An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

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.

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.

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.

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.

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

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.

→ 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.

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.

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.

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.

→ 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.

→ nested; → multiplication.

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

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.

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.

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.

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."

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.

From → neuter + → -al.

→ neuter.

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

→ neutral; → atom.

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

→ neutral; → density; → filter.

Same as → neutral density filter.

→ neutral; → filter.

A gas which is not ionized.

→ 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.

→ 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.

→ 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.

→ neutral; → point.