An Etymological Dictionary of Astronomy and Astrophysics

A → white dwarf whose spectrum shows the → Balmer lines of hydrogen only, with no helium or metals.

See also: D short for → dwarf; A a convention; → white.

A → white dwarf whose spectrum shows the → Balmer lines of hydrogen only, with no helium or metals.

See also: D short for → dwarf; A a convention; → white.

A 40-year period of unusually low → solar activity, from about 1790 to 1830. See also the → Maunder minimum.

See also: Named after John Dalton (1766-1844), British meteorologist; → minimum.

A 40-year period of unusually low → solar activity, from about 1790 to 1830. See also the → Maunder minimum.

See also: Named after John Dalton (1766-1844), British meteorologist; → minimum.

Of an oscillating system, the progressive decrease with time in the amplitude of the oscillation, due to friction (internal or external) or other resistance.

Etymology (EN): M.E. damp “black damp, a poison gas occurring in a mine,” from Mid.Du. or Mid. Low German; akin to O.H.G. damph “vapor.”

Etymology (PE): Mirâyi, noun from mirâ “getting extinguished, going out, expiring, dying,” from mordan, present tense stem mir- “to die,” Mid.Pers. murdan “to die,” O.Pers. mrt- “to die,” amriyta “dies,” martiya- “(mortal) man” (Mod.Pers. mard “man”), Av. mərəta- “died,” Skt. mar- “to die,” mrti- “death;” PIE base *mor-/*mr- “to die.” Cognates in other IE languages: Gk. emorten “died,” ambrotos “immortal,”
L. morior “I die,” mortuus “dead” (Fr. mourir “to die,” mort “dead”), Arm. merani- “to die,” O.C.S. mrutvu “dead,” O.Ir. marb, Welsh marw “died,” O.E. morþ “murder,” Lith. mirtis “man.”

Of an oscillating system, the progressive decrease with time in the amplitude of the oscillation, due to friction (internal or external) or other resistance.

Etymology (EN): M.E. damp “black damp, a poison gas occurring in a mine,” from Mid.Du. or Mid. Low German; akin to O.H.G. damph “vapor.”

Etymology (PE): Mirâyi, noun from mirâ “getting extinguished, going out, expiring, dying,” from mordan, present tense stem mir- “to die,” Mid.Pers. murdan “to die,” O.Pers. mrt- “to die,” amriyta “dies,” martiya- “(mortal) man” (Mod.Pers. mard “man”), Av. mərəta- “died,” Skt. mar- “to die,” mrti- “death;” PIE base *mor-/*mr- “to die.” Cognates in other IE languages: Gk. emorten “died,” ambrotos “immortal,”
L. morior “I die,” mortuus “dead” (Fr. mourir “to die,” mort “dead”), Arm. merani- “to die,” O.C.S. mrutvu “dead,” O.Ir. marb, Welsh marw “died,” O.E. morþ “murder,” Lith. mirtis “man.”

1a) A successive group of rhythmical steps or bodily motions, or both, usually executed to music.

1b) An act or round of dancing.

2a) To move one’s feet or body, or both, rhythmically in a pattern of steps, especially to the accompaniment of music.

2b) To leap, skip, etc., as from excitement or emotion; move nimbly or quickly (Dictionary.com).

Etymology (EN): M.E. da(u)ncen “to dance,” from O.Fr. dancier of unknown origin, perhaps related to O.H.G. *dansjan “to lead (someone) to a dance.”

Etymology (PE): Vašt, variant of gašt, gardidan, gel, gelidan “to turn,” → revolve, cf.
Eastern Gilâni gilâr “dance.”

1a) A successive group of rhythmical steps or bodily motions, or both, usually executed to music.

1b) An act or round of dancing.

2a) To move one’s feet or body, or both, rhythmically in a pattern of steps, especially to the accompaniment of music.

2b) To leap, skip, etc., as from excitement or emotion; move nimbly or quickly (Dictionary.com).

Etymology (EN): M.E. da(u)ncen “to dance,” from O.Fr. dancier of unknown origin, perhaps related to O.H.G. *dansjan “to lead (someone) to a dance.”

Etymology (PE): Vašt, variant of gašt, gardidan, gel, gelidan “to turn,” → revolve, cf.
Eastern Gilâni gilâr “dance.”

1. A person who dances.
   

   2. A person who dances professionally, as on the stage (Dictionary.com).

Etymology (EN): → dance; → -er.

Etymology (PE): Vaštâr, from vašt “dnace,” + agent noun suffix -âr, as in parastâr, padidâr; vaštande, vaštgar with agent noun suffixes, -ande and -gar, → -or.

1. A person who dances.
   

   2. A person who dances professionally, as on the stage (Dictionary.com).

Etymology (EN): → dance; → -er.

Etymology (PE): Vaštâr, from vašt “dnace,” + agent noun suffix -âr, as in parastâr, padidâr; vaštande, vaštgar with agent noun suffixes, -ande and -gar, → -or.

1. Liability or exposure to harm or injury; risk; peril.
   

2. An instance or cause of peril; menace (Dictionary.com).

Etymology (EN): M.E. daunger, from O.Fr. dangier “power, power to harm, authority, control,” alteration of dongier, from V.L. *dominarium “power of a lord,” from L. dominus “lord, master,” → domain.

Etymology (PE): Xatar “danger,” loan from Ar.

1. Liability or exposure to harm or injury; risk; peril.
   

2. An instance or cause of peril; menace (Dictionary.com).

Etymology (EN): M.E. daunger, from O.Fr. dangier “power, power to harm, authority, control,” alteration of dongier, from V.L. *dominarium “power of a lord,” from L. dominus “lord, master,” → domain.

Etymology (PE): Xatar “danger,” loan from Ar.

A modern unportable astrolabe which is used for high precision measuring of stellar and geographical coordinates. The instrument
uses the simultaneous observations of two images of the same star, one of the images
formed directly by the lower face of a prism and the other by the light rays reflected first from a mercury bath and then by the upper face of the prism. The images coincide when the zenithal distance of the star attains a prefixed value (Gauss method of equal altitudes, → almucantar). Apart from astrometry, the Danjon astrolabe was used for studying the Earth’s rotation and is currently used for solar radius measurements.

See also: After André Danjon (1890-1967), French astronomer, who developed the instrument at the Strasbourg Observatory before the Second World War and at the Paris Observatory in 1948. The concept of prism astrolabe was initially invented by the French Auguste Claude (1858-1938) around 1900 and was later modified in collaboration with Ludovic Driencourt (1861-1940); → astrolabe.

A modern unportable astrolabe which is used for high precision measuring of stellar and geographical coordinates. The instrument
uses the simultaneous observations of two images of the same star, one of the images
formed directly by the lower face of a prism and the other by the light rays reflected first from a mercury bath and then by the upper face of the prism. The images coincide when the zenithal distance of the star attains a prefixed value (Gauss method of equal altitudes, → almucantar). Apart from astrometry, the Danjon astrolabe was used for studying the Earth’s rotation and is currently used for solar radius measurements.

See also: After André Danjon (1890-1967), French astronomer, who developed the instrument at the Strasbourg Observatory before the Second World War and at the Paris Observatory in 1948. The concept of prism astrolabe was initially invented by the French Auguste Claude (1858-1938) around 1900 and was later modified in collaboration with Ludovic Driencourt (1861-1940); → astrolabe.

A scale to evaluate as exactly as possible the darkening degree of a total → lunar eclipse. The five steps of the scale run from 0 (extremely dark, invisible Moon) to 4 (extremely bright, the eclipse having a very weak effect on the Moon’s visibility). The darkening at a lunar eclipse is determined to a great extent by the transparency of the terrestrial atmosphere, which is affected by clouds and the dust from the volcanic eruptions (M.S.: SDE).

See also: Named after André Danjon, who set up the scale, → Danjon astrolabe; → scale.

A scale to evaluate as exactly as possible the darkening degree of a total → lunar eclipse. The five steps of the scale run from 0 (extremely dark, invisible Moon) to 4 (extremely bright, the eclipse having a very weak effect on the Moon’s visibility). The darkening at a lunar eclipse is determined to a great extent by the transparency of the terrestrial atmosphere, which is affected by clouds and the dust from the volcanic eruptions (M.S.: SDE).

See also: Named after André Danjon, who set up the scale, → Danjon astrolabe; → scale.

1. To be courageous enough to try to do something.
   

   2. A challenge, especially to prove courage.

Etymology (EN): M.E. durren, from O.E. durran “be bold enough, have courage” (to do something); cf. O.Norse dearr, O.H.G. giturran, Gothic gadaursan, from PIE root *dhers- “bold” source also of O.Pers. darš-, as below.

Etymology (PE): Daršidan, from O.Pers. darš- “to dare,” Av. darš- (prefixed *upa- in upadarəš- “to dare”); cf. Khotanese darv- “to dare;” Baluci durrit/durr- “to take courage;” Skt. dhars “to venture;” Gk. thrasus “bold;” Goth. ga-daursan “to venture;” E. “to dare;” PIE *d^hers- “to attack, venture, dare” (Cheung 2007).

1. To be courageous enough to try to do something.
   

   2. A challenge, especially to prove courage.

Etymology (EN): M.E. durren, from O.E. durran “be bold enough, have courage” (to do something); cf. O.Norse dearr, O.H.G. giturran, Gothic gadaursan, from PIE root *dhers- “bold” source also of O.Pers. darš-, as below.

Etymology (PE): Daršidan, from O.Pers. darš- “to dare,” Av. darš- (prefixed *upa- in upadarəš- “to dare”); cf. Khotanese darv- “to dare;” Baluci durrit/durr- “to take courage;” Skt. dhars “to venture;” Gk. thrasus “bold;” Goth. ga-daursan “to venture;” E. “to dare;” PIE *d^hers- “to attack, venture, dare” (Cheung 2007).

Taking or willing to take risks; audaciousness.

See also: → dare; → -ing.

Taking or willing to take risks; audaciousness.

See also: → dare; → -ing.

Having very little or no light.

Etymology (EN): M.E. derk, O.E. deorc, from P.Gmc. *derkaz.

Etymology (PE): Târik, Mid.Pers. târig “dark,” târ “darkness,” Av. taθra- “darkness,” taθrya- “dark,” cf. Skt. támisrâ- “darkness, dark night,” L. tenebrae “darkness,” Hittite taš(u)uant- “blind,” O.H.G. demar “twilight.”

Having very little or no light.

Etymology (EN): M.E. derk, O.E. deorc, from P.Gmc. *derkaz.

Etymology (PE): Târik, Mid.Pers. târig “dark,” târ “darkness,” Av. taθra- “darkness,” taθrya- “dark,” cf. Skt. támisrâ- “darkness, dark night,” L. tenebrae “darkness,” Hittite taš(u)uant- “blind,” O.H.G. demar “twilight.”

The automatic adjustment of the iris and retina of the eye to allow maximum vision in the dark, following exposure of the eye to a relatively brighter illumination.

See also: → dark; → adaptation.

The automatic adjustment of the iris and retina of the eye to allow maximum vision in the dark, following exposure of the eye to a relatively brighter illumination.

See also: → dark; → adaptation.

A relatively dense cloud of → interstellar gas, mainly molecular, whose dust particles obscure the light of stars behind it. A famous example is the → Horsehead Nebula silhouetted against the reddish glow of the → H II region IC 434. Individual dark clouds come in a range of sizes from tens of → light-years to tiny → Bok globules of only a few thousands → astronomical units.

See also: → dark; → cloud.

A relatively dense cloud of → interstellar gas, mainly molecular, whose dust particles obscure the light of stars behind it. A famous example is the → Horsehead Nebula silhouetted against the reddish glow of the → H II region IC 434. Individual dark clouds come in a range of sizes from tens of → light-years to tiny → Bok globules of only a few thousands → astronomical units.

See also: → dark; → cloud.

Current generated in an electronic detector by thermal effects, even in the absence of input signal. In a → CCD detector, the current rises from thermal energy within the silicon lattice comprising the CCD. These electrons are captured by the CCD’s potential wells and counted as signal. → dark current noise.

See also: → dark; → current.

Current generated in an electronic detector by thermal effects, even in the absence of input signal. In a → CCD detector, the current rises from thermal energy within the silicon lattice comprising the CCD. These electrons are captured by the CCD’s potential wells and counted as signal. → dark current noise.

See also: → dark; → current.

In a → CCD detector, statistical fluctuation of the → dark current, equal to the square root of the dark current. CCDs can be cooled either with thermoelectric coolers or liquid nitrogen to reduce this effect. Ideally, the dark current noise should be reduced to a point where its contribution is negligible over a typical exposure time.

See also: → dark; → current; → noise.

In a → CCD detector, statistical fluctuation of the → dark current, equal to the square root of the dark current. CCDs can be cooled either with thermoelectric coolers or liquid nitrogen to reduce this effect. Ideally, the dark current noise should be reduced to a point where its contribution is negligible over a typical exposure time.

See also: → dark; → current; → noise.

A hypothetical form of energy that fills all the space and tends to increase the rate of expansion of the Universe. Assuming the existence of dark energy is a way to explain recent observations that the Universe appears to be expanding at an increasing rate (→ accelerating Universe). Dark energy seems to be a kind of anti-gravity force and is supposed to be related to → vacuum energy. Where gravity pulls things together at the more local level, dark energy tears them apart on the grander scale. The acceleration equation, one of Einstein’s equations for the homogeneous Universe, indicates that if the Universe is accelerating, the pressure of the driving component should be strongly negative.
The dark energy density relates to the → cosmological constant via: ρ_&Lambda = Λc²/(8πG), where G is the → gravitational constant and c the → speed of light. The first indication of dark energy was provided by the observation of → Type Ia supernovae. Other probes of dark energy are: → baryon acoustic oscillations, → weak gravitational lensing, and clusters of galaxies. In the standard model of cosmology, dark energy currently accounts for almost 74% of the total mass-energy of the Universe.
Two proposed forms for dark energy are the cosmological constant and exotic component such as → quintessence.

See also: → dark; → energy.

A hypothetical form of energy that fills all the space and tends to increase the rate of expansion of the Universe. Assuming the existence of dark energy is a way to explain recent observations that the Universe appears to be expanding at an increasing rate (→ accelerating Universe). Dark energy seems to be a kind of anti-gravity force and is supposed to be related to → vacuum energy. Where gravity pulls things together at the more local level, dark energy tears them apart on the grander scale. The acceleration equation, one of Einstein’s equations for the homogeneous Universe, indicates that if the Universe is accelerating, the pressure of the driving component should be strongly negative.
The dark energy density relates to the → cosmological constant via: ρ_&Lambda = Λc²/(8πG), where G is the → gravitational constant and c the → speed of light. The first indication of dark energy was provided by the observation of → Type Ia supernovae. Other probes of dark energy are: → baryon acoustic oscillations, → weak gravitational lensing, and clusters of galaxies. In the standard model of cosmology, dark energy currently accounts for almost 74% of the total mass-energy of the Universe.
Two proposed forms for dark energy are the cosmological constant and exotic component such as → quintessence.

See also: → dark; → energy.

A → CCD frame obtained with closed → shutters in the absence of any light source, in order to estimate the → dark current of the → detector.

See also: → dark; → exposure.

A → CCD frame obtained with closed → shutters in the absence of any light source, in order to estimate the → dark current of the → detector.

See also: → dark; → exposure.

One of the successive dark and light bands produced by diffraction or interference of light.

Etymology (EN): From O.Fr. frange, from V.L. *frimbia alteration by metathesis of L. fimbria “fringe, edge of garment.”

Etymology (PE): Fariz, variants farviz, farâviz “fringe, edge of garment.”

One of the successive dark and light bands produced by diffraction or interference of light.

Etymology (EN): From O.Fr. frange, from V.L. *frimbia alteration by metathesis of L. fimbria “fringe, edge of garment.”

Etymology (PE): Fariz, variants farviz, farâviz “fringe, edge of garment.”

Matter that has no radiation and therefore cannot be detected directly,
but whose presence can be inferred from dynamical phenomena produced by its gravitational influence. The existence of dark matter is deduced mainly from the rotational speeds of galaxies, velocities of galaxies in clusters, gravitational lensing by galaxy clusters, and the temperature distribution of hot gas in galaxies and clusters of galaxies. Dark matter plays also a central role in cosmic structure formation. There exists a large number of → non-baryonic dark matter candidates. They include, the hypothetical stable particles → WIMPs, → neutralinos, → axions,
→ gravitinos, etc. Among unstable candidates are gravitinos with mild R-parity violation and sterile neutrinos. See also → baryonic dark matter, → dark matter candidate.

See also: The concept of dark matter was first introduced by J.H. Oort (1932, Bull. Astron. Inst. Netherlands, 6, 249), who studied the vertical motions of the stars in the solar neighborhood and found that the visible matter could account for at most 50% of the derived surface density. → dark; → matter.

Matter that has no radiation and therefore cannot be detected directly,
but whose presence can be inferred from dynamical phenomena produced by its gravitational influence. The existence of dark matter is deduced mainly from the rotational speeds of galaxies, velocities of galaxies in clusters, gravitational lensing by galaxy clusters, and the temperature distribution of hot gas in galaxies and clusters of galaxies. Dark matter plays also a central role in cosmic structure formation. There exists a large number of → non-baryonic dark matter candidates. They include, the hypothetical stable particles → WIMPs, → neutralinos, → axions,
→ gravitinos, etc. Among unstable candidates are gravitinos with mild R-parity violation and sterile neutrinos. See also → baryonic dark matter, → dark matter candidate.

See also: The concept of dark matter was first introduced by J.H. Oort (1932, Bull. Astron. Inst. Netherlands, 6, 249), who studied the vertical motions of the stars in the solar neighborhood and found that the visible matter could account for at most 50% of the derived surface density. → dark; → matter.

A hypothetical process whereby hypothetical → non-baryonic dark matter particles undergo → annihilation interactions with themselves. The process results in observable by-products such as high-energy photons, neutrinos, and other detectable particles. See also
→ dark matter decay.

See also: → dark; → matter; → annihilation.

A hypothetical process whereby hypothetical → non-baryonic dark matter particles undergo → annihilation interactions with themselves. The process results in observable by-products such as high-energy photons, neutrinos, and other detectable particles. See also
→ dark matter decay.

See also: → dark; → matter; → annihilation.

A hypothetical physical entity capable of accounting for the corresponding observed phenomena involving → dark matter. → Non-baryonic dark matter candidates include → WIMPs, → neutralinos, → axions, → gravitinos. Among → baryonic dark matter
candidates can be noted ordinary and heavy → neutrinos, clouds of → neutral hydrogen gas, and compact objects.

See also: → dark; → matter; → candidate.

A hypothetical physical entity capable of accounting for the corresponding observed phenomena involving → dark matter. → Non-baryonic dark matter candidates include → WIMPs, → neutralinos, → axions, → gravitinos. Among → baryonic dark matter
candidates can be noted ordinary and heavy → neutrinos, clouds of → neutral hydrogen gas, and compact objects.

See also: → dark; → matter; → candidate.

In theoretical models, the hypothetical transformation of a → non-baryonic dark matter particle when symmetry is violated at special physical conditions. Dark matter decay and → dark matter annihilation are expected to produce enormous amounts of energy in the form of gamma-rays, cosmic rays, etc.

See also: → dark; → matter; → decay.

In theoretical models, the hypothetical transformation of a → non-baryonic dark matter particle when symmetry is violated at special physical conditions. Dark matter decay and → dark matter annihilation are expected to produce enormous amounts of energy in the form of gamma-rays, cosmic rays, etc.

See also: → dark; → matter; → decay.

A vast region surrounding a galaxy where dynamical tracers reveal a large
amount of → hidden mass. The halo has considerable mass but relatively low luminosity, suggesting the presence of a lot of → dark matter.

See also: → dark; → matter; → halo.

A vast region surrounding a galaxy where dynamical tracers reveal a large
amount of → hidden mass. The halo has considerable mass but relatively low luminosity, suggesting the presence of a lot of → dark matter.

See also: → dark; → matter; → halo.

An interstellar cloud of absorbing matter whose dust particles obscure the light from stars beyond it and give the cloud the appearance of a dark, starless region.

See also: → dark; → nebula.

An interstellar cloud of absorbing matter whose dust particles obscure the light from stars beyond it and give the cloud the appearance of a dark, starless region.

See also: → dark; → nebula.

A hypothetical stellar object whose structure or evolution has been affected by → dark matter. Dark matter models predict that in the → early Universe dark matter (in the form of → WIMPs) should congregate and annihilate in the cores of → Population III stars. The result would be dark stars with properties very different from ordinary stars. The reason is that the presence of large amounts of dark matter during the formation of a star inhibits the collapse and can partially prevent further cooling of the gas beyond a certain critical point, well before a → main sequence object has formed. As a consequence, dark matter stars should be more massive, more luminous, and live longer than Pop. III stars, but would be cooler. The formation of dark stars could have had an
impact on the → reionization history of the Universe (see, e.g., P. Scott, 2011, astro-ph/1101.1029, and references therein).

See also: → dark; → star.

A hypothetical stellar object whose structure or evolution has been affected by → dark matter. Dark matter models predict that in the → early Universe dark matter (in the form of → WIMPs) should congregate and annihilate in the cores of → Population III stars. The result would be dark stars with properties very different from ordinary stars. The reason is that the presence of large amounts of dark matter during the formation of a star inhibits the collapse and can partially prevent further cooling of the gas beyond a certain critical point, well before a → main sequence object has formed. As a consequence, dark matter stars should be more massive, more luminous, and live longer than Pop. III stars, but would be cooler. The formation of dark stars could have had an
impact on the → reionization history of the Universe (see, e.g., P. Scott, 2011, astro-ph/1101.1029, and references therein).

See also: → dark; → star.

To become dark or darker. → darkening.

See also: Verb of → dark.

To become dark or darker. → darkening.

See also: Verb of → dark.

The act or process of becoming dark or darker. → limb darkening.

See also: Verbal noun of of → darken.

The act or process of becoming dark or darker. → limb darkening.

See also: Verbal noun of of → darken.

Items of information.

Etymology (EN): L. data, plural of → datum.

Etymology (PE): Dâdehâ, plural of dâdé, → datum.

Items of information.

Etymology (EN): L. data, plural of → datum.

Etymology (PE): Dâdehâ, plural of dâdé, → datum.

In the → software architecture, the code that deals with reading from or writing to the data store, hiding its nature and complexity.

See also: → data; → access; → layer.

In the → software architecture, the code that deals with reading from or writing to the data store, hiding its nature and complexity.

See also: → data; → access; → layer.

The process of controlling telescope operations during observation and obtaining data.

Etymology (EN): → data; acquisition, from L. acquisitionem, from acquirere “get in addition,” from → ad- “extra” + quærere “to search for, obtain.”

Etymology (PE): Alfanješ, verbal noun of alfanjidan (variant alfaqdan) “to acquire, get,” Bactrian αλφανζ “to acquire,” Sogdian δβ’yz “to acquire, gain, get” (Cheung 2007); → data.

The process of controlling telescope operations during observation and obtaining data.

Etymology (EN): → data; acquisition, from L. acquisitionem, from acquirere “get in addition,” from → ad- “extra” + quærere “to search for, obtain.”

Etymology (PE): Alfanješ, verbal noun of alfanjidan (variant alfaqdan) “to acquire, get,” Bactrian αλφανζ “to acquire,” Sogdian δβ’yz “to acquire, gain, get” (Cheung 2007); → data.

The evaluation of reduced data; → data reduction.

See also: → data; → analysis.

The evaluation of reduced data; → data reduction.

See also: → data; → analysis.

Any extensive record or collection of data, observational (usually obtained with a particular instrument) or theoretical (grid of models usually regarding a particular branch of astrophysics).

See also: → data; → archive.

Any extensive record or collection of data, observational (usually obtained with a particular instrument) or theoretical (grid of models usually regarding a particular branch of astrophysics).

See also: → data; → archive.

A set of data related to a given subject and organized in such a way that it can be consulted by users.

Etymology (EN): → data; bank, from M.Fr. banque, from O.It. banca “table,” because of “the moneylender’s exchange table,” from P.Gmc. *bankiz (O.H.G. bank “bench”).

Etymology (PE): Bânk, from Fr. banque, see above; dâdehâ, plural of dâdé→ datum.

A set of data related to a given subject and organized in such a way that it can be consulted by users.

Etymology (EN): → data; bank, from M.Fr. banque, from O.It. banca “table,” because of “the moneylender’s exchange table,” from P.Gmc. *bankiz (O.H.G. bank “bench”).

Etymology (PE): Bânk, from Fr. banque, see above; dâdehâ, plural of dâdé→ datum.

The process of digging through large quantities of raw data stored in → databases to uncover new characteristics, patterns, and correlations using various automatic or semi-automatic statistical/mathematical means.

Etymology (EN): → data; mining, from mine, M.E.,
from O.Fr. mine, probably from a Celtic source.

Etymology (PE): Kânkâvi, literally “digging mine,” from kân “mine,” related to kandan “to dig” (Mid.Pers. kan, qn; O.Pers. ka(n) “to dig;” Av. kan- “to dig;” cf. Skt. khan- “to dig”) + kâvi from kâvidan/kâftan “to split; to dig” (Mid.Pers. kandan “to dig;” cf. Gk. skaptein “to dig;” L. scabere “to scratch, rub”).

The process of digging through large quantities of raw data stored in → databases to uncover new characteristics, patterns, and correlations using various automatic or semi-automatic statistical/mathematical means.

Etymology (EN): → data; mining, from mine, M.E.,
from O.Fr. mine, probably from a Celtic source.

Etymology (PE): Kânkâvi, literally “digging mine,” from kân “mine,” related to kandan “to dig” (Mid.Pers. kan, qn; O.Pers. ka(n) “to dig;” Av. kan- “to dig;” cf. Skt. khan- “to dig”) + kâvi from kâvidan/kâftan “to split; to dig” (Mid.Pers. kandan “to dig;” cf. Gk. skaptein “to dig;” L. scabere “to scratch, rub”).

An abstract entity that describes the structure of → database by including the formal description of the information system used in the database.

See also: → data; → model.

An abstract entity that describes the structure of → database by including the formal description of the information system used in the database.

See also: → data; → model.

Unit of the analog-to-digital conversion system of a CCD apparatus. For example a 16 bit system may use a maximum of 65536 DN. The acronym ADU, for analog-to-digital unit, is also used.

See also: → data; → number.

Unit of the analog-to-digital conversion system of a CCD apparatus. For example a 16 bit system may use a maximum of 65536 DN. The acronym ADU, for analog-to-digital unit, is also used.

See also: → data; → number.

Systematic operations on data, such as handling, merging, sorting, and computing.

See also: → data; → processing.

Systematic operations on data, such as handling, merging, sorting, and computing.

See also: → data; → processing.

A machine for handling data in → data processing.

See also: → data; → processor.

A machine for handling data in → data processing.

See also: → data; → processor.

The process of converting crude observational data into usable information for scientific interpretation, by correcting, rearranging, ordering, and simplifying.

See also: → data; → reduction.

The process of converting crude observational data into usable information for scientific interpretation, by correcting, rearranging, ordering, and simplifying.

See also: → data; → reduction.

A → method or → format for organizing and storing data. Any data structure is designed to organize data to suit a specific purpose so that it can be accessed and worked with in appropriate ways. In computer programming, a data structure may be selected or designed to store data for the purpose of working on it with various algorithms.

See also: → data; → structure.

A → method or → format for organizing and storing data. Any data structure is designed to organize data to suit a specific purpose so that it can be accessed and worked with in appropriate ways. In computer programming, a data structure may be selected or designed to store data for the purpose of working on it with various algorithms.

See also: → data; → structure.

A combined and coordinated set of data that supplies information for a specific purpose in a variety of forms.

See also: → data; → base.

A combined and coordinated set of data that supplies information for a specific purpose in a variety of forms.

See also: → data; → base.

A particular day, month, and year at which some event happened or will happen.

Etymology (EN): Date, from O.Fr. date, from M.L. data, from datus “given,” p.p. of dare “to give, grant, offer,” from PIE base *do- “to give” (cf. Pers. dâdan “to give,” as below).
The Roman convention of closing a document by writing “given” and the day and month (meaning “given to messenger”) led to data becoming a term for “the time stated.”

Etymology (PE): Gâhdâd, from gâh “time” (Mid.Pers. gâh, gâs “time;” O.Pers. gāθu-; Av. gātav-, gātu- “place, throne, spot;” cf. Skt. gâtu- “going, motion; free space for moving; place of abode;” PIE *gwem- “to go, come”) + dâd “given,” as in Latin;
p.p. of dâdan “to give” (Mid.Pers. dâdan “to give,” O.Pers./Av. dā- “to give, grant, yield,” Av. dadāiti “he gives,” Skt. dadáti “he gives,” Gk. didomi “I give;” akin to L. data, as above); cf. Mid.Pers., Mod.Pers. dâd “year, age, period of life,” Lori, Laki dâ(d) “age,” homdâ “of equal age.”
Note: In current Persian a single term, târix (تاریخ), is used for two different but related concepts: date and history. This may be confusing, → history (تاریخ).

A particular day, month, and year at which some event happened or will happen.

Etymology (EN): Date, from O.Fr. date, from M.L. data, from datus “given,” p.p. of dare “to give, grant, offer,” from PIE base *do- “to give” (cf. Pers. dâdan “to give,” as below).
The Roman convention of closing a document by writing “given” and the day and month (meaning “given to messenger”) led to data becoming a term for “the time stated.”

Etymology (PE): Gâhdâd, from gâh “time” (Mid.Pers. gâh, gâs “time;” O.Pers. gāθu-; Av. gātav-, gātu- “place, throne, spot;” cf. Skt. gâtu- “going, motion; free space for moving; place of abode;” PIE *gwem- “to go, come”) + dâd “given,” as in Latin;
p.p. of dâdan “to give” (Mid.Pers. dâdan “to give,” O.Pers./Av. dā- “to give, grant, yield,” Av. dadāiti “he gives,” Skt. dadáti “he gives,” Gk. didomi “I give;” akin to L. data, as above); cf. Mid.Pers., Mod.Pers. dâd “year, age, period of life,” Lori, Laki dâ(d) “age,” homdâ “of equal age.”
Note: In current Persian a single term, târix (تاریخ), is used for two different but related concepts: date and history. This may be confusing, → history (تاریخ).

Use of appropriate techniques to estimate the age of geological specimens or astronomical objects such as meteorites.

Etymology (EN): Verbal noun of date, from O.Fr. date, from M.L. → data.

Etymology (PE): Sen yâbi, from Ar. sen “age” + yâbi verbal noun of
yâftan, yâbidan “to find, discover; to obtain, acquire,” Mid.Pers. ayâftan, ayâpênitan “to reach, attain,” Manichean Mid.Pers. ‘y’b “to attain,” Parthian, Sogdian (+ *pati-) pty’b “to reach, obtain,” Av. ap- “to reach, overtake,” apayeiti “achieved, reached,” Skt. âp- “to reach, gain,”
âpnoti “reaches, gains,” Gk. hapto, haptomai “to touch, cling to, adhere to,” L. apiscor “touch, reach;” PIE base *ap- “to take, reach.”

Use of appropriate techniques to estimate the age of geological specimens or astronomical objects such as meteorites.

Etymology (EN): Verbal noun of date, from O.Fr. date, from M.L. → data.

Etymology (PE): Sen yâbi, from Ar. sen “age” + yâbi verbal noun of
yâftan, yâbidan “to find, discover; to obtain, acquire,” Mid.Pers. ayâftan, ayâpênitan “to reach, attain,” Manichean Mid.Pers. ‘y’b “to attain,” Parthian, Sogdian (+ *pati-) pty’b “to reach, obtain,” Av. ap- “to reach, overtake,” apayeiti “achieved, reached,” Skt. âp- “to reach, gain,”
âpnoti “reaches, gains,” Gk. hapto, haptomai “to touch, cling to, adhere to,” L. apiscor “touch, reach;” PIE base *ap- “to take, reach.”

The form of a word (in Latin and other inflected languages) indicating the noun or pronoun for which an action happens or a quality exists. In English loosely used for → indirect object (for example, him in Give him the book).

Etymology (EN): From L. casus dativus (“case for giving”), a translation of Gk. dotike ptosis (“inflection for giving”), from dativus “pertaining to giving,” from datus “given” (from PIE root *do- “to give”), → datum; → case.

Etymology (PE): Kâte, → case; barâyi, adj. of barâye, “→ because of,” “→ for.”

The form of a word (in Latin and other inflected languages) indicating the noun or pronoun for which an action happens or a quality exists. In English loosely used for → indirect object (for example, him in Give him the book).

Etymology (EN): From L. casus dativus (“case for giving”), a translation of Gk. dotike ptosis (“inflection for giving”), from dativus “pertaining to giving,” from datus “given” (from PIE root *do- “to give”), → datum; → case.

Etymology (PE): Kâte, → case; barâyi, adj. of barâye, “→ because of,” “→ for.”

1. A single piece of information, as a fact, statistic, or code.
   

2. Any numerical or geometric quantity which serves as a reference or a base for measurement of other quantities.
   

3. Surveying: Any basis level (surface, line, or point) used as a reference in measuring elevations.

Etymology (EN): L. datum “given,” neuter p.p. of dare “to give, offer,” cf. Av. and O.Pers. dā- “to give, grant, yield,” Av. dadāiti “he gives,” Skt. dadáti “he gives,” Gk. didomi “I give,” PIE base *do- “to give.”

Etymology (PE): Dâdé “given,” p.p. of dâdan “to give,” Mid.Pers. dâdan “to give,” O.Pers./Av. dā- “to give, grant, yield,” akin to L. data, as above.
Dâdebon, from dâdé “datum,” + bon “basis, base,” → element.
Farâzbon, from farâz “above, up, upon,” → height,

• bon “basis, base,” as above.

1. A single piece of information, as a fact, statistic, or code.
   

2. Any numerical or geometric quantity which serves as a reference or a base for measurement of other quantities.
   

3. Surveying: Any basis level (surface, line, or point) used as a reference in measuring elevations.

Etymology (EN): L. datum “given,” neuter p.p. of dare “to give, offer,” cf. Av. and O.Pers. dā- “to give, grant, yield,” Av. dadāiti “he gives,” Skt. dadáti “he gives,” Gk. didomi “I give,” PIE base *do- “to give.”

Etymology (PE): Dâdé “given,” p.p. of dâdan “to give,” Mid.Pers. dâdan “to give,” O.Pers./Av. dā- “to give, grant, yield,” akin to L. data, as above.
Dâdebon, from dâdé “datum,” + bon “basis, base,” → element.
Farâzbon, from farâz “above, up, upon,” → height,

• bon “basis, base,” as above.

A term used in → nuclear physics to denote a → nuclide produced by the → radioactive decay of a → parent nuclide.

Etymology (EN): From M.E. doughter, O.E. dohtor, from P.Gmc. *dochter
(Ger. Tochter), from PIE *dhug(h)əter-; cf. Av. dugədar-, duγdar-, Mod.Pers. doxtar,
Skt. duhitár-, Gk. thygater, Arm. dowstr, Lith. dukte.

Etymology (PE): Doxtar, from Mid.Pers. duxtar, duxt, O.Pers. *duxçi-, Av. dugədar-, duγdar-, cognate with daughter, as above.

A term used in → nuclear physics to denote a → nuclide produced by the → radioactive decay of a → parent nuclide.

Etymology (EN): From M.E. doughter, O.E. dohtor, from P.Gmc. *dochter
(Ger. Tochter), from PIE *dhug(h)əter-; cf. Av. dugədar-, duγdar-, Mod.Pers. doxtar,
Skt. duhitár-, Gk. thygater, Arm. dowstr, Lith. dukte.

Etymology (PE): Doxtar, from Mid.Pers. duxtar, duxt, O.Pers. *duxçi-, Av. dugədar-, duγdar-, cognate with daughter, as above.

In → nuclear physics, same as → daughter.

See also: → daughter; → product.

In → nuclear physics, same as → daughter.

See also: → daughter; → product.

The experiment carried out in 1927 that confirmed the
→ de Broglie hypothesis as to the → wave nature of the → electron. It showed that electrons scattering off crystals form a → diffraction pattern. The experimental setup consisted of a → nickle chloride → crystal as → target, an electron gun, and a → detector placed on a graduated circular scale. The intensity of the reflected electrons was measured as a function of angle and electron energy. The observations showed a strong intensity peak at a certain angle. The nickel crystal acted as a → diffraction grating. → Constructive interference occurred
at a particular angle, where the peak intensity was observed in accord with → Bragg’s law. Interestingly, the intent of the initial experiment was was not to confirm the de Broglie hypothesis. In fact, the discovery was made by accident.

See also: Carried out by American physicists Clinton Davisson (1881-1958) and Lester Germer (1896-1971); → experiment.

The experiment carried out in 1927 that confirmed the
→ de Broglie hypothesis as to the → wave nature of the → electron. It showed that electrons scattering off crystals form a → diffraction pattern. The experimental setup consisted of a → nickle chloride → crystal as → target, an electron gun, and a → detector placed on a graduated circular scale. The intensity of the reflected electrons was measured as a function of angle and electron energy. The observations showed a strong intensity peak at a certain angle. The nickel crystal acted as a → diffraction grating. → Constructive interference occurred
at a particular angle, where the peak intensity was observed in accord with → Bragg’s law. Interestingly, the intent of the initial experiment was was not to confirm the de Broglie hypothesis. In fact, the discovery was made by accident.

See also: Carried out by American physicists Clinton Davisson (1881-1958) and Lester Germer (1896-1971); → experiment.

The first daylight in the sky before sunrise, equivalent to morning astronomical → twilight; opposed to → dusk.

Etymology (EN): M.E. dawen (v.), from O.E. dagung, from dagian “to become day,” from root of dæg→ day.

Etymology (PE): Pegâh, from Mid.Pers. pa gâh, literally “soon; near the time (of sunrise),” from pa “to; for; in; on; with; by; according to,” O.Pers. upā, Av. upa “toward, with, on, in, in the time of” (cf. Skt. úpa “toward, together with, under, near to, on,” Gk. hypo “under, below,” L. sub “under,” Ger. auf, E. up; PIE *upo “under, up from under, over”) + gâh “time,” O.Pers. gāθu-, Av. gātav-, gātu- “place, throne, spot” (Skt. gátu- “going, motion; free space for moving; place of abode,” PIE *gwem- “to go, come”).
Sepidedam, from sepidé “whitish; dawn,” from sepid “white” (Mid.Pers. spêt, Av. spita- “white,” Skt. śveta- “white,” Lith. sviesti “to shine,” svaityti “to brighten,” P.Gmc. *khwitaz, O.E. hwit, E. white, Ger. weiss, PIE *kwintos/*kwindos “bright”) + dam “moment, time; to blow, breathe; smoke” (Mod./Mid.Pers. damidan “to blow, breathe,” 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”).
Bâmdâd, from Mid.Pers. bâmdât, Av. bāmya- “the dawn,” from bā- “to shine” (cf. Skt. bhā- “light, brightness,” Gk. phainomai “to appear, shine, gleam,” Arm. banam “to open, uncover,” PIE *bhā- “to shine”).

The first daylight in the sky before sunrise, equivalent to morning astronomical → twilight; opposed to → dusk.

Etymology (EN): M.E. dawen (v.), from O.E. dagung, from dagian “to become day,” from root of dæg→ day.

Etymology (PE): Pegâh, from Mid.Pers. pa gâh, literally “soon; near the time (of sunrise),” from pa “to; for; in; on; with; by; according to,” O.Pers. upā, Av. upa “toward, with, on, in, in the time of” (cf. Skt. úpa “toward, together with, under, near to, on,” Gk. hypo “under, below,” L. sub “under,” Ger. auf, E. up; PIE *upo “under, up from under, over”) + gâh “time,” O.Pers. gāθu-, Av. gātav-, gātu- “place, throne, spot” (Skt. gátu- “going, motion; free space for moving; place of abode,” PIE *gwem- “to go, come”).
Sepidedam, from sepidé “whitish; dawn,” from sepid “white” (Mid.Pers. spêt, Av. spita- “white,” Skt. śveta- “white,” Lith. sviesti “to shine,” svaityti “to brighten,” P.Gmc. *khwitaz, O.E. hwit, E. white, Ger. weiss, PIE *kwintos/*kwindos “bright”) + dam “moment, time; to blow, breathe; smoke” (Mod./Mid.Pers. damidan “to blow, breathe,” 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”).
Bâmdâd, from Mid.Pers. bâmdât, Av. bāmya- “the dawn,” from bā- “to shine” (cf. Skt. bhā- “light, brightness,” Gk. phainomai “to appear, shine, gleam,” Arm. banam “to open, uncover,” PIE *bhā- “to shine”).

NASA’s mission to explore the two largest objects in the → asteroid belt, the asteroid Vesta and the → dawarf planet Ceres, gathering data relating to their composition, internal structure, density and shape. Launched in September 2007, Dawn entered the orbit of → Vesta in July 2011 and spent 16 months there before leaving for → Ceres. It entered Ceres orbit on March 6, 2015. The Dawn spacecraft is made of aluminium and graphite composite, it has a dry mass of 747.1 kg and a mass of 1217.7 kg when fully fuelled prior to launch. The spacecraft is a box-shaped design measuring 1.64m × 1.27m × 1.77m. Dawn ran out of fuel on Nov. 1, 2018, but the spacecraft will continue to orbit Ceres for several decades.

See also: → dawn; → spacecraft.

NASA’s mission to explore the two largest objects in the → asteroid belt, the asteroid Vesta and the → dawarf planet Ceres, gathering data relating to their composition, internal structure, density and shape. Launched in September 2007, Dawn entered the orbit of → Vesta in July 2011 and spent 16 months there before leaving for → Ceres. It entered Ceres orbit on March 6, 2015. The Dawn spacecraft is made of aluminium and graphite composite, it has a dry mass of 747.1 kg and a mass of 1217.7 kg when fully fuelled prior to launch. The spacecraft is a box-shaped design measuring 1.64m × 1.27m × 1.77m. Dawn ran out of fuel on Nov. 1, 2018, but the spacecraft will continue to orbit Ceres for several decades.

See also: → dawn; → spacecraft.

The length of time it takes Earth (or a planet) to rotate once on its axis relative to some external reference. The day is measured in several ways, depending on this reference, → sidereal day; → solar day; → mean solar day.

Etymology (EN): M.E., from O.E. dæg (cf. Ger. Tag, Swedish and Danish dag “day”), from PIE base *dhegh- “to burn.” Not related to L. dies “day” (from *dyeu- “to shine,” → diurnal), but rather to Av. dag- “to burn,” dažaiti “burns,” Mod.Pers. dâq “hot,” Skt. dah- “to burn,” dáhati, Gk. tephra “ash,” L. fovere “to boil,” Albanian djeg “to burn,” Russ. žeč’ “to burn,” Lith. dagas “hot season,” degti “to burn,” O.Prus. dagis “summer.”

Etymology (PE): Ruz “day,” from Mid.Pers. rôc, O.Pers. raucah-, Av. raocah- “light, luminous; daylight,” Skt. roka- “brightness, light,” cognate with Gk. leukos “white, clear,” L. lux “light” (also lumen, luna), PIE base *leuk- “light, brightness”. The Persian words rowšan “bright, clear,” foruq “light,” and afruxtan “to light, kindle” also belong to this family, as well as the E. light, Ger. Licht, and Fr. lumière.

The length of time it takes Earth (or a planet) to rotate once on its axis relative to some external reference. The day is measured in several ways, depending on this reference, → sidereal day; → solar day; → mean solar day.

Etymology (EN): M.E., from O.E. dæg (cf. Ger. Tag, Swedish and Danish dag “day”), from PIE base *dhegh- “to burn.” Not related to L. dies “day” (from *dyeu- “to shine,” → diurnal), but rather to Av. dag- “to burn,” dažaiti “burns,” Mod.Pers. dâq “hot,” Skt. dah- “to burn,” dáhati, Gk. tephra “ash,” L. fovere “to boil,” Albanian djeg “to burn,” Russ. žeč’ “to burn,” Lith. dagas “hot season,” degti “to burn,” O.Prus. dagis “summer.”

Etymology (PE): Ruz “day,” from Mid.Pers. rôc, O.Pers. raucah-, Av. raocah- “light, luminous; daylight,” Skt. roka- “brightness, light,” cognate with Gk. leukos “white, clear,” L. lux “light” (also lumen, luna), PIE base *leuk- “light, brightness”. The Persian words rowšan “bright, clear,” foruq “light,” and afruxtan “to light, kindle” also belong to this family, as well as the E. light, Ger. Licht, and Fr. lumière.

A → meteor detected using → radar techniques during daylight or when skies are cloudy.

See also: → day; → light; → meteor.

A → meteor detected using → radar techniques during daylight or when skies are cloudy.

See also: → day; → light; → meteor.

A system of adjusting the official local time in some countries in order to provide a better match between the hours of daylight and the active hours of work and school. The “saved” daylight is spent on evening activities which get more daylight, rather than being “wasted” while people sleep past dawn. Although known also as summer time, it includes the spring season and nearly half of autumn.

Etymology (EN): → day; → light; saving, from save, from O.Fr. sauver, from L.L. salvare “to secure,” from L. salvus “safe,” PIE *solwos, from base *sol- “whole” (cf. O.Pers. haruva-, Av. haurva- “whole, intact,” Mod.Pers. har “every, all; any,” Skt. sarva- “whole, entire,” Gk. holos “whole”); → time.

Etymology (PE): Vaxt, written vaqtوقت but pronounced vaxtوخت, is a Pers. word meaning “portion (of time)”. Its variants and related words in Mod./Mid.Pers. are: baxt “what is alloted, fate, fortune,” baxš “portion, part, division,” baxšidan, baxtan “to divide, distribute, grant,” Av. base bag- “to attribute, allot, distribute,” baxš- “to apportion, divide, give to,”
baxta- “what is alloted (luck, fortune),” baxədra- “part, portion,” baγa- “master, god,” O.Pers. bāji- “tribute, tax,” cf. Skt. bhaj- “to share, divide, distribute, apportion,” bhájati “divides,” bhakta- “alloted; occupied with; a share; food or a meal, time of eating?,” Gk. phagein “to eat (to have a share of food)”; PIE base *bhag- “to share out, apportion.”
nur→ light.
anduzi, verbal noun of anduxtan “to save; acquire, gather,” from Mid.Pers. handôxtan, handôz- “to gain, acquire, amass,” from *ham-tuj-, from ham- “together,” → com- + *tuj- “to save, gather, (re)pay,” cf. Skt. tuj- “to promote, be strong, move quickly.”

A system of adjusting the official local time in some countries in order to provide a better match between the hours of daylight and the active hours of work and school. The “saved” daylight is spent on evening activities which get more daylight, rather than being “wasted” while people sleep past dawn. Although known also as summer time, it includes the spring season and nearly half of autumn.

Etymology (EN): → day; → light; saving, from save, from O.Fr. sauver, from L.L. salvare “to secure,” from L. salvus “safe,” PIE *solwos, from base *sol- “whole” (cf. O.Pers. haruva-, Av. haurva- “whole, intact,” Mod.Pers. har “every, all; any,” Skt. sarva- “whole, entire,” Gk. holos “whole”); → time.

Etymology (PE): Vaxt, written vaqtوقت but pronounced vaxtوخت, is a Pers. word meaning “portion (of time)”. Its variants and related words in Mod./Mid.Pers. are: baxt “what is alloted, fate, fortune,” baxš “portion, part, division,” baxšidan, baxtan “to divide, distribute, grant,” Av. base bag- “to attribute, allot, distribute,” baxš- “to apportion, divide, give to,”
baxta- “what is alloted (luck, fortune),” baxədra- “part, portion,” baγa- “master, god,” O.Pers. bāji- “tribute, tax,” cf. Skt. bhaj- “to share, divide, distribute, apportion,” bhájati “divides,” bhakta- “alloted; occupied with; a share; food or a meal, time of eating?,” Gk. phagein “to eat (to have a share of food)”; PIE base *bhag- “to share out, apportion.”
nur→ light.
anduzi, verbal noun of anduxtan “to save; acquire, gather,” from Mid.Pers. handôxtan, handôz- “to gain, acquire, amass,” from *ham-tuj-, from ham- “together,” → com- + *tuj- “to save, gather, (re)pay,” cf. Skt. tuj- “to promote, be strong, move quickly.”

The time interval when the Sun is above the horizon for a given position.

Etymology (EN): → day; → time.

Etymology (PE): Ruzhangâm, from ruz→ day + hangâm “time, hour, season,” Mid.Pers. hangâm “time, epoch, season,” Av. ham-gam- “to meet together,” from ham- “together,” → com- + gam- “to come; to go,” jamaiti “goes,” O.Pers. gam- “to come; to go,” 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.”

The time interval when the Sun is above the horizon for a given position.

Etymology (EN): → day; → time.

Etymology (PE): Ruzhangâm, from ruz→ day + hangâm “time, hour, season,” Mid.Pers. hangâm “time, epoch, season,” Av. ham-gam- “to meet together,” from ham- “together,” → com- + gam- “to come; to go,” jamaiti “goes,” O.Pers. gam- “to come; to go,” 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.”