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

A physical entity resulting from the union of space and time concepts. In its most simple version space-time is the four-dimensional continuum, having three spatial coordinates and one temporal coordinate, in which any → event or physical object is located. In → special relativity it is Minkowski's flat space-time. In → general relativity, it is described by a curved entity characterized by a → metric. Free-fall motion describes the → geodesic of this curved space-time. It may have additional dimensions in the context of speculative theories, such as → string theory.

→ space; → time.

→ curvature of space-time.

→ space; → time; → curvature.

A simple way of representing the → space-time continuum, usually including time and only one spatial dimension. The curve of a particle's equation of motion on a space-time diagram is called a → world line. Same as → Minkowski diagram.

→ space; → time; → diagram.

1) In Einstein's → theory of relativity, ds² = c²dt² - dx² - dy² - dz².
2) In → Newtonian mechanics, time interval: dt; space interval at fixed time: dl² = dx² + dy² + dz².

→ space-time; → interval.

A vehicle designed to travel or operate, with or without a → crew, in a controlled → flight pattern in space beyond the Earth's atmosphere or in → orbit around the Earth. Also called spaceship.

→ space; → craft.

Of, pertaining to, or describing an → event being outside the → light cone.

→ space; → like.

The → space-time interval between two → events if it is imaginary, i.e. ds²< 0.

→ spacelike; → interval.

→ space-time.

→ space; → time.

A digging tool with a flat blade attached to a shaft so that it can be pushed into the ground with the foot.

M.E., from O.E. spadu; cognate with Gk. spathe "blade of a sword or oar."

Bil "spade," variants Kurd. bêr, Baluci bard, Gabri bard(a); Mid.Pers. bêl, bêr; Proto-Iranian *barda- metathesis of *badar-; cf. Av. vadar- "weapon" (Gershevitch 1962).

1) A chip or splinter.
2) To break up into small chips, flakes, or splinters, or to cause to break off in flakes.

M.E. spalle "a chip," verb spald "to split," from M.L.G. spalden, cognate with O.H.G. spaltan "to split."

Terišé "a chip," from tarâšidan "to cut, hew; scape; shave;" Mid.Pers. tâšitan "to cut, cleave; create by putting together different elements;" Av. taš- "to cut off, fashion, shape, create," taša- "axe" (Mod.Pers. taš, tišé "axe"), tašan- "creator;" cf. Skt. taks- "to form by cutting, tool, hammer, form," taksan- "wood-cutter, carpenter;" Gk. tekton "carpenter," tekhne "art, skill, craft, method, system;" L. textere "to weave;" PIE *teks- "to fashion."

A nuclear reaction in which a high energy particle that collides with a nucleus causes the target to eject several particles, thus changing both its mass number and its atomic number.

From → spall + -ation.

Verbal noun from terišidan, → spall.

1) Aeronautics: The distance between the wing tips of an airplane.
2) Math.: The smallest subspace of a → vector space that contains a given element or set of elements.

M.E. spanne, sponne, spayn; O.E. span(n), spon(n) "distance between the thumb and little finger of an extended hand;" cf. Ger. Spanne, Du. span.

Bâzé "extension of both arms when streched out," related to bâzu "arm" (Mid.Pers. bâzûk "arm;" Av. bāzu- "arm;" cf. Skt. bāhu- "arm, forearm;" Gk. pechys "forearm, arm, ell;" O.H.G. buog "shoulder;" Ger. Bug "shoulder;" Du. boeg; O.E. bôg, bôh "shoulder, bough;" E. bough " a branch of a tree;" PIE *bhaghu- "arm"); from Av. vībāzu- "fathom, measure of the outstretched arms."

Visible disruptive discharge of electricity between two places at opposite high potential. It is preceded by ionization of the path.

M.E., from O.E. spearca; cf. M.L.G. sparke, M.Du. spranke.

Laki âger "fire accompanied by flame," Lori azgel daaneh-ye aatash-e sorx shodeh va godaaxteh Kurd. agir "fire" Gilaki val "prominence, flame" Tâleši kel "blazing flame" standard Pers. gorr Laki gorron "flame;" jaraqé, probably word made by sound imitation.

A device consisting of two electrodes separated by a small gap that is filled by a gas, usually air. A high → potential difference applied to the electrodes ionizes the gas and current flows across it for a brief time causing a spark across the gap. Spark gaps have a wide application. As spark plugs, they are used to ignite a mixture of fuel and air in the piston cylinders of an internal combustion engine. The electricity is provided by the battery and ignition coil, and the spark timing is controlled by the distributor. Spark gaps are also used as safety devices on equipment to prevent damage from voltage surges.

→ spark; → gap.

The emission spectrum produced through a gas or vapor as a result of a high-voltage discharge between metallic electrodes.

→ spark; → spectrum.

In a wave train, a correlation between the phases of waves at points separated in space at a given time.

→ spatial; → coherence.

The smallest detail that can be seen in an image. Same as → angular resolution.

→ spatial; → resolution.

A period of low → solar activity that lasted from about A.D. 1420 to 1570. It occurred before → sunspots had been studied, and was discovered by analysis of the proportion of carbon-14 in tree rings, which is strongly correlated with solar activity.

Named for the German astronomer Gustav Spörer (1822-1895); → minimum.

The empirical law that predicts the variation of → sunspot latitudes during a → solar cycle. At the start of a sunspot cycle, sunspots tend to appear around 30° to 45° latitude on the Sun's surface. As the cycle progresses, they appear at lower and lower latitudes, until 5° to 10°, at the end of the cycle. This tendency is revealed on a → butterfly diagram. Although named after Gustav Spörer, the "law" was first discovered by Richard Carrington.

→ Sporer minimum; → law.

To utter words with the ordinary voice (not singing) to communicate; to talk.

From M.E. speken "to speak," from O.E. specan, alteration of earlier sprecan "to speak;" cf. Low Germ. spreken "to speak," Du. spreken, Ger. sprechen "to speak;" ultimately from PIE *spreg- "to make a sound, utter, speak."

From M.P. saxwanitan "to speak, to talk," → speech.