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

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.

An approximation used in many stellar atmosphere models that depict the atmosphere as being only one-dimensional and bounded at the top and bottom by horizontal plane surfaces normal to the direction of gravity.

→ plane; → parallel; → atmosphere.

The study of the structure, composition, as well as physical and chemical properties of the planets of the solar system, including their atmospheres and their immediate cosmic environment.

→ planetary; → physics.

A projection or representation of the whole or a part of a sphere on a plane. In particular, a polar projection of the celestial sphere or the Earth on a plane.

→ plani-; → sphere.

Of or relating to → planisphere.

→ planisphere + → -ic..

The most common form of the → astrolabe in which both the → celestial sphere and the observer's horizon are projected on to one or more plane surfaces by means of the stereographic projection. See also → universal astrolabe and → particular astrolabe.

→ planispheric; → astrolabe.

The study of the physical properties of the various forms of plasmas and their processing.

→ plasma; → physics.

In the magnetosphere, a region of relatively cool (low energy) and dense plasma that may be considered an outer extension of the ionosphere with which it is coupled. Like the ionosphere, the plasmasphere tends to co-rotate with the Earth.

→ plasma + → sphere.

A representation that permits an easy visualisation of all different states of → polarization of a vector wave. The equator represents → linear polarization; the north pole corresponds to right-circular and the south pole to left- → circular polarization.

Named after Henri Poincaré (1854-1912), French mathematician and theoretical physicist, and a philosopher of science; → sphere.

An asteroid that could make a threatening close approach to the Earth. In technical terms a PHA is defined as having an → absolute magnitude of 22 or brighter and an → Earth Minimum Orbit Intersection Distance (MOID) of less than 0.05 → astronomical unit or 7.5 million km.

→ potentially; → hazardous; → asteroid.

An ellipsoid produced by rotating an ellipse through 360° about its major axis. → oblate spheroid.

→ prolate; → spheroid.