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

Magnitude defined for the combination of a photographic plate and a yellow filter, approximating the spectral sensitivity of the eye.

→ photo- + → visual; → magnitude.

A detector usually constituted by a p-n junction. Upon irradiation, the electron-hole pairs which are created, are immediately separated by the strong electric field across the junction, and a current is generated, which is proportional to the number of incident photons per second.

→ photo- + → voltaic; → detector.

A sequence of two or more words arranged in a grammatical construction and acting as a unit in a → sentence.

From L.L. phrasis "diction," from Gk. phrasis "speech, way of speaking, enunciation," from phrazein "to express, tell," from phrazesthai "to consider."

Vatpâr, literally "part of speech," from vat-, "to speak, say;" cf. (Kurd.) wittin "to speak, say," → letter, + pâr "piece, part, portion," → partial.

Pertaining to the physical sciences, especially physics.

→ physics + → -al.

Same as → physisorption.

→ physical; → adsorption.

The branch of chemistry dealing with the relations between the physical properties of substances and their chemical composition and transformations.

→ physical; → chemistry.

The state of a → physical system regarding its temperature, density, pressure, etc. at a given time.

→ physical; → condition.

A fundamental → physical quantity that is generally believed to be both universal in nature and constant in time.

→ physical; → constant.

Any of basic physical quantities, such as mass, length, time, electric charge, and temperature in terms of which all other kinds of quantity can be expressed.

→ physical; → dimension.

A theoretical principle which is deduced from particular observational facts regarding the behavior of matter. Physical laws are expressed by a general statement that a particular → physical phenomenon always occurs if certain → conditions are present.

→ physical; → law.

A real periodic variation in the rotation rate of a celestial object, as distinct from a → geometrical libration. In particular, slight oscillations in the → Moon's rotation caused by the → gravitational attraction of the Earth on the → equatorial bulge of the Moon's near side. The Moon's physical libration is about 0.03° in longitude and about 0.04° in latitude.

→ physical; → libration.

The branch of optics concerned with the wave properties of light, → diffraction, → polarization, and other phenomena for which the ray approximation of → geometric optics is not valid. Also called → wave optics.

→ physical; → optics.

Any of a set of physical properties whose values determine the characteristics or behavior of a system; for example, → mass, → size, → temperature, → luminosity, etc.

→ physical; → parameter.

A natural → phenomenon that can be explained by → physical laws.

→ physical; → phenomenon.

A physical → property that can be measured and/or calculated.

→ physical; → quantity.

A set of physical components chosen to study their relations.

→ physical; → system.

A specialist in → physics.

From physic, → physics, + → -ist.

Fizikdân, from fizik, → physics, + -dân "knower," present stem of dânestan "to know," → science.

The science that deals with matter and energy and their interactions.

M.E. fisyk(e), phisik(e), from O.Fr. fisique, from L. physica (fem. sing.) "study of nature," from Gk. physike episteme "knowledge of nature," from fem. of physikos "pertaining to nature," from physis "nature," from phyein "to bring forth, produce, make to grow," Gk. phy- "to become;" L. fui "I was," futurus "that is to be, future;" Ger. present first and second person sing. bin, bist; E. to be; O.Ir. bi'u "I am;" Lith. bu'ti "to be;" Rus. byt' "to be."

Loan from Fr. physique, as above.

A kind of → adsorption in which the forces involved are → intermolecular  → van der Waals forces. Same as → physical adsorption. See also → chemisorption.

Physi-, from → physical; → sorption.

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.