An Etymological Dictionary of Astronomy and Astrophysics
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A → binary system in which the distance separating the stars is comparable to their size. Most close binaries are spectroscopic binaries (→ spectroscopic binary) and/or eclipsing binaries (→ eclipsing binary). In most of them → mass transfer occurs at some stage, an event which profoundly affects the → stellar evolution of the components. The evolution of close binaries depends on the → initial masses of the two stars and their → separation. When the more massive star evolves into a → red giant first, material will spill through the inner point onto its companion, thereby affecting its companion's evolution. Mass transfer can also alter the separation and → orbital period of the binary star.

→ close; → binary; → system.

1) In a → star cluster, coming across of two stars so closely that their → orbits alter by their mutual → gravitational attractions.
2) As regards an → asteroid or → comet, a situation when it crosses the Moon's orbit and approaches the Earth with a risk of collision. See also → close approach, → encounter.

→ close; → encounter.

Having boundaries; limited. → closed curve; → closed Universe.

Closed, p.p. of close, from M.E. clos, from O.Fr., from clore "to shut," from L. clausus, p.p. of claudere "to close."

Basté p.p.of bastan, from Mid.Pers. bastan/vastan "to bind, shut," Av./O.Pers. band- "to bind, fetter," banda- "band, tie," Skt. bandh- "to bind, tie, fasten," PIE *bhendh- "to bind," cf. Ger. binden, E. bind, → band.

A curve whose ends are joined.

→ closed; → curve.

A bounded space the surface of which has the property that if one travels in any direction upon it without changing direction, one will end up back to the departure point. An example is a sphere. Triangles which lie on the surface of a closed space will have a sum of angles which is greater than 180°. An closed space has a positive → curvature. See also → closed Universe, → open space.

→ closed; → space.

Thermodynamics: A system which can exchange energy with the surroundings but not matter. → open system; → isolated system.

→ closed; → system.

A → cosmological model, first formulated by Friedmann and Lemaître, in which the Universe has a → finite size and lifetime and → space has a → positive → curvature, e.g. a Universe with a density greater than the → critical density. See also → closed space.

→ closed; → Universe.

In → predicate logic, a → wff with no → free occurrences of any → variable. Also called a → sentence.

→ closed; → wff.

Math.: The property of a set in which the application of a given mathematical operation to any member of the set always has another member of the set as its result.
The intersection of all closed sets that contain a given set.

M.E., from M.Fr., from O.Fr. closure "that which encloses," from L. clausura "lock, fortress, a closing," from p.p. stem of claudere "to close."

Bandeš, verbal noun of bastan "to shut, bind; to clot; to form seed buds," from Mid.Pers. bastan/vastan "to bind, shut," Av./O.Pers. band- "to bind, fetter," banda- "band, tie;" Skt. bandh- "to bind, tie, fasten;" PIE *bhendh- "to bind," cf. Ger. binden, E. bind.

A basic rule in → group theory stating that if a and b are a group element then a * b is also a group element.

→ closure; → axiom.

In astronomical interferometry, a method using triplets of telescopes in an array to calculate the phase information and get over the effects of atmospheric turbulence. The method, used in high-resolution astronomical observations, both at radio and at optical wavelengths, allows imaging of complex objects in the presence of severe aberrations.

→ closure; → phase.

A plane curve of spiral form, → Cornu's spiral.

From Gk. kloth, from klothein "to spin" + epenthetic vowel -o- + eides "form," → -oid; because the curve is reminiscent of the thread that winds around a weaving loom. → Klotho.

1) A visible mass of water droplets and/or ice particles in the atmosphere above the Earth's surface.
2) → interstellar cloud.

Cloud, from O.E. clud "mass of rock," from P.Gmc. *kludas.

Abr, from Mid.Pers. awr, abr (Laki owr, Baluchi haur, Kordi Soriani hewr), Av. awra- "rain cloud, rain," cf. Skt. abhra-"thunder cloud," Gk. afros "scum, foam," L. imber "rain;" also Sk. ambha- "water," Gk. ombros "rain," PIE *mbhros "rain cloud, rain," from *mbh-.

An early type of → bubble chamber used for detecting particles of ionizing radiation. It was invented in 1900 by Charles Thomson Rees Wilson (1869-1959), a Scottish physicist, who along with Arthur Compton (1892-1962 ) received the Nobel Prize for physics in 1927.

→ cloud; → chamber.

The fraction of the sky covered by clouds. It is expressed in tenths, so that 0.0 indicates a clear sky and 1.0 (or 10/10) indicates a completely covered sky.

→ cloud; → cover.

Process by which a → collapsing → giant molecular cloud breaks into dense → clumps, eventually bringing about → pre-stellar cores.

→ cloud; → fragmentation.

A large, faintly colored arc formed usually by sunlight falling on a cloud. Also called white rainbow, fogbow, and mistbow. Cloudbow appears white because the water droplets in the cloud or fog are very small compared with those of ordinary rainbows.

→ cloud; → bow.

Any sudden and heavy fall of → rain, always of the → shower type.

→ cloud; → burst.

Ragbâr, from rag + bâr. The second component bâr, variant bârân "rain," from bâridan "to rain." The origin of the first component is not clear. Rag in Persian means "blood vein, vessel," but this sense seems irrelevant here. In Gilaki the bare râk (without bâr) means cloudburst. Râk/rag may be related (via an extinct Iranian parent) to the Skt. stem ri- "to flow, to drop, to become liquid."

Same as → cloud cover.

From cloudy, from cloudy, from → cloud + → -ness.

Light from nearby stars scattered by → dust grains in low-density outer regions of → molecular clouds. It is seen not only in the → near infrared bands JHK, but also continuously from the visible to 5 μm. Cloudshine could be considered as an intermediate between → scattering in the visible and the → coreshine effect (Foster & Goodman, 2006, ApJ 636, L105). See also

→ cloud; → shine.