An Etymological Dictionary of Astronomy and Astrophysics

Tide which occurs during the → first quarter and → third quarter of the → Moon when the pull of the Sun is at → right angles to that of the Moon.

Etymology (EN): Neap, from M.E. neep, from O.E. nepflod “neap tide” + → tide.

Etymology (PE): Kehkešan “small tide,” from keh- “small, little,” → low, + kešand, → tide.

Tide which occurs during the → first quarter and → third quarter of the → Moon when the pull of the Sun is at → right angles to that of the Moon.

Etymology (EN): Neap, from M.E. neep, from O.E. nepflod “neap tide” + → tide.

Etymology (PE): Kehkešan “small tide,” from keh- “small, little,” → low, + kešand, → tide.

Close; to a point or place not far away.

Etymology (EN): O.E. near “closer, nearer,” comparative of neah, neh “nigh.”

Etymology (PE): Nazdik, from Mid.Pers. nazdik “near,” from nazd “close” (Mid.Pers. nazd, nazdik “near,” nazdist “first;” O.Pers. ašna- “close;” Av. nazdišta- “nearest, next,” nazdyo “nearer to,” nas- “to come near, approach, reach;” cf. Skt. nédīyas- “closer, very close,”
nas- “to approach, to reach”) + -ik, → -ic.

Close; to a point or place not far away.

Etymology (EN): O.E. near “closer, nearer,” comparative of neah, neh “nigh.”

Etymology (PE): Nazdik, from Mid.Pers. nazdik “near,” from nazd “close” (Mid.Pers. nazd, nazdik “near,” nazdist “first;” O.Pers. ašna- “close;” Av. nazdišta- “nearest, next,” nazdyo “nearer to,” nas- “to come near, approach, reach;” cf. Skt. nédīyas- “closer, very close,”
nas- “to approach, to reach”) + -ik, → -ic.

The longest wavelengths of the ultraviolet region, which are adjacent to the visible, from 200 to 350 nm.

See also: → near; → ultraviolet.

The longest wavelengths of the ultraviolet region, which are adjacent to the visible, from 200 to 350 nm.

See also: → near; → ultraviolet.

An → asteroid whose orbit lies partly between 0.983 and 1.3 → astronomical units from the Sun, so that it passes close to the Earth. Currently thousands of near-Earth asteroids are known, ranging in size up to about 30 km. Among them,
there are between 500 and 1,000 such asteroids larger than one km in diameter. They are divided into three subclasses: → Amor asteroids, → Apollo asteroids, and → Aten asteroids. See also → near-Earth object.

See also: → near; → earth; → asteroid.

An → asteroid whose orbit lies partly between 0.983 and 1.3 → astronomical units from the Sun, so that it passes close to the Earth. Currently thousands of near-Earth asteroids are known, ranging in size up to about 30 km. Among them,
there are between 500 and 1,000 such asteroids larger than one km in diameter. They are divided into three subclasses: → Amor asteroids, → Apollo asteroids, and → Aten asteroids. See also → near-Earth object.

See also: → near; → earth; → asteroid.

An → asteroid, → comet, or large → meteoroid whose orbit brings it exceptionally close to the Earth, and which may therefore pose a collision danger. Most such objects are in orbits around the Sun with → perihelion distance less than 1.3 → astronomical units. See also → near-Earth asteroid.

See also: → near; → earth; → object.

An → asteroid, → comet, or large → meteoroid whose orbit brings it exceptionally close to the Earth, and which may therefore pose a collision danger. Most such objects are in orbits around the Sun with → perihelion distance less than 1.3 → astronomical units. See also → near-Earth asteroid.

See also: → near; → earth; → object.

That region of the → electromagnetic spectrum covering shorter infrared wavelengths. It contains the → infrared windows between about 0.8 and 8 → microns, but the longer wavelength limit is not well defined. See also: → infrared radiation, → mid-infrared, → far-infrared, → submillimeter radiation.

See also: → near; → infrared.

That region of the → electromagnetic spectrum covering shorter infrared wavelengths. It contains the → infrared windows between about 0.8 and 8 → microns, but the longer wavelength limit is not well defined. See also: → infrared radiation, → mid-infrared, → far-infrared, → submillimeter radiation.

See also: → near; → infrared.

1. A cloud of gas and dust in the interstellar space. There are three general types: → emission nebulae,
   → reflection nebulae, and → dark nebulae.
   

2. A celestial body appearing nebulous or fuzzy when seen with the telescope. Formerly, galaxies, which appeared nebular but are constituted of billions of stars, were not distinguished from truly nebular objects, made of gas and dust.

Etymology (EN): From L. nebula “mist,” nimbus “rainstorm, rain cloud;” cognate with Av. napta- “moist,” nabās-câ- “cloud,” nabah- “sky;” Pers. nam “moisture;” cf. Gk. nephos “cloud, mass of clouds,” nephele “cloud;” Skt. nábhas- “moisture, cloud, mist;” O.H.G. nebul; Ger. Nebel “fog;” O.E. nifol “dark;” PIE base *nebh- “cloud, vapor, fog, moist, sky.”

Etymology (PE): Miq “nebula” (used by Tusi, in Pers. translation of Sufi’s “Book of Fixed Stars”),
variants meh “fog,” mož, Tabari miyâ, Lori/Laki (kara) mozy, Ossetic mig/megæ,
from Mid.Pers. mēq “cloud, mist;” Av. mēγa- “cloud;” cf. Skt. meghá- “cloud, overcast weather;” Gk. omikhle “mist;” Lith. miglà “mist, haze;” PIE base *mighlā- “cloud.”

1. A cloud of gas and dust in the interstellar space. There are three general types: → emission nebulae,
   → reflection nebulae, and → dark nebulae.
   

2. A celestial body appearing nebulous or fuzzy when seen with the telescope. Formerly, galaxies, which appeared nebular but are constituted of billions of stars, were not distinguished from truly nebular objects, made of gas and dust.

Etymology (EN): From L. nebula “mist,” nimbus “rainstorm, rain cloud;” cognate with Av. napta- “moist,” nabās-câ- “cloud,” nabah- “sky;” Pers. nam “moisture;” cf. Gk. nephos “cloud, mass of clouds,” nephele “cloud;” Skt. nábhas- “moisture, cloud, mist;” O.H.G. nebul; Ger. Nebel “fog;” O.E. nifol “dark;” PIE base *nebh- “cloud, vapor, fog, moist, sky.”

Etymology (PE): Miq “nebula” (used by Tusi, in Pers. translation of Sufi’s “Book of Fixed Stars”),
variants meh “fog,” mož, Tabari miyâ, Lori/Laki (kara) mozy, Ossetic mig/megæ,
from Mid.Pers. mēq “cloud, mist;” Av. mēγa- “cloud;” cf. Skt. meghá- “cloud, overcast weather;” Gk. omikhle “mist;” Lith. miglà “mist, haze;” PIE base *mighlā- “cloud.”

Of or relating to or resembling a → nebula.

See also: → nebula + → -ar.

Of or relating to or resembling a → nebula.

See also: → nebula + → -ar.

The part of a nebular object’s → spectrum that is created by → free-free emission.

See also: → nebular; → continuum.

The part of a nebular object’s → spectrum that is created by → free-free emission.

See also: → nebular; → continuum.

The hypothesis first put forward in the 18-th century that the solar system formed from a primeval nebula around the Sun. Same as the → Kant-Laplace hypothesis.

See also: → nebular; → hypothesis.

The hypothesis first put forward in the 18-th century that the solar system formed from a primeval nebula around the Sun. Same as the → Kant-Laplace hypothesis.

See also: → nebular; → hypothesis.

A → forbidden line that is found in the spectra of → interstellar  → ionized gas. The nebular lines are emitted by several
atomic species (e.g. O, O⁺, O⁺⁺, N⁺, S⁺⁺) and correspond to the → transition from the electronic → metastable state ¹D to the → ground state  ³P. Examples are the doubly ionized oxygen lines [O III] at 4959 and 5007 Å (→ [O III] doublet) and the ionized nitrogen doublet [N II] at 6548 and 6583 Å. See also → auroral line; → transauroral line.

See also: → nebular; → line.

A → forbidden line that is found in the spectra of → interstellar  → ionized gas. The nebular lines are emitted by several
atomic species (e.g. O, O⁺, O⁺⁺, N⁺, S⁺⁺) and correspond to the → transition from the electronic → metastable state ¹D to the → ground state  ³P. Examples are the doubly ionized oxygen lines [O III] at 4959 and 5007 Å (→ [O III] doublet) and the ionized nitrogen doublet [N II] at 6548 and 6583 Å. See also → auroral line; → transauroral line.

See also: → nebular; → line.

A type of eruptive variable star, mainly young FU Orionis and T Tauri types, associated with nebulosity.

See also: → nebular; → variable.

A type of eruptive variable star, mainly young FU Orionis and T Tauri types, associated with nebulosity.

See also: → nebular; → variable.

A hypothetical element, the existence of which was postulated in the nineteenth century to account for unidentified emission lines
(e.g. at 3727 and 5007 Å) in the spectra of some luminous nebulae. It was also believed that this element had a small atomic weight. However, the advances of chemistry and physics showed that all the light elements were known and there was no place for this elusive element. Those unidentified lines have now been shown to come from known elements, but they are not usually observable under laboratory conditions. → forbidden lines.

See also: From nebul(a), → nebula, + -ium L. neuter suffix.

A hypothetical element, the existence of which was postulated in the nineteenth century to account for unidentified emission lines
(e.g. at 3727 and 5007 Å) in the spectra of some luminous nebulae. It was also believed that this element had a small atomic weight. However, the advances of chemistry and physics showed that all the light elements were known and there was no place for this elusive element. Those unidentified lines have now been shown to come from known elements, but they are not usually observable under laboratory conditions. → forbidden lines.

See also: From nebul(a), → nebula, + -ium L. neuter suffix.

1. A nebulous form, shape, or mass.
   

2. The state or condition of being nebulous.
   

3. A fuzzy celestial object, constituted of gas and dust, generally part of a larger → nebula.

See also: → nebulous; → -ity.

1. A nebulous form, shape, or mass.
   

2. The state or condition of being nebulous.
   

3. A fuzzy celestial object, constituted of gas and dust, generally part of a larger → nebula.

See also: → nebulous; → -ity.

1. Hazy, vague, indistinct, or confused.
   

2. Cloudy or cloudlike.
   

3. Of or resembling a nebula or nebulae; nebular (Dictionary.com).

See also: → nebula; → -ous.

1. Hazy, vague, indistinct, or confused.
   

2. Cloudy or cloudlike.
   

3. Of or resembling a nebula or nebulae; nebular (Dictionary.com).

See also: → nebula; → -ous.

1. Being essential or indispensable.
   

2. Logic, Math.: A condition which must hold for a result to be true, but which does not guarantee it to be true. → if and only if.

Etymology (EN): M.E. necessaire, from L. necessarius “unavoidable,” , from necesse “unavoidable, indispensable,” from ne- “not,” → un-, + cedere “to withdraw, go away, yield,” → precession.

Etymology (PE): Bâyesté, p.p. of bây-, bâyestan “to be necessary,” from Mid.Pers. abây-, abâyistan “to be necessary” (abâyišn “necessity,” abâyišnig “necessary”), from Proto-Ir. *upa-aya- “to reach,” from upa-, → hypo-, + ay- “to go, to come,” → precession.

1. Being essential or indispensable.
   

2. Logic, Math.: A condition which must hold for a result to be true, but which does not guarantee it to be true. → if and only if.

Etymology (EN): M.E. necessaire, from L. necessarius “unavoidable,” , from necesse “unavoidable, indispensable,” from ne- “not,” → un-, + cedere “to withdraw, go away, yield,” → precession.

Etymology (PE): Bâyesté, p.p. of bây-, bâyestan “to be necessary,” from Mid.Pers. abây-, abâyistan “to be necessary” (abâyišn “necessity,” abâyišnig “necessary”), from Proto-Ir. *upa-aya- “to reach,” from upa-, → hypo-, + ay- “to go, to come,” → precession.

If event A must occur for event B to occur, then it is said that A is → necessary for B. If event A may cause B but there could be some other cause as well, then it is said that A is sufficient to cause B. See also → if and only if (iff).

See also: → necessary; → and; → sufficient; → condition.

If event A must occur for event B to occur, then it is said that A is → necessary for B. If event A may cause B but there could be some other cause as well, then it is said that A is sufficient to cause B. See also → if and only if (iff).

See also: → necessary; → and; → sufficient; → condition.

Logic: A → proposition if its → denial is self-contradictory. Also called “logical truth” and “non-contingent truth.”

See also: → necessary; → truth.

Logic: A → proposition if its → denial is self-contradictory. Also called “logical truth” and “non-contingent truth.”

See also: → necessary; → truth.

1. The fact of being necessary or indispensable.
   

2. Something necessary or indispensable.

See also: → necessary; → -ity.

1. The fact of being necessary or indispensable.
   

2. Something necessary or indispensable.

See also: → necessary; → -ity.

The part of a person’s or animal’s → body that connecting the → head to the rest of the body.

Etymology (EN): M.E. nekke, from O.E. hnecca, cognate with Du. nek “the nape of the neck;” Ger. Nacken, O.Norse hnakki “the nape of the neck.”

Etymology (PE): Gardan “neck;” related to geri, geribân “collar,” gerivé “low hill,” galu “throat;” Mid.Pers. gartan “neck,” galôg, griv “throat;” Av. grīvā- “neck;” cf. Skt. gala- “throat, neck;” Gk. bora “food;” L. gula “throat” (Fr. gueule “(animal) mouth”), gluttire “to gulp down,” vorare “to devour;” PIE base *g^wer- “to swallow, devour.” L. gula; cf. Mod.Pers. galu “throat.”

The part of a person’s or animal’s → body that connecting the → head to the rest of the body.

Etymology (EN): M.E. nekke, from O.E. hnecca, cognate with Du. nek “the nape of the neck;” Ger. Nacken, O.Norse hnakki “the nape of the neck.”

Etymology (PE): Gardan “neck;” related to geri, geribân “collar,” gerivé “low hill,” galu “throat;” Mid.Pers. gartan “neck,” galôg, griv “throat;” Av. grīvā- “neck;” cf. Skt. gala- “throat, neck;” Gk. bora “food;” L. gula “throat” (Fr. gueule “(animal) mouth”), gluttire “to gulp down,” vorare “to devour;” PIE base *g^wer- “to swallow, devour.” L. gula; cf. Mod.Pers. galu “throat.”

A slender pointed piece of metal, usually steel. → magnetic needle.

Etymology (EN): M.E. nedle, O.E. naeðlæ, nedlæ
(cf. O.S. nathla, O.N. nal, O.Fris. nedle, O.H.G. nadala, Ger. Nadel); PIE root *(s)ne- “to sew, to spin;” cf. Skt. snayati “wraps up;” Gk. nein “to spin;” L. nere “to spin.”

Etymology (PE): Suzan, Mid.Pers. sôzan, sucan, related to sok “pointed stick for driving cattle;” Av. sūkā- “needle;” cf. Skt. sūcī- “sting;” L. cuneus “wedge;” PIE base kū- “sharp; spike.”

A slender pointed piece of metal, usually steel. → magnetic needle.

Etymology (EN): M.E. nedle, O.E. naeðlæ, nedlæ
(cf. O.S. nathla, O.N. nal, O.Fris. nedle, O.H.G. nadala, Ger. Nadel); PIE root *(s)ne- “to sew, to spin;” cf. Skt. snayati “wraps up;” Gk. nein “to spin;” L. nere “to spin.”

Etymology (PE): Suzan, Mid.Pers. sôzan, sucan, related to sok “pointed stick for driving cattle;” Av. sūkā- “needle;” cf. Skt. sūcī- “sting;” L. cuneus “wedge;” PIE base kū- “sharp; spike.”

1. To deny the existence or truth of.
   

2. To cause to be ineffective or invalid.

Etymology (EN): From L. negatus p.p. of negare “to say ’no’, deny,” from Old L. nec “not,” from PIE base *ne- “no, not.”

Etymology (PE): Nâyidan infinitive from nâ “no, not,” variants na, ni, ma- (prohitive); from Mid.Pers. nê, ma “no, not;” O.Pers. naiy, nai “not;” Av. nôit, naē “not;” cf. Skt. ná “not;” cf. L. ne-, in-, un-; Gk. ni; Lith. nè; O.C.S. ne “not;” PIE *ne-, as above.

1. To deny the existence or truth of.
   

2. To cause to be ineffective or invalid.

Etymology (EN): From L. negatus p.p. of negare “to say ’no’, deny,” from Old L. nec “not,” from PIE base *ne- “no, not.”

Etymology (PE): Nâyidan infinitive from nâ “no, not,” variants na, ni, ma- (prohitive); from Mid.Pers. nê, ma “no, not;” O.Pers. naiy, nai “not;” Av. nôit, naē “not;” cf. Skt. ná “not;” cf. L. ne-, in-, un-; Gk. ni; Lith. nè; O.C.S. ne “not;” PIE *ne-, as above.

1. The act of denying; → denial.
   

2. The absence or → opposite of something that is actual, positive, or affirmative.
   

3. A → negative statement, idea, doctrine; a contradiction, refutation, or rebuttal.
   

4. Logic: If p is a → proposition, then the statement “not p,” denoted ¬ p, is the negation or opposite of p. If p is “It is sunny,” then ¬ p is “It is not sunny.” If p is → true, then ¬ p is → false, and vice versa.

See also: Verbal noun of → negate.

1. The act of denying; → denial.
   

2. The absence or → opposite of something that is actual, positive, or affirmative.
   

3. A → negative statement, idea, doctrine; a contradiction, refutation, or rebuttal.
   

4. Logic: If p is a → proposition, then the statement “not p,” denoted ¬ p, is the negation or opposite of p. If p is “It is sunny,” then ¬ p is “It is not sunny.” If p is → true, then ¬ p is → false, and vice versa.

See also: Verbal noun of → negate.

1. General: Expressing, containing, or consisting of a negation, refusal, or denial.
   

2. Math.: Of or relating to a quantity less than zero. Of or relating to the sign (-).
   

3. Physics: Of or relating to an electric charge of the same sign as that of an electron.
   

4. Photography: Having dark for light and light for dark.
   

5. Opposite of → positive.
   

See also:
→ negative charge, → negative correlation, → negative crystal, → negative feedback, → negative lens, → negative number, → negative polarization, → negative pressure, → negative skewness.

Etymology (EN): From O.Fr. negatif (fem. negative), from L. negativus, “denying, inhibiting (legal actions); denied/refused; negative,” from negare “to refuse, say ’no’” from Old L. nec “not”, from Italic base *nek- “not,” from PIE base *ne- “no, not.”

Etymology (PE): Nâyidâr, from nâyidan, → negate, on the model of xaridâr, foruxtâr, xâstâr, virâstâr, etc.

1. General: Expressing, containing, or consisting of a negation, refusal, or denial.
   

2. Math.: Of or relating to a quantity less than zero. Of or relating to the sign (-).
   

3. Physics: Of or relating to an electric charge of the same sign as that of an electron.
   

4. Photography: Having dark for light and light for dark.
   

5. Opposite of → positive.
   

See also:
→ negative charge, → negative correlation, → negative crystal, → negative feedback, → negative lens, → negative number, → negative polarization, → negative pressure, → negative skewness.

Etymology (EN): From O.Fr. negatif (fem. negative), from L. negativus, “denying, inhibiting (legal actions); denied/refused; negative,” from negare “to refuse, say ’no’” from Old L. nec “not”, from Italic base *nek- “not,” from PIE base *ne- “no, not.”

Etymology (PE): Nâyidâr, from nâyidan, → negate, on the model of xaridâr, foruxtâr, xâstâr, virâstâr, etc.

An electric charge that has the same sign as the electron.

See also: → negative; → charge.

An electric charge that has the same sign as the electron.

See also: → negative; → charge.

A correlation between two variables such that as one variable’s values tend to increase, the other variable’s values tend to decrease.

See also: → negative; → correlation.

A correlation between two variables such that as one variable’s values tend to increase, the other variable’s values tend to decrease.

See also: → negative; → correlation.

A uniaxial, birefringent crystal in which the velocity of the extraordinary ray surpasses that of the ordinary ray.

See also: → negative; → crystal.

A uniaxial, birefringent crystal in which the velocity of the extraordinary ray surpasses that of the ordinary ray.

See also: → negative; → crystal.

A → feedback process in which the → output reacts on the → input so as to reduce the initial → effect.

See also: → negative; → feedback.

A → feedback process in which the → output reacts on the → input so as to reduce the initial → effect.

See also: → negative; → feedback.

Same as → divergent lens.

See also: → negative; → lens.

Same as → divergent lens.

See also: → negative; → lens.

A → real number that is less than zero. A negative number is indicated by the → minus sign.

See also: → negative; → number.

A → real number that is less than zero. A negative number is indicated by the → minus sign.

See also: → negative; → number.

A type of polarization in which the direction of polarization becomes reversed.

See also: → negative; → polarization.

A type of polarization in which the direction of polarization becomes reversed.

See also: → negative; → polarization.

A kind of pressure that contrarily to ordinary pressure pushes inward. In contrast with the → Newtonian mechanics, in → general relativity there are situations in which pressure can be negative. Positive pressure gives rise to attractive gravity, whereas negative pressure creates → repulsive gravity.

See also: → negative; → pressure.

A kind of pressure that contrarily to ordinary pressure pushes inward. In contrast with the → Newtonian mechanics, in → general relativity there are situations in which pressure can be negative. Positive pressure gives rise to attractive gravity, whereas negative pressure creates → repulsive gravity.

See also: → negative; → pressure.

Of a distribution function, a skewness in which the left tail (tail at small end of the distribution) is more pronounced that the right tail (tail at the large end of the distribution). → positive skewness.

See also: → negative; → skewness.

Of a distribution function, a skewness in which the left tail (tail at small end of the distribution) is more pronounced that the right tail (tail at the large end of the distribution). → positive skewness.

See also: → negative; → skewness.

An obsolete term denoting a negatively charged electron, as opposed to a positron.

See also: From → negative + → electron.

An obsolete term denoting a negatively charged electron, as opposed to a positron.

See also: From → negative + → electron.

1. The area or region around or near some place or thing; vicinity. → solar neighborhood.
   

2. Math.: An → open set that contains a given point.

Etymology (EN): From neighbor, M.E., O.E. neahgebur, from neah→ near + -hood suffix denoting “state or condition of being;” M.E. -hode, -hod;
O.E. -had “condition, position,” cognate with Ger. -heit, Du. -heid.

Etymology (PE): Hamsâyegi, noun from hamsâyé “neighbor,” literally “under, sharing the same shade,” from ham-, → syn-, + sâyé,
→ shadow.

1. The area or region around or near some place or thing; vicinity. → solar neighborhood.
   

2. Math.: An → open set that contains a given point.

Etymology (EN): From neighbor, M.E., O.E. neahgebur, from neah→ near + -hood suffix denoting “state or condition of being;” M.E. -hode, -hod;
O.E. -had “condition, position,” cognate with Ger. -heit, Du. -heid.

Etymology (PE): Hamsâyegi, noun from hamsâyé “neighbor,” literally “under, sharing the same shade,” from ham-, → syn-, + sâyé,
→ shadow.

A period of → geologic time within the Cenozoic era, between 23 and 2.6 million years ago, which comprises the Miocene and Pliocene epochs.

See also: From L. neo-, → new, + -gene, → gene.

A period of → geologic time within the Cenozoic era, between 23 and 2.6 million years ago, which comprises the Miocene and Pliocene epochs.

See also: From L. neo-, → new, + -gene, → gene.

A colorless, odorless, and tasteless gaseous chemical element; symbol Ne.
Atomic number 10, atomic weight 20.179; melting point -248.67°C; boiling point
-246.048°C. It was discovered from its bright red spectral lines by the Scottish chemist William Ramsay and the English chemist Morris William Travers in 1898 from a liquefied air sample. Neon is produced by carbon burning in massive stars and released into the Galaxy when they explode.

See also: From Gk. neon neuter of neos, → new, so called because it was a newly discovered element.

A colorless, odorless, and tasteless gaseous chemical element; symbol Ne.
Atomic number 10, atomic weight 20.179; melting point -248.67°C; boiling point
-246.048°C. It was discovered from its bright red spectral lines by the Scottish chemist William Ramsay and the English chemist Morris William Travers in 1898 from a liquefied air sample. Neon is produced by carbon burning in massive stars and released into the Galaxy when they explode.

See also: From Gk. neon neuter of neos, → new, so called because it was a newly discovered element.

A → nuclear fusion process that takes place in → massive stars and leads to
the → production of → oxygen and → magnesium. It requires high temperatures and densities (around 1.2 × 10⁹ K and 4 × 10⁹ kg/m³).

See also: → neon; → burning.

A → nuclear fusion process that takes place in → massive stars and leads to
the → production of → oxygen and → magnesium. It requires high temperatures and densities (around 1.2 × 10⁹ K and 4 × 10⁹ kg/m³).

See also: → neon; → burning.

The branch of meteorology that deals with clouds.

Etymology (EN): From Gk. nephos “cloud,” nephele “cloud;” cognate with Pers. nam “moisture;” Av. napta- “moist,” nabās-cā- “cloud,” nabah- “sky;” L. nebula “mist,” nimbus “rainstorm, rain cloud;” Skt. nábhas- “moisture, cloud, mist;” O.H.G. nebul; Ger. Nebel “fog;” O.E. nifol “dark;” PIE base *nebh- “cloud, vapor, fog, moist, sky”

• → -logy.

Etymology (PE): Abršenâsi, from abr “cloud,” from Mid.Pers. awr, abr (Laki owr, Baluchi haur, Kurd. Soriani hewr);
Av. awra- “rain cloud, rain;” cf. Skt. abhra-“thunder cloud;” Gk. afros “scum, foam;” L. imber “rain;” also Sk. ambha- “water;” Gk. ombros “rain,” PIE *mbhros “rain cloud, rain,” from *mbh- + -šenâsi→ -logy.

The branch of meteorology that deals with clouds.

Etymology (EN): From Gk. nephos “cloud,” nephele “cloud;” cognate with Pers. nam “moisture;” Av. napta- “moist,” nabās-cā- “cloud,” nabah- “sky;” L. nebula “mist,” nimbus “rainstorm, rain cloud;” Skt. nábhas- “moisture, cloud, mist;” O.H.G. nebul; Ger. Nebel “fog;” O.E. nifol “dark;” PIE base *nebh- “cloud, vapor, fog, moist, sky”

• → -logy.

Etymology (PE): Abršenâsi, from abr “cloud,” from Mid.Pers. awr, abr (Laki owr, Baluchi haur, Kurd. Soriani hewr);
Av. awra- “rain cloud, rain;” cf. Skt. abhra-“thunder cloud;” Gk. afros “scum, foam;” L. imber “rain;” also Sk. ambha- “water;” Gk. ombros “rain,” PIE *mbhros “rain cloud, rain,” from *mbh- + -šenâsi→ -logy.

The eighth planet from the Sun and the fourth largest by size in the → solar system. The equatorial radius of Neptune is 24,764 km (3.883 Earths), its → semi-major axis is 30.11 → astronomical units (4.50 × 10⁹ km), and its → orbital period is 164.8 yr.

Neptune has at least 14 moons, the largest ones are → Triton, → Proteus, and → Nereid, whereas its smaller moons are: Naiad, Thalassa, Despina, Galatea, Larissa, Halimede, Sao, Laomedeia, Psamathe, and Neso. Neptune has an incredibly thick atmosphere comprised of 74% → hydrogen, 25% → helium, and approximately 1% → methane. Particles of icy methane in its upper atmosphere give Neptune its deep blue color. Large storms whirl through Neptune’s upper atmosphere, and high-speed winds track around the planet at up 600 m/s, fastest recorded in the solar system.

One of the largest storms ever seen was recorded in 1989. Called the → Great Dark Spot, it lasted about five years.

Neptune has a very thin collection of → rings. They are likely made up of ice particles mixed with → dust grains and possibly coated with a carbon-based substance.

See also: Named for the Roman god of the sea Neptune, Gk. Poseidon.

The eighth planet from the Sun and the fourth largest by size in the → solar system. The equatorial radius of Neptune is 24,764 km (3.883 Earths), its → semi-major axis is 30.11 → astronomical units (4.50 × 10⁹ km), and its → orbital period is 164.8 yr.

Neptune has at least 14 moons, the largest ones are → Triton, → Proteus, and → Nereid, whereas its smaller moons are: Naiad, Thalassa, Despina, Galatea, Larissa, Halimede, Sao, Laomedeia, Psamathe, and Neso. Neptune has an incredibly thick atmosphere comprised of 74% → hydrogen, 25% → helium, and approximately 1% → methane. Particles of icy methane in its upper atmosphere give Neptune its deep blue color. Large storms whirl through Neptune’s upper atmosphere, and high-speed winds track around the planet at up 600 m/s, fastest recorded in the solar system.

One of the largest storms ever seen was recorded in 1989. Called the → Great Dark Spot, it lasted about five years.

Neptune has a very thin collection of → rings. They are likely made up of ice particles mixed with → dust grains and possibly coated with a carbon-based substance.

See also: Named for the Roman god of the sea Neptune, Gk. Poseidon.

A ductile, silvery radioactive metal, a member of the actinide series; symbol Np. Atomic number 93; atomic weight 237.0482; melting point about 640°C; boiling point 3,902°C (estimated). It was discovered in 1940 by Edwin M. McMillan and Philip H. Abelson, who produced neptunium-239 (half-life 2.3 days) by bombarding uranium with neutrons from a cyclotron at the University of California at Berkeley.

See also: The name derives from the planet → Neptune, since it is the next outer-most planet beyond the planet Uranus in the solar system and this element is the next one beyond uranium in the periodic table.

A ductile, silvery radioactive metal, a member of the actinide series; symbol Np. Atomic number 93; atomic weight 237.0482; melting point about 640°C; boiling point 3,902°C (estimated). It was discovered in 1940 by Edwin M. McMillan and Philip H. Abelson, who produced neptunium-239 (half-life 2.3 days) by bombarding uranium with neutrons from a cyclotron at the University of California at Berkeley.

See also: The name derives from the planet → Neptune, since it is the next outer-most planet beyond the planet Uranus in the solar system and this element is the next one beyond uranium in the periodic table.

The outermost satellite of Neptune (radius 150-250 km), discovered on May 1, 1949 by Gerard P. Kuiper. Its period is about 360 days and it has the most eccentric orbit (e = 0.76) of any natural satellite.

See also: Named after the Nereids, the 50 sea-nymph daughters of Nereus, a Gk. sea god.

The outermost satellite of Neptune (radius 150-250 km), discovered on May 1, 1949 by Gerard P. Kuiper. Its period is about 360 days and it has the most eccentric orbit (e = 0.76) of any natural satellite.

See also: Named after the Nereids, the 50 sea-nymph daughters of Nereus, a Gk. sea god.

When a temperature gradient is maintained through a strip of metal in a magnetic field, the direction of flow being across the lines of force, a potential difference will be produced across the conductor.

Etymology (EN): Walter Nernst (1864-1941), German physical chemist; → effect.

Etymology (PE): Oskar, → effect.

When a temperature gradient is maintained through a strip of metal in a magnetic field, the direction of flow being across the lines of force, a potential difference will be produced across the conductor.

Etymology (EN): Walter Nernst (1864-1941), German physical chemist; → effect.

Etymology (PE): Oskar, → effect.

The entropy change for chemical reactions involving crystalline solid is zero at the absolute zero of temperature. Also known as the third law of thermodynamics.

See also: → Nernst effect; → heat; → theorem.

The entropy change for chemical reactions involving crystalline solid is zero at the absolute zero of temperature. Also known as the third law of thermodynamics.

See also: → Nernst effect; → heat; → theorem.

The outermost natural satellite of → Neptune, discovered in 2002. Also known as Neptune XIII, it follows a highly inclined and highly eccentric orbit at about 48 million km from Neptune. According to preliminary estimates, Neso is about 60 km in diameter.

See also: In Gk. mythology, one of the Nereids, the fifty daughters of Nereus and Doris.

The outermost natural satellite of → Neptune, discovered in 2002. Also known as Neptune XIII, it follows a highly inclined and highly eccentric orbit at about 48 million km from Neptune. According to preliminary estimates, Neso is about 60 km in diameter.

See also: In Gk. mythology, one of the Nereids, the fifty daughters of Nereus and Doris.

Math.: Of an ordered collection of terms, having the property that each term is contained in the preceding one. → nested function, → nested multiplication.

Etymology (EN): From nest, from M.E., O.E. nest “bird’s nest;”
cf. M.L.G., M.Du. nest, Ger. Nest, ultimately from PIE *nizdo- (cf. Skt. nidah “resting place, nest,” L. nidus “nest,” O.C.S. gnezdo, O.Ir. net, Breton nez “nest”), probably from → ni- (PIE) + *sed- “sit” (cf. Pers. nešastan “to sit”), → lander.

Etymology (PE): Tu-dar-tu literally “inside in inside,” from tu “inside, in;” dar, → in-.

Math.: Of an ordered collection of terms, having the property that each term is contained in the preceding one. → nested function, → nested multiplication.

Etymology (EN): From nest, from M.E., O.E. nest “bird’s nest;”
cf. M.L.G., M.Du. nest, Ger. Nest, ultimately from PIE *nizdo- (cf. Skt. nidah “resting place, nest,” L. nidus “nest,” O.C.S. gnezdo, O.Ir. net, Breton nez “nest”), probably from → ni- (PIE) + *sed- “sit” (cf. Pers. nešastan “to sit”), → lander.

Etymology (PE): Tu-dar-tu literally “inside in inside,” from tu “inside, in;” dar, → in-.

In computer programing, a function that is defined inside the definition of another function.

See also: → nested; → function.

In computer programing, a function that is defined inside the definition of another function.

See also: → nested; → function.

A method in the evaluation of polynomials which involves fewer basic operations and allows simpler computation, especially for polynomials of high degree. More specifically, the polynomial P(x) = a₀ + a₁x + a₂x² + a₃x³ + … + a_nxⁿ

can be written in the nested form as:

P(x) = a₀ + x(a₁ + x(a₂ + … + x(a_{n - 1} + a_nx) …)). For example, the polynomial P(x) = x³ - 5x² + 10x - 3 has the following nested form:
P(x) = ((x - 5)x + 10)x - 3.

Same as the → Ruffini-Horner method.

See also: → nested; → multiplication.

A method in the evaluation of polynomials which involves fewer basic operations and allows simpler computation, especially for polynomials of high degree. More specifically, the polynomial P(x) = a₀ + a₁x + a₂x² + a₃x³ + … + a_nxⁿ

can be written in the nested form as:

P(x) = a₀ + x(a₁ + x(a₂ + … + x(a_{n - 1} + a_nx) …)). For example, the polynomial P(x) = x³ - 5x² + 10x - 3 has the following nested form:
P(x) = ((x - 5)x + 10)x - 3.

Same as the → Ruffini-Horner method.

See also: → nested; → multiplication.

Any net-like combination of elements in a system; an interconnection of several communicating entities.

Etymology (EN): O.E. net “mesh,” from P.Gmc. *natjan (cf. Du. net, Swed. nät, O.H.G. nezzi, Ger. Netz, Goth. nati “net”), originally “something knotted,” from PIE *ned- “to twist, knot” (cf. L. nodus “knot;” Skt. nahyati “binds, ties”) + → work.

Etymology (PE): Turbast literally “joined, tied by a net,” from tur “net, fishing net, snare,” related to
târ “thread, warp, string,” tâl “thread” (Borujerdi dialect), tân “thread, warp of a web,” from tanidan, tan-
“to spin, twist, weave” (Mid.Pers. tanitan; Av. tan- to stretch, extend;" cf. Skt. tan- to stretch, extend;" tanoti “stretches,” tántra- “warp; essence, main point;” Gk. teinein “to stretch, pull tight;” L. tendere “to stretch;”
Lith. tiñklas “net, fishing net, snare,” Latv. tikls “net;” PIE base *ten- “to stretch”)

• bast “joined, tied,” from
  bastan, vastan “to bind, shut” (O.Pers./Av. band- “to bind, fetter,” banda- “band, tie” (cf.
  Skt. bandh- “to bind, tie, fasten;” PIE *bhendh- “to bind;” Ger. binden; E. bind).

Any net-like combination of elements in a system; an interconnection of several communicating entities.

Etymology (EN): O.E. net “mesh,” from P.Gmc. *natjan (cf. Du. net, Swed. nät, O.H.G. nezzi, Ger. Netz, Goth. nati “net”), originally “something knotted,” from PIE *ned- “to twist, knot” (cf. L. nodus “knot;” Skt. nahyati “binds, ties”) + → work.

Etymology (PE): Turbast literally “joined, tied by a net,” from tur “net, fishing net, snare,” related to
târ “thread, warp, string,” tâl “thread” (Borujerdi dialect), tân “thread, warp of a web,” from tanidan, tan-
“to spin, twist, weave” (Mid.Pers. tanitan; Av. tan- to stretch, extend;" cf. Skt. tan- to stretch, extend;" tanoti “stretches,” tántra- “warp; essence, main point;” Gk. teinein “to stretch, pull tight;” L. tendere “to stretch;”
Lith. tiñklas “net, fishing net, snare,” Latv. tikls “net;” PIE base *ten- “to stretch”)

• bast “joined, tied,” from
  bastan, vastan “to bind, shut” (O.Pers./Av. band- “to bind, fetter,” banda- “band, tie” (cf.
  Skt. bandh- “to bind, tie, fasten;” PIE *bhendh- “to bind;” Ger. binden; E. bind).

In → iron meteorites, any of very fine parallel lines that cross each other at various angles. They can be seen after cutting diagonally across the sample.

See also: Named after Johann G. Neumann, who discovered them in 1848 in the iron meteorite Braunau, which fell in 1847; → line.

In → iron meteorites, any of very fine parallel lines that cross each other at various angles. They can be seen after cutting diagonally across the sample.

See also: Named after Johann G. Neumann, who discovered them in 1848 in the iron meteorite Braunau, which fell in 1847; → line.

Grammar: Noting or pertaining to a gender that refers to things classed as neither masculine nor feminine.
Biology: Having no organs of reproduction; without sex; asexual. → neutral.

Etymology (EN): From M.E., from M.Fr., from L. neuter, literally “neither one nor the other,” from ne- “not, no” + uter “either of two;” cf. Av. atāra- “this of the two, which of the two;” Gk. poteros; Lith. katras “which of the two,” Russ. kotoryj “which.”

Etymology (PE): Natâr, from negation prefix na-, → non-,

• Mid.Pers. atâr, from Av. atāra- “this of the two,” cognate with L. uter “either of two;” Av. katāra- “which of two; each of two;” Skt. katará- “who or which of two.”

Grammar: Noting or pertaining to a gender that refers to things classed as neither masculine nor feminine.
Biology: Having no organs of reproduction; without sex; asexual. → neutral.

Etymology (EN): From M.E., from M.Fr., from L. neuter, literally “neither one nor the other,” from ne- “not, no” + uter “either of two;” cf. Av. atāra- “this of the two, which of the two;” Gk. poteros; Lith. katras “which of the two,” Russ. kotoryj “which.”

Etymology (PE): Natâr, from negation prefix na-, → non-,

• Mid.Pers. atâr, from Av. atāra- “this of the two,” cognate with L. uter “either of two;” Av. katāra- “which of two; each of two;” Skt. katará- “who or which of two.”

Physics: Of an atom, molecule, collection of particles, having no net charge; not electrified.
Chemistry: Exhibiting neither acid nor alkaline qualities.

Etymology (EN): From → neuter + → -al.

Etymology (PE): → neuter.

Physics: Of an atom, molecule, collection of particles, having no net charge; not electrified.
Chemistry: Exhibiting neither acid nor alkaline qualities.

Etymology (EN): From → neuter + → -al.

Etymology (PE): → neuter.

An atom in which the number of → protons equals the number of → electrons and therefore has no net → electric charge.

See also: → neutral; → atom.

An atom in which the number of → protons equals the number of → electrons and therefore has no net → electric charge.

See also: → neutral; → atom.

A filter having a flat response over the range of wavelengths of interest. Also called neutral filter or gray filter.

See also: → neutral; → density; → filter.

A filter having a flat response over the range of wavelengths of interest. Also called neutral filter or gray filter.

See also: → neutral; → density; → filter.

Same as → neutral density filter.

See also: → neutral; → filter.

Same as → neutral density filter.

See also: → neutral; → filter.

A gas which is not ionized.

See also: → neutral; → gas.

A gas which is not ionized.

See also: → neutral; → gas.

Non-ionized → atomic hydrogen gas which constitutes an important component of the → interstellar medium, accounting for perhaps half its mass, even though its density is very low. Its radio emission
→ 21-centimeter line has made it possible to map the distribution of neutral hydrogen in the → spiral arms of our own Galaxy and other nearby galaxies.

See also: → neutral; → hydrogen.

Non-ionized → atomic hydrogen gas which constitutes an important component of the → interstellar medium, accounting for perhaps half its mass, even though its density is very low. Its radio emission
→ 21-centimeter line has made it possible to map the distribution of neutral hydrogen in the → spiral arms of our own Galaxy and other nearby galaxies.

See also: → neutral; → hydrogen.

In hydrodynamic instability theory, a wave solution the amplitude of which does not change with time; it neither grows nor decays. Also called neutral wave.

See also: → neutral; → mode.

In hydrodynamic instability theory, a wave solution the amplitude of which does not change with time; it neither grows nor decays. Also called neutral wave.

See also: → neutral; → mode.

1. A point where two fields are equal in magnitude and opposite in direction so that the net force exerted on it is zero.
   

2. One of several points in the sky for which the → degree of polarization of diffuse sky light is zero.

See also: → neutral; → point.

1. A point where two fields are equal in magnitude and opposite in direction so that the net force exerted on it is zero.
   

2. One of several points in the sky for which the → degree of polarization of diffuse sky light is zero.

See also: → neutral; → point.

Same as → sodium tail.

See also: → neutral; → tail.

Same as → sodium tail.

See also: → neutral; → tail.

Same as → neutral mode.

See also: → neutral; → wave.

Same as → neutral mode.

See also: → neutral; → wave.

A hypothetical particle predicted by supersymmetry theories, which aim at relating bosons to fermions. Under certain assumptions, the lightest such partner particle would be stable, and if it is neutral (a “neutralino”), would make a good dark matter candidate. Reasonable neutralino masses range from 30 GeV to 10 TeV.

Etymology (EN): From → neutral + -ino diminutive suffix.

A hypothetical particle predicted by supersymmetry theories, which aim at relating bosons to fermions. Under certain assumptions, the lightest such partner particle would be stable, and if it is neutral (a “neutralino”), would make a good dark matter candidate. Reasonable neutralino masses range from 30 GeV to 10 TeV.

Etymology (EN): From → neutral + -ino diminutive suffix.

In optics, the process of combining two lenses having equal and opposite powers to produce a result having no power.

See also: Verbal noun of → neutralize.

In optics, the process of combining two lenses having equal and opposite powers to produce a result having no power.

See also: Verbal noun of → neutralize.

To make neutral; cause to undergo neutralization.
To render electrically or magnetically neutral.

See also: Infinitive from → neutral.

To make neutral; cause to undergo neutralization.
To render electrically or magnetically neutral.

See also: Infinitive from → neutral.

An → elementary particle with zero → charge, → spin 1/2, and very small → rest mass. The three types of neutrino (electron neutrino, muon neutrino, tau neutrino) experience only the → weak nuclear force and gravitational force, and pass easily through matter.

The neutrino undergoes a quantum mechanical phenomenon in which → neutrino flavor changes spontaneously to another flavor (→ neutrino oscillation). The neutrino was first postulated by Wolfgang Pauli in 1931 to account for the problem of energy → conservation in → beta decay. It was discovered in 1956.
See also:

→ antineutrino, → atmospheric neutrino, → cosmic neutrino background (CNB), → cosmogenic neutrino, → high-energy neutrino, → low-energy neutrino, → solar neutrino, → solar neutrino problem, → solar neutrino unit (SNU), → sterile neutrino, → ultra-high-energy neutrino.

See also: Neutrino, coined by Enrico Fermi (1901-1954), from neutr(o)→ neuter + -ino diminutive suffix.

An → elementary particle with zero → charge, → spin 1/2, and very small → rest mass. The three types of neutrino (electron neutrino, muon neutrino, tau neutrino) experience only the → weak nuclear force and gravitational force, and pass easily through matter.

The neutrino undergoes a quantum mechanical phenomenon in which → neutrino flavor changes spontaneously to another flavor (→ neutrino oscillation). The neutrino was first postulated by Wolfgang Pauli in 1931 to account for the problem of energy → conservation in → beta decay. It was discovered in 1956.
See also:

→ antineutrino, → atmospheric neutrino, → cosmic neutrino background (CNB), → cosmogenic neutrino, → high-energy neutrino, → low-energy neutrino, → solar neutrino, → solar neutrino problem, → solar neutrino unit (SNU), → sterile neutrino, → ultra-high-energy neutrino.

See also: Neutrino, coined by Enrico Fermi (1901-1954), from neutr(o)→ neuter + -ino diminutive suffix.

Any of the six different varieties of the neutrinos: electron neutrinos, muon neutrinos, tau neutrinos, and their antiparticles.

See also: → neutrino; → flavor.

Any of the six different varieties of the neutrinos: electron neutrinos, muon neutrinos, tau neutrinos, and their antiparticles.

See also: → neutrino; → flavor.

The transition between neutrino types (→ neutrino flavor) which is a probabilistic consequence of → quantum mechanics. A neutrino, when produced, is in a quantum state which has three different masses. Therefore, an electron neutrino emitted during a reaction can be detected as a muon or tau neutrino. In other words, the flavor eigenstates are different from the propagation eigenstates. This phenomenon was discovered in → solar neutrinos as well as in → atmospheric neutrinos. Neutrino oscillation violates the conservation of the → lepton number; it is possible only if neutrinos have a mass. First predicted by Bruno Pontecorvo in 1957, neutrino oscillation has since been observed by several experiments. It resolved the long-standing → solar neutrino problem. The smaller the mass difference between the flavors, the longer the oscillation period,
so that oscillations would not occur if all of the flavors were equal in mass or were massless. Moreover, the oscillation period increases with neutrino energy.

See also: → neutrino; → oscillation.

The transition between neutrino types (→ neutrino flavor) which is a probabilistic consequence of → quantum mechanics. A neutrino, when produced, is in a quantum state which has three different masses. Therefore, an electron neutrino emitted during a reaction can be detected as a muon or tau neutrino. In other words, the flavor eigenstates are different from the propagation eigenstates. This phenomenon was discovered in → solar neutrinos as well as in → atmospheric neutrinos. Neutrino oscillation violates the conservation of the → lepton number; it is possible only if neutrinos have a mass. First predicted by Bruno Pontecorvo in 1957, neutrino oscillation has since been observed by several experiments. It resolved the long-standing → solar neutrino problem. The smaller the mass difference between the flavors, the longer the oscillation period,
so that oscillations would not occur if all of the flavors were equal in mass or were massless. Moreover, the oscillation period increases with neutrino energy.

See also: → neutrino; → oscillation.

An uncharged → subatomic particle found in the nucleus of every → atom heavier than → hydrogen. It has a → rest mass of 1.67492 x 10^-24 g, 939.566 → MeV, slightly greater than that of the → proton. The neutron is composed of three → quarks (two down and one up). Although the neutron is electrically neutral,
it owns a → spin of 1/2 and a → magnetic moment; it can therefore interact magnetically with matter. A free neutron is unstable and disintegrates by → beta decay to a proton, an → electron, and → antineutrino of the electron type: n→ p + e^- + ν^__e + 0.7823 MeV. Its → mean life is about 15 minutes. The decay of the neutron is associated with a → quark transformation in which a down quark is converted to an up by the → weak interaction.

See also: From neutro-, a combining form representing → neutral, + → -on a suffix used in the names of → subatomic particles.

An uncharged → subatomic particle found in the nucleus of every → atom heavier than → hydrogen. It has a → rest mass of 1.67492 x 10^-24 g, 939.566 → MeV, slightly greater than that of the → proton. The neutron is composed of three → quarks (two down and one up). Although the neutron is electrically neutral,
it owns a → spin of 1/2 and a → magnetic moment; it can therefore interact magnetically with matter. A free neutron is unstable and disintegrates by → beta decay to a proton, an → electron, and → antineutrino of the electron type: n→ p + e^- + ν^__e + 0.7823 MeV. Its → mean life is about 15 minutes. The decay of the neutron is associated with a → quark transformation in which a down quark is converted to an up by the → weak interaction.

See also: From neutro-, a combining form representing → neutral, + → -on a suffix used in the names of → subatomic particles.

The → nuclear reaction that occurs when an → atomic nucleus captures a → neutron. Neutron capture is the primary mechanism (principally, the → s-process and → r-process)
by which very massive nuclei are formed in stars and during → supernova explosions.
Instead of → fusion of similar nuclei, heavy, → neutron-capture elements are created by the addition of more and more neutrons to existing nuclei.

See also: → neutron; → capture.

The → nuclear reaction that occurs when an → atomic nucleus captures a → neutron. Neutron capture is the primary mechanism (principally, the → s-process and → r-process)
by which very massive nuclei are formed in stars and during → supernova explosions.
Instead of → fusion of similar nuclei, heavy, → neutron-capture elements are created by the addition of more and more neutrons to existing nuclei.

See also: → neutron; → capture.

The state of degeneracy created when the density of matter is so high that neutrons cannot be packed any more closely together. This condition occurs in the core of stars above 1.44 solar masses (→ Chandrasekhar limit) where under the gravitational collapse electrons and protons are forced to combine into neutrons. Therefore, in a → neutron star all the lowest neutron energy levels are filled and the neutrons are forced into higher and higher energy levels, since according to Pauli Exclusion Principle no two neutrons (fermions) can occupy identical states. This creates an effective pressure which prevents further gravitational collapse. However, for masses greater than 3 solar masses, even neutron degeneracy cannot prevent further collapse and it continues toward the black hole state.

See also: → neutron; → degeneracy.

The state of degeneracy created when the density of matter is so high that neutrons cannot be packed any more closely together. This condition occurs in the core of stars above 1.44 solar masses (→ Chandrasekhar limit) where under the gravitational collapse electrons and protons are forced to combine into neutrons. Therefore, in a → neutron star all the lowest neutron energy levels are filled and the neutrons are forced into higher and higher energy levels, since according to Pauli Exclusion Principle no two neutrons (fermions) can occupy identical states. This creates an effective pressure which prevents further gravitational collapse. However, for masses greater than 3 solar masses, even neutron degeneracy cannot prevent further collapse and it continues toward the black hole state.

See also: → neutron; → degeneracy.

A type of radioactive decay of atoms containing excess neutrons, in which a neutron is ejected from the nucleus.

See also: → neutron; → emission.

A type of radioactive decay of atoms containing excess neutrons, in which a neutron is ejected from the nucleus.

See also: → neutron; → emission.

The excess of → neutrons over → protons in an → atomic nucleus:

η = (N_n - N_p) / (N_n + N_p).

See also: → neutron; → excess.

The excess of → neutrons over → protons in an → atomic nucleus:

η = (N_n - N_p) / (N_n + N_p).

See also: → neutron; → excess.

An extremely compact ball of matter created from the central core of a star that has collapsed under gravity to such an extent that it consists almost entirely of → neutrons. Neutron stars result from two possible evolutionary scenarios: 1) The → collapse of a → massive star during a → supernova explosion; and 2) The accumulation of mass by a → white dwarf in a → binary system. The mass of a neutron star is the same as or larger than the → Chandrasekhar limit (1.4 → solar masses). Neutron stars are only about 10 km across and have a density of 10¹⁴ g cm^-3, representing the densest objects having a visible surface. The structure of neutron stars consists of a thin outer crust of about 1 km thickness composed of
→ degenerate electrons and nuclei, which becomes progressively neutron rich with increasing depth and pressure due to → inverse beta decays. In the main body the matter consists of → superfluid neutrons in equilibrium with their decay products, a few percent protons and electrons. Neutron stars have extremely strong magnetic fields, from 3 x 10¹⁰ to 10¹⁵ gauss. As of 2010 more than 2000 neutron stars have been catalogued, which show a large variety of manifestations, mainly → pulsars.

See also: → neutron; → star.

An extremely compact ball of matter created from the central core of a star that has collapsed under gravity to such an extent that it consists almost entirely of → neutrons. Neutron stars result from two possible evolutionary scenarios: 1) The → collapse of a → massive star during a → supernova explosion; and 2) The accumulation of mass by a → white dwarf in a → binary system. The mass of a neutron star is the same as or larger than the → Chandrasekhar limit (1.4 → solar masses). Neutron stars are only about 10 km across and have a density of 10¹⁴ g cm^-3, representing the densest objects having a visible surface. The structure of neutron stars consists of a thin outer crust of about 1 km thickness composed of
→ degenerate electrons and nuclei, which becomes progressively neutron rich with increasing depth and pressure due to → inverse beta decays. In the main body the matter consists of → superfluid neutrons in equilibrium with their decay products, a few percent protons and electrons. Neutron stars have extremely strong magnetic fields, from 3 x 10¹⁰ to 10¹⁵ gauss. As of 2010 more than 2000 neutron stars have been catalogued, which show a large variety of manifestations, mainly → pulsars.

See also: → neutron; → star.

A → binary system composed of two → neutron stars.

See also: → neutron; → star; → binary; → system.

A → binary system composed of two → neutron stars.

See also: → neutron; → star; → binary; → system.

A → nucleosynthesis process responsible for the generation of the → chemical elements heavier than the → iron peak elements. There are two possibilities for → neutron capture: the slow neutron-capture process (the → s-process) and the rapid neutron-capture process (the → r-process).

The s-process is further divided into two categories: the weak s-component and the main s-component. Massive stars are sites of the weak component of s-process nucleosynthesis, which is mainly responsible for the production of lighter neutron-capture elements (e.g. Sr, Y, and Zr). The s-process contribution to heavier neutron-capture elements (heavier than Ba) is due only to the main s-component. The low- to intermediate-mass stars (about 1.3-8 Msun) in the → asymptotic giant branch (AGB) are usually considered to be sites in which the main s-process occur. There is abundant evidence suggesting that → Type II supernova (SNe II) are sites for the synthesis of the r-process nuclei, although this has not yet been fully confirmed. The observations and analysis on → very metal-poor stars imply that the stars with [Fe/H] ≤ -2.5 might form from gas clouds polluted by a few supernovae (SNe). Therefore, the abundances of → heavy elements in → metal-poor stars have been used to learn about the nature of the nucleosynthetic processes in the early Galaxy (See, e.g., H. Li et al., 2013, arXiv:1301.6097).

See also: → neutron;→ capture; → element.

A → nucleosynthesis process responsible for the generation of the → chemical elements heavier than the → iron peak elements. There are two possibilities for → neutron capture: the slow neutron-capture process (the → s-process) and the rapid neutron-capture process (the → r-process).

The s-process is further divided into two categories: the weak s-component and the main s-component. Massive stars are sites of the weak component of s-process nucleosynthesis, which is mainly responsible for the production of lighter neutron-capture elements (e.g. Sr, Y, and Zr). The s-process contribution to heavier neutron-capture elements (heavier than Ba) is due only to the main s-component. The low- to intermediate-mass stars (about 1.3-8 Msun) in the → asymptotic giant branch (AGB) are usually considered to be sites in which the main s-process occur. There is abundant evidence suggesting that → Type II supernova (SNe II) are sites for the synthesis of the r-process nuclei, although this has not yet been fully confirmed. The observations and analysis on → very metal-poor stars imply that the stars with [Fe/H] ≤ -2.5 might form from gas clouds polluted by a few supernovae (SNe). Therefore, the abundances of → heavy elements in → metal-poor stars have been used to learn about the nature of the nucleosynthetic processes in the early Galaxy (See, e.g., H. Li et al., 2013, arXiv:1301.6097).

See also: → neutron;→ capture; → element.

The reaction that transforms a → proton into a → neutron when a proton and an → electron are forced together to make a neutron: p + e^-→ n + ν^__e. In astronomy, this process occurs during the → core collapse of → massive stars which leads to the formation of → neutron stars.

See also: → neutron; → -ize; → -tion.

The reaction that transforms a → proton into a → neutron when a proton and an → electron are forced together to make a neutron: p + e^-→ n + ν^__e. In astronomy, this process occurs during the → core collapse of → massive stars which leads to the formation of → neutron stars.

See also: → neutron; → -ize; → -tion.

1. Not ever; at no time.
   

2. Not at all; absolutely not.

Etymology (EN): M.E., from O.E. næfre “never,” compound of ne “not, no,”
→ un- + æfre “ever.”

Etymology (PE): Hargez, variant hagarz; Mid.Pers. hagriz, hakarc “ever, always, never;” O.Pers. hakarnciy “once”; Av. hakərət “once;” cf. Skt. sakrt “once; repeated; ever; never;” Gk. hapax “once;” L. semel “once,” semper “always;” PIE *smkrt.

1. Not ever; at no time.
   

2. Not at all; absolutely not.

Etymology (EN): M.E., from O.E. næfre “never,” compound of ne “not, no,”
→ un- + æfre “ever.”

Etymology (PE): Hargez, variant hagarz; Mid.Pers. hagriz, hakarc “ever, always, never;” O.Pers. hakarnciy “once”; Av. hakərət “once;” cf. Skt. sakrt “once; repeated; ever; never;” Gk. hapax “once;” L. semel “once,” semper “always;” PIE *smkrt.

However, notwithstanding, in spite of, still.

Etymology (EN): M.E. natheles, notheles, natheless, from O.E. neuerþeles, that is → never +
the “in or by that,” “on that account,” “in or by so much,” + less→ -less, cf. Fr. néanmoins = pas moins; Ger. nichtsdestoweniger.

Etymology (PE): Hagarzkam, from hagarz, → never, + kam “less,” → -less.

However, notwithstanding, in spite of, still.

Etymology (EN): M.E. natheles, notheles, natheless, from O.E. neuerþeles, that is → never +
the “in or by that,” “on that account,” “in or by so much,” + less→ -less, cf. Fr. néanmoins = pas moins; Ger. nichtsdestoweniger.

Etymology (PE): Hagarzkam, from hagarz, → never, + kam “less,” → -less.

Of recent origin, production.
Of a kind now existing or appearing for the first time. → new moon; → New General Catalogue (NGC).

Etymology (EN): O.E. neowe, niowe, niwe; cf. Du. nieuw, Ger. neu, Dan., Swed. ny; cognate with Pers. now, as below, L. novus “new, recent, fresh” (Fr. nouveau, neuf), from PIE *neu- “new, young.”

Etymology (PE): Now, from Mid.Pers. nôg “new, fresh;” Av. nauua- “new, fresh;” cf. Skt. náva- “new, fresh, young;” Gk. neos “new, young;” L. novus, as above, cognate with E. new, as above.

Of recent origin, production.
Of a kind now existing or appearing for the first time. → new moon; → New General Catalogue (NGC).

Etymology (EN): O.E. neowe, niowe, niwe; cf. Du. nieuw, Ger. neu, Dan., Swed. ny; cognate with Pers. now, as below, L. novus “new, recent, fresh” (Fr. nouveau, neuf), from PIE *neu- “new, young.”

Etymology (PE): Now, from Mid.Pers. nôg “new, fresh;” Av. nauua- “new, fresh;” cf. Skt. náva- “new, fresh, young;” Gk. neos “new, young;” L. novus, as above, cognate with E. new, as above.

A catalogue of 7,840 non-stellar objects compiled by J. L. E. Dreyer and published in 1888. A further 1,529 objects were listed in a supplement that appeared seven years later, called the → Index Catalogue (IC). The Second Index Catalogue of 1908 extended the supplementary list to 5,386 objects.

See also: → new; → general;
→ catalog

A catalogue of 7,840 non-stellar objects compiled by J. L. E. Dreyer and published in 1888. A further 1,529 objects were listed in a supplement that appeared seven years later, called the → Index Catalogue (IC). The Second Index Catalogue of 1908 extended the supplementary list to 5,386 objects.

See also: → new; → general;
→ catalog

A space mission by → NASA whose main goal is to study the → dwarf planet Pluto and it satellites. New Horizons was launched on January 19, 2006; it swung past → Jupiter for a → gravity assist and scientific studies in February 2007, and conducted a six-month-long reconnaissance → flyby study of → Pluto and its moons in summer 2015, culminating with Pluto closest approach on July 14, 2015. It flew 12,500 km above the surface of Pluto, making it the first spacecraft to explore the dwarf planet. Its science payload includes seven instruments: Ralph (visible and infrared imager/spectrometer), Alice (ultraviolet imaging spectrometer), REX (Radio Science EXperiment), LORRI (Long Range Reconnaissance Imager), SWAP (Solar Wind Around Pluto), PEPSSI: (Pluto Energetic Particle Spectrometer Science Investigation), and SDC: (Student Dust Counter). As part of an extended mission, New Horizons has maneuvered for a flyby of → Kuiper belt object 2014 MU69, expected to take place on January 1, 2019, when it is 43.4 → astronomical units (AU) from the Sun.

See also: → new; → horizon.

A space mission by → NASA whose main goal is to study the → dwarf planet Pluto and it satellites. New Horizons was launched on January 19, 2006; it swung past → Jupiter for a → gravity assist and scientific studies in February 2007, and conducted a six-month-long reconnaissance → flyby study of → Pluto and its moons in summer 2015, culminating with Pluto closest approach on July 14, 2015. It flew 12,500 km above the surface of Pluto, making it the first spacecraft to explore the dwarf planet. Its science payload includes seven instruments: Ralph (visible and infrared imager/spectrometer), Alice (ultraviolet imaging spectrometer), REX (Radio Science EXperiment), LORRI (Long Range Reconnaissance Imager), SWAP (Solar Wind Around Pluto), PEPSSI: (Pluto Energetic Particle Spectrometer Science Investigation), and SDC: (Student Dust Counter). As part of an extended mission, New Horizons has maneuvered for a flyby of → Kuiper belt object 2014 MU69, expected to take place on January 1, 2019, when it is 43.4 → astronomical units (AU) from the Sun.

See also: → new; → horizon.

The Moon’s phase when it is at the same celestial longitude as the Sun and thus totally un-illuminated as seen from Earth.

See also: → new; → moon.

The Moon’s phase when it is at the same celestial longitude as the Sun and thus totally un-illuminated as seen from Earth.

See also: → new; → moon.

The unit of force in the SI system of units. 1 newton (N) is defined as the force required to give a mass of 1 kilogram an acceleration of 1 m s^-2. 1 N = 10⁵  → dynes.

See also: Named after Sir Isaac Newton (1642-1727), the English highly prominent physicist and mathematician.

The unit of force in the SI system of units. 1 newton (N) is defined as the force required to give a mass of 1 kilogram an acceleration of 1 m s^-2. 1 N = 10⁵  → dynes.

See also: Named after Sir Isaac Newton (1642-1727), the English highly prominent physicist and mathematician.

Same as the → gravitational constant.

See also: → Newton; → constant.

Same as the → gravitational constant.

See also: → Newton; → constant.

The formula expressing the value of a → definite integral of a given function over an interval as the difference of the values at the end points of the interval of any → antiderivative of the function: ∫f(x)dx = F(b) - F(a), summed from x = a to x = b.

See also: Named after Isaac → Newton and Gottfried Wilhelm Leibniz (1646-1716), who both knew the rule, although it was published later; → formula.

The formula expressing the value of a → definite integral of a given function over an interval as the difference of the values at the end points of the interval of any → antiderivative of the function: ∫f(x)dx = F(b) - F(a), summed from x = a to x = b.

See also: Named after Isaac → Newton and Gottfried Wilhelm Leibniz (1646-1716), who both knew the rule, although it was published later; → formula.

The incompatibility between → Galilean relativity and Mawxell’s theory of → electromagnetism. Maxwell demonstrated that electrical and magnetic fields propagate as waves in space. The propagation speed of these waves in a vacuum is given by the expression c = (ε₀.μ₀)^-0.5, where ε₀ is the electric → permittivity and μ₀ is the magnetic → permeability, both → physical constants. Maxwell noticed that this value corresponds exactly to the → speed of light in vacuum. This implies, however, that the speed of light must also be a universal constant, just as are the electrical and the magnetic field constants! The problem is that → Maxwell’s equations do not relate this velocity to an absolute background and specify no → reference frame against which it is measured. If we accept that the principle of relativity not only applies to mechanics, then it must also be true that Maxwell’s equations apply in any → inertial frame, with the same values for the universal constants. Therefore, the speed of light should be independent of the movement of its source. This, however, contradicts the vector addition of velocities, which is a verified principle within → Newtonian mechanics. Einstein was bold enough to conclude that the principle of Newtonian relativity and Maxwell’s theory of electromagnetism are incompatible! In other words, the → Galilean transformation and the → Newtonian relativity principle based on this transformation were wrong. There exists, therefore, a new relativity principle, → Einsteinian relativity, for both mechanics and electrodynamics that is based on the → Lorentz transformation.

See also: → Newton; → Maxwell; → incompatibility.

The incompatibility between → Galilean relativity and Mawxell’s theory of → electromagnetism. Maxwell demonstrated that electrical and magnetic fields propagate as waves in space. The propagation speed of these waves in a vacuum is given by the expression c = (ε₀.μ₀)^-0.5, where ε₀ is the electric → permittivity and μ₀ is the magnetic → permeability, both → physical constants. Maxwell noticed that this value corresponds exactly to the → speed of light in vacuum. This implies, however, that the speed of light must also be a universal constant, just as are the electrical and the magnetic field constants! The problem is that → Maxwell’s equations do not relate this velocity to an absolute background and specify no → reference frame against which it is measured. If we accept that the principle of relativity not only applies to mechanics, then it must also be true that Maxwell’s equations apply in any → inertial frame, with the same values for the universal constants. Therefore, the speed of light should be independent of the movement of its source. This, however, contradicts the vector addition of velocities, which is a verified principle within → Newtonian mechanics. Einstein was bold enough to conclude that the principle of Newtonian relativity and Maxwell’s theory of electromagnetism are incompatible! In other words, the → Galilean transformation and the → Newtonian relativity principle based on this transformation were wrong. There exists, therefore, a new relativity principle, → Einsteinian relativity, for both mechanics and electrodynamics that is based on the → Lorentz transformation.

See also: → Newton; → Maxwell; → incompatibility.

A method for finding roots of a → polynomial that makes explicit use of the → derivative of the function. It uses → iteration to continually improve the accuracy of the estimated root.

If f(x) has a → simple root near x_n then a closer estimate to the root is x_n + 1</SUB where x_n + 1</SUB = x_n - f(x_n)/f’(x_n).
The iteration begins with an initial estimate of the root, x₀, and continues to find x₁, x₂, . . . until a suitably accurate estimate of the position of the root is obtained. Also called → Newton’s method.

See also: → Newton found the method in 1671, but it was not actually published until 1736;
Joseph Raphson (1648-1715), English mathematician, independently published the method in 1690.

A method for finding roots of a → polynomial that makes explicit use of the → derivative of the function. It uses → iteration to continually improve the accuracy of the estimated root.

If f(x) has a → simple root near x_n then a closer estimate to the root is x_n + 1</SUB where x_n + 1</SUB = x_n - f(x_n)/f’(x_n).
The iteration begins with an initial estimate of the root, x₀, and continues to find x₁, x₂, . . . until a suitably accurate estimate of the position of the root is obtained. Also called → Newton’s method.

See also: → Newton found the method in 1671, but it was not actually published until 1736;
Joseph Raphson (1648-1715), English mathematician, independently published the method in 1690.

The arrangement of the seven colors of the rainbow on a disk. When the disk rotates very fast, the eye cannot distinguish between individual colors and the disk is perceived as white. This apparatus demonstrates the discovery made by Newton (Opticks, 1704) that light is composed of seven colors.

See also: → Newton; → color; → wheel.

The arrangement of the seven colors of the rainbow on a disk. When the disk rotates very fast, the eye cannot distinguish between individual colors and the disk is perceived as white. This apparatus demonstrates the discovery made by Newton (Opticks, 1704) that light is composed of seven colors.

See also: → Newton; → color; → wheel.

Same as the → gravitational constant.

See also: → Newton; → constant.

Same as the → gravitational constant.

See also: → Newton; → constant.

A device consisting of a series of equal → pendulums
in a row used to demonstrate the laws of → conservation of momentum and → conservation of energy.

See also: → Newton; → cradle.

A device consisting of a series of equal → pendulums
in a row used to demonstrate the laws of → conservation of momentum and → conservation of energy.

See also: → Newton; → cradle.

→ Newton’s color wheel.

See also: → Newton; → disk.

→ Newton’s color wheel.

See also: → Newton; → disk.

In → geometric optics, an expression relating the → focal lengths of an → optical system (f and f’) and the object x and image x’ distances measured from the respective focal points. Thus, ff’ = xx’. Same as Newton’s formula.

See also: → Newton; → equation.

In → geometric optics, an expression relating the → focal lengths of an → optical system (f and f’) and the object x and image x’ distances measured from the respective focal points. Thus, ff’ = xx’. Same as Newton’s formula.

See also: → Newton; → equation.

A body continues in its state of constant velocity (which may be zero) unless it is acted upon by an external force.

See also: → Newton; → first; → law; → motion.

A body continues in its state of constant velocity (which may be zero) unless it is acted upon by an external force.

See also: → Newton; → first; → law; → motion.

An approximate empirical relation between the rate of → heat transfer to or from an object and the temperature difference between the object and its surrounding environment. When the temperature difference is not too large: dT/dt = -k(T - T_s), where T is the temperature of the object, T_s is that of its surroundings, t is time, and k is a constant, different for different bodies.

See also: → Newton; → law; → cooling.

An approximate empirical relation between the rate of → heat transfer to or from an object and the temperature difference between the object and its surrounding environment. When the temperature difference is not too large: dT/dt = -k(T - T_s), where T is the temperature of the object, T_s is that of its surroundings, t is time, and k is a constant, different for different bodies.

See also: → Newton; → law; → cooling.

The universal law which states that the force of attraction between any two bodies is proportional to the product of their masses and inversely proportional to the square of the distance between them: F = G (m₁.m₂)/r², where G is the → gravitational constant.

See also: → Newton; → law; → gravitation.

The universal law which states that the force of attraction between any two bodies is proportional to the product of their masses and inversely proportional to the square of the distance between them: F = G (m₁.m₂)/r², where G is the → gravitational constant.

See also: → Newton; → law; → gravitation.

The three fundamental laws which are the basis of → Newtonian mechanics. They were stated in Newton’s Principia (1687). → Newton’s first law, → Newton’s second law , → Newton’s third law.

See also: → Newton; → law; → motion.

The three fundamental laws which are the basis of → Newtonian mechanics. They were stated in Newton’s Principia (1687). → Newton’s first law, → Newton’s second law , → Newton’s third law.

See also: → Newton; → law; → motion.

Same as the → Newton-Raphson method.

See also: → Newton; → method.

Same as the → Newton-Raphson method.

See also: → Newton; → method.

Colored circular → fringes formed when light beams reflected from two polished, adjacent surfaces, placed together with a thin film of air between them, interfere.
→ interference.

See also: → Newton; → ring.

Colored circular → fringes formed when light beams reflected from two polished, adjacent surfaces, placed together with a thin film of air between them, interfere.
→ interference.

See also: → Newton; → ring.

For an unbalanced force acting on a body, the acceleration produced is proportional to the force impressed; the constant of proportionality is the inertial mass of the body.

See also: → Newton; → second; → law; → motion.

For an unbalanced force acting on a body, the acceleration produced is proportional to the force impressed; the constant of proportionality is the inertial mass of the body.

See also: → Newton; → second; → law; → motion.

In classical mechanics, an analytical method applied to a material sphere to determine the gravitational field at a point outside or inside the sphere. Newton’s shell theorem states that:

1. The gravitational field outside a uniform spherical shell (i.e. a hollow ball) is the same as if the entire mass of the shell is concentrated at the center of the sphere.

2. The gravitational field inside the spherical shell is zero, regardless of the location within the shell.

3. Inside a solid sphere of constant density, the gravitational force varies linearly with distance from the center, being zero at the center of mass.
   For the relativistic generalization of this theorem,
   see → Birkhoff’s theorem.

See also: → Newton; → shell; → theorem.

In classical mechanics, an analytical method applied to a material sphere to determine the gravitational field at a point outside or inside the sphere. Newton’s shell theorem states that:

1. The gravitational field outside a uniform spherical shell (i.e. a hollow ball) is the same as if the entire mass of the shell is concentrated at the center of the sphere.

2. The gravitational field inside the spherical shell is zero, regardless of the location within the shell.

3. Inside a solid sphere of constant density, the gravitational force varies linearly with distance from the center, being zero at the center of mass.
   For the relativistic generalization of this theorem,
   see → Birkhoff’s theorem.

See also: → Newton; → shell; → theorem.

In a system where no external forces are present, every action force is always opposed by an equal and opposite reaction.

See also: → Newton; → third; → law; → motion.

In a system where no external forces are present, every action force is always opposed by an equal and opposite reaction.

See also: → Newton; → third; → law; → motion.

Of or pertaining to Sir Isaac Newton or to his theories or discoveries.

See also: Newtonian, from → Newton + -ian a suffix forming adjectives.

Of or pertaining to Sir Isaac Newton or to his theories or discoveries.

See also: Newtonian, from → Newton + -ian a suffix forming adjectives.

A particular solution of the → general relativity when the → gravitational mass is small. The → space-time is then approximated to the → Minkowski’s and this leads to
→ Newtonian mechanics.

See also: → Newtonian; → approximation.

A particular solution of the → general relativity when the → gravitational mass is small. The → space-time is then approximated to the → Minkowski’s and this leads to
→ Newtonian mechanics.

See also: → Newtonian; → approximation.

Same as the → gravitational constant.

See also: → Newtonian; → constant; → gravitation.

Same as the → gravitational constant.

See also: → Newtonian; → constant; → gravitation.

The use of → Newtonian mechanics to derive homogeneous and isotropic solutions of → Einstein’s field equations, which represent models of expanding Universe. The Newtonian cosmology deviates from the prediction of → general relativity in the general case of anisotropic and inhomogeneous models.

See also: → Newtonian; → cosmology.

The use of → Newtonian mechanics to derive homogeneous and isotropic solutions of → Einstein’s field equations, which represent models of expanding Universe. The Newtonian cosmology deviates from the prediction of → general relativity in the general case of anisotropic and inhomogeneous models.

See also: → Newtonian; → cosmology.

Any → fluid with a constant → viscosity at a given temperature regardless of the rate of → shear.

See also: → Newtonian; → fluid.

Any → fluid with a constant → viscosity at a given temperature regardless of the rate of → shear.

See also: → Newtonian; → fluid.

The focus obtained by diverting the converging light beam of a reflecting telescope to the side of the tube.

See also: → Newtonian; → focus.

The focus obtained by diverting the converging light beam of a reflecting telescope to the side of the tube.

See also: → Newtonian; → focus.

The limit attained by → general relativity when velocities are very smaller than the → speed of light or gravitational fields are weak. This limit corresponds to the transition between general relativity and the → Newtonian mechanics. See also → Newtonian approximation.

See also: → Newtonian; → limit.

The limit attained by → general relativity when velocities are very smaller than the → speed of light or gravitational fields are weak. This limit corresponds to the transition between general relativity and the → Newtonian mechanics. See also → Newtonian approximation.

See also: → Newtonian; → limit.

A system of mechanics based on → Newton’s law of gravitation and its derivatives. Same as → classical mechanics.

See also: → Newtonian; → mechanics.

A system of mechanics based on → Newton’s law of gravitation and its derivatives. Same as → classical mechanics.

See also: → Newtonian; → mechanics.

A potential in a field of force obeying the inverse-square law such as → gravitational potential.

See also: → Newtonian; → potential.

A potential in a field of force obeying the inverse-square law such as → gravitational potential.

See also: → Newtonian; → potential.

The Newton’s equations of motion, if they hold in any → reference frame,
they are valid also in any other reference frame moving with uniform velocity relative to the first.

See also: → Newtonian; → principle; → relativity.

The Newton’s equations of motion, if they hold in any → reference frame,
they are valid also in any other reference frame moving with uniform velocity relative to the first.

See also: → Newtonian; → principle; → relativity.

The laws of physics are unchanged under → Galilean transformation. This implies that no mechanical experiment can detect any intrinsic diff between two → inertial frames. Same as → Galilean relativity.

See also: → Newton; → relativity.

The laws of physics are unchanged under → Galilean transformation. This implies that no mechanical experiment can detect any intrinsic diff between two → inertial frames. Same as → Galilean relativity.

See also: → Newton; → relativity.

A telescope with a concave paraboloidal objective mirror and a small plane mirror that reflects rays from the primary mirror laterally outside the tube where the image is viewed with an eyepiece.

See also: → Newtonian; → telescope.

A telescope with a concave paraboloidal objective mirror and a small plane mirror that reflects rays from the primary mirror laterally outside the tube where the image is viewed with an eyepiece.

See also: → Newtonian; → telescope.

Immediately following in time, order, place, and so on.

Etymology (EN): M.E., from O.E. next, nehst, niehsta, nyhsta “nearest, closest,” superlative of neah “nigh” + superlative suffix. Cognate with Du. naast “next,” O.H.G. nahisto “neighbor,” Ger. nächst “next.”

Etymology (PE): Podâ, literally “placed after,” from *upada-, from *upa- “near, next, after,” + *dâ- “to place, put,” → thesis; cf. Baluci pôši “the day after tomorrow,” from pô- contraction of *upa- + *aušah- “dawn,”

• → aurora, + suffix -i; cf. also Baluci godâ (from *uidâ-?) “then, next;” Bašâgardi, Baluci randâ “next, then.”

Immediately following in time, order, place, and so on.

Etymology (EN): M.E., from O.E. next, nehst, niehsta, nyhsta “nearest, closest,” superlative of neah “nigh” + superlative suffix. Cognate with Du. naast “next,” O.H.G. nahisto “neighbor,” Ger. nächst “next.”

Etymology (PE): Podâ, literally “placed after,” from *upada-, from *upa- “near, next, after,” + *dâ- “to place, put,” → thesis; cf. Baluci pôši “the day after tomorrow,” from pô- contraction of *upa- + *aušah- “dawn,”

• → aurora, + suffix -i; cf. also Baluci godâ (from *uidâ-?) “then, next;” Bašâgardi, Baluci randâ “next, then.”