An Etymological Dictionary of Astronomy and Astrophysics

A member of a class of → pre-main sequence stars that experience dramatic changes in magnitude and → spectral type. During an outburst the luminosity of such an object can increase by several orders of magnitude on short time-scales (few months to few years). The phenomenon is explained by abrupt mass transfer from an → accretion disk to a young, low mass → T Tauri star (accretion rates 10^-4 to 10^-3 solar masses per year). → EX Lupi; → Z CMa.

See also: F and U, alphabet letters; Orionis, → Orion; → object.

Completely filled; containing all that can be held; complete; entire; maximum.

Etymology (EN): O.E. full “completely, full,” from P.Gmc. *fullaz (cf. O.Fris. ful, O.N. fullr, O.H.G. fol, Ger. voll), akin to Pers. por, as below.

Etymology (PE): Por “full;” Mid.Pers. purr “full;” O.Pers. paru- “much, many;” Av. parav-, pauru-, pouru-, from
par- “to fill;” PIE base *pelu- “full,” from *pel- “to be full;” cf. Skt. puru- “much, abundant;” Gk. polus “many,” plethos “great number, multitude;” O.E. full.

Same as → apogee full Moon.

See also: → full; → micro-; → Moon.

1. The moon at → opposition, when it appears as a round disk to an observer on the Earth because the illuminated side is toward him.
   

2. The phase when the → age of the moon, measured from → new moon, is 14.5 days.

Etymology (EN): → full; → moon.

Etymology (PE): Pormâh, from Mid.Pers. purrmâh, from Av. pərənô.manha- “full moon” (cf. Skt. pūrná-mās-);
→ full; → moon.

Same as → perigee full Moon.

See also: → full; → super-; → Moon.

The full width of a → profile (spectral line or a cross-cut in an image component) at half-maximum intensity.

Etymology (EN): → full; → width; → half; → maximum.

Etymology (PE): Pahnâ, → width; nim, → half; bišiné, → maximum.

A mathematical rule between two sets which assigns to each element of the first exactly one element of the second, as the expression y = ax^b.

Etymology (EN): From M.Fr. fonction, from O.Fr. function, from L. functio (gen. functionis) “performance, execution,” from functus, p.p. of fungor “to perform, execute.”

Etymology (PE): Karyâ, from Av. kairya- “function;” cf.
Mod.Pers. Laki karyâ “done,” Awromâni kiriyây, kiria “to be done,”
from kar- “to do” (Mod.Pers. kar-, kardan “to do, to make;” Mid.Pers. kardan; O.Pers./Av. kar- “to do, make, build;” Av. kərənaoiti “he makes;” cf. Skt. kr- “to do, to make,” krnoti “he makes, he does,” karoti “he makes, he does,” karma “act, deed;” PIE base k^wer- “to do, to make”)

• -ya suffix of verbal adjectives and nouns (e.g. išya- “desirable,” jivya- “living, fresh,” haiθya- “true,” maidya- “middle,” dadya- “grain”); cf. Skt. kāryá- “work, duty, performance.”

1. Math.: Of, relating to, or affecting a function.
   

2. A → function that associates a → real number
   or → complex number to a function or a → set of functions. A functional can be considered as a function of a set of several infinite and continuous → variables.

See also: → function; → -al.

1. Being an original or primary source.
   
2. A basic principle, rule, law, or the like, that serves as the groundwork of a system.

Etymology (EN): L.L. fundamentalis “of the foundation,” from L. fundamentum “foundation,” from fundare “to found.”

Etymology (PE): Bonyâdin, adj. of bonyâd “foundation, basis,” from *bondâd (Mid.Pers. bune dâtak “foundation, basis”), from bon “basis; root; foundation; bottom” (Mid.Pers. bun “root; foundation; beginning,” Av. būna- “base, depth,” cf. Skt. bundha-, budhná- “base, bottom,” Pali bunda- “root of tree”)

• dâd “given,” from dâdan “to give” (Mid.Pers. dâdan “to give,” O.Pers./Av. dā- “to give, grant, yield,” dadāiti “he gives;” Skt. dadáti “he gives,” Gk. didomi “I give,” tithenai “to put, set, place;” L. dare “to give, offer;” Rus. delat “to do;” O.H.G. tuon, Ger. tun, O.E. don “to do”).

A physical constant that cannot be expressed in terms of other constants of nature, such as the charge of the electron.

See also: → fundamental; → constant.

Same as the → fundamental interaction.

See also: → fundamental; → force.

The lowest frequency in a complex wave.

See also: → fundamental; → frequency.

Any of the four interactions in nature between bodies of matter and that are mediated by one or more particles. Also called the
→ fundamental force. In order of decreasing strength, the four fundamental interactions are the → strong interaction, the → electromagnetic interaction, the → weak interaction, and the → gravitational interaction.

See also: → fundamental; → interaction.

Same as → elementary particle.

See also: → fundamental; → particle.

A relatively bright star for which coordinates and proper motion have been determined to a very high degree of accuracy.

See also: → fundamental; → star.

1. To unite or blend into a whole, as if by melting together. Related terms: → coalesce; → merge; → unify.
   

2. To combine or blend by melting together; melt (Dictionary.com).

Etymology (EN): From L. fusus “poured, melt, cast,” p.p. of fundere “to pour, melt.”

Etymology (PE): 1) Ividan, literally “to make (combine) into one entity,” from iv, → one, + -idan infinitive suffix.

2. Godâxtan “to melt,” from Mid.Pers. vitâxtan, vitâcitan “to melt,” from Av. vi-taxti- “flowing away, melting,” from vi- “apart, away from, out” (O.Pers. viy- “apart, away;” cf. Skt. vi- “apart, asunder, away, out;” L. vitare “to avoid, turn aside”) + tak- “to run, to flow,” taciāp- “flowing water,” tacinti (3pl.pers.act.) “to flow,”
   tacar- “course,” tacan “current, streaming;” Mod.Pers. tâz-, tâxtan “to run; to hasten; to assault,” tâzi “swift (greyhound),” tak “running, rush;”
   Mid.Pers. tâz-, tâxtan “to flow, to cause to walk,” tc- “to flow, to walk,” tag “running, attack,” tâzig “swift, fast;”
   Khotanese ttajs- “to flow, to walk;” cf. Skt. tak- “to rush, to hurry,” takti “runs;” O.Ir. tech- “to flow;” Lith. teketi “to walk, to flow;” O.C.S. tešti “to walk, to hurry;” Tokharian B cake “river;” PIE base *tek^w- “to run; to flow;” → flow.

1. The act or process of fusing; the state of being → fused; that which is fused; the result of fusing.
   

2. A → nuclear reaction between atomic nuclei (→ nucleus) as a result of which a heavier nucleus is formed and a large quantity of → nuclear energy is released. → proton-proton chain, → CNO cycle, → nucleosynthesis.
   

3. Change of the → state of a → substance from → solid to → liquid which occurs at a definite → temperature at a given applied → pressure. Same as melting.

Etymology (EN): From M.Fr. fusion, from L. fusionem, from fusus, p.p. of fundere “to pour, melt.”

Etymology (PE): Verbal noun form of → fuse.

General: Time that is to be or come hereafter.
In a → space-time diagram, those events that could be influenced by a given element.

Etymology (EN): M.E. futur, from O.Fr., from L. futurus “about to be,” irregular suppletive future participle of esse “to be.”

Etymology (PE): Âyandé “future” agent noun/adjective of âmadan “to come, to occur, to become,” from Mid.Pers. âmatan;
O.Pers. gam- “to come; to go,” Av. gam- “to come; to go,” jamaiti “goes;” Proto-Iranian *āgmatani; Skt. gamati “goes;” Gk. bainein “to go, walk, step;” L. venire “to come;” Tocharian A käm- “to come;” O.H.G. queman “to come;” E. come; PIE root *gwem- “to go, come.”

The set of all points in a → space-time diagram that are reached by signals travelling from a specified point at the speed of light.

See also: → future; → light; → cone.

1. Loose, light, fibrous, or → fluffy matter.
   

2. A mass or coating of such matter.
   

3. (Of an image) A blur. (Dictionary.com).

Etymology (EN): Of unknown origin; cf. Du. voos “spongy, woolly.”

Etymology (PE): Porz “short fuzzy ends of fibers on the surface of cloth, any downy coating,” of unknown etymology.

The first step carried out in a → fuzzy logic system during which a → crisp set of → input data are gathered and converted to a → fuzzy set using fuzzy → linguistic variables, fuzzy linguistic terms, and → membership functions.

See also: Verbal noun of → fuzzify; → -tion.

To convert a → crisp set to a → fuzzy set in a → fuzzy logic system.

See also: → fuzzy; → -fy.

The state or condition of being → fuzzy.

See also: → fuzzy; → -ness.

1. Of the nature of or resembling → fuzz.
   

2. Covered with fuzz.
   

3. Indistinct; → blurred (Dictionary.com).
   See also: → fuzzy image, → fuzzy logic, → fuzzy set.

Etymology (EN): From → fuzz + -y adj. suffix, from O.E. -ig, cognate with L. -icus, → -ic.

Etymology (PE): Porzvâr “resembling fuzz,” from porz, → fuzz,

• -var, a suffix of possession, similarity, and aptitude (e.g., omidvâr, sezâvâr, sugvâr, šâhvâr, gušvâr), → -oid.

Same as → blurred image.

See also: → fuzzy; → image.

A way of → mapping an → input space to an → output space using → fuzzy logic. FIS uses a collection of fuzzy → membership functions and rules, instead of Boolean logic, to reason about data. Also called → fuzzy logic system.

See also: → fuzzy; → inference; → system.

A process used in a → fuzzy logic system where the → truth value for the premise of each rule is computed and applied to the conclusion part of each rule.
This results in one fuzzy set to be assigned to each output variable for each rule.

See also: → fuzzy; → inference.

A mathematical logic that recognizes more than simple → true and → false → propositions. With fuzzy logic, propositions can be represented with degrees of truthfulness and falsehood. In this system, → truth values are → fuzzy sets without sharp boundaries (→ crisp set)
in contrast with → classical logic. Fuzzy logic is applied to a wide range of problems including: industrial control, domestic goods, decision making, robotics, intelligent machines, and image processing in medicine.

See also: → fuzzy; → logic.

An engineering system which uses → fuzzy logic. It
generally consists of four main components: → fuzzification interface (fuzzifier), → fuzzy rule base, → fuzzy inferencing unit, and
→ defuzzification interface (difuzzifier). Also called → fuzzy inference system.

See also: → fuzzy; → logic; → system.

A rule base in a → fuzzy logic system constructed to control the → output variable. A fuzzy rule is a simple if-then rule with a condition and a conclusion.

See also: → fuzzy; → rule; → base.

A set of → truth values in → fuzzy logic that does not have sharp boundaries. Instead, set members have degrees of membership. If the value of 1 is assigned to objects entirely within the set and a 0 is assigned to objects outside of the set, then any object partially in the set will have a value between 0 and 1. This contrast with → crisp sets in → classical logic where members assume a precise value of 1 or 0. Fuzzy sets were first introduced by Lotfi A. Zadeh (1965) and defined as follows. Let X be a space of points, with a generic element of X denoted by x. Thus X = {x}. A fuzzy set A in X is characterized by a → membership function  f_A(x) which associates with each point in X a real number in the interval [0,1], with the values of f_A(x) at x representing the “grade of membership” of x in A. Thus, the nearer the value of f_A(x) to unity, the higher the grade of membership of x in A. Generally, the intersection operations of fuzzy sets are the expansion of that operation on → nonfuzzy sets. In other words, operations on nonfuzzy sets are a particular case of operations on fuzzy sets.

See also: → fuzzy; → set.