] “toward the back;” cf. Skt. ápāñc “situated behind”) + tarz “mode, manner” + -idan infinitive suffix.

General: To regulate by or adjust to a certain measure or proportion; tone down. Physics: To alter the value of some parameter characterizing a periodic oscillation. → modulation.

Etymology (EN): From L. modulatus pr.p. of modulari “to regulate, measure off properly,” from modulus “small measure,” diminutive of modus “measure, manner,” → mode.

Etymology (PE): Degarâhangidan, from degar “other, another,” denoting change,
variant digar
(Mid.Pers. dit, ditikar “the other, the second;” O.Pers. duvitiya- “second,” Av. daibitya-, bitya- “second;” Skt. dvitiya- “second,” PIE *duitiio- “second”)

• âhang “melody, pitch, tune, modulation” (ultimately from Proto-Iranian *āhang-, from prefix ā-
• *hang-, from PIE base *seng^wh- “to sing, make an incantation;” cf. O.H.G. singan; Ger. singen; Goth. siggwan; Swed. sjunga; O.E. singan “to chant, sing, tell in song;” maybe cognate with Gk. omphe “voice; oracle”) +
  -idan infinitive suffix.

General: To regulate by or adjust to a certain measure or proportion; tone down. Physics: To alter the value of some parameter characterizing a periodic oscillation. → modulation.

Etymology (EN): From L. modulatus pr.p. of modulari “to regulate, measure off properly,” from modulus “small measure,” diminutive of modus “measure, manner,” → mode.

Etymology (PE): Degarâhangidan, from degar “other, another,” denoting change,
variant digar
(Mid.Pers. dit, ditikar “the other, the second;” O.Pers. duvitiya- “second,” Av. daibitya-, bitya- “second;” Skt. dvitiya- “second,” PIE *duitiio- “second”)

• âhang “melody, pitch, tune, modulation” (ultimately from Proto-Iranian *āhang-, from prefix ā-
• *hang-, from PIE base *seng^wh- “to sing, make an incantation;” cf. O.H.G. singan; Ger. singen; Goth. siggwan; Swed. sjunga; O.E. singan “to chant, sing, tell in song;” maybe cognate with Gk. omphe “voice; oracle”) +
  -idan infinitive suffix.

A combination of two or more waves resulting in the production of frequencies not present in the original waves, the new frequencies being usually the sums and differences of integral multiples of the frequencies in the original waves.
A wave which varies in some characteristic in accordance with the variations of a modulating signal. Compare continuous wave. See modulation

See also: Modulated, p.p. of → modulate; → wave.

A combination of two or more waves resulting in the production of frequencies not present in the original waves, the new frequencies being usually the sums and differences of integral multiples of the frequencies in the original waves.
A wave which varies in some characteristic in accordance with the variations of a modulating signal. Compare continuous wave. See modulation

See also: Modulated, p.p. of → modulate; → wave.

General: The modification of some property of a phenomenon by another distinct phenomenon.
Physics: Variation of some characteristic (amplitude, phase, or frequency) of a radio wave,
called the carrier wave, in accordance with instantaneous values of another wave, called the modulating wave. → amplitude modulation; → frequency modulation.
Optics: A synonym for contrast, particularly when applied to a series of parallel lines and spaces imaged by a lens.

See also: Verbal noun of → modulate.

General: The modification of some property of a phenomenon by another distinct phenomenon.
Physics: Variation of some characteristic (amplitude, phase, or frequency) of a radio wave,
called the carrier wave, in accordance with instantaneous values of another wave, called the modulating wave. → amplitude modulation; → frequency modulation.
Optics: A synonym for contrast, particularly when applied to a series of parallel lines and spaces imaged by a lens.

See also: Verbal noun of → modulate.

A measure of the ability of an optical system to reproduce (transfer) various levels of detail from the object to the image, as shown by the degree of contrast (modulation) in the image. → optical transfer function.

See also: → modulation; → transfer; → function.

A measure of the ability of an optical system to reproduce (transfer) various levels of detail from the object to the image, as shown by the degree of contrast (modulation) in the image. → optical transfer function.

See also: → modulation; → transfer; → function.

Any device for effecting the process of modulation.

Etymology (EN): from L. modulator, from → modulate + -tor a suffix forming personal agent nouns from verbs.

Etymology (PE): Vâhangâr, from vâhang, → modulation,

• -âr, contraction of âvar agent noun of âvardan “to bring; to cause, produce” (Mid.Pers. âwurtan, âvaritan; Av. ābar- “to bring; to possess,” from prefix ā- + Av./O.Pers. bar- “to bear, carry,” bareθre “to bear (infinitive),” bareθri “a female that bears (children), a mother;” Mod.Pers. bordan “to carry;” Skt. bharati “he carries;” Gk. pherein; L. fero “to carry”).

Any device for effecting the process of modulation.

Etymology (EN): from L. modulator, from → modulate + -tor a suffix forming personal agent nouns from verbs.

Etymology (PE): Vâhangâr, from vâhang, → modulation,

• -âr, contraction of âvar agent noun of âvardan “to bring; to cause, produce” (Mid.Pers. âwurtan, âvaritan; Av. ābar- “to bring; to possess,” from prefix ā- + Av./O.Pers. bar- “to bear, carry,” bareθre “to bear (infinitive),” bareθri “a female that bears (children), a mother;” Mod.Pers. bordan “to carry;” Skt. bharati “he carries;” Gk. pherein; L. fero “to carry”).

A distinct and separable element of a spacecraft or space station.

Etymology (EN): From M.Fr. module, from L. modulus “small measure,” diminutive of modus “measure, manner,” → mode.

Etymology (PE): Modul, loan as above. Tarzul, from tarz→ mode

• -ul, → -ula.

A distinct and separable element of a spacecraft or space station.

Etymology (EN): From M.Fr. module, from L. modulus “small measure,” diminutive of modus “measure, manner,” → mode.

Etymology (PE): Modul, loan as above. Tarzul, from tarz→ mode

• -ul, → -ula.

An open-source, one-dimensional astrophysical code which is capable of calculating the evolution of stars in a wide range of environments. It works according to the → Henyey method and uses many modules that deal with various aspects of the theoretical models, such as the → equation of state (EOS), → nuclear reaction networks, → chemical composition, micro-physics, or macro-physics. The EOS and corresponding opacities or nuclear networks are provided in tabulated formats and can be selected by the user, while the micro-physics and macro-physics can be controlled by inlists of relevant parameters and settings (Paxton et al. 2015, ApJS 220, 15 and references therein).

See also: → module; → experiment; → stellar; → astrophysics.

An open-source, one-dimensional astrophysical code which is capable of calculating the evolution of stars in a wide range of environments. It works according to the → Henyey method and uses many modules that deal with various aspects of the theoretical models, such as the → equation of state (EOS), → nuclear reaction networks, → chemical composition, micro-physics, or macro-physics. The EOS and corresponding opacities or nuclear networks are provided in tabulated formats and can be selected by the user, while the micro-physics and macro-physics can be controlled by inlists of relevant parameters and settings (Paxton et al. 2015, ApJS 220, 15 and references therein).

See also: → module; → experiment; → stellar; → astrophysics.

A real, positive quantity that measures the magnitude of some number. For instance, the modulus of a complex number is the square root of the sum of the squares of its components. Often it means, simply, the numerical (“absolute”) value of an algebraic quantity.

Etymology (EN): From L. modulus, → module.

Etymology (PE): Peymun, variant of peymâné “a measure either for dry or wet goods; a bushel, cup, bowl,” from peymudan, peymâyidan “to measure,”
from Mid.Pers. patmudan, paymudan “to measure (against),” from *pati-māya-.
The first element *pati- “against, back” (cf. Mod.Pers. pâd- “agaist, contrary to;” Mid.Pers. pât-; O.Pers. paity “agaist, back, opposite to, toward, face to face, in front of;” Av. paiti; 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 second element from *mā- “to measure;” O.Pers./Av. mā(y)- “to measure;” cf. Skt. mati “measures,” matra- “measure;” Gk. metron “measure;” L. metrum; PIE base *me- “to measure.” Apart from peymâné, several other terms in Mod.Pers. are related to this second element, which occurs also as mun, mân, man, mâ, mu, and mây:
pirâmun “perimeter,” âzmun, âzmây- “test, trial,”
peymân “measuring, agreement,” man “a measure weighing forty seers”),
nemudan, nemâ- “to show, display,”
âmâdan, âmây- “to prepare.”

A real, positive quantity that measures the magnitude of some number. For instance, the modulus of a complex number is the square root of the sum of the squares of its components. Often it means, simply, the numerical (“absolute”) value of an algebraic quantity.

Etymology (EN): From L. modulus, → module.

Etymology (PE): Peymun, variant of peymâné “a measure either for dry or wet goods; a bushel, cup, bowl,” from peymudan, peymâyidan “to measure,”
from Mid.Pers. patmudan, paymudan “to measure (against),” from *pati-māya-.
The first element *pati- “against, back” (cf. Mod.Pers. pâd- “agaist, contrary to;” Mid.Pers. pât-; O.Pers. paity “agaist, back, opposite to, toward, face to face, in front of;” Av. paiti; 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 second element from *mā- “to measure;” O.Pers./Av. mā(y)- “to measure;” cf. Skt. mati “measures,” matra- “measure;” Gk. metron “measure;” L. metrum; PIE base *me- “to measure.” Apart from peymâné, several other terms in Mod.Pers. are related to this second element, which occurs also as mun, mân, man, mâ, mu, and mây:
pirâmun “perimeter,” âzmun, âzmây- “test, trial,”
peymân “measuring, agreement,” man “a measure weighing forty seers”),
nemudan, nemâ- “to show, display,”
âmâdan, âmây- “to prepare.”

Same as → shear modulus.

See also: → modulus; → rigidity.

Same as → shear modulus.

See also: → modulus; → rigidity.

Describing a quantity of substance that is proportional to its molecular weight. Relating to a → mole.

See also: → mole + → -ar.

Describing a quantity of substance that is proportional to its molecular weight. Relating to a → mole.

See also: → mole + → -ar.

Of a gas included in the composition of a → gas mixture, the ratio of the number of moles of this gas to the total number of moles of all the gases in the mixture. Same as mole fraction and mole-fraction concentration.

See also: → molar; → concentration.

Of a gas included in the composition of a → gas mixture, the ratio of the number of moles of this gas to the total number of moles of all the gases in the mixture. Same as mole fraction and mole-fraction concentration.

See also: → molar; → concentration.

The → heat capacity of one → mole of substance: C_μ = μ C, where μ is the → molecular weight and C the → specific heat capacity. The molar heat capacity of water is practically 18 cal/mole.C°.

See also: Molar, adj. of → mole; → heat; → capacity.

The → heat capacity of one → mole of substance: C_μ = μ C, where μ is the → molecular weight and C the → specific heat capacity. The molar heat capacity of water is practically 18 cal/mole.C°.

See also: Molar, adj. of → mole; → heat; → capacity.

The amount of heat energy required to vaporize 1 mole of a liquid at its
→ boiling point, usually expressed in kJ/mol.

See also: → molar; → heat; → vaporization.

The amount of heat energy required to vaporize 1 mole of a liquid at its
→ boiling point, usually expressed in kJ/mol.

See also: → molar; → heat; → vaporization.

The → SI unit of amount of → substance; symbol mol. One mole contains exactly 6.022 140 76 × 10²³ elementary entities. This number is the fixed numerical value of the → Avogadro constant, N_A, when expressed in the unit mol^-1.

See also: From Ger. Mole, short for Molekül, from Fr. → molecule.

The → SI unit of amount of → substance; symbol mol. One mole contains exactly 6.022 140 76 × 10²³ elementary entities. This number is the fixed numerical value of the → Avogadro constant, N_A, when expressed in the unit mol^-1.

See also: From Ger. Mole, short for Molekül, from Fr. → molecule.

Of or pertaining to or caused by molecules.

Etymology (EN): From → molecule + -ar variant of the adjective-forming suffix → -al, joined to words in which an l precedes the suffix.

Etymology (PE): Molekuli, from molekul→ molecule + -i adj. suffix.

Of or pertaining to or caused by molecules.

Etymology (EN): From → molecule + -ar variant of the adjective-forming suffix → -al, joined to words in which an l precedes the suffix.

Etymology (PE): Molekuli, from molekul→ molecule + -i adj. suffix.

A band of molecular origin present in a spectrum.
See for example → cyanogen band, → S star.

See also: → molecular; → band.

A band of molecular origin present in a spectrum.
See for example → cyanogen band, → S star.

See also: → molecular; → band.

A relatively dense, cold region of interstellar matter where the atoms are primarily bound together as molecules rather than free atoms or ionized particles. Molecular clouds represent the coldest and densest phase of the → interstellar medium. They consist primarily of → molecular hydrogen (H₂), with temperatures in the range 10-100 K. Molecular hydrogen is not directly observable under most conditions in molecular clouds. Therefore, almost all current knowledge about the properties of molecular clouds has been deduced from observations of molecules such as → carbon monoxide (CO), which have strong emission lines mainly in the → millimeter portion of the → electromagnetic spectrum. So far 129 molecular species have been detected in molecular clouds, among which complex organic molecules. → Dust grains in molecular clouds play a crucial role in the formation of molecules. Molecular clouds are the principal sites where stars form. → giant molecular cloud; → Orion molecular cloud.

See also: → molecular; → cloud.

A relatively dense, cold region of interstellar matter where the atoms are primarily bound together as molecules rather than free atoms or ionized particles. Molecular clouds represent the coldest and densest phase of the → interstellar medium. They consist primarily of → molecular hydrogen (H₂), with temperatures in the range 10-100 K. Molecular hydrogen is not directly observable under most conditions in molecular clouds. Therefore, almost all current knowledge about the properties of molecular clouds has been deduced from observations of molecules such as → carbon monoxide (CO), which have strong emission lines mainly in the → millimeter portion of the → electromagnetic spectrum. So far 129 molecular species have been detected in molecular clouds, among which complex organic molecules. → Dust grains in molecular clouds play a crucial role in the formation of molecules. Molecular clouds are the principal sites where stars form. → giant molecular cloud; → Orion molecular cloud.

See also: → molecular; → cloud.

One of many compact and dense sub-structures in a → molecular cloud. Their typical sizes are about 0.5-10 → parsecs and their masses range from about 50 to 10³ → solar masses. The gas temperatures are about 10-20 K, and the number densities from about 10³ to 10⁴ cm^-3.

See also: → molecular; → clump.

One of many compact and dense sub-structures in a → molecular cloud. Their typical sizes are about 0.5-10 → parsecs and their masses range from about 50 to 10³ → solar masses. The gas temperatures are about 10-20 K, and the number densities from about 10³ to 10⁴ cm^-3.

See also: → molecular; → clump.

A mixing process in a → fluid caused by the → random relative motions due to → Brownian motion of the individual particles. See also → eddy diffusion.

See also: → molecular; → diffusion.

A mixing process in a → fluid caused by the → random relative motions due to → Brownian motion of the individual particles. See also → eddy diffusion.

See also: → molecular; → diffusion.

An → electromagnetic radiation emitted by → interstellar molecules through → transitions between → energy states of → molecules.

See also: → molecular; → emission.

An → electromagnetic radiation emitted by → interstellar molecules through → transitions between → energy states of → molecules.

See also: → molecular; → emission.

The formula of a chemical compound, showing the kind and arrangement of atoms.

See also: → molecular; → formula.

The formula of a chemical compound, showing the kind and arrangement of atoms.

See also: → molecular; → formula.

A molecule consisting of two hydrogen atoms (H₂) which is the most abundant molecule in the Universe. Molecular hydrogen plays a fundamental role in many astrophysical contexts. It is found in all regions where
→ self-shielding against the ultraviolet photons, responsible for its → photodissociation, is sufficiently large. Containing two identical hydrogen atoms, H₂ is highly symmetric. Due to this property, the molecule has no → dipole moment and all → rotation-vibrational transitions within the electronic → ground state are → quadrupolar with low → spontaneous emission  → Einstein coefficient values. The molecule exists in two almost independent states, namely → orthohydrogen and → parahydrogen. H₂ may be excited through several mechanisms, including: 1)
→ far ultraviolet (FUV) induced → optical pumping and
→ collisional excitation in → photodissociation regions (PDRs) associated with → star formation; 2)
→ hard X-rays penetrating and heating regions within → molecular clouds, which in turn excite H₂ via collisions with electrons or hydrogen atoms; and 3)
collisional excitation of H₂ due to acceleration produced by interstellar → shock waves. H₂ is thought to be chiefly produced via surface reactions on → interstellar grains, but the exact formation mechanism is not fully understood.

See also: → molecular; → hydrogen.

A molecule consisting of two hydrogen atoms (H₂) which is the most abundant molecule in the Universe. Molecular hydrogen plays a fundamental role in many astrophysical contexts. It is found in all regions where
→ self-shielding against the ultraviolet photons, responsible for its → photodissociation, is sufficiently large. Containing two identical hydrogen atoms, H₂ is highly symmetric. Due to this property, the molecule has no → dipole moment and all → rotation-vibrational transitions within the electronic → ground state are → quadrupolar with low → spontaneous emission  → Einstein coefficient values. The molecule exists in two almost independent states, namely → orthohydrogen and → parahydrogen. H₂ may be excited through several mechanisms, including: 1)
→ far ultraviolet (FUV) induced → optical pumping and
→ collisional excitation in → photodissociation regions (PDRs) associated with → star formation; 2)
→ hard X-rays penetrating and heating regions within → molecular clouds, which in turn excite H₂ via collisions with electrons or hydrogen atoms; and 3)
collisional excitation of H₂ due to acceleration produced by interstellar → shock waves. H₂ is thought to be chiefly produced via surface reactions on → interstellar grains, but the exact formation mechanism is not fully understood.

See also: → molecular; → hydrogen.

An outflow of molecular material, often → bipolar, observed in the regions of → star formation. Molecular outflows are thought to be driven by → bipolar jets from → protostars. They are probably → bow shocks which have had time to cool and be observable in molecular lines. Molecular outflows
are poorly → collimated compared to the jets and tend to be slow moving
(velocities 10-20 km s^-1). Some bipolar outflows may be driven by → stellar winds.

See also: → molecular; → outflow.

An outflow of molecular material, often → bipolar, observed in the regions of → star formation. Molecular outflows are thought to be driven by → bipolar jets from → protostars. They are probably → bow shocks which have had time to cool and be observable in molecular lines. Molecular outflows
are poorly → collimated compared to the jets and tend to be slow moving
(velocities 10-20 km s^-1). Some bipolar outflows may be driven by → stellar winds.

See also: → molecular; → outflow.

The ability of a molecular entity to be distorted from its normal shape by an external → electric field. When a molecule is subjected to an electric field there is a small displacement of electrical centers which induces a dipole in the molecule. More specifically, the molecular polarizability α is defined as the ratio of the induced → dipole moment (p) to the local electric field (E) that produces this dipole moment: α = p/E (in cgse units).

See also: → molecular; → polaizable; → -ity.

The ability of a molecular entity to be distorted from its normal shape by an external → electric field. When a molecule is subjected to an electric field there is a small displacement of electrical centers which induces a dipole in the molecule. More specifically, the molecular polarizability α is defined as the ratio of the induced → dipole moment (p) to the local electric field (E) that produces this dipole moment: α = p/E (in cgse units).

See also: → molecular; → polaizable; → -ity.

In → propositional logic, a → sentence containing at least one → connectives. See also → atomic proposition.

See also: → atomic; → proposition.

In → propositional logic, a → sentence containing at least one → connectives. See also → atomic proposition.

See also: → atomic; → proposition.

The dynamical motion of chemically bound atoms which constantly change their position with each other. The vibration of molecules is treated within → quantum theory. Therefore, the energy of molecular vibration can only take → discrete values. To a first approximation, molecular vibrations can be approximated as
→ simple harmonic oscillator assigned to each mode.

See also: → molecular; → vibration.

The dynamical motion of chemically bound atoms which constantly change their position with each other. The vibration of molecules is treated within → quantum theory. Therefore, the energy of molecular vibration can only take → discrete values. To a first approximation, molecular vibrations can be approximated as
→ simple harmonic oscillator assigned to each mode.

See also: → molecular; → vibration.

The sum of the atomic weights of all the atoms in a molecule.

See also: → molecular; → weight.

The sum of the atomic weights of all the atoms in a molecule.

See also: → molecular; → weight.

The smallest unit of a chemical compound. A molecule consist of two or more atoms held together by covalent bonds.

See also: From Fr. moléclue, from Mod.L.molecula, diminutive of L. moles “mass, massive structure, barrier;” → -ula

The smallest unit of a chemical compound. A molecule consist of two or more atoms held together by covalent bonds.

See also: From Fr. moléclue, from Mod.L.molecula, diminutive of L. moles “mass, massive structure, barrier;” → -ula

A hypothetical, large molecular sphere, as a component of the → stellar atmosphere, suggested to encompass → red giant and → supergiant stars. This suggestion has offered satisfactory explanations to the spectrum of → Mu Cephei (Tsuji 2003), but it is not clear whether MOLspheres are common features of the atmospheres of all such stars.

See also: MOL, from → molecular; → sphere.

A hypothetical, large molecular sphere, as a component of the → stellar atmosphere, suggested to encompass → red giant and → supergiant stars. This suggestion has offered satisfactory explanations to the spectrum of → Mu Cephei (Tsuji 2003), but it is not clear whether MOLspheres are common features of the atmospheres of all such stars.

See also: MOL, from → molecular; → sphere.

1. Physics: An expression involving the → product a → quantity, such as → force or → mass, and its perpendicular → distance from a reference point, such as → moment of force (or → torque), → moment of inertia, → moment of momentum.
   

2. Statistics: For a → random variable X, its nth moment about the mean is the expected value of the nth power of X, where n is a positive integer. The nth moment of the deviation of X from the mean is called the nth central moment. The first moment is the → mean,
   the second central moment is the → variance.
   

3. A short indefinite period of time.

Etymology (EN): From O.Fr. moment, from L. momentum “movement, moving power,” also “instant, importance,” contraction of *movimentum, from movere, → move.

Etymology (PE): Gaštâvar literally “that which makes turn, turning agent,” from gašt “turning,” past stem of gaštan, gardidan “to turn, to change” (Mid.Pers. vartitan; Av. varət- “to turn, revolve;” Skt. vrt- “to turn, roll,” vartate “it turns round, rolls;” L. vertere “to turn;” O.H.G. werden “to become;” PIE base *wer- “to turn, bend”) + âvar
agent noun of âvardan “to bring; to cause, produce” (Mid.Pers. âwurtan, âvaritan; Av. ābar- “to bring; to possess,” from prefix ā- + Av./O.Pers. bar- “to bear, carry,” bareθre “to bear (infinitive),” bareθri “a female that bears (children), a mother;” Mod.Pers. bordan “to carry;” Skt. bharati “he carries;” Gk. pherein; L. fero “to carry”).
Dam, “breath; moment; time,” from Mod./Mid.Pers. damidan “to breathe, blow;”
Av. dāδmainya- “blowing up,”
Skt. dahm- “to blow,” dhámati “blows,”
Gk. themeros “austere, dark-looking,” Lith. dumti “to blow,” PIE dhem-/dhemə-
“to smoke, to blow”.

1. Physics: An expression involving the → product a → quantity, such as → force or → mass, and its perpendicular → distance from a reference point, such as → moment of force (or → torque), → moment of inertia, → moment of momentum.
   

2. Statistics: For a → random variable X, its nth moment about the mean is the expected value of the nth power of X, where n is a positive integer. The nth moment of the deviation of X from the mean is called the nth central moment. The first moment is the → mean,
   the second central moment is the → variance.
   

3. A short indefinite period of time.

Etymology (EN): From O.Fr. moment, from L. momentum “movement, moving power,” also “instant, importance,” contraction of *movimentum, from movere, → move.

Etymology (PE): Gaštâvar literally “that which makes turn, turning agent,” from gašt “turning,” past stem of gaštan, gardidan “to turn, to change” (Mid.Pers. vartitan; Av. varət- “to turn, revolve;” Skt. vrt- “to turn, roll,” vartate “it turns round, rolls;” L. vertere “to turn;” O.H.G. werden “to become;” PIE base *wer- “to turn, bend”) + âvar
agent noun of âvardan “to bring; to cause, produce” (Mid.Pers. âwurtan, âvaritan; Av. ābar- “to bring; to possess,” from prefix ā- + Av./O.Pers. bar- “to bear, carry,” bareθre “to bear (infinitive),” bareθri “a female that bears (children), a mother;” Mod.Pers. bordan “to carry;” Skt. bharati “he carries;” Gk. pherein; L. fero “to carry”).
Dam, “breath; moment; time,” from Mod./Mid.Pers. damidan “to breathe, blow;”
Av. dāδmainya- “blowing up,”
Skt. dahm- “to blow,” dhámati “blows,”
Gk. themeros “austere, dark-looking,” Lith. dumti “to blow,” PIE dhem-/dhemə-
“to smoke, to blow”.

A measure of a force’s tendency to cause a body to → rotate about a specified → axis. It is given by the force times the perpendicular → distance of the → line of action from the axis. Same as → torque

See also: → moment; → force.

A measure of a force’s tendency to cause a body to → rotate about a specified → axis. It is given by the force times the perpendicular → distance of the → line of action from the axis. Same as → torque

See also: → moment; → force.

A quantity which is a measure of the inertness of a body in rotatory motion about an axis. It is equal to the sum of the products of the masses of all particles of the body by the squares of their distances from this axis:
I = Σm_ir_i², where r_i is the distance of the particle of mass m_i from the axis. Moment of inertia depends only upon the shape of the body and the arrangement of its mass with respect to the axis. For a solid sphere it is (2/5)MR². Moment of inertia is used in place of mass in problems involving rotation. Thus, the → angular momentum is Iω and → angular kinetic energy is (1/2)Iω², where ω is → angular velocity.

See also: → moment; → inertia.

A quantity which is a measure of the inertness of a body in rotatory motion about an axis. It is equal to the sum of the products of the masses of all particles of the body by the squares of their distances from this axis:
I = Σm_ir_i², where r_i is the distance of the particle of mass m_i from the axis. Moment of inertia depends only upon the shape of the body and the arrangement of its mass with respect to the axis. For a solid sphere it is (2/5)MR². Moment of inertia is used in place of mass in problems involving rotation. Thus, the → angular momentum is Iω and → angular kinetic energy is (1/2)Iω², where ω is → angular velocity.

See also: → moment; → inertia.

Same as → angular momentum.

See also: → moment; → momentum.

Same as → angular momentum.

See also: → moment; → momentum.

In → Newtonian mechanics, the momentum p of a body with → mass m and → velocity v is the product of these two quantities: p = mv. Momentum usually means → linear momentum as opposed to → angular momentum.

Etymology (EN): From L. momentum “movement, moving power,” from movere “to move,” → move.

Etymology (PE): Jonbâk, from jonb present stem of jonbidan “to move” (Mid.Pers. jumbidan, jumb- “to move,” Lori, Laki jem “motion,” related to gâm “step, pace;”
O.Pers. gam- “to come; to go,” Av. gam- “to come; to go,” jamaiti “goes,” gāman- “step, pac;” Mod.Pers. âmadan “to come;” Skt. gamati “goes;” Gk. bainein “to go, walk, step,” L. venire “to come;” Tocharian A käm- “to come;” O.H.G. queman “to come;” E. come; PIE root *gwem- “to go, come”) + -âk noun suffix.

In → Newtonian mechanics, the momentum p of a body with → mass m and → velocity v is the product of these two quantities: p = mv. Momentum usually means → linear momentum as opposed to → angular momentum.

Etymology (EN): From L. momentum “movement, moving power,” from movere “to move,” → move.

Etymology (PE): Jonbâk, from jonb present stem of jonbidan “to move” (Mid.Pers. jumbidan, jumb- “to move,” Lori, Laki jem “motion,” related to gâm “step, pace;”
O.Pers. gam- “to come; to go,” Av. gam- “to come; to go,” jamaiti “goes,” gāman- “step, pac;” Mod.Pers. âmadan “to come;” Skt. gamati “goes;” Gk. bainein “to go, walk, step,” L. venire “to come;” Tocharian A käm- “to come;” O.H.G. queman “to come;” E. come; PIE root *gwem- “to go, come”) + -âk noun suffix.

1. Philo.: The doctrine that reality consists of an unchanging whole in which change is mere illusion. → pluralism.
   

2. Philo.: The doctrine that the person consists of only a single substance, or that there is no crucial difference between mental and physical events or properties.
   

3. The attempt to explain anything in terms of one principle only. → dualism, → materalism, → idealism (Dictionary.com).

See also: → mono-; → -ism.

1. Philo.: The doctrine that reality consists of an unchanging whole in which change is mere illusion. → pluralism.
   

2. Philo.: The doctrine that the person consists of only a single substance, or that there is no crucial difference between mental and physical events or properties.
   

3. The attempt to explain anything in terms of one principle only. → dualism, → materalism, → idealism (Dictionary.com).

See also: → mono-; → -ism.

1. (v.) To watch closely or evaluate something on a constant or regular basis.
   To oversee, supervise, or regulate.
   

2. (n.) A video device that displays data or images generated by a computer or terminal.

Etymology (EN): From L. monitor “one who reminds, admonishes, or checks,” from monere
“to remind, warn, advise,” related to memini “I remember, I am mindful of,” mens “mind,” from PIE base *men- “to think;” Pers. cognates under → idea.

Etymology (PE): Pahregar “watch, guard,”
agent noun from pahré (Dehxodâ) “watch, guarding,” from Mid.Pers. pahr, pahrag “guard;” Av. pāθra.vant “guard, watchman,” from *pāθra-, from Av. pā- “to protect,” pāti “guards,” nipā(y)- (with → ni-) “to watch, observe, guard,” nipātar- “protector, watcher,” nipāθri- “protectress;”
cf. Skt. pā- “to protect, keep,” tanû.pā- “protecting the body,” paś.pā- “shepherd;” Gk. poma “lid, cover,” poimen “shepherd;” L. pascere “to put out to graze,” pastor “shepherd;” Lith. piemuo “shepherd;” PIE base *pā- “to protect, feed.”
Pahridan verb from pahr, as above.

1. (v.) To watch closely or evaluate something on a constant or regular basis.
   To oversee, supervise, or regulate.
   

2. (n.) A video device that displays data or images generated by a computer or terminal.

Etymology (EN): From L. monitor “one who reminds, admonishes, or checks,” from monere
“to remind, warn, advise,” related to memini “I remember, I am mindful of,” mens “mind,” from PIE base *men- “to think;” Pers. cognates under → idea.

Etymology (PE): Pahregar “watch, guard,”
agent noun from pahré (Dehxodâ) “watch, guarding,” from Mid.Pers. pahr, pahrag “guard;” Av. pāθra.vant “guard, watchman,” from *pāθra-, from Av. pā- “to protect,” pāti “guards,” nipā(y)- (with → ni-) “to watch, observe, guard,” nipātar- “protector, watcher,” nipāθri- “protectress;”
cf. Skt. pā- “to protect, keep,” tanû.pā- “protecting the body,” paś.pā- “shepherd;” Gk. poma “lid, cover,” poimen “shepherd;” L. pascere “to put out to graze,” pastor “shepherd;” Lith. piemuo “shepherd;” PIE base *pā- “to protect, feed.”
Pahridan verb from pahr, as above.

1. A combining form meaning “alone, single, one,” as in monochromatic, Monoceros, monotonic.
   

2. In chemistry applied to compounds containing one atom of a particular element (monohydrate).

Etymology (EN): From Gk. mono-, from monos “single, alone,” from PIE base *men- “small, isolated,” also represented by Gk. manos “rare, sparse.”

Etymology (PE): Tak “single, alone”, from Mid.Pers. tak “single, alone,” maybe related to tâk, tâi “unit, piece.”
Yek “one, alone,” from Mid.Pers. êwak (Proto-Iranian *aiua-ka-); O.Pers. aiva- “one, alone;” Av. aēuua- “one, alone;” cf. Skt. éka- “one, alone, single; " Gk. oios “alone, lonely;” L. unus “one;” Ger. ein; E. one.
Yektâ-, from yek, as above, + tâ “fold, plait, ply; piece, part,” also a multiplicative suffix; Mid.Pers. tâg “piece, part.”
Mono-, loan from Gk., as above.

1. A combining form meaning “alone, single, one,” as in monochromatic, Monoceros, monotonic.
   

2. In chemistry applied to compounds containing one atom of a particular element (monohydrate).

Etymology (EN): From Gk. mono-, from monos “single, alone,” from PIE base *men- “small, isolated,” also represented by Gk. manos “rare, sparse.”

Etymology (PE): Tak “single, alone”, from Mid.Pers. tak “single, alone,” maybe related to tâk, tâi “unit, piece.”
Yek “one, alone,” from Mid.Pers. êwak (Proto-Iranian *aiua-ka-); O.Pers. aiva- “one, alone;” Av. aēuua- “one, alone;” cf. Skt. éka- “one, alone, single; " Gk. oios “alone, lonely;” L. unus “one;” Ger. ein; E. one.
Yektâ-, from yek, as above, + tâ “fold, plait, ply; piece, part,” also a multiplicative suffix; Mid.Pers. tâg “piece, part.”
Mono-, loan from Gk., as above.

The Unicorn. An extensive but faint constellation across the celestial equator , at 7h right ascension, 4° south declination. Abbreviation: Mon; genitive: Monocerotis.

Etymology (EN): Monoceros “the unicorn,” from O.Fr., from L., from Gk. monokeros, from → mono- “single” + keras “horn,” kara “head,” karena “head, top;” cf. Pers. soru “horn,” sar “head;”
L. cornu “horn,” cerebrum “brain;” Skt. śiras- “head, chief;” O.E. horn “horn of an animal,” also “wind instrument” (originally made from animal horns), from P.Gmc. *khurnaz (Ger. Horn, Du. horen), from PIE *ker- “head, horn, top, summit.”

Etymology (PE): Takšâx, from tak “single” → mono- + šâx “horn, branch” (Mid.Pers šâk; cf. Skt. sakha- “a branch, a limb;” Arm. cax; Lith. šaka; O.S. soxa;
PIE *kakhâ “branch”).

The Unicorn. An extensive but faint constellation across the celestial equator , at 7h right ascension, 4° south declination. Abbreviation: Mon; genitive: Monocerotis.

Etymology (EN): Monoceros “the unicorn,” from O.Fr., from L., from Gk. monokeros, from → mono- “single” + keras “horn,” kara “head,” karena “head, top;” cf. Pers. soru “horn,” sar “head;”
L. cornu “horn,” cerebrum “brain;” Skt. śiras- “head, chief;” O.E. horn “horn of an animal,” also “wind instrument” (originally made from animal horns), from P.Gmc. *khurnaz (Ger. Horn, Du. horen), from PIE *ker- “head, horn, top, summit.”

Etymology (PE): Takšâx, from tak “single” → mono- + šâx “horn, branch” (Mid.Pers šâk; cf. Skt. sakha- “a branch, a limb;” Arm. cax; Lith. šaka; O.S. soxa;
PIE *kakhâ “branch”).

A faint filamentary loop of nebulosity about 1 kpc distant, the remnant of a supernova that occurred about 300,000 years ago. It contains the Rosette Nebula as well as the Cone Nebula.

See also: → Monoceros; → loop.

A faint filamentary loop of nebulosity about 1 kpc distant, the remnant of a supernova that occurred about 300,000 years ago. It contains the Rosette Nebula as well as the Cone Nebula.

See also: → Monoceros; → loop.

Characterized by light of one color or by radiation of a single wavelength or narrow range of wavelengths.

See also: → mono-; → chromatic.

Characterized by light of one color or by radiation of a single wavelength or narrow range of wavelengths.

See also: → mono-; → chromatic.

The sum of → absorption coefficient (κ_ν) and → scattering coefficient (σ_ν) at a given frequency: k_ν = κ_ν + σ_ν. See also the → Rosseland mean opacity.

See also: → monochromatic; → opacity.

The sum of → absorption coefficient (κ_ν) and → scattering coefficient (σ_ν) at a given frequency: k_ν = κ_ν + σ_ν. See also the → Rosseland mean opacity.

See also: → monochromatic; → opacity.

1. A single algebraic term, such as 2xy, 125, 2x². The → degree of the monomial is the sum of the exponents of all included variables. Constants have the monomial degree of 0.
   

2. Of, pertaining to, or consisting of a monomial.

See also: → mono- + nomial, short for → nomnial.

1. A single algebraic term, such as 2xy, 125, 2x². The → degree of the monomial is the sum of the exponents of all included variables. Constants have the monomial degree of 0.
   

2. Of, pertaining to, or consisting of a monomial.

See also: → mono- + nomial, short for → nomnial.

A → morphismf : Y → X if, for any two morphisms u,v : Z → Y, f u = f v  implies that u =v.

See also: → mono-; → morphism.

A → morphismf : Y → X if, for any two morphisms u,v : Z → Y, f u = f v  implies that u =v.

See also: → mono-; → morphism.

The fact of having only a single meaning. Same as → univocity. Compare with → polysemy.

Etymology (EN): From → mono- “single,” + sem, from sema “sign,” → semantic, + -y.

Etymology (PE): Takcemi, from tak-, → mono-, + cem, → meaning, + noun suffix -i.

The fact of having only a single meaning. Same as → univocity. Compare with → polysemy.

Etymology (EN): From → mono- “single,” + sem, from sema “sign,” → semantic, + -y.

Etymology (PE): Takcemi, from tak-, → mono-, + cem, → meaning, + noun suffix -i.

The belief or doctrine that there is only one → God.

See also: → mono-; → theism.

The belief or doctrine that there is only one → God.

See also: → mono-; → theism.

Of a mathematical function, either continuously increasing or decreasing.

Etymology (EN): From Fr. monotone, from Gk. monotonos “monotonous, of one tone,” from monos, → mono- “single, alone” + tonos “tone” + → -ic.

Etymology (PE): Yeknavâxt “monotonous,” from yek “one, single,” + navâxt“rhythm,” from navâxtan, navâzidan “to play an instrument; to gratify,” navâ “music, song, melody;” Mid.Pers. nw’c “to treat kindly, honour,” niwag “music, melody;” Proto-Iranian *ni-uac-, from *ni- (→ ni-) + *uac- “to speak, treat kindly,” → word.

Of a mathematical function, either continuously increasing or decreasing.

Etymology (EN): From Fr. monotone, from Gk. monotonos “monotonous, of one tone,” from monos, → mono- “single, alone” + tonos “tone” + → -ic.

Etymology (PE): Yeknavâxt “monotonous,” from yek “one, single,” + navâxt“rhythm,” from navâxtan, navâzidan “to play an instrument; to gratify,” navâ “music, song, melody;” Mid.Pers. nw’c “to treat kindly, honour,” niwag “music, melody;” Proto-Iranian *ni-uac-, from *ni- (→ ni-) + *uac- “to speak, treat kindly,” → word.

A seasonal change in wind direction bringing dry air or heavy rain in India and nearby lands.

Etymology (EN): Monsoon, from Du. monssoen, from Port. monçao, from Ar. mausim “season.” It was first applied to the winds over the Arabian Sea, which blow for six months from northeast and for six months from southwest, but it has been extended to similar winds in other parts of the world.

Etymology (PE): Bâd, → “wind;” mowsem, related to mowsem, from Ar. mausim, as above.

A seasonal change in wind direction bringing dry air or heavy rain in India and nearby lands.

Etymology (EN): Monsoon, from Du. monssoen, from Port. monçao, from Ar. mausim “season.” It was first applied to the winds over the Arabian Sea, which blow for six months from northeast and for six months from southwest, but it has been extended to similar winds in other parts of the world.

Etymology (PE): Bâd, → “wind;” mowsem, related to mowsem, from Ar. mausim, as above.

A computer-intensive technique that relies on repeated random sampling of a statistical population to compute its results. Monte Carlo simulation is often used for approximate numerical computations when application of strict methods requires too much calculation, or when it is infeasible or impossible to compute an exact result with a deterministic algorithm.

See also: The term Monte Carlo was coined in the 1940s by physicists (Stanislaw Ulam, Enrico Fermi, John von Neumann, and Nicholas Metropolis) working on nuclear weapon projects in the Los Alamos National Laboratory. The name is a reference to a famous casino in Monaco which, it is said that,
Ulam’s uncle would borrow money to gamble at. → method.

A computer-intensive technique that relies on repeated random sampling of a statistical population to compute its results. Monte Carlo simulation is often used for approximate numerical computations when application of strict methods requires too much calculation, or when it is infeasible or impossible to compute an exact result with a deterministic algorithm.

See also: The term Monte Carlo was coined in the 1940s by physicists (Stanislaw Ulam, Enrico Fermi, John von Neumann, and Nicholas Metropolis) working on nuclear weapon projects in the Los Alamos National Laboratory. The name is a reference to a famous casino in Monaco which, it is said that,
Ulam’s uncle would borrow money to gamble at. → method.

A period of time based on the revolution of the Moon around the Earth. Several types of months are defined: → anomalistic month; → draconic month; → sidereal month; → synodic month; → tropical month.

Etymology (EN): O.E. monað, from P.Gmc. *mænoth- (O.N. manaðr, M.Du. manet, Du. maand, O.H.G. manod, Ger. Monat, Goth. menoþs “month”), related to *mænon-, → moon.

Etymology (PE): Mâh and mâng in Pers. are variants of the same term, the dominant form being
mâh, while mâng (Av. from, see below) is used in classical literature as well as in some dialects: Tabari, Kurd. mâng, Laki, Tâti, Taeši mong, Šahmirzâdi, Sangesari mung; Mid.Pers. mâh “moon, month;” O.Pers. māha- “moon, month;” Av. māh- “month, moon,” also māwngh-; cf. Skt. mās- “moon, month;” Gk. mene “moon,” men “month;” L. mensis “month;” O.C.S. meseci, Lith. menesis “moon, month;” O.Ir. mi, Welsh mis, Bret. miz “month;” O.E. mona; E. moon, month; Ger. Mond, Monat; Du. maan; PIE base *me(n)ses- “moon, month.”

Note: In Persian the same term, mâh, is used for two different, but related, concepts: moon and month. This was also the case for other IE languages, as shows the above etymology. However, other IE languages have evolved toward more accuracy by using different forms of the same initial term, as in E. moon / month or
Ger. Mond / Monat. The Latin family uses two unrelated words, as in Fr. lune “moon” / mois “month” and Sp. luna / mes. An additional difficulty in present Pers. is that the adj. mâhi not only means “lunar” and “monthly” it also denotes “fish.” For the sake of clarity and precision, this dictionary uses mângi for “lunar.”

A period of time based on the revolution of the Moon around the Earth. Several types of months are defined: → anomalistic month; → draconic month; → sidereal month; → synodic month; → tropical month.

Etymology (EN): O.E. monað, from P.Gmc. *mænoth- (O.N. manaðr, M.Du. manet, Du. maand, O.H.G. manod, Ger. Monat, Goth. menoþs “month”), related to *mænon-, → moon.

Etymology (PE): Mâh and mâng in Pers. are variants of the same term, the dominant form being
mâh, while mâng (Av. from, see below) is used in classical literature as well as in some dialects: Tabari, Kurd. mâng, Laki, Tâti, Taeši mong, Šahmirzâdi, Sangesari mung; Mid.Pers. mâh “moon, month;” O.Pers. māha- “moon, month;” Av. māh- “month, moon,” also māwngh-; cf. Skt. mās- “moon, month;” Gk. mene “moon,” men “month;” L. mensis “month;” O.C.S. meseci, Lith. menesis “moon, month;” O.Ir. mi, Welsh mis, Bret. miz “month;” O.E. mona; E. moon, month; Ger. Mond, Monat; Du. maan; PIE base *me(n)ses- “moon, month.”

Note: In Persian the same term, mâh, is used for two different, but related, concepts: moon and month. This was also the case for other IE languages, as shows the above etymology. However, other IE languages have evolved toward more accuracy by using different forms of the same initial term, as in E. moon / month or
Ger. Mond / Monat. The Latin family uses two unrelated words, as in Fr. lune “moon” / mois “month” and Sp. luna / mes. An additional difficulty in present Pers. is that the adj. mâhi not only means “lunar” and “monthly” it also denotes “fish.” For the sake of clarity and precision, this dictionary uses mângi for “lunar.”

1. Natural satellite of the Earth. Mass 7.35 x 10²⁵ g = 1/81 or 0.0123 Earth’s. Mean radius 1740 km = ~ 1/4 the Earth’s; this relatively small size ratio makes the Earth-Moon system unique in the → solar system. Mean density 3.34 g cm^-3. Mean distance from Earth 384,400 km. → Escape velocity 2.38 km s^-1. → Surface gravity 162.2 cm s^-2 = 0.165 Earth’s. → Sidereal period 27d 7h 43m 11s. → Eccentricity 0.0549. → Inclination of → orbital plane to → ecliptic 5° 8’ 43’’. → Obliquity 6° 41’. → Synodic period 29d 12h 44m 2s.9. → Orbital velocity 1.02 km s^-1. The Moon’s average visual → Albedo is 0.12, a factor of three smaller than that of Earth.
   The Moon’s → center of mass is displaced about 2 km in the direction of Earth.
   The average temperature on the surface of the Moon during the day is 107 °C. During the night, the average temperature drops to -153 °C.

Studies of lunar rock have shown that melting and separation must have begun at least 4.5 x 10⁹ years ago, so the → crust of the Moon was beginning to form a very short time after the → solar system itself. Thickness of crust ~ 60 km; of mantle ~ 1000 km. Temperature of core ~ 1500 K. It would have taken only 10⁷ years to slow the Moon’s rotation into its present lock with its → orbital period. Because of this → synchronous rotation, the Moon revolves once on its axis each time it orbits the Earth, thus always presenting the same face, the nearside, toward Earth. The Moon may have formed during a collision between the early Earth and a Mars-sized rocky planet about 4.6 billion years ago; → Theia.

2. A large body orbiting a planet.

Etymology (EN): O.E. mona, from P.Gmc. *mænon- (cf. O.S., O.H.G. mano, O.Fris. mona, O.N. mani, Du. maan, Ger. Mond, Goth. mena “moon”), cognate with Pers. mâh, as below, from PIE *me(n)ses- “moon, month.”

Etymology (PE): Mâh and mâng in Pers. are variants of the same term, the dominant form being
mâh, while mâng (Av. from, see below) is used in classical literature as well as in some dialects: Tabari, Kurd. mâng, Laki, Tâti, Taelši mong, Šahmirzâdi, Sangesari mung; Mid.Pers. mâh “moon, month;” O.Pers. māha- “moon, month;” Av. māh- “month, moon,” also māwngh-; cf. Skt. mās- “moon, month;” Gk. mene “moon,” men “month;” L. mensis “month;” O.C.S. meseci, Lith. menesis “moon, month;” O.Ir. mi, Welsh mis, Bret. miz “month;” O.E. mona; E. moon, month; Ger. Mond, Monat; Du. maan; PIE base *me(n)ses- “moon, month.”

Note: In Persian the same term, mâh, is used for two different, but related, concepts: moon and month. This was also the case for other IE languages, as shows the above etymology. However, other IE languages have evolved toward more accuracy by using different forms of the same initial term, as in E. moon / month or
Ger. Mond / Monat. The Latin family uses two unrelated words, as in Fr. lune “moon” / mois “month” and Sp. luna / mes. An additional difficulty in present Pers. is that the adj. mâhi not only means “lunar” and “monthly” it also denotes “fish.” For the sake of clarity and precision, this dictionary uses mângi for “lunar.”

1. Natural satellite of the Earth. Mass 7.35 x 10²⁵ g = 1/81 or 0.0123 Earth’s. Mean radius 1740 km = ~ 1/4 the Earth’s; this relatively small size ratio makes the Earth-Moon system unique in the → solar system. Mean density 3.34 g cm^-3. Mean distance from Earth 384,400 km. → Escape velocity 2.38 km s^-1. → Surface gravity 162.2 cm s^-2 = 0.165 Earth’s. → Sidereal period 27d 7h 43m 11s. → Eccentricity 0.0549. → Inclination of → orbital plane to → ecliptic 5° 8’ 43’’. → Obliquity 6° 41’. → Synodic period 29d 12h 44m 2s.9. → Orbital velocity 1.02 km s^-1. The Moon’s average visual → Albedo is 0.12, a factor of three smaller than that of Earth.
   The Moon’s → center of mass is displaced about 2 km in the direction of Earth.
   The average temperature on the surface of the Moon during the day is 107 °C. During the night, the average temperature drops to -153 °C.

Studies of lunar rock have shown that melting and separation must have begun at least 4.5 x 10⁹ years ago, so the → crust of the Moon was beginning to form a very short time after the → solar system itself. Thickness of crust ~ 60 km; of mantle ~ 1000 km. Temperature of core ~ 1500 K. It would have taken only 10⁷ years to slow the Moon’s rotation into its present lock with its → orbital period. Because of this → synchronous rotation, the Moon revolves once on its axis each time it orbits the Earth, thus always presenting the same face, the nearside, toward Earth. The Moon may have formed during a collision between the early Earth and a Mars-sized rocky planet about 4.6 billion years ago; → Theia.

2. A large body orbiting a planet.

Etymology (EN): O.E. mona, from P.Gmc. *mænon- (cf. O.S., O.H.G. mano, O.Fris. mona, O.N. mani, Du. maan, Ger. Mond, Goth. mena “moon”), cognate with Pers. mâh, as below, from PIE *me(n)ses- “moon, month.”

Etymology (PE): Mâh and mâng in Pers. are variants of the same term, the dominant form being
mâh, while mâng (Av. from, see below) is used in classical literature as well as in some dialects: Tabari, Kurd. mâng, Laki, Tâti, Taelši mong, Šahmirzâdi, Sangesari mung; Mid.Pers. mâh “moon, month;” O.Pers. māha- “moon, month;” Av. māh- “month, moon,” also māwngh-; cf. Skt. mās- “moon, month;” Gk. mene “moon,” men “month;” L. mensis “month;” O.C.S. meseci, Lith. menesis “moon, month;” O.Ir. mi, Welsh mis, Bret. miz “month;” O.E. mona; E. moon, month; Ger. Mond, Monat; Du. maan; PIE base *me(n)ses- “moon, month.”

Note: In Persian the same term, mâh, is used for two different, but related, concepts: moon and month. This was also the case for other IE languages, as shows the above etymology. However, other IE languages have evolved toward more accuracy by using different forms of the same initial term, as in E. moon / month or
Ger. Mond / Monat. The Latin family uses two unrelated words, as in Fr. lune “moon” / mois “month” and Sp. luna / mes. An additional difficulty in present Pers. is that the adj. mâhi not only means “lunar” and “monthly” it also denotes “fish.” For the sake of clarity and precision, this dictionary uses mângi for “lunar.”

Any of several theories about how the → Moon originated, among which: → fission theory, → capture theory, → co-formation theory, and → giant impact hypothesis. The model that is best supported by all the available data is the giant impact hypothesis. See also → canonical model.

See also: → lunar; → formation.

Any of several theories about how the → Moon originated, among which: → fission theory, → capture theory, → co-formation theory, and → giant impact hypothesis. The model that is best supported by all the available data is the giant impact hypothesis. See also → canonical model.

See also: → lunar; → formation.

Same as → lunar halo.

See also: → Moon; → halo.

Same as → lunar halo.

See also: → Moon; → halo.

1. The number of days that have elapsed since the last → conjunction of the Sun and Moon. It is 7 days at → first quarter, 15 days at → full moon, and 22 days at → third quarter.
   

2. The time past since the → formation of the Moon.

Etymology (EN): → Moon; → age.

Etymology (PE): 1) Kohan-ruzi literally “age in days,” from kohan-ruz “old in days,” from kohan “old, ancient,” kohné “worn;”
Mid.Pers. kahwan “old, aged, worn;”
pir; Mid.Pers. pir “old, aged, ancient;” Av. parô (adv.) “before, before (of time),” in front (of space); cf. Skt. puáh, combining form of puras “before (of time and place), in front, in advance;” mâh, → Moon.
2) Senn, → age.

1. The number of days that have elapsed since the last → conjunction of the Sun and Moon. It is 7 days at → first quarter, 15 days at → full moon, and 22 days at → third quarter.
   

2. The time past since the → formation of the Moon.

Etymology (EN): → Moon; → age.

Etymology (PE): 1) Kohan-ruzi literally “age in days,” from kohan-ruz “old in days,” from kohan “old, ancient,” kohné “worn;”
Mid.Pers. kahwan “old, aged, worn;”
pir; Mid.Pers. pir “old, aged, ancient;” Av. parô (adv.) “before, before (of time),” in front (of space); cf. Skt. puáh, combining form of puras “before (of time and place), in front, in advance;” mâh, → Moon.
2) Senn, → age.

The → rotation of the Moon’s → orbit within the → orbital plane, whereby the axes of the ellipse change direction. The Moon’s → major axis makes one complete revolution every 8.85 Earth years, or 3,232.6054 days, as it rotates slowly in the same direction as the Moon itself (direct, or → prograde motion). The Moon’s apsidal precession is a → relativistic effect, and should not be confused with its → axial procession.

See also: → Moon; → apsidal; → precession.

The → rotation of the Moon’s → orbit within the → orbital plane, whereby the axes of the ellipse change direction. The Moon’s → major axis makes one complete revolution every 8.85 Earth years, or 3,232.6054 days, as it rotates slowly in the same direction as the Moon itself (direct, or → prograde motion). The Moon’s apsidal precession is a → relativistic effect, and should not be confused with its → axial procession.

See also: → Moon; → apsidal; → precession.

The line connecting the Moon’s north pole with its south pole, and passing through the center of the lunar disk. The longitude of the Moon’s prime meridian is zero degrees.

See also: → Moon; → prime meridian.

The line connecting the Moon’s north pole with its south pole, and passing through the center of the lunar disk. The longitude of the Moon’s prime meridian is zero degrees.

See also: → Moon; → prime meridian.

A rainbow that arises from the refraction and reflection of moonlight on rain drops or mist.

See also: → moon; → bow.

A rainbow that arises from the refraction and reflection of moonlight on rain drops or mist.

See also: → moon; → bow.

A very small natural or artificial satellite orbiting a planet. Saturn has dozens of moonlets often associated with its → planetary rings.

See also: → moon; → -let.

A very small natural or artificial satellite orbiting a planet. Saturn has dozens of moonlets often associated with its → planetary rings.

See also: → moon; → -let.

Local disturbances in the ring structure caused by the gravitational influence of embedded satellites. If the satellite (moonlet) is large enough to clear a gap in the rings, the moonlet wakes become edge waves that precede the satellite on the inner edge and trail the satellite on the outer edge. For smaller satellites, the “gap-less” wakes have been nicknamed propellors (Ellis et al., 2007, Planetary Ring Systems, Springer).

See also: → moonlet; → wake.

Local disturbances in the ring structure caused by the gravitational influence of embedded satellites. If the satellite (moonlet) is large enough to clear a gap in the rings, the moonlet wakes become edge waves that precede the satellite on the inner edge and trail the satellite on the outer edge. For smaller satellites, the “gap-less” wakes have been nicknamed propellors (Ellis et al., 2007, Planetary Ring Systems, Springer).

See also: → moonlet; → wake.

The light of the Moon.

Etymology (EN): From → moon + → light.

Etymology (PE): Mahtâb (Gilaki mângtâb) from mah, mâh (mâng), → moon, + tâb “light,” from tâbidan, tâftan “to shine,” tafsidan “to become hot” (Av. tāp-, taf- “to warm up, heat,” tafsat “became hot,” tāpaiieiti “to create warmth;” cf.
Skt. tap- “to spoil, injure, damage; to suffer; to heat, be/become hot,” tapati “burns;” L. tepere “to be warm,” tepidus “warm;” PIE base *tep- “warm”).

The light of the Moon.

Etymology (EN): From → moon + → light.

Etymology (PE): Mahtâb (Gilaki mângtâb) from mah, mâh (mâng), → moon, + tâb “light,” from tâbidan, tâftan “to shine,” tafsidan “to become hot” (Av. tāp-, taf- “to warm up, heat,” tafsat “became hot,” tāpaiieiti “to create warmth;” cf.
Skt. tap- “to spoil, injure, damage; to suffer; to heat, be/become hot,” tapati “burns;” L. tepere “to be warm,” tepidus “warm;” PIE base *tep- “warm”).

A → seismic event occurring on the → Moon; the lunar equivalent of an → earthquake.

Moonquakes were first detected by the → seismometers placed on the Moon by Apollo astronauts from 1969 through 1972. The instruments placed by the Apollo 12, 14, 15, and 16 missions were functional until 1977. Unlike earthquakes, moonquakes are not believed to be caused by → tectonic plate movement, but by → tidal forces between Earth and the Moon.

There are at least four different kinds of moonquakes: (1) deep moonquakes about 700 km below the surface.

They occur at monthly intervals at about 100 distinct sites, indicating that these moonquakes are caused by → stresses from changes in lunar tides as the Moon orbits the Earth; (2) vibrations from the impact of → meteorites; (3) thermal quakes caused by the expansion of the frigid crust when first illuminated by the morning sun after two weeks of deep-freeze lunar night; and (4) shallow moonquakes only 20 or 30 km below the surface (science.nasa.gov/science-news).

See also: → moon; → quake.

A → seismic event occurring on the → Moon; the lunar equivalent of an → earthquake.

Moonquakes were first detected by the → seismometers placed on the Moon by Apollo astronauts from 1969 through 1972. The instruments placed by the Apollo 12, 14, 15, and 16 missions were functional until 1977. Unlike earthquakes, moonquakes are not believed to be caused by → tectonic plate movement, but by → tidal forces between Earth and the Moon.

There are at least four different kinds of moonquakes: (1) deep moonquakes about 700 km below the surface.

They occur at monthly intervals at about 100 distinct sites, indicating that these moonquakes are caused by → stresses from changes in lunar tides as the Moon orbits the Earth; (2) vibrations from the impact of → meteorites; (3) thermal quakes caused by the expansion of the frigid crust when first illuminated by the morning sun after two weeks of deep-freeze lunar night; and (4) shallow moonquakes only 20 or 30 km below the surface (science.nasa.gov/science-news).

See also: → moon; → quake.

The times at which the apparent upper limb of the ascending Moon is on the astronomical horizon.

See also: → moon; → rise.

The times at which the apparent upper limb of the ascending Moon is on the astronomical horizon.

See also: → moon; → rise.

The crossing of the visible horizon by the upper limb of the descending Moon.

See also: → moon; → set.

The crossing of the visible horizon by the upper limb of the descending Moon.

See also: → moon; → set.

The delay between → sunset and → moonset.

See also: → moonset; → lag.

The delay between → sunset and → moonset.

See also: → moonset; → lag.

A unique feature of → Pluto’s large satellite → Charon. It appears as a dark reddish area about 475 km in diameter in Charon’s north polar region, as revealed in → New Horizons’ approach images. It has been proposed that the feature is due to gas from Pluto. A part of Pluto’s → atmosphere (→ methane molecules) is transiently cold-trapped and processed at Charon’s winter pole (W. M. Grundy et al., 2016, Nature, 14 September).

See also: Unofficial name.

A unique feature of → Pluto’s large satellite → Charon. It appears as a dark reddish area about 475 km in diameter in Charon’s north polar region, as revealed in → New Horizons’ approach images. It has been proposed that the feature is due to gas from Pluto. A part of Pluto’s → atmosphere (→ methane molecules) is transiently cold-trapped and processed at Charon’s winter pole (W. M. Grundy et al., 2016, Nature, 14 September).

See also: Unofficial name.

A large-scale → shock wave observed in Hα on the Sun’s → chromosphere that is generated by the impact of a → solar flare. Moreton waves expand outward at about 1,000 km/s, and
may travel for several hundred thousand kilometers. They are accompanied by meter-wave radio bursts.

See also: Named after the American astronomer Gail E. Moreton (1960, A.J. 65, 494); → wave.

A large-scale → shock wave observed in Hα on the Sun’s → chromosphere that is generated by the impact of a → solar flare. Moreton waves expand outward at about 1,000 km/s, and
may travel for several hundred thousand kilometers. They are accompanied by meter-wave radio bursts.

See also: Named after the American astronomer Gail E. Moreton (1960, A.J. 65, 494); → wave.

A system of → spectral classification introduced in 1943 by William W. Morgan (1906-1994), Philip C. Keenan (1908-2000), and Edith M. Kellman (1911-2007) at Yerkes Observatory. Also known as the MK (or MKK) classification or the → Yerkes system.

Etymology (EN): Named after the two main astronomers, as above; → classification.

A system of → spectral classification introduced in 1943 by William W. Morgan (1906-1994), Philip C. Keenan (1908-2000), and Edith M. Kellman (1911-2007) at Yerkes Observatory. Also known as the MK (or MKK) classification or the → Yerkes system.

Etymology (EN): Named after the two main astronomers, as above; → classification.

The first part or period of the day, extending from dawn, or from midnight, to noon. Not a precise astronomical term.

Etymology (EN): From M.E. morn, morwen, from O.E. margen earlier morgen (cf. O.H.G. morgen, Goth. maurgins) + → -ing.

Etymology (PE): Bâmdâd, from Mid.Pers. bâmdâd “morning, dawn,” from bâm “beam of light, splendor,” bâmik “brilliant” (from Av. *bāma- “light,” bāmya- “light, luminous, bright,” vīspô.bāma- “all resplendent,” from bā- “to shine;” cf. Skt. bhāti- “light, splendor”) + dâd “given,” from dâdan “to give” (O.Pers./Av. dā- “to give, grant, yield,” dadāiti “he gives;” Skt. dadáti “he gives;” Gk. tithenai “to place, put, set,” didomi “I give;”
L. dare “to give, offer,” facere “to do, to make;” Rus. delat’ “to do;” O.H.G. tuon, Ger. tun, O.E. don “to do;” PIE base *dhe- “to put, to do”).

The first part or period of the day, extending from dawn, or from midnight, to noon. Not a precise astronomical term.

Etymology (EN): From M.E. morn, morwen, from O.E. margen earlier morgen (cf. O.H.G. morgen, Goth. maurgins) + → -ing.

Etymology (PE): Bâmdâd, from Mid.Pers. bâmdâd “morning, dawn,” from bâm “beam of light, splendor,” bâmik “brilliant” (from Av. *bāma- “light,” bāmya- “light, luminous, bright,” vīspô.bāma- “all resplendent,” from bā- “to shine;” cf. Skt. bhāti- “light, splendor”) + dâd “given,” from dâdan “to give” (O.Pers./Av. dā- “to give, grant, yield,” dadāiti “he gives;” Skt. dadáti “he gives;” Gk. tithenai “to place, put, set,” didomi “I give;”
L. dare “to give, offer,” facere “to do, to make;” Rus. delat’ “to do;” O.H.G. tuon, Ger. tun, O.E. don “to do;” PIE base *dhe- “to put, to do”).

Not actually a star, but the planet Venus shining brightly in the east just before or at sunrise. Opposed to → evening star.

Etymology (EN): → morning; → star.

Etymology (PE): Rujâ “morning star” in Tabari, “star” in Gilaki. This word is a variant of official Pers. ruz “day,” since in Tabari and Gilaki the phoneme z is sometimes changed into j, as in rujin = rowzan “window” and jir or jer = zir “under.” Therefore it is related to rowšan “bright, clear,” rowzan “window, aperture;” foruq “light,”
afruxtan “to light, kindle;”
Mid.Pers. rôšn “light; bright, luminous,” rôc “day;” O.Pers. raucah-rocânak “window;” O.Pers. raocah- “light, luminous; daylight;”
Av. raocana- “bright, shining, radiant;”
akin to Skt. rocaná- “bright, shining,” roka- “brightness, light;” Gk. leukos “white, clear;”
L. lumen (gen. luminis) “light,” from lucere “to shine,” related to lux “light,” lucidus “clear,” luna, “moon;” Fr. lumière “light;” O.E. leoht, leht, from W.Gmc. *leukhtam (cf. O.Fris. liacht, M.Du. lucht, Ger. Licht), from PIE *leuk- “light, brightness;” → morning; → star.

Not actually a star, but the planet Venus shining brightly in the east just before or at sunrise. Opposed to → evening star.

Etymology (EN): → morning; → star.

Etymology (PE): Rujâ “morning star” in Tabari, “star” in Gilaki. This word is a variant of official Pers. ruz “day,” since in Tabari and Gilaki the phoneme z is sometimes changed into j, as in rujin = rowzan “window” and jir or jer = zir “under.” Therefore it is related to rowšan “bright, clear,” rowzan “window, aperture;” foruq “light,”
afruxtan “to light, kindle;”
Mid.Pers. rôšn “light; bright, luminous,” rôc “day;” O.Pers. raucah-rocânak “window;” O.Pers. raocah- “light, luminous; daylight;”
Av. raocana- “bright, shining, radiant;”
akin to Skt. rocaná- “bright, shining,” roka- “brightness, light;” Gk. leukos “white, clear;”
L. lumen (gen. luminis) “light,” from lucere “to shine,” related to lux “light,” lucidus “clear,” luna, “moon;” Fr. lumière “light;” O.E. leoht, leht, from W.Gmc. *leukhtam (cf. O.Fris. liacht, M.Du. lucht, Ger. Licht), from PIE *leuk- “light, brightness;” → morning; → star.

A → mapping between two → objects in a → category.

Etymology (EN): → morphology; → -ism.

Etymology (PE): From rixt, → morphology, + -mandi, → ism.

A → mapping between two → objects in a → category.

Etymology (EN): → morphology; → -ism.

Etymology (PE): From rixt, → morphology, + -mandi, → ism.

Of or relating to → morphology. Same as
morphological

See also: → morphology; → -ic.

Of or relating to → morphology. Same as
morphological

See also: → morphology; → -ic.

Of or relating to → morphology. Same as
morphological

See also: → morphologic; → -al.

Of or relating to → morphology. Same as
morphological

See also: → morphologic; → -al.

A classification scheme of galaxies based on their apparent shape. → Hubble classification.

See also: → morphological; → classification.

A classification scheme of galaxies based on their apparent shape. → Hubble classification.

See also: → morphological; → classification.

1. The study of the form or → structure of anything.
   

2. The → form and structure of a whole entity under study.
   

3. Linguistics: The structure of → words in a → language, including patterns of → inflections and → derivation. The study and description of such structures.

Etymology (EN): From Gk. morphe “form, shape, outward appearance” + → -logy.

Etymology (PE): Rixt “shape, the way something is cast, as in founding,” past stem of rixtan “to cast; to pour; to flow” (Mid.Pers. rēxtan and rēcitan “to flow;” Av. raēk- “to leave, set free; to yield, transfer,” infinitive *ricyā; Mod.Pers; rig in morderig “heritage” (literally, “left by the dead”); cf. Skt. rinakti “he leaves,” riti- “stream; motion, course;” L. rivus “stream, brook;” Old Church Slavic rēka “river;” Rus. reka “river;” Goth. rinnan “run, flow,” rinno “brook;” O.E. ridh “stream.” šenâsi, → -logy.

1. The study of the form or → structure of anything.
   

2. The → form and structure of a whole entity under study.
   

3. Linguistics: The structure of → words in a → language, including patterns of → inflections and → derivation. The study and description of such structures.

Etymology (EN): From Gk. morphe “form, shape, outward appearance” + → -logy.

Etymology (PE): Rixt “shape, the way something is cast, as in founding,” past stem of rixtan “to cast; to pour; to flow” (Mid.Pers. rēxtan and rēcitan “to flow;” Av. raēk- “to leave, set free; to yield, transfer,” infinitive *ricyā; Mod.Pers; rig in morderig “heritage” (literally, “left by the dead”); cf. Skt. rinakti “he leaves,” riti- “stream; motion, course;” L. rivus “stream, brook;” Old Church Slavic rēka “river;” Rus. reka “river;” Goth. rinnan “run, flow,” rinno “brook;” O.E. ridh “stream.” šenâsi, → -logy.

An observationally determined relationship between the → morphological classification of galaxies and the → environments in which they are located. Specifically, the morphology-density relation indicates that early-type galaxies (→ ETG) are preferentially located in high density environments, whereas late-type galaxies (→ LTG) are preferentially found in low density environments. Hence, spiral galaxies are rare in the high densities of clusters and are common in the lower density group environments. Early-type galaxies, on the other hand, are common in clusters and are rarely found in isolation.

See also: → morphology; → density; → relation.

An observationally determined relationship between the → morphological classification of galaxies and the → environments in which they are located. Specifically, the morphology-density relation indicates that early-type galaxies (→ ETG) are preferentially located in high density environments, whereas late-type galaxies (→ LTG) are preferentially found in low density environments. Hence, spiral galaxies are rare in the high densities of clusters and are common in the lower density group environments. Early-type galaxies, on the other hand, are common in clusters and are rarely found in isolation.

See also: → morphology; → density; → relation.

A composite image built up from a number of image segments.

See also: From O.Fr. mosaicq “mosaic work,” from M.L. musaicum “mosaic work, work of the Muses,” from musaicus “of the Muses,” from L. Musa.

A composite image built up from a number of image segments.

See also: From O.Fr. mosaicq “mosaic work,” from M.L. musaicum “mosaic work, work of the Muses,” from musaicus “of the Muses,” from L. Musa.

A small telescope dedicated entirely to → asterolseismology. MOST is the first space telescope entirely designed and constructed by Canada. It was launched into space in 2003.

The satellite weighs only 54 kg and is equipped with an ultra high precision telescope that measures only 15 centimetres in diameter. Despite its tiny size, it is ten times more sensitive than the → Hubble Space Telescope in detecting the minuscule variations in a star’s luminosity caused by vibrations that shake its surface. MOST completes one orbit around the Earth every 101 minutes by passing over each of Earth’s poles.

See also: MOST, short for Microvariability and Oscillations of STars telescope.

A small telescope dedicated entirely to → asterolseismology. MOST is the first space telescope entirely designed and constructed by Canada. It was launched into space in 2003.

The satellite weighs only 54 kg and is equipped with an ultra high precision telescope that measures only 15 centimetres in diameter. Despite its tiny size, it is ten times more sensitive than the → Hubble Space Telescope in detecting the minuscule variations in a star’s luminosity caused by vibrations that shake its surface. MOST completes one orbit around the Earth every 101 minutes by passing over each of Earth’s poles.

See also: MOST, short for Microvariability and Oscillations of STars telescope.

A female → parent.

Etymology (EN): M.E. mother, moder, O.E. modor; cf. O.S. modar, O.N. moðir, Da. moder, Du. moeder, O.H.G. muoter, Ger. Mutter; PIE *mater- “mother;” akin to Pers. mâdar, as below.

Etymology (PE): Mâdar, from Mid.Pers. mâd, mâdar; O.Pers./Av. mātar- “mother;” cf. Ossetic mad/madae “mother;” Khotanese mâta “mother;” Skt. mātár- “mother;” Gk. meter, mater; L. mater (Fr. mère, Sp. madre).

A female → parent.

Etymology (EN): M.E. mother, moder, O.E. modor; cf. O.S. modar, O.N. moðir, Da. moder, Du. moeder, O.H.G. muoter, Ger. Mutter; PIE *mater- “mother;” akin to Pers. mâdar, as below.

Etymology (PE): Mâdar, from Mid.Pers. mâd, mâdar; O.Pers./Av. mātar- “mother;” cf. Ossetic mad/madae “mother;” Khotanese mâta “mother;” Skt. mātár- “mother;” Gk. meter, mater; L. mater (Fr. mère, Sp. madre).

The action or process of moving or of changing place or position; movement.

See also: Verbal noun of → move.

The action or process of moving or of changing place or position; movement.

See also: Verbal noun of → move.

A device that imparts motion through reaction.

Etymology (EN): From L. motor “mover,” from movere “to move.”

Etymology (PE): Motor, loanword from Fr. moteur, as above.

A device that imparts motion through reaction.

Etymology (EN): From L. motor “mover,” from movere “to move.”

Etymology (PE): Motor, loanword from Fr. moteur, as above.

A general term for a relatively bright or dark feature seen in monochromatic images taken in the red Hα → Balmer line of the solar → chromosphere. Mottles constitute the fine structure of the quiet solar chromosphere and are found near bright points at → supergranulation boundaries.

Etymology (EN): Probably back formation from motley, from M.E., O.E. mot “speck,” of unknown origin; maybe related to Du. mot “sawdust, grit;” Norw. mutt “speck.”

Etymology (PE): Capârak noun from capâr “spotted, speckled, mottled” + -ak diminutive/similarity suffix.

A general term for a relatively bright or dark feature seen in monochromatic images taken in the red Hα → Balmer line of the solar → chromosphere. Mottles constitute the fine structure of the quiet solar chromosphere and are found near bright points at → supergranulation boundaries.

Etymology (EN): Probably back formation from motley, from M.E., O.E. mot “speck,” of unknown origin; maybe related to Du. mot “sawdust, grit;” Norw. mutt “speck.”

Etymology (PE): Capârak noun from capâr “spotted, speckled, mottled” + -ak diminutive/similarity suffix.

An observatory situated on a mountain 1700 m above sea level near Pasadena, California.

It was built in 1904 by American astronomer George Ellery Hale as a solar-observing station for the Yerkes Observatory, but it became an independent observatory funded by the Carnegie Institution of Washington. In 1908 a 60-inch (152-cm) reflector, then the largest in the world, was added for observations of stars and galaxies.

Ten years later a 100-inch (254-cm) reflecting telescope was put into service. It was the most powerful telescope in the world until the construction of the Palomar 200-inch reflector in 1948.

The 100-inch telescope’s most important discovery was Edwin Hubble’s determination of the distance to the Andromeda Nebula in 1924. He showed that the nebula lay beyond the bounds of the Milky Way Galaxy and hence was a galaxy in its own right. Then in 1929, following the work of Vesto Slipher, Hubble and his assistant Milton Humason demonstrated that galaxies were moving away from one another. This movement is the expansion of the Universe.

See also: → mountain; a peak of the San Gabriel Mountains, located in northern Los Angeles County, California, named after Benjamin D. Wilson (1811-1878) a California statesman and politician; → observatory .

An observatory situated on a mountain 1700 m above sea level near Pasadena, California.

It was built in 1904 by American astronomer George Ellery Hale as a solar-observing station for the Yerkes Observatory, but it became an independent observatory funded by the Carnegie Institution of Washington. In 1908 a 60-inch (152-cm) reflector, then the largest in the world, was added for observations of stars and galaxies.

Ten years later a 100-inch (254-cm) reflecting telescope was put into service. It was the most powerful telescope in the world until the construction of the Palomar 200-inch reflector in 1948.

The 100-inch telescope’s most important discovery was Edwin Hubble’s determination of the distance to the Andromeda Nebula in 1924. He showed that the nebula lay beyond the bounds of the Milky Way Galaxy and hence was a galaxy in its own right. Then in 1929, following the work of Vesto Slipher, Hubble and his assistant Milton Humason demonstrated that galaxies were moving away from one another. This movement is the expansion of the Universe.

See also: → mountain; a peak of the San Gabriel Mountains, located in northern Los Angeles County, California, named after Benjamin D. Wilson (1811-1878) a California statesman and politician; → observatory .

A natural elevation of the Earth’s surface rising to a summit, and attaining an altitude greater than that of a hill.

Etymology (EN): From O.Fr. montaigne, from V.L. *montanea “mountain, mountain region,” from L. montanus “mountainous,” from mons (gen. montis) “mountain,” minere “to project, jut, threaten,” from PIE base *men- “to project;” cf. Av. matay-, mati- “protrusion of mountain range,” framanyente “to be protruding, jutting;”
from PIE base *men- “to stand out, to project;” (other related terms: mouth, prominent, amount, etc.).

Etymology (PE): Kuh “mountain,” from Mid.Pers. kôf “mountain, hill; hump;” O.Pers. kaufa- “mountain;” Av. kaofa- “mountain.”

A natural elevation of the Earth’s surface rising to a summit, and attaining an altitude greater than that of a hill.

Etymology (EN): From O.Fr. montaigne, from V.L. *montanea “mountain, mountain region,” from L. montanus “mountainous,” from mons (gen. montis) “mountain,” minere “to project, jut, threaten,” from PIE base *men- “to project;” cf. Av. matay-, mati- “protrusion of mountain range,” framanyente “to be protruding, jutting;”
from PIE base *men- “to stand out, to project;” (other related terms: mouth, prominent, amount, etc.).

Etymology (PE): Kuh “mountain,” from Mid.Pers. kôf “mountain, hill; hump;” O.Pers. kaufa- “mountain;” Av. kaofa- “mountain.”

Climate of relatively high elevations, specifically where optical observatories are situated.

See also: → mountain; → climate.

Climate of relatively high elevations, specifically where optical observatories are situated.

See also: → mountain; → climate.

The support structure for a telescope that bears the weight of the telescope and allows it to be pointed at a target.

Etymology (EN): From verb mount, from O.Fr. monter “to go up, climb, mount,” from V.L. *montare, from L. mons (genitive montis) → mountain

Etymology (PE): Barnešând, noun of Barnešândan “to set, to fix, make sit,”
from bar- “on, upon, up” (Mid.Pers. abar; O.Pers. upariy “above; over, upon, according to;” Av. upairi “above, over,” upairi.zəma- “located above the earth;” cf. Gk. hyper- “over, above;” L. super-; O.H.G. ubir “over;” PIE base *uper “over”) + nešândan “to place one thing upon another, to fix, insert,” from
nešastan “to sit;” Mid.Pers. nišastan “to sit;” O.Pers. nišādayam [1 sg.impf.caus.act.] “to sit down, to establish,” hadiš- “abode;” Av. nišasiiā [1 sg.subj.acr.] “I shall sit down,” from nihad- “to sit down,” from ni- “down, below, into,” → ni-,

• had- “to sit;” PIE base *sed- “to sit;” cf. Skt. sad- “to sit,” sidati “sits;”
  Gk. hezomai “to sit,” hedra “seat, chair;” L. sedere “to sit;” O.Ir. suide “seat, sitting;” Welsh sedd “seat;” Lith. sedmi “to sit;” Rus. sad “garden;” Goth. sitan, Ger. sitzen; E. sit.

The support structure for a telescope that bears the weight of the telescope and allows it to be pointed at a target.

Etymology (EN): From verb mount, from O.Fr. monter “to go up, climb, mount,” from V.L. *montare, from L. mons (genitive montis) → mountain

Etymology (PE): Barnešând, noun of Barnešândan “to set, to fix, make sit,”
from bar- “on, upon, up” (Mid.Pers. abar; O.Pers. upariy “above; over, upon, according to;” Av. upairi “above, over,” upairi.zəma- “located above the earth;” cf. Gk. hyper- “over, above;” L. super-; O.H.G. ubir “over;” PIE base *uper “over”) + nešândan “to place one thing upon another, to fix, insert,” from
nešastan “to sit;” Mid.Pers. nišastan “to sit;” O.Pers. nišādayam [1 sg.impf.caus.act.] “to sit down, to establish,” hadiš- “abode;” Av. nišasiiā [1 sg.subj.acr.] “I shall sit down,” from nihad- “to sit down,” from ni- “down, below, into,” → ni-,

• had- “to sit;” PIE base *sed- “to sit;” cf. Skt. sad- “to sit,” sidati “sits;”
  Gk. hezomai “to sit,” hedra “seat, chair;” L. sedere “to sit;” O.Ir. suide “seat, sitting;” Welsh sedd “seat;” Lith. sedmi “to sit;” Rus. sad “garden;” Goth. sitan, Ger. sitzen; E. sit.

1. Any of numerous small Old World rodents of the family Muridae, especially of the genus Mus, introduced widely in other parts of the world.
   

2. Computers: A palm-sized, button-operated pointing device that can be used to move, select, activate, and change items on a computer screen (Dictionary.com).

Etymology (EN): M.E. mous (plural mis), from O.E. mus “small rodent;” cf. O.N., O.Fr., M.Du., Dan., Sw. mus, Du. muis, Ger. Maus, Pers. muš, as below.

Etymology (PE): Muš “mouse,” dialectal Lori, Laki miš; Mid.Pers. mušk; cf. Skt. muš-, muš-; Gk. mys; L. mus; O.E. mys; Ger. Maus.

1. Any of numerous small Old World rodents of the family Muridae, especially of the genus Mus, introduced widely in other parts of the world.
   

2. Computers: A palm-sized, button-operated pointing device that can be used to move, select, activate, and change items on a computer screen (Dictionary.com).

Etymology (EN): M.E. mous (plural mis), from O.E. mus “small rodent;” cf. O.N., O.Fr., M.Du., Dan., Sw. mus, Du. muis, Ger. Maus, Pers. muš, as below.

Etymology (PE): Muš “mouse,” dialectal Lori, Laki miš; Mid.Pers. mušk; cf. Skt. muš-, muš-; Gk. mys; L. mus; O.E. mys; Ger. Maus.

1. The body opening through which an animal takes in food.
   

   2. This cavity regarded as the source of sounds and speech (TheFreeDictionary.com).

Etymology (EN): M.E., from O.E. muth “mouth, opening, door, gate;” cf. O.Sax., O.Norse munnr, Dan. mund, Du. mond, Ger. Mund.

Etymology (PE): Dahân “mouth,” variant zafar “mouth;” Mid.Pers. dahân “mouth;” from *dafân the south-west form of Av. zafan, zafar “mouth;” cf. Skt. jambha- “set of teeth, mouth, jaws;” Ger. Kiefer “jaw.”

1. The body opening through which an animal takes in food.
   

   2. This cavity regarded as the source of sounds and speech (TheFreeDictionary.com).

Etymology (EN): M.E., from O.E. muth “mouth, opening, door, gate;” cf. O.Sax., O.Norse munnr, Dan. mund, Du. mond, Ger. Mund.

Etymology (PE): Dahân “mouth,” variant zafar “mouth;” Mid.Pers. dahân “mouth;” from *dafân the south-west form of Av. zafan, zafar “mouth;” cf. Skt. jambha- “set of teeth, mouth, jaws;” Ger. Kiefer “jaw.”

Capable of being moved; not fixed in one place, position, or posture (Dictionary.com).

See also: → move; → -able.

Capable of being moved; not fixed in one place, position, or posture (Dictionary.com).

See also: → move; → -able.

1. To go from one place or position to another.
   
2. To change the position or location of something.

Etymology (EN): M.E. meven, moven; O.Fr. moveir; L. movere “move, set in motion;” Av. miuu- “to shove,” as below.

Etymology (PE): Jonbidan “to move;” Lori, Laki jem “motion,” Kurd. -žim- “to move, stir,” žimây-/žimn- “to rock a cradle,” Sogd. âyamb “to pervert, seduce, deceive,” yâb “to wander, travel, rove;” Mid.Pers. jumbidan, jumb- “to move;” cf. Tocharian yâw-, yâp- “to enter;” Luwian /iba-/ “west;” PIE base *ieb^(h)- “to go, move inside” (Cheung 2007).
Miyâvidan, ultimately from Proto-Ir. *miHu- “to move;” cf. Av. auua.miuu- “to remove;” Khotanese mvīr- “to move;” Mid.Pers. pr-mws- “to be terrified;” Skt. mīv-/mu- “to move, remove, push;” L. movere, as above; PIE root *mieuH- “to set into motion” (Cheung 2007).

1. To go from one place or position to another.
   
2. To change the position or location of something.

Etymology (EN): M.E. meven, moven; O.Fr. moveir; L. movere “move, set in motion;” Av. miuu- “to shove,” as below.

Etymology (PE): Jonbidan “to move;” Lori, Laki jem “motion,” Kurd. -žim- “to move, stir,” žimây-/žimn- “to rock a cradle,” Sogd. âyamb “to pervert, seduce, deceive,” yâb “to wander, travel, rove;” Mid.Pers. jumbidan, jumb- “to move;” cf. Tocharian yâw-, yâp- “to enter;” Luwian /iba-/ “west;” PIE base *ieb^(h)- “to go, move inside” (Cheung 2007).
Miyâvidan, ultimately from Proto-Ir. *miHu- “to move;” cf. Av. auua.miuu- “to remove;” Khotanese mvīr- “to move;” Mid.Pers. pr-mws- “to be terrified;” Skt. mīv-/mu- “to move, remove, push;” L. movere, as above; PIE root *mieuH- “to set into motion” (Cheung 2007).

The act, process, or result of moving. A particular manner or style of moving.

See also: → move; → -ment.

The act, process, or result of moving. A particular manner or style of moving.

See also: → move; → -ment.

In a state of movement. → moving cluster; → moving frame.

See also: Verbal adj. of move, → motion.

In a state of movement. → moving cluster; → moving frame.

See also: Verbal adj. of move, → motion.

A group of stars dynamically associated so that they have a common motion with respect to the local standard of rest.

See also: → moving; → cluster.

A group of stars dynamically associated so that they have a common motion with respect to the local standard of rest.

See also: → moving; → cluster.

A → frame of reference that moves relative to the observer. The moving frame may be → inertial or → non-inertial. See also → rest frame.

See also: → moving; → frame.

A → frame of reference that moves relative to the observer. The moving frame may be → inertial or → non-inertial. See also → rest frame.

See also: → moving; → frame.

A young → stellar population that shares a common space motion. A moving group remains kinematically distinct within the general field stars at ages < 1 billion years, before being dispersed. As progenitor gas is cleared by OB star winds, and the natal cluster expands, stars with sufficiently high velocities become unbound and form a young, coeval moving group, possibly leaving behind a bound open cluster. Because of their common origin, moving group members have a shared age and composition. The nearest moving group is the → TW Hydrae association.

See also: → moving; → group.

A young → stellar population that shares a common space motion. A moving group remains kinematically distinct within the general field stars at ages < 1 billion years, before being dispersed. As progenitor gas is cleared by OB star winds, and the natal cluster expands, stars with sufficiently high velocities become unbound and form a young, coeval moving group, possibly leaving behind a bound open cluster. Because of their common origin, moving group members have a shared age and composition. The nearest moving group is the → TW Hydrae association.

See also: → moving; → group.