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

A theory that suggests the Moon was formed at the same time as Earth. A spinning Earth ejected a large piece of its material into space which then developed into the shape and orbit of the Moon. This event was also thought to be at the origin of the Pacific Ocean. This first modern idea about the formation of the Moon is due to George Darwin, the son of the great naturalist Charles Darwin. The fission theory explained the lack of volatile substances on the Earth. The volatile materials on the Earth would have been thrown out into space The fission theory is almost completely abandoned today. The analysis of lunar rocks brought to Earth by NASA astronauts showed that the Moon rocks are older than the rocks at the bottom of the Pacific Ocean. Moreover, modern → plate tectonics gives a better explanation of the origin of the Pacific Ocean. See also → giant impact hypothesis, → capture theory, → co-formation theory.

→ fission; → theory.

The material that can be fissioned by fast neutrons, such as uranium-238. Commonly used as a synonym for → fissile material.

From → fission + → -able.

The act of fixing or the state of being fixed.

Verbal noun of → fix; → -tion.

A stellar designation system in which each star is assigned a number followed by the Latin genitive of its corresponding → constellation, such as → 61 Cygni and 82 Eridani. Compare with the → Bayer designation.

Named after John Flamsteed (1646-1719), founder of the Greenwich Observatory, and the first astronomer royal of England, who introduced this system in his catalog Historia Coelestis Britannica (1725); → designation.

A galactic → rotation curve in which the → rotation velocity is constant in the outer parts. The flat component is preceded by a rising curve that shows solid body rotation in the very center of the → galaxy. A flat rotation curve implies that the mass is still increasing linearly with radius. See also → dark matter.

→ flat; → rotation; → curve.

1) The act of bending, the state of being bent.
2) The position that a limb assumes when it is bent.

→ flex; → -tion.

1) The act or state of remaining on the surface of a liquid. → buoyancy.
2) The process of separating different materials, especially minerals, by agitating a pulverized mixture of the materials with water, oil, and chemicals based on their tendency to sink in, or float on.

From float, from M.E. floten,  O.E. flotian (cf. O.N. flota, M.Du. vloten), akin to fleet + -ation.

Šenâvari "flotation," from šenâvar "that swims, floats," from šenâ "swimming;" Mid.Pers. šnâz "swim," šnâzidan "to swim;" Av. snā- "to wash, swim;" cf. Skt. snā- "to bathe, to wash;" L. nare, natare "to swim" (Fr. nage, nager, natation; Sp.nadar, natacion).

Continual rise and fall.

Verbal noun of → fluctuate.

Oftâxiz "fall and rise," from oft "fall" stem of oftâdan "to fall" (Mid.Pers. opastan "to fall," patet "falls;" Av. pat- " to fly, fall, rush," patarəta- "winged;" cf. Skt. patati "he flies, falls," pátra- "wing, feather, leaf;" Gk. piptein "to fall," pterux "wing;" L. penna "feather, wing;" O.E. feðer "feather;" PIE base *pet- "to fly, rush") + -â- interfix + xiz present stem of xâstan, xizidan "to rise, get up" (Mid.Pers. xyz- "to stand up, rise;" Proto-Iranian *xiz- "to rise, ascend; increase").

The → calibration of the flux received by a detector in terms of absolute units.

→ flux; → calibration.

In Newton's work on → calculus, the rate of change of a fluent (i.e. a flowing quantity), today commonly known as → variable. For a fluent x, the fluxion is denoted dx/dt. An obsolete mathematical term.

From L. → fluxion-, stem of fluere "to flow," → flux.

A modified form of → Boltzmann's equation allowing for collision terms in an approximate way. It describes the rate of change of a particle's velocity as a result of small-angle collisional deflections.

After Dutch physicist Adriaan Fokker (1887-1972) and the German physicist Max Planck (1858-1947); → equation.

An observation which expands previous observations and aims at obtaining complementary data in particular with other telescopes/instruments.

Follow-up, from follow, from O.E. folgian, fylgan "to follow, pursue," from W.Gmc. *fulg- (cf. O.Fris. folgia, M.Du. volghen, Ger. folgen "to follow") + up, O.E. up, uppe (cf. Du. op, Ger. auf "up, upward"), from PIE base *upo "up from below;" cf. O.Pers./Av. upā; Skt. úpa; Gk. hypo; L. sub, → hypo-; → observation.

Nepâheš, → observation; peygir, from pey "after; step," related to pâ "foot, step, track," → foot, + gir present stem of gereftan "to take, seize" (Mid.Pers. griftan, Av./O.Pers. grab- "to take, seize," cf. Skt. grah-, grabh- "to seize, take," graha "seizing, holding, perceiving," M.L.G. grabben "to grab," from P.Gmc. *grab, E. grab "to take or grasp suddenly;" PIE base *ghrebh- "to seize").

A → forbidden line in → emission.

→ forbidden; → emission; → line.

A transition between two quantum mechanical → states that → violates the quantum mechanical → selection rules.

→ forbidden; → transition.

The oscillation of a system or object induced by an external periodic force. See also → free oscillation.

→ forced; → oscillation.

Loss of radiant energy received from an astronomical object due to the presence of absorbing matter situated between the object and observer.

→ foreground; → absorption.

1) The act of giving something a form or structure by introducing rules and procedures.
2) The act of formalizing.

→ formalize; → -tion.

1) The act or process of forming or the state of being formed, such as → star formation.
2) Geology: A laterally continuous rock unit with a distinctive set of characteristics that make it possible to recognize and map from one → outcrop or well to another. The basic rock unit of stratigraphy.

Verbal noun of → form, + -ate + -ion.

Diseš, verbal noun of disidan, → from dis-, → form, + -eš.

1) The act or process of formulating.
2) A particular expression of an idea, thought, or theory.
3) Something prepared according to a → formula.

→ formulate; → -tion.

An operator defined as: ▫ = (∂/∂x, ∂/∂y, ∂/∂z, 1/(jc∂/∂t).

→ four; → dimensional; → operator.