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

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%.

→ 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.

Nulling, from → null; → interferometry.

A → pulsar that undergoes → pulse nulling.

→ null; → -ing; → pulsar.

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

From M.E. nombre, from O.Fr. nombre, from L. numerus "a number, quantity," from PIE base *nem- "to divide, distribute, allot."

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.

→ 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).

→ 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.

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.

→ 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.

→ number; → system; → conversion.

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

→ 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.

From L.L. numeralis "of, or belonging to number," → number + → -al

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.

→ numeral; → system.

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

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.

Šomârân, agent noun of šomârdan, → number.

Relating to or expressed in numbers.

Adj. of → number.

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

→ numerical; → analysis.

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

→ numerical; → modeling.

Another name for → numerical modeling.

→ 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.

Unusual name of Babylonian origin, of unknown significance.

To undergo or show → nutation.

Nutate, back formation from → nutation.

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.

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.

Kaltâv, from Kermâni keletow, Malâyeri kallatow "wobbling," from kal, kalleh "head" + tâv, tow, tâb "swing, twist," from tâbidan "to twist, to spin."