An Etymological Dictionary of Astronomy and Astrophysics

→ D line.

See also: Na, → sodium; → D line.

→ D line.

See also: Na, → sodium; → D line.

Same as → Iota Orionis.

See also: From Ar. Nayyir al-Saif (نیر‌السیف) “the Bright One in the Sword,” from nayyir (نیر) “bright” + al-saif (السیف) “sword.”

Same as → Iota Orionis.

See also: From Ar. Nayyir al-Saif (نیر‌السیف) “the Bright One in the Sword,” from nayyir (نیر) “bright” + al-saif (السیف) “sword.”

The mathematical symbol for the → del operator.

See also: From Gk. nabla an ancient stringed instrument, triangular in shape and held like a harp, thus of the shape of ∇.

The mathematical symbol for the → del operator.

See also: From Gk. nabla an ancient stringed instrument, triangular in shape and held like a harp, thus of the shape of ∇.

An → adaptive optics instrument at the → European Southern Observatory (ESO) → Very Large Telescope (VLT) in service since 2001. It provides adaptive optics assisted imaging, imaging polarimetry, and → coronagraphy (only L) in the 1-5 μm range. It consists of two components: NAOS (Nasmyth Adaptive Optics System) and CONICA (COudé Near Infrared CAmera).

The adaptive optics system, NAOS, is equipped with both
→ <i><a class="linkVoir" href="/terms/visible/">visible</a></i> and → <i><a class="linkVoir" href="/terms/infrared/">infrared</a></i>→ <i><a class="linkVoir" href="/terms/wavefront-sensor/">wavefront sensor</a></i>s. 
It contains five → <i><a class="linkVoir" href="/terms/dichroic-filter/">dichroic filter</a></i>s 
which split the light from the telescope between CONICA and one of the
NAOS wavefront sensors. 

CONICA is the → <i><a class="linkVoir" href="/terms/infrared-camera/">infrared camera</a></i> and
→ <i><a class="linkVoir" href="/terms/spectrometer/">spectrometer</a></i> attached to NAOS and 
equipped with an Aladdin 1024 × 1024 pixel InSb array detector. It
possesses several wheels carrying masks/slits (including focal plane
coronagraphic masks), filters, polarizing elements,
→ <i><a class="linkVoir" href="/terms/grism/">grism</a></i>s and several
cameras allowing → <i><a class="linkVoir" href="/terms/diffraction-limited/">diffraction-limited</a></i>
sampling across the full wavelength range.

See also: NaCo, from NAOS (→ Nasmyth, → adaptive; → optics; → system) + CONICA (→ coude; → near-infrared; → camera).

An → adaptive optics instrument at the → European Southern Observatory (ESO) → Very Large Telescope (VLT) in service since 2001. It provides adaptive optics assisted imaging, imaging polarimetry, and → coronagraphy (only L) in the 1-5 μm range. It consists of two components: NAOS (Nasmyth Adaptive Optics System) and CONICA (COudé Near Infrared CAmera).

The adaptive optics system, NAOS, is equipped with both
→ <i><a class="linkVoir" href="/terms/visible/">visible</a></i> and → <i><a class="linkVoir" href="/terms/infrared/">infrared</a></i>→ <i><a class="linkVoir" href="/terms/wavefront-sensor/">wavefront sensor</a></i>s. 
It contains five → <i><a class="linkVoir" href="/terms/dichroic-filter/">dichroic filter</a></i>s 
which split the light from the telescope between CONICA and one of the
NAOS wavefront sensors. 

CONICA is the → <i><a class="linkVoir" href="/terms/infrared-camera/">infrared camera</a></i> and
→ <i><a class="linkVoir" href="/terms/spectrometer/">spectrometer</a></i> attached to NAOS and 
equipped with an Aladdin 1024 × 1024 pixel InSb array detector. It
possesses several wheels carrying masks/slits (including focal plane
coronagraphic masks), filters, polarizing elements,
→ <i><a class="linkVoir" href="/terms/grism/">grism</a></i>s and several
cameras allowing → <i><a class="linkVoir" href="/terms/diffraction-limited/">diffraction-limited</a></i>
sampling across the full wavelength range.

See also: NaCo, from NAOS (→ Nasmyth, → adaptive; → optics; → system) + CONICA (→ coude; → near-infrared; → camera).

The point on the celestial sphere
blocked from view by Earth and diametrically opposite to the → zenith (سرسو).

Etymology (EN): From M.L. nadir, from Ar. nazir “opposite to,” contraction of nazir as-samt (نظیر‌السمت), literally “opposite of the zenith,” from nazir “opposite” + samt “zenith.”

Etymology (PE): Pâsu, literally “direction of the foot,” from pâ “foot, step” (from
Mid.Pers. pâd, pây; Khotanese fad; Av. pad- “foot;” cf. Skt. pat; Gk. pos, genitive podos; L. pes, genitive pedis; P.Gmc. *fot; E. foot; Ger. Fuss; Fr. pied; PIE *pod-/*ped-) + su “direction, side” (from Mid.Pers. sôk “direction, side”).

The point on the celestial sphere
blocked from view by Earth and diametrically opposite to the → zenith (سرسو).

Etymology (EN): From M.L. nadir, from Ar. nazir “opposite to,” contraction of nazir as-samt (نظیر‌السمت), literally “opposite of the zenith,” from nazir “opposite” + samt “zenith.”

Etymology (PE): Pâsu, literally “direction of the foot,” from pâ “foot, step” (from
Mid.Pers. pâd, pây; Khotanese fad; Av. pad- “foot;” cf. Skt. pat; Gk. pos, genitive podos; L. pes, genitive pedis; P.Gmc. *fot; E. foot; Ger. Fuss; Fr. pied; PIE *pod-/*ped-) + su “direction, side” (from Mid.Pers. sôk “direction, side”).

1. A small metal spike with a broadened flat head, driven into wood to join things together or to serve as a hook.
   

   2. A horny covering on the upper surface of the tip of the finger and toe in humans and other primates (OxfordDictionaries.com).

Etymology (EN): M.E. nail(l), nayl(l), O.E. negel “metal pin,” nægl “fingernail;” cf. O.Norse nagl “fingernail,” nagli “metal nail;” O.H.G. nagel, M.Du. naghel, Du. nagel, Ger. Nagel “fingernail, small metal spike;” from PIE root *h3nog^h- “nail” (source also of Gk. onyx “claw, fingernail;” L. unguis (Fr. ongle, from diminutive L. ungula) “nail, claw;” Pers. nâxon, as below; Lithuanian naga “hoof,” nagutis “fingernail.”

Etymology (PE): 1) Mix, from Mid.Pers. mêx “peg, nail;” O.Pers. mayūxa- “doorknob;” cf. Skt. mayūkha- “peg for stretching the woof”).

2. Nâxon “nail;” Mid.Pers. nâxun “nail;” cf. Skt. nakha-; Russ. noga; E. nail, as above.

1. A small metal spike with a broadened flat head, driven into wood to join things together or to serve as a hook.
   

   2. A horny covering on the upper surface of the tip of the finger and toe in humans and other primates (OxfordDictionaries.com).

Etymology (EN): M.E. nail(l), nayl(l), O.E. negel “metal pin,” nægl “fingernail;” cf. O.Norse nagl “fingernail,” nagli “metal nail;” O.H.G. nagel, M.Du. naghel, Du. nagel, Ger. Nagel “fingernail, small metal spike;” from PIE root *h3nog^h- “nail” (source also of Gk. onyx “claw, fingernail;” L. unguis (Fr. ongle, from diminutive L. ungula) “nail, claw;” Pers. nâxon, as below; Lithuanian naga “hoof,” nagutis “fingernail.”

Etymology (PE): 1) Mix, from Mid.Pers. mêx “peg, nail;” O.Pers. mayūxa- “doorknob;” cf. Skt. mayūkha- “peg for stretching the woof”).

2. Nâxon “nail;” Mid.Pers. nâxun “nail;” cf. Skt. nakha-; Russ. noga; E. nail, as above.

Not accompanied or supplemented by anything else.

→ naked eye, → naked singularity, → naked-eye star.

Etymology (EN): O.E. nacod “nude;” cf. M.Du. naket, Du. naakt, Ger. nackt, cognate with Pers. berehné, as below, , from PIE base *neg^w-no- “naked.”

Etymology (PE): Berehné, from Mid.Pers. brahnag (with secondary -r-) “naked;” Av. maγna- “naked;” cf. Skt. nagná- “naked;” Gk. gumnos “naked;” L. nudus “naked;” Arm. merk “naked;” Lith. nuogas “naked;”

Not accompanied or supplemented by anything else.

→ naked eye, → naked singularity, → naked-eye star.

Etymology (EN): O.E. nacod “nude;” cf. M.Du. naket, Du. naakt, Ger. nackt, cognate with Pers. berehné, as below, , from PIE base *neg^w-no- “naked.”

Etymology (PE): Berehné, from Mid.Pers. brahnag (with secondary -r-) “naked;” Av. maγna- “naked;” cf. Skt. nagná- “naked;” Gk. gumnos “naked;” L. nudus “naked;” Arm. merk “naked;” Lith. nuogas “naked;”

The qualifier of an eye which is not assisted by any optical device, except for eyeglasses. Same as → unaided eye.

See also: → naked; → eye.

The qualifier of an eye which is not assisted by any optical device, except for eyeglasses. Same as → unaided eye.

See also: → naked; → eye.

A singularity that is not surrounded by an event horizon. It will therefore be visible and communicable to the outside world.

See also: → naked; → singularity.

A singularity that is not surrounded by an event horizon. It will therefore be visible and communicable to the outside world.

See also: → naked; → singularity.

A star visible without a telescope. In principle, stars down to about sixth magnitude are visible to the naked eye under ideal conditions, but this depends on the individual, the location, and the conditions of the observation.

See also: → naked; → eye; → star.

A star visible without a telescope. In principle, stars down to about sixth magnitude are visible to the naked eye under ideal conditions, but this depends on the individual, the location, and the conditions of the observation.

See also: → naked; → eye; → star.

A word or term by which somebody or something is commonly and distinctively known.

Etymology (EN): M.E., from O.E. nama; cf. O.H.G. namo, Ger. Name, Du. naam, Goth. namo “name;” cognate with Pers. nâm, as below.

Etymology (PE): Nâm “name;” Mid.Pers. nâm; O.Pers./Av. nâman-; cf. Skt. nama-;
Gk. onoma, onuma; L. nomen; PIE *nomen-.

A word or term by which somebody or something is commonly and distinctively known.

Etymology (EN): M.E., from O.E. nama; cf. O.H.G. namo, Ger. Name, Du. naam, Goth. namo “name;” cognate with Pers. nâm, as below.

Etymology (PE): Nâm “name;” Mid.Pers. nâm; O.Pers./Av. nâman-; cf. Skt. nama-;
Gk. onoma, onuma; L. nomen; PIE *nomen-.

A prefix denoting 10^-9.

See also: Combining form of Gk nanos “dwarf.”

A prefix denoting 10^-9.

See also: Combining form of Gk nanos “dwarf.”

The most stable carbon compound with an average particle size of about 5 → nanometers (50 Å). Nanodiamonds are synthesized by detonation of → T.N.T. and then gathering the soot that remains from the explosion.

See also: → nano-; → diamond.

The most stable carbon compound with an average particle size of about 5 → nanometers (50 Å). Nanodiamonds are synthesized by detonation of → T.N.T. and then gathering the soot that remains from the explosion.

See also: → nano-; → diamond.

Dust grains at → nanoscale sizes found in various astrophysical environments, such as → interstellar medium and → interplanetary space of our Solar System.

See also: → nano-; → dust.

Dust grains at → nanoscale sizes found in various astrophysical environments, such as → interstellar medium and → interplanetary space of our Solar System.

See also: → nano-; → dust.

A unit of length equal to 10^-9 m, or 10 Å.

See also: → nano-; → meter.

A unit of length equal to 10^-9 m, or 10 Å.

See also: → nano-; → meter.

A solid particle of → nanoscale size; e.g. a → nanodust grain.

See also: → nano-; → particle.

A solid particle of → nanoscale size; e.g. a → nanodust grain.

See also: → nano-; → particle.

The size range from approximately 1 → nanometer (nm) to 100 nm.

See also: → nano-; → scale.

The size range from approximately 1 → nanometer (nm) to 100 nm.

See also: → nano-; → scale.

The science and technology of producing and exploiting structures and systems at dimensions of roughly 1 to 100 → nanometers, that is those of single atoms and molecules. Materials with such minute structures possess mechanical, optical, chemical, magnetic or electronic properties not found in ordinary materials.

See also: → nano-; → technology.

The science and technology of producing and exploiting structures and systems at dimensions of roughly 1 to 100 → nanometers, that is those of single atoms and molecules. Materials with such minute structures possess mechanical, optical, chemical, magnetic or electronic properties not found in ordinary materials.

See also: → nano-; → technology.

A bright, blue star of V = 2.25 in the constellation → Puppis. It is a hot → supergiant of type O5, with a → surface temperature of 42,000 K, lying 1,400 → light-years away. Naos is one of the rarest → O-type stars visible to the → naked eye.

See also: Naos, from Gk. naos “ship,” since it used to be the Zeta star of Argo Navis (Jason’s vessel Argos) before becoming Zeta in Puppis.

A bright, blue star of V = 2.25 in the constellation → Puppis. It is a hot → supergiant of type O5, with a → surface temperature of 42,000 K, lying 1,400 → light-years away. Naos is one of the rarest → O-type stars visible to the → naked eye.

See also: Naos, from Gk. naos “ship,” since it used to be the Zeta star of Argo Navis (Jason’s vessel Argos) before becoming Zeta in Puppis.

Same as the → natural logarithm.

See also: After John Laird Napier (1550-1617), the Scottish mathematician who invented logarithm; → logarithm.

Same as the → natural logarithm.

See also: After John Laird Napier (1550-1617), the Scottish mathematician who invented logarithm; → logarithm.

Of little breadth or → width.

Etymology (EN): M.E., from O.E. nearu; cf. O.S. naru “narrow,” Du. naar “unpleasant;” akin to Ger. Narbe “scar,” literally, “narrow mark.”

Etymology (PE): Bârik, from Mid.Pers. bârîk “narrow,” from O.Iranian *bāra-ya-ka-, from stem *bāra- “to cut;”
cf. Av. bāra- “edge, blade,” in ti&#382i-bāra- “sharp-edged,” from brī- “to cut, shave, shear;”
cf. Skt. bhrī- “to hurt, injure,” bhrinanti “they hurt;” O.C.S. briti “to shave;” PIE base *bhrē- “to cut, pierce.”

Of little breadth or → width.

Etymology (EN): M.E., from O.E. nearu; cf. O.S. naru “narrow,” Du. naar “unpleasant;” akin to Ger. Narbe “scar,” literally, “narrow mark.”

Etymology (PE): Bârik, from Mid.Pers. bârîk “narrow,” from O.Iranian *bāra-ya-ka-, from stem *bāra- “to cut;”
cf. Av. bāra- “edge, blade,” in ti&#382i-bāra- “sharp-edged,” from brī- “to cut, shave, shear;”
cf. Skt. bhrī- “to hurt, injure,” bhrinanti “they hurt;” O.C.S. briti “to shave;” PIE base *bhrē- “to cut, pierce.”

Optics: Of a filter, same as → interference filter.
Radio.: Encompassing a small frequency range, typically less than 300 Hz.

See also: → narrow; → band.

Optics: Of a filter, same as → interference filter.
Radio.: Encompassing a small frequency range, typically less than 300 Hz.

See also: → narrow; → band.

Photometry using narrow-band filters to isolate a particular spectroscopic line or molecular band.

See also: → narrow band; → photometry.

Photometry using narrow-band filters to isolate a particular spectroscopic line or molecular band.

See also: → narrow band; → photometry.

The outer region of a → quasar or an → active galactic nucleus displaying narrow spectral lines. Also called Type II AGN. See also → obscuring torus.

See also: → narrow; → line; → region.

The outer region of a → quasar or an → active galactic nucleus displaying narrow spectral lines. Also called Type II AGN. See also → obscuring torus.

See also: → narrow; → line; → region.

1. Of, in, or relating to the → nose.
   

   2. Phonetics: A → nasal consonant.

See also: Adjective, from → nose.

1. Of, in, or relating to the → nose.
   

   2. Phonetics: A → nasal consonant.

See also: Adjective, from → nose.

The interior of the → nose. It is the structure which extends from the external opening, the → nostrils, to the → pharynx, where it joins the respiratory system.

See also: → nasal; → cavity.

The interior of the → nose. It is the structure which extends from the external opening, the → nostrils, to the → pharynx, where it joins the respiratory system.

See also: → nasal; → cavity.

A consonant produced with air escaping through the → nose. For this to happen the → soft palate is lowered and at the same time the mouth passage blocked at some point, so that all the air is pushed out of the nose. Examples of this sound include the English sounds [m], [n], and [ng].

See also: → nasal; → consonant.

A consonant produced with air escaping through the → nose. For this to happen the → soft palate is lowered and at the same time the mouth passage blocked at some point, so that all the air is pushed out of the nose. Examples of this sound include the English sounds [m], [n], and [ng].

See also: → nasal; → consonant.

A lunar → impact crater that is located in the southern part of the Moon’s near side. Latitude: 41.0°S, longitude: 0.2°E, diameter: 52 km, depth: 3.35 km.

See also: Named after the Iranian mathematician and astronomer Nasireddin Tusi (1201-1274), → Nasireddin couple.

A lunar → impact crater that is located in the southern part of the Moon’s near side. Latitude: 41.0°S, longitude: 0.2°E, diameter: 52 km, depth: 3.35 km.

See also: Named after the Iranian mathematician and astronomer Nasireddin Tusi (1201-1274), → Nasireddin couple.

A theorem put forward by the 13th century Persian mathematician and astronomer Nasireddin Tusi to generate linear motion from a combination of circular motions, and thus improve the geocentric model of Ptolemy. A circle of radius R rotates inside a circle of radius 2R. The smaller circle rotates at twice the speed of the larger one and in opposite direction. The initial tangent point will travel in linear motion back and forth along the diameter of the larger circle. A particular case of → hypocycloid curves.

See also: Named for Nasireddin Tusi (1201-1274), director of Marâgha observatory who created the Ilkhani zij; → couple.

A theorem put forward by the 13th century Persian mathematician and astronomer Nasireddin Tusi to generate linear motion from a combination of circular motions, and thus improve the geocentric model of Ptolemy. A circle of radius R rotates inside a circle of radius 2R. The smaller circle rotates at twice the speed of the larger one and in opposite direction. The initial tangent point will travel in linear motion back and forth along the diameter of the larger circle. A particular case of → hypocycloid curves.

See also: Named for Nasireddin Tusi (1201-1274), director of Marâgha observatory who created the Ilkhani zij; → couple.

In an altazimuth-mounted telescope, a focal point to one side of the tube, created by placing a third deflecting mirror in the optical path. This extra mirror directs the beam along the altitude axis, and through a hole in the supporting trunnions. Nasmyth focus has the advantage of remaining at a fixed position relative to the telescope wherever the instrument is pointed. Moreover, bulky or heavy instruments can be mounted there on a permanent platform, which rotates only in azimuth.

Etymology (EN): Named after the inventor James Nasmyth (1808-1890), who first used it in the 19-th century.

In an altazimuth-mounted telescope, a focal point to one side of the tube, created by placing a third deflecting mirror in the optical path. This extra mirror directs the beam along the altitude axis, and through a hole in the supporting trunnions. Nasmyth focus has the advantage of remaining at a fixed position relative to the telescope wherever the instrument is pointed. Moreover, bulky or heavy instruments can be mounted there on a permanent platform, which rotates only in azimuth.

Etymology (EN): Named after the inventor James Nasmyth (1808-1890), who first used it in the 19-th century.

A large body of people united by common descent, history, culture, or language, inhabiting a particular state. → national, → international.

Etymology (EN): Nation, from O.Fr. nacion, from L. nationem (nom. natio) “nation, stock, race,” literally “that which has been born,” from natus, p.p. of nasci “to be born;” cognate with Pers. zâdan, → generate.

Etymology (PE): Nafân, from Av. nāfaēna- “family,” hama.nāfaēna- “of the same family,” related to nāfa- “near relationship, family, navel,” napāt- “grandson” (Mod.Pers. navé “grandson”); cf.
Mid.Pers. nâf “family,” nâfag “navel,” naft “descendant, " Parthian nap “family” (Mod.Pers. nâf “navel”); Sogd. nâf “country;” Sorani Kurd. natawa (Kurmanji Kurd. netewe) “family, race, nation,” from *nafata (with metathesis);
cf. Skt. nábhi- “nave, navel, central part; home, origin;” Gk. anepsios “cousin, sister’s son;” L. nepos “grandchild; descendant;” O.Lithuanian neputis “grandson; nephew;” O.H.G. nabalo “navel;” Ger. Nabel “navel;” O.E. nefa “grandson; descendant;”

• -ân suffix denoting family relationship, as in Bâbakân “family of Bâbak.”

A large body of people united by common descent, history, culture, or language, inhabiting a particular state. → national, → international.

Etymology (EN): Nation, from O.Fr. nacion, from L. nationem (nom. natio) “nation, stock, race,” literally “that which has been born,” from natus, p.p. of nasci “to be born;” cognate with Pers. zâdan, → generate.

Etymology (PE): Nafân, from Av. nāfaēna- “family,” hama.nāfaēna- “of the same family,” related to nāfa- “near relationship, family, navel,” napāt- “grandson” (Mod.Pers. navé “grandson”); cf.
Mid.Pers. nâf “family,” nâfag “navel,” naft “descendant, " Parthian nap “family” (Mod.Pers. nâf “navel”); Sogd. nâf “country;” Sorani Kurd. natawa (Kurmanji Kurd. netewe) “family, race, nation,” from *nafata (with metathesis);
cf. Skt. nábhi- “nave, navel, central part; home, origin;” Gk. anepsios “cousin, sister’s son;” L. nepos “grandchild; descendant;” O.Lithuanian neputis “grandson; nephew;” O.H.G. nabalo “navel;” Ger. Nabel “navel;” O.E. nefa “grandson; descendant;”

• -ân suffix denoting family relationship, as in Bâbakân “family of Bâbak.”

Of, involving, or relating to a nation as a whole. → National Aeronautics and Space Administration (NASA).

See also: → nation; → -al.

Of, involving, or relating to a nation as a whole. → National Aeronautics and Space Administration (NASA).

See also: → nation; → -al.

A federal agency of the United States government founded in 1958 for civil aeronautical research and space exploration, superseding the National Advisory Committee for Aeronautics (NACA). Its goals include improving human understanding of the universe, the solar system, and Earth and establishing a permanent human presence in space. NASA is headquarted at Washington, D.C., and operates several research, development, and test facilities, as follows alphabetically: 1) Ames Research Center; 2) Dryden Flight Research Facility at Edwards, California, used for flight testing and as a landing site for the Space Shuttle; 3) Glenn Research Center at Cleveland, Ohio, concerned with aircraft and rocket propulsion; 4) Goddard Space Flight Center; 5) Jet Propulsion Laboratory; 6) Johnson Space center; 7) Kennedy Space Center; 8) Langley Research Center at Hampton, Virginia, which carries out research in aeronautics and space technology; 9) Marshall Space Flight Center; 10) the Space Telescope Science Institute; 11) Stennis Space Center, near Bay St Louis, Mississippi, for testing rocket engines; and 12) Wallops Flight Facility on Wallops Island, Virginia, which manages NASA’s sounding rocket and scientific balloon programs.

Etymology (EN): → national; → aeronautics; → space; administration, verbal noun of administer, from M.E. amynistre, from O.Fr. aministrer, from L. administrare “to serve, carry out, manage,” from → ad- “to” + ministrare “to serve,” from minister “servant, priest’s assistant,” from minus, minor “less,” hence “subordinate,” + comparative suffix *-teros.

Etymology (PE): Sâzmân, → organization; fazâyi pertaining to fazâ, → space; Âmrikâ “United State of America.”

A federal agency of the United States government founded in 1958 for civil aeronautical research and space exploration, superseding the National Advisory Committee for Aeronautics (NACA). Its goals include improving human understanding of the universe, the solar system, and Earth and establishing a permanent human presence in space. NASA is headquarted at Washington, D.C., and operates several research, development, and test facilities, as follows alphabetically: 1) Ames Research Center; 2) Dryden Flight Research Facility at Edwards, California, used for flight testing and as a landing site for the Space Shuttle; 3) Glenn Research Center at Cleveland, Ohio, concerned with aircraft and rocket propulsion; 4) Goddard Space Flight Center; 5) Jet Propulsion Laboratory; 6) Johnson Space center; 7) Kennedy Space Center; 8) Langley Research Center at Hampton, Virginia, which carries out research in aeronautics and space technology; 9) Marshall Space Flight Center; 10) the Space Telescope Science Institute; 11) Stennis Space Center, near Bay St Louis, Mississippi, for testing rocket engines; and 12) Wallops Flight Facility on Wallops Island, Virginia, which manages NASA’s sounding rocket and scientific balloon programs.

Etymology (EN): → national; → aeronautics; → space; administration, verbal noun of administer, from M.E. amynistre, from O.Fr. aministrer, from L. administrare “to serve, carry out, manage,” from → ad- “to” + ministrare “to serve,” from minister “servant, priest’s assistant,” from minus, minor “less,” hence “subordinate,” + comparative suffix *-teros.

Etymology (PE): Sâzmân, → organization; fazâyi pertaining to fazâ, → space; Âmrikâ “United State of America.”

Loyalty and devotion to a nation; especially: a sense of national consciousness exalting one nation above all others and placing primary emphasis on promotion of its culture and interests as opposed to those of other nations or supranational groups (Merriam-Webster.com).

See also: → national; → -ism.

Loyalty and devotion to a nation; especially: a sense of national consciousness exalting one nation above all others and placing primary emphasis on promotion of its culture and interests as opposed to those of other nations or supranational groups (Merriam-Webster.com).

See also: → national; → -ism.

1. National status; specifically: a legal relationship involving allegiance on the part of an individual and usually protection on the part of the state b : membership in a particular nation.
   

2. Membership in a particular nation (Merriam-Webster.com).

See also: → national; → -ity.

1. National status; specifically: a legal relationship involving allegiance on the part of an individual and usually protection on the part of the state b : membership in a particular nation.
   

2. Membership in a particular nation (Merriam-Webster.com).

See also: → national; → -ity.

The transfer of a major branch of industry or commerce from private to state ownership or control (OxfordDictionaries.com)

See also: → nationalize; → -tion.

The transfer of a major branch of industry or commerce from private to state ownership or control (OxfordDictionaries.com)

See also: → nationalize; → -tion.

1. To bring under the ownership or control of a nation, as industries and land (Dictionary.com).

See also: → national; → -ize.

1. To bring under the ownership or control of a nation, as industries and land (Dictionary.com).

See also: → national; → -ize.

Occurring in nature; not artificially prepared. → nature.

See also: Adj. of → nature.

Occurring in nature; not artificially prepared. → nature.

See also: Adj. of → nature.

Any frequency of small-amplitude oscillation for a system with a position of stable equilibrium and in the absence of external forces. In other words, the frequency of → free oscillation. Also called characteristic frequency.

See also: → natural; → frequency.

Any frequency of small-amplitude oscillation for a system with a position of stable equilibrium and in the absence of external forces. In other words, the frequency of → free oscillation. Also called characteristic frequency.

See also: → natural; → frequency.

The → sciences, as → botany, → mineralogy, or → zoology,
dealing with the study of all objects in → nature: used especially in reference to the beginnings of these sciences in former times (Dictionary.com).

See also: → natural; → history.

The → sciences, as → botany, → mineralogy, or → zoology,
dealing with the study of all objects in → nature: used especially in reference to the beginnings of these sciences in former times (Dictionary.com).

See also: → natural; → history.

Linguistics: A language that has evolved naturally as a means of communication among people, as opposed to → artificial language and → formal language (Dictionary.com).

See also: → natural; → language.

Linguistics: A language that has evolved naturally as a means of communication among people, as opposed to → artificial language and → formal language (Dictionary.com).

See also: → natural; → language.

The broadening of any spectral line due to the fact that excited levels have mean lives, which, by virtue of the uncertainty principle, implies a spread in the energy values.

See also: → natural; → line;
→ broadening.

The broadening of any spectral line due to the fact that excited levels have mean lives, which, by virtue of the uncertainty principle, implies a spread in the energy values.

See also: → natural; → line;
→ broadening.

The logarithm in which the → base is the → irrational number e = 2.718281828…. Also called → Napierian logarithm. The natural logarithm is denoted ln, an abbreviation of logarithmus naturalis. Natural logarithms are related to → common logarithms through: ln x = (1/M) log x, with M = (1/ln 10) ≅ 0.434294.

See also: → natural; → logarithm.

The logarithm in which the → base is the → irrational number e = 2.718281828…. Also called → Napierian logarithm. The natural logarithm is denoted ln, an abbreviation of logarithmus naturalis. Natural logarithms are related to → common logarithms through: ln x = (1/M) log x, with M = (1/ln 10) ≅ 0.434294.

See also: → natural; → logarithm.

Either a member of the set of positive integers 1, 2, 3, …, or the set of non-negative integers 0, 1, 2, 3, … There seems to be no general agreement about whether to include 0 in the set of natural numbers.

See also: → natural; → number.

Either a member of the set of positive integers 1, 2, 3, …, or the set of non-negative integers 0, 1, 2, 3, … There seems to be no general agreement about whether to include 0 in the set of natural numbers.

See also: → natural; → number.

Of a body or system, the period of → free oscillation.

See also: → natural; → period.

Of a body or system, the period of → free oscillation.

See also: → natural; → period.

A resonance such that the period of the driving force is the same as the natural period of the system.

See also: → natural; → resonance.

A resonance such that the period of the driving force is the same as the natural period of the system.

See also: → natural; → resonance.

A solar system → object that → revolves around a → primary body and is not man made.

See also: → natural; → satellite.

A solar system → object that → revolves around a → primary body and is not man made.

See also: → natural; → satellite.

A science that deals with matter, energy, their interrelations and transformations,
In other words, natural sciences are concerned with physical processes observable in nature. They can be divided into physical and biological sciences.

See also: → natural; → science.

A science that deals with matter, energy, their interrelations and transformations,
In other words, natural sciences are concerned with physical processes observable in nature. They can be divided into physical and biological sciences.

See also: → natural; → science.

Physical units of measurement defined in terms of universal physical constants in such a manner that some chosen physical constants (e.g. the speed of light, Planck’s constant, Boltzmann’s constant, etc.) are equal to unity. The use of natural units allows these constants to be omitted from mathematical equations, leading to simpler calculations.

See also: → natural; → unit.

Physical units of measurement defined in terms of universal physical constants in such a manner that some chosen physical constants (e.g. the speed of light, Planck’s constant, Boltzmann’s constant, etc.) are equal to unity. The use of natural units allows these constants to be omitted from mathematical equations, leading to simpler calculations.

See also: → natural; → unit.

Uranium as found in nature. It contains 0.7% uranium-235, 99.3% uranium-238, and a trace of uranium-234 by weight.

See also: → natural; → uranium.

Uranium as found in nature. It contains 0.7% uranium-235, 99.3% uranium-238, and a trace of uranium-234 by weight.

See also: → natural; → uranium.

Philosophy: 1) The view of the world that takes account only of natural elements and forces, excluding the supernatural or spiritual.

2. The belief that all phenomena are covered by laws of science and that all teleological explanations are therefore without value (Dictionary.com).

See also: → natural; → -ism.

Philosophy: 1) The view of the world that takes account only of natural elements and forces, excluding the supernatural or spiritual.

2. The belief that all phenomena are covered by laws of science and that all teleological explanations are therefore without value (Dictionary.com).

See also: → natural; → -ism.

The natural world as it exists without human beings or civilization.

Etymology (EN): M.E. natur(e), from O.Fr. nature from L. natura “the things at the outset, as it was when brought into existence; conditions of birth; essence, natural qualities,” from natus “born,” p.p. of nasci “to be born,” from PIE *gen- “to give birth, beget,” cognate with Pers. zâdan “to give birth,” as below.

Etymology (PE): Zâstâr, literally “birth,” from zâst past stem of [Dehxodâ] zâstan, variant of zâdan “to bring forth, give birth;” (Lâsgardi, Sorxeyi, Aftari) nestor “barren, sterile” (Mid.Pers. zâtan; Av. zan- “to bear, give birth to a child, be born,” infinitive zazāite, zāta- “born;” cf. Skt. janati “begets, bears;”
L. gignere “to beget,” nasci “to be born,” as above, PIE base *gen- “to give birth, beget”) + suffix -âr (forming verbal nouns as in raftâr, kerdâr, goftâr, didâr, jostâr, and so on; or forming accusative nouns, as in gereftâr, koštâr, etc.).

The natural world as it exists without human beings or civilization.

Etymology (EN): M.E. natur(e), from O.Fr. nature from L. natura “the things at the outset, as it was when brought into existence; conditions of birth; essence, natural qualities,” from natus “born,” p.p. of nasci “to be born,” from PIE *gen- “to give birth, beget,” cognate with Pers. zâdan “to give birth,” as below.

Etymology (PE): Zâstâr, literally “birth,” from zâst past stem of [Dehxodâ] zâstan, variant of zâdan “to bring forth, give birth;” (Lâsgardi, Sorxeyi, Aftari) nestor “barren, sterile” (Mid.Pers. zâtan; Av. zan- “to bear, give birth to a child, be born,” infinitive zazāite, zāta- “born;” cf. Skt. janati “begets, bears;”
L. gignere “to beget,” nasci “to be born,” as above, PIE base *gen- “to give birth, beget”) + suffix -âr (forming verbal nouns as in raftâr, kerdâr, goftâr, didâr, jostâr, and so on; or forming accusative nouns, as in gereftâr, koštâr, etc.).

The branch of practical astronomy concerned with the determination of position and direction on sea by observation of celestial objects.

Etymology (EN): Nautical, from M.Fr. nautique, from L. nauticus “pertaining to ships or sailors,” from Gk. nautikos, from nautes “sailor,” from naus “ship,” from PIE *nau- “boat;” cf. Pers. nâv “ship;” O.Pers./Av. *nāv-, O.Pers. nāviyā- “fleet;” Skt. nau-, nava- “ship, boat;” → astronomy.

Etymology (PE): Axtaršenâsi→ astronomy; daryâ-navardik, relating to daryâ-navardi “sea navigation,” from daryâ “sea” (Mid.Pers. daryâp variant zrah; O.Pers. drayah-; Av. zrayah- “sea;” cf. Skt. jráyas- “expanse, space, flat surface”)

• navardi, noun of navardidan, navardan “to travel, walk, pass by and over” + -ik, → -ic.

The branch of practical astronomy concerned with the determination of position and direction on sea by observation of celestial objects.

Etymology (EN): Nautical, from M.Fr. nautique, from L. nauticus “pertaining to ships or sailors,” from Gk. nautikos, from nautes “sailor,” from naus “ship,” from PIE *nau- “boat;” cf. Pers. nâv “ship;” O.Pers./Av. *nāv-, O.Pers. nāviyā- “fleet;” Skt. nau-, nava- “ship, boat;” → astronomy.

Etymology (PE): Axtaršenâsi→ astronomy; daryâ-navardik, relating to daryâ-navardi “sea navigation,” from daryâ “sea” (Mid.Pers. daryâp variant zrah; O.Pers. drayah-; Av. zrayah- “sea;” cf. Skt. jráyas- “expanse, space, flat surface”)

• navardi, noun of navardidan, navardan “to travel, walk, pass by and over” + -ik, → -ic.

One of the three twilight phases which is the period before sunrise and after sunset when the center of the Sun’s disk is between 6° and 12° below the horizon. This twilight phase is followed or preceded by → civil twilight. See also → astronomical twilight. In clear weather conditions, the horizon is faintly visible during this phase. Many of the brighter stars can also be seen, making it possible to use the position of the stars in relation to the horizon to navigate at sea. This is why it is called nautical twilight.

See also: → nautical astronomy; → twilight.

One of the three twilight phases which is the period before sunrise and after sunset when the center of the Sun’s disk is between 6° and 12° below the horizon. This twilight phase is followed or preceded by → civil twilight. See also → astronomical twilight. In clear weather conditions, the horizon is faintly visible during this phase. Many of the brighter stars can also be seen, making it possible to use the position of the stars in relation to the horizon to navigate at sea. This is why it is called nautical twilight.

See also: → nautical astronomy; → twilight.

One of a set of → differential equations that describes the motion of a → fluid as a function of → pressure, → density, total external force, and → viscosity. See also
→ Euler equation.

See also: Named after Claude-Louis Navier (1785-1836), a French engineer and physicist,
and George Gabriel Stokes, → stokes; → equation.

One of a set of → differential equations that describes the motion of a → fluid as a function of → pressure, → density, total external force, and → viscosity. See also
→ Euler equation.

See also: Named after Claude-Louis Navier (1785-1836), a French engineer and physicist,
and George Gabriel Stokes, → stokes; → equation.

Same as → nautical astronomy.

Etymology (EN): Navigational, adj. of navigation, from L. navigationem (nom. navigatio), from navigatus, p.p. of navigare “to sail, steer a ship,” from navis “ship,” cognate with Pers. nâv “ship,” as below, + root of agere “to drive,” → act; → astronomy.

Etymology (PE): Axtaršenâsi→ astronomy; nâvrâni “navigation,” from nâv “ship;” O.Pers./Av. *nāv-, O.Pers. nāviyā- “fleet;” cf. Skt. nau-, nava- “ship, boat” + râni verbal noun of rândan “to drive, to cause to go,” causative of raftan “to go, walk, proceed” (present tense stem row-, Mid.Pers. raftan, raw-, Proto-Iranian *rab/f- “to go; to attack”).

Same as → nautical astronomy.

Etymology (EN): Navigational, adj. of navigation, from L. navigationem (nom. navigatio), from navigatus, p.p. of navigare “to sail, steer a ship,” from navis “ship,” cognate with Pers. nâv “ship,” as below, + root of agere “to drive,” → act; → astronomy.

Etymology (PE): Axtaršenâsi→ astronomy; nâvrâni “navigation,” from nâv “ship;” O.Pers./Av. *nāv-, O.Pers. nāviyā- “fleet;” cf. Skt. nau-, nava- “ship, boat” + râni verbal noun of rândan “to drive, to cause to go,” causative of raftan “to go, walk, proceed” (present tense stem row-, Mid.Pers. raftan, raw-, Proto-Iranian *rab/f- “to go; to attack”).