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

A spectral line whose origin is not clearly established. → line identification.

→ unidentified; → line.

1) The process of unifying or uniting; union.
2) The state or condition of being unified (Dictionary.com).

Verbal noun of → unify.

Without variations; identical, always the same in quality, degree, character, or manner.

→ uni- + → form.

Yekdis, from yek, → uni-, + dis, → form; yeknavâxt, literally "with one rhythm," from yek, → one, + navâxt "rhythm," from navâxtan, navâzidan "to play an instrument; to gratify," navâ "music, song, melody" (Mid.Pers. nw'c "to treat kindly, honour," niwag "music, melody;" Proto-Iranian *ni-uac-, from ni- "down; into," → ni- (PIE), + *uac- "to speak, treat kindly").

The motion of an object around a fixed point at a constant angular speed, and at constant radius.

→ uniform; → circular; → motion.

A field that at a given instant has the same value at all points within a specified region of interest.

→ uniform; field.

A → magnetic field whose direction does not change and whose strength is constant at every point.

→ uniform; → magnetic; → field.

Motion at a constant → velocity. The state of rest is a special case of uniform motion. → accelerated motion; → inertial motion.

→ uniform; motion.

1) Of, characterized by, or conforming to → uniformity.
2) Of or relating to → uniformitarianism.

→ uniformity + -arian.

The doctrine whereby geologic processes (→ erosion, → deposition, → compaction, and → uplift) observed at Earth's surface now are the same that have shaped Earth's landscape over long periods of time in the past. The term uniformitarianism was first used in 1832 by William Whewell, to present an alternative explanation for the origin of the Earth. The prevailing view at that time was that the Earth was created through supernatural means and had been affected by a series of catastrophic events such as the biblical Flood. This theory is called → catastrophism. The ideas behind uniformitarianism originated with the work of Scottish geologist James Hutton. In 1785, Hutton presented at the meetings of the Royal Society of Edinburgh that the Earth had a long history and that this history could be interpreted in terms of processes currently observed. For example, he suggested that deep soil profiles were formed by the weathering of bedrock over thousands of years. He also suggested that supernatural theories were not needed to explain the geologic history of the Earth (PhysicalGeography.net).

→ uniformitarian; → -ism.

The state or quality of being uniform.

→ uniform; → -ity.

To make or become a single unit or entity. → grand unified theory

M.Fr. unifier, from L.L. unificare "to make one," from L. uni-, → one, + facere "to make" (cf. Fr. faire, Sp. hacer), from PIE base *dhe- "to put, to do" (cognate with Mod.Pers. dâdan "to give;" O.Pers./Av. dā- "to give, grant, yield," dadāiti "he gives; puts;" Skt. dadáti "puts, places;" Hitt. dai- "to place;" Gk. tithenai "to put, set, place;" Lith. deti "to put;" Czech diti, Pol. dziac', Rus. det' "to hide," delat' "to do;" O.H.G. tuon, Ger. tun, O.E. don "to do").

Yegânestan, yegânidan "to make one," infinitive from yek, → one.

Difficult or impossible to believe.

→ un-; → imaginable.

General: The act of uniting two or more things.
A number of persons, organizations, states, etc., joined or associated together for some common purpose, e.g. → International Astronomical Union (IAU).
Math.: A set containing all the elements of two or more sets being combined. It is represented by ∪.

M.E. from O.Fr. union from L.L. unionem (nominative unio) "oneness, unity," from unus, → one, cognate with Pers. yek, as below.

Yekâyeš, from yek, → one, + -ây- epenthetic vowel, + -eš verbal noun suffix, → -tion.

Existing as the only one or as the sole example.
Limited to a single outcome or result. → uniqueness theorem.

From Fr. unique, from L. unicus "single, sole," from unus, → one.

Yektâ "unique," from yek, → one, + tâ "fold, plait, ply; piece, part" (Mid.Pers. tâg "piece, part").

The state or condition of being → unique.

Noun from → unique.

1) Physics: A → potential that satisfies both → Poisson's equation and the → boundary conditions pertinent to a particular field is the only possible potential.
2) Math.: If two → continuous functions φ(t) and ψ(t) have one and the same → Laplace transform F(p), then these functions are identically equal.
3) Astro.: A → black hole can only be characterized by its → mass, → electric charge, and → angular momentum. See also → no hair theorem.

→ uniqueness; → theorem.

A quantity or dimension adopted as a standard of measurement.
Math.: The lowest positive natural number.
The first digit to the left of the decimal point in decimal notation, representing a whole number less than ten.
An element in a ring that has a multiplicative inverse.

Back formation from → unity.

Yekâ, yekân, from yek, → one.

A vector of length 1, also called a direction vector.

→ unit; → vector.

1) The condition of being → unitary.
2) → quantum unitarity.

→ unitary; → -ity.

1) Of or pertaining to a unit or units; having the indivisible character of a unit.
2) Math.: An → operator  U satisfying the relations: U⁺ U = 1, U U⁺ = 1, where U⁺ is the → adjoint .

→ unit + -ary.