An Etymological Dictionary of Astronomy and Astrophysics

1. A subtle difference or distinction in expression, meaning, response, etc.
   

2. A very slight difference or variation in color or tone (Dictionary.com).

Etymology (EN): From Fr. nuance “shade of color, hue,” from nuer “to shade,” from nue “cloud,” from L. nubes “a cloud, mist, vapor,” → nebula.

Etymology (PE): Sâgen, from Xoyini sâgené “shade, shadow,” related to sâyé, → shadow.

Of or pertaining to a → nucleus.

Etymology (EN): From nucle(us), → nucleus, + -ar variant of the adjective-forming suffix → -al.

Etymology (PE): Haste-yi, from hasté, → nucleus, + -i adjective-forming suffix.

The region of high potential energy through which a charged particle must pass on entering or leaving an atomic nucleus. → Gamow barrier.

See also: → nuclear; → barrier.

A → nuclear reaction inside a star that produces the energy to make the star shine and also transform chemical elements into others.

See also: → nuclear; → burning.

The positive electric charge on the nucleus of an atom.

See also: → nuclear; → charge.

→ nuclear burning.

See also: → nuclear; → combustion.

Apparent cross-section possessed by an atomic nucleus when it undergoes a particular type of collision process.

See also: → nuclear; → cross section.

The density of an atomic nucleus (about 10¹⁴ g/cm³).

See also: → nuclear; → density.

Energy released during a nuclear reaction as the result of the conversion of mass into energy. → mass-energy equivalence.

See also: → nuclear; → energy.

A → nuclear reaction in which a heavy atomic nucleus splits into two or more approximately equal parts, usually as the result of the capture of a slow, or → thermal neutron
by the nucleus. It is normally accompanied by the emission of further neutrons or → gamma rays and very large amounts of energy. The neutrons can continue the process as a → chain reaction, so that it becomes the source of energy in a → nuclear reactor or an atomic bomb. It may also be a trigger for → nuclear fusion in a hydrogen bomb. Fission occurs spontaneously in nuclei of uranium-235, the main fuel used in nuclear reactors.

See also: → nuclear; → fission.

The attractive force which acts between nucleons when they are extremely close together (closer than 10^-13 cm).

See also: → nuclear; → force.

A substance, such as uranium-238 or plutonium-239, which undergoes nuclear fission in a nuclear reactor.

See also: → nuclear; → fuel.

A → nuclear reaction between atomic nuclei as a result of which a heavier → atomic nucleus is formed, a small fraction of mass is lost, and a large quantity of energy is released. Nuclear fusion is the source of the energy of stars.

See also: → nuclear; → fusion.

An analysis technique applied to some atomic nuclei that have the property to behave as small magnets and respond to the application of a magnetic field by absorbing or emitting electromagnetic radiation. When nuclei which have a magnetic moment (such as ¹H, ¹³C, ²⁹Si, or ³¹P) are submitted to a constant magnetic field and at the same time to a radio-frequency alternating magnetic field, the nuclear magnetic moment is excited to higher energy states if the alternating field has the specific resonance frequency. This technique is especially used in spectroscopic studies of molecular structure and in particular provides valuable information in medicine that can be used to deduce the structure of organic compounds.

See also: → nuclear; → magnetic; → resonance.

The magnetism associated with the magnetic field generated by atomic nuclei.

See also: → nuclear; → magnetism.

The quantity of matter in a nucleus, which is less than the total mass of its nucleons by its binding energy divided by the square of the speed of light.

See also: → nuclear; → mass.

The branch of physics which is concerned with the study of
atomic nuclei, subatomic particles, and their exploitation.

See also: → nuclear; → physics.

Electric or motive power whose primary source is nuclear energy.

See also: → nuclear; → power.

A process in which an → atomic nucleus changes, including → radioactive decay of naturally occurring and man-made → isotopes, → nuclear fission, and → nuclear fusion.

See also: → nuclear; → process.

A process in which the energy, composition, or structure of an atomic nucleus changes.

See also: → nuclear; → reaction.

A device in which a nuclear fission chain reaction is maintained and controlled for the production of nuclear energy or radioactive isotopes.

See also: → nuclear; → reactor.

The total → angular momentum of a → nucleus, represented by symbol I. The nucleus, which is composed of neutrons and protons, acts as if it is a single entity which has intrinsic angular momentum. The nuclear spin depends on the → mass number; if the mass number is odd then the nucleus has half-integer spin like the electron while if the nucleus has even mass number then its spin will be integer spin.

See also: → nuclear; → spin.

In → nucleosynthesis models, the condition in which all nuclear species are in equilibrium under exchange of → protons and → neutrons. Matter in nuclear statistical equilibrium is characterized by a large abundance of iron peak nuclei.

In such equilibria abundance of each nuclide can be calculated from
repeated application of → <i><a class="linkVoir" href="/terms/saha-equation/">Saha equation</a></i>.

See also: → nuclear; → statistical; → equilibrium.

The time required for a star to exhaust its hydrogen (H) supply in → nuclear fusion. The nuclear time scale is given by the relation t = E/L, where E is the total nuclear energy that can be generated by a star and L is the stellar → luminosity. Assuming that the end point of fusion is → iron (Fe), the → atomic mass difference between H and Fe is Δm = 0.008 m_H. Therefore, the maximum amount of energy a star with a hydrogen mass M can release is Δ M = 0.008 Mc². The nuclear time scale is then: t = 0.008 c²M/L. However, stars use up only a fraction of their hydrogen supply, because only the inner part of the star is hot enough for fusion. For example, the Sun will spend only about 10% of its hydrogen supply before evolving into a → red giant. In other words, the solar life time on the → main sequence is about 10¹⁰ years.

See also: → nuclear; → time;
→ scale.

A change in the → energy level or state of an atomic → nucleus involving a → quantum of energy.

See also: → nuclear; → transition.

The changing of atoms of one element into those of another by suitable nuclear reactions.

See also: → nuclear; → transmutation.

A particular type of radioactive waste that is produced as part of the nuclear fuel cycle. These include extraction of uranium from ore, concentration of uranium, processing into nuclear fuel, and disposal of byproducts.

See also: → nuclear; → waste.

A constituent of the atomic nucleus, i.e. a proton or a neutron.

Etymology (EN): From nucle(us), → nucleus, + -on a suffix used in the names of subatomic particles, probably extracted from → ion.

Etymology (PE): Haston, from hast(é)→ nucleus + -on, as above.

The practical applications of nuclear physics, and the techniques associated with those applications.

Etymology (EN): From → nucleon + → -ics.

The process by which → nuclear reactions at very high temperatures and pressures produce the various → chemical elements of the → periodic table, either in the → Big Bang or in stellar interiors. See also → primordial nucleosynthesis, → stellar nucleosynthesis, → explosive nucleosynthesis.

Etymology (EN): From nucleo-, combining form of → nucleus +
→ synthesis.

Etymology (PE): Haste-handâyeš, from hasté→ nucleus + handâyeš→ synthesis.

Produce through → nucleosynthesis.

See also: → nucleosynthesis; → -ize.

Of, pertaining to, proceeding by, or involving → nucleosynthesis.

See also: Adj. of → nucleosynthesis.

The era following the leptonic era, between 1 second and 1000 seconds after the Big Bang, when neutrons were abundant and helium and deuterium were synthesized.

See also: → nucleosynthetic; → era.

A process involving → nucleosynthesis, such as → r-process and → r-process.

See also: → nucleosynthetic; → process.

1. Core of an atom, where most mass and all positive charge is concentrated. It consists of protons and neutrons.
   
2. Of a comet, the stellar-appearing frozen core, containing most of the cometary mass, in the head of a comet.

Etymology (EN): From L. nucleus “kernel,” from nucula “little nut,” diminutive of nux “nut,” from PIE *knu(k) “lump” (cf. M.Ir. cnu, Welsh cneuen, M.Bret. knoen “nut,” O.N. hnot, O.E. hnutu “nut”).

Etymology (PE): Hasté, variants asté “kernel, fruit stone,” ostoxân “bone,”
from Mid.Pers. astak “fruit stone, bone,” ast “bone;” Av. ast- “bone;” cf. Skt. asthi- “bone;” Gk. osteon; L. os; Hittite hashtai-; PIE base *os-.

A species of atom characterized by the constitution of its nucleus, i.e. by the numbers of protons and neutrons it contains.

Etymology (EN): From nucl(eo), → nucleus,

• -ide, from Gk. eidos “shape.”

Etymology (PE): Hastevâr, from hasté, → nucleus, + -vâr a suffix meaning “resembling, like,” from Mid.Pers. -wâr, Av. -vara, -var, cf. Skt. -vara.

1a) General: Being or amounting to nothing; nil; nonexistent; without value, effect, or significance.

1b) Math.: Of a set, empty. Of measure zero.

1c) Electronics: A point of minimum signal reception, as on a radio direction finder or other electronic meter.

2. To make null; cancel.

Etymology (EN): From M.Fr. nul, from L. nullus “not any, none,” from ne- “not, no” → non- + illus “any,” dimunitive of unus “one.”

Etymology (PE): Nul, from na-, → non-, + -ul
a variant of the Pers. suffix → -al. Nulidan, infinitive from nul.

1. The path taken by a light ray in a curved → space-time just as a → timelike geodesic describes the path of a material particle.
   

2. A → geodesic of length zero.

See also: → null; → geodesic.

Statistics: The assumption of the absence of a particular pattern in a set of data. The null hypothesis, denoted by H₀, is put forward to be rejected in order to support an → alternative hypothesis.

See also: → null; → hypothesis.

A lens used in the optical testing of an aspheric surface. It converts a spherical wavefront into one that precisely matches the surface under test. When the wavefront is reflected from that surface, it reverses its path and, if the surface is perfect, results in a perfect emerging spherical wavefront, which is easily evaluated.

See also: → null; → lens.

An m × n matrix whose elements are all zeros. Also
known as zero matrix.

See also: → null; → matrix.

A method of comparing, or measuring, forces, electric currents, etc., by so opposing them that the pointer of an indicating apparatus remains at, or is brought to, zero, as contrasted with methods in which the deflection is observed directly. Same as zero method.

See also: → null; → method.

A device using the → nulling interferometry technique.

See also: Agent noun of the verb → null.

The fraction of time that a → pulsar undergoes → pulse nulling. For most → nulling pulsars this fraction can range from zero (for the → Vela pulsar) to more than 50%.

See also: → null; → -ing; → fraction.

A technique for blocking the light of a bright source in order to reveal a faint source near it. This technique uses destructive → interference
between two or more → coherent beams from a number of telescopes to make the bright center dark. Nulling interferometry can be used to search the region immediately around a star for → extrasolar planets and
→ circumstellar dust clouds by suppressing the star’s glare.

See also: Nulling, from → null; → interferometry.

A → pulsar that undergoes → pulse nulling.

See also: → null; → -ing; → pulsar.

1. Any real or complex numeral quantity.
   
2. The sum, total, count, or aggregate of a collection of units.

Etymology (EN): From M.E. nombre, from O.Fr. nombre, from L. numerus “a number, quantity,” from PIE base *nem- “to divide, distribute, allot.”

Etymology (PE): Adad, loan from Ar.
Šomâr, šomâré, noun from šomârdan “to count, reckon, calculate, enumerate, account for,” from Mid.Pers. ôšmârtan; Av. base (š)mar- “to have in mind, remember, recall,” pati-šmar- “to recall; to long for,” hišmar-; cf. Skt. smar- “to remember, become aware,” smarati “he remembers;” L. memor, memoria; Gk. mermera “care,” merimna “anxious thought, sorrow,” martyr “witness.”

Number of a particular type of object found in each unit volume.

See also: → number; → density.

The → base of the → natural logarithm.
It is defined as:

e = lim (1 + 1/n)ⁿ when n→ ∞. For n = 1, e = 2 and for n = 10, e = 2.5937424601, etc. The number e is → irrational (Euler, 1737) and → transcendental (Hermite, 1873).

See also: → number;

Symbol, π, for the ratio of the circumference of a circle to its diameter in Euclidean geometry; a fundamental mathematical constant, equal to 3.14159… π is an → irrational number
(Lambert, 1761) and also a → transcendental number (von Lindemann, 1882). The most accurate determination of π prior to the Scientific Revolution belongs to the Iranian mathematician Jamshid Kashani, who gave 16 correct decimal places in A.D. 1424. With the advent of → calculus and more recently the invention of powerful computers, the decimal representation of π has now been computed to more than 10¹² digits.

See also: The π notation, representing the first letter of the Gk. word περιμετρον → perimeter, was first used by the British mathematician William Jones (1675-1749) in 1706. Its use was generalized after its adoption by the Swiss mathematician Leonard Euler (1707-1783) in 1737; → number.

Same as → numeral system.

See also: → number; → system.

The conversion of a → number system with a given → base to another system with a different base; such as the conversion of a → decimal number (base 10) to a → binary number system (base 2). In order to convert a number into its representation in a different number base, we have to express the number in terms of powers of the other base. For example, to convert the decimal number 100 to base 3, we must figure out how to express 100 as the sum of powers of 3. We proceed as follows:

1: Divide the decimal number to be converted (100) by the value of the new base (3).

2: Get the remainder from Step 1 (that is 1) as the rightmost digit (least significant digit) of new base number.

3: Divide the quotient of the previous divide (33) by the new base.

4: Record the remainder from Step 3 (0) as the next digit (to the left) of the new base number.

Repeat Steps 3 and 4, getting remainders from right to left, until the quotient becomes zero in Step 3 (2 and 0).

The last remainder thus obtained (1) will be the most significant digit of the new base number.

Therefore, 100₁₀ = 10201₃.

Conversely, to convert from another base to decimal we must:

1: Determine the column (positional) value of each digit.

2: Multiply the obtained column values (in Step 1) by the digits in the corresponding columns.

3: Sum the products calculated in Step 2. The total is the equivalent value in decimal.

For example, the binary number 1100100 is determined by computing the place value of each of the digits of the number:

(1 × 2⁶) + (1 × 2⁵) + (0 × 2⁴) +
(0 × 2³) + (1 × 2²) + (0 × 2¹) + (0 × 2⁰) = 64 + 32 + 0 + 0 + 4 + 0 + 0 = 100.

See also: → number; → system; → conversion.

The branch of mathematics that studies the relationship between integers and their generalization.

See also: → number; → theory.

1. A symbol, group of symbols, or word used to express a number. For any number there is an infinite number of numeral expressions. For example, the number two can be written as 2, II, binary 10, 4/2, 18/8, etc.
   
2. Of, pertaining to, or consisting of numbers or numerals.

Etymology (EN): From L.L. numeralis “of, or belonging to number,” → number + → -al

Etymology (PE): Šomârâl, from šomâr, → number,

• -al, → -al.

A set of → symbols and → rules for representing → numbers. Same as → number system. See also:

→ Greek numeral system, → Roman numeral system, → Indian numeral system.

See also: → numeral; → system.

The quantity x in a fraction x/y). The quantity y is
the → denominator.

Etymology (EN): L.L. numerator “a counter, numberer,” from L. numera(re)
“to number,” → number + -tor a suffix forming personal agent nouns from verbs and, less commonly, from nouns.

Etymology (PE): Šomârân, agent noun of šomârdan, → number.

Relating to or expressed in numbers.

See also: Adj. of → number.

The study of methods for approximation of solutions of various classes of mathematical problems including error analysis.

See also: → numerical; → analysis.

The prediction of the evolution of a system via numerical construction of approximate solutions to the governing equations.

See also: → numerical; → modeling.

Another name for → numerical modeling.

See also: → numerical; → simulation.

The second brightest star in the constellation → Sagittarius. It is a blue-white → massive star of → spectral type B2.5 V lying 225 → light-years away.

See also: Unusual name of Babylonian origin, of unknown significance.

To undergo or show → nutation.

Etymology (EN): Nutate, back formation from → nutation.

Etymology (PE): Langârdan, from lang “lame” + ârdan short form of âvardan “to cause or produce; to bring,” → production.

1. Mechanics: A wobbling motion of a spinning → rigid body, such as a top, as it → precesses about its vertical axis.
   

2. Astro.: A slight nodding motion of the Earth’s axis of rotation, which has a principal period of 18.6 years. It is primarily caused by lunar → perturbations, and is superimposed on the → precession of the equinoxes and moves the equinox as much as 17’’ ahead of or behind its mean position.

Etymology (EN): Fromm L. nutation-, from nutat(us), p.p. of nutare “to wobble, to sway, to nod repeatedly,” from nu “nod” + -ta frequentative suffix + -tus p.p. ending + -ion a suffix denoting action or condition.

Etymology (PE): Kaltâv, from Kermâni keletow, Malâyeri kallatow “wobbling,” from kal, kalleh “head” + tâv, tow, tâb “swing, twist,” from tâbidan “to twist, to spin.”

Same as → equation of the equinoxes.

See also: → nutation; → right ascension.

A drive mechanism used to move a radar beam in a circular, spiral, or conical path periodically.

See also: Agent noun of → nutate.

1. Nourishing; providing nourishment or nutriment.
   

2. Containing or conveying nutriment, as solutions or vessels of the body.
   

3. A nutrient substance (Dictionary.com).

Etymology (EN): From L. nutrientem, pr.p. of nutrire, → nourish.

Etymology (PE): Fârmand, from present stem of fâridan, + -mand.

1. Any substance or matter that, taken into a living organism, serves to sustain it in its existence, promoting growth, replacing loss, and providing energy.
   

2. Anything that nourishes; nourishment; food (Dictionary.com).

Etymology (EN): From L. nutrimentum “nourishment; support,” from nutrire, → nourish.

Etymology (PE): Fârâk, from present stem of fâridan, → nourish,

• -âk (as in xorâk, pušâk, etc.).

1. The act or process of nourishing or of being nourished.
   

2. The science or study of, or a course of study in, nutrition, especially of humans (Dictionary.com).

See also: Verbal noun from L. nutrire, → nourish.

A person who is trained or expert in the science of nutrition.

See also: → nutrition; → -ist.

1. Serving to nourish; providing nutriment; nutritious.
   

2. Of, pertaining to, or concerned with nutrition (Dictionary.com).

See also: Adjective and agent noun from L. nutrire, → nourish.