What is "double star"

Double \Dou"ble\ (d[u^]b"'l), a. [OE. doble, duble, double, OF. doble, duble, double, F. double, fr. L. duplus, fr. the root of duo two, and perh. that of plenus full; akin to Gr. diplo`os double. See Two, and Full, and cf. Diploma, Duple.]

1. Twofold; multiplied by two; increased by its equivalent; made twice as large or as much, etc.

   Let a double portion of thy spirit be upon me. -- 2 Kings ii. 9.

   Darkness and tempest make a double night.
   --Dryden.

2. Being in pairs; presenting two of a kind, or two in a set together; coupled.

   [Let] The swan, on still St. Mary's lake, Float double, swan and shadow.
   --Wordsworth.

3. Divided into two; acting two parts, one openly and the other secretly; equivocal; deceitful; insincere.

   With a double heart do they speak. -- Ps. xii. 2.

4. (Bot.) Having the petals in a flower considerably increased beyond the natural number, usually as the result of cultivation and the expense of the stamens, or stamens and pistils. The white water lily and some other plants have their blossoms naturally double. Note: Double is often used as the first part of a compound word, generally denoting two ways, or twice the number, quantity, force, etc., twofold, or having two. Double base, or Double bass (Mus.), the largest and lowest-toned instrument in the violin form; the contrabasso or violone. Double convex. See under Convex. Double counterpoint (Mus.), that species of counterpoint or composition, in which two of the parts may be inverted, by setting one of them an octave higher or lower. Double court (Lawn Tennis), a court laid out for four players, two on each side. Double dagger (Print.), a reference mark ([dag]) next to the dagger ([dagger]) in order; a diesis. Double drum (Mus.), a large drum that is beaten at both ends. Double eagle, a gold coin of the United States having the value of 20 dollars. Double entry. See under Bookkeeping. Double floor (Arch.), a floor in which binding joists support flooring joists above and ceiling joists below. See Illust. of Double-framed floor. Double flower. See Double, a., 4. Double-framed floor (Arch.), a double floor having girders into which the binding joists are framed. Double fugue (Mus.), a fugue on two subjects. Double letter.

   1. (Print.) Two letters on one shank; a ligature.

   2. A mail requiring double postage. Double note (Mus.), a note of double the length of the semibreve; a breve. See Breve. Double octave (Mus.), an interval composed of two octaves, or fifteen notes, in diatonic progression; a fifteenth. Double pica. See under Pica. Double play (Baseball), a play by which two players are put out at the same time. Double plea (Law), a plea alleging several matters in answer to the declaration, where either of such matters alone would be a sufficient bar to the action. --Stephen. Double point (Geom.), a point of a curve at which two branches cross each other. Conjugate or isolated points of a curve are called double points, since they possess most of the properties of double points (see Conjugate). They are also called acnodes, and those points where the branches of the curve really cross are called crunodes. The extremity of a cusp is also a double point. Double quarrel. (Eccl. Law) See Duplex querela, under Duplex. Double refraction. (Opt.) See Refraction. Double salt. (Chem.)

      1. A mixed salt of any polybasic acid which has been saturated by different bases or basic radicals, as the double carbonate of sodium and potassium, NaKCO3.6H2O.

      2. A molecular combination of two distinct salts, as common alum, which consists of the sulphate of aluminium, and the sulphate of potassium or ammonium.

         Double shuffle, a low, noisy dance.

         Double standard (Polit. Econ.), a double standard of monetary values; i. e., a gold standard and a silver standard, both of which are made legal tender.

         Double star (Astron.), two stars so near to each other as to be seen separate only by means of a telescope. Such stars may be only optically near to each other, or may be physically connected so that they revolve round their common center of gravity, and in the latter case are called also binary stars.

         Double time (Mil.). Same as Double-quick.

         Double window, a window having two sets of glazed sashes with an air space between them.

Star \Star\ (st[aum]r), n. [OE. sterre, AS. steorra; akin to OFries. stera, OS. sterro, D. ster, OHG. sterno, sterro, G. stern, Icel. stjarna, Sw. stjerna, Dan. stierne, Goth. sta['i]rn[=o], Armor. & Corn. steren, L. stella, Gr. 'asth`r, 'a`stron, Skr. star; perhaps from a root meaning, to scatter, Skr. st[.r], L. sternere (cf. Stratum), and originally applied to the stars as being strewn over the sky, or as being scatterers or spreaders of light. [root]296. Cf. Aster, Asteroid, Constellation, Disaster, Stellar.]

1. One of the innumerable luminous bodies seen in the heavens; any heavenly body other than the sun, moon, comets, and nebul[ae].

   His eyen twinkled in his head aright, As do the stars in the frosty night.
   --Chaucer.

   Note: The stars are distinguished as planets, and fixed stars. See Planet, Fixed stars under Fixed, and Magnitude of a star under Magnitude.

2. The polestar; the north star.
   --Shak.

3. (Astrol.) A planet supposed to influence one's destiny; (usually pl.) a configuration of the planets, supposed to influence fortune.

   O malignant and ill-brooding stars.
   --Shak.

   Blesses his stars, and thinks it luxury.
   --Addison.

4. That which resembles the figure of a star, as an ornament worn on the breast to indicate rank or honor.

   On whom . . . Lavish Honor showered all her stars.
   --Tennyson.

5. Specifically, a radiated mark in writing or printing; an asterisk [thus, *]; -- used as a reference to a note, or to fill a blank where something is omitted, etc.

6. (Pyrotechny) A composition of combustible matter used in the heading of rockets, in mines, etc., which, exploding in the air, presents a starlike appearance.

7. A person of brilliant and attractive qualities, especially on public occasions, as a distinguished orator, a leading theatrical performer, etc. Note: Star is used in the formation of compound words generally of obvious signification; as, star-aspiring, star-bespangled, star-bestudded, star-blasting, star-bright, star-crowned, star-directed, star-eyed, star-headed, star-paved, star-roofed, star-sprinkled, star-wreathed. Blazing star, Double star, Multiple star, Shooting star, etc. See under Blazing, Double, etc. Nebulous star (Astron.), a small well-defined circular nebula, having a bright nucleus at its center like a star. Star anise (Bot.), any plant of the genus Illicium; -- so called from its star-shaped capsules. Star apple (Bot.), a tropical American tree ( Chrysophyllum Cainito), having a milky juice and oblong leaves with a silky-golden pubescence beneath. It bears an applelike fruit, the carpels of which present a starlike figure when cut across. The name is extended to the whole genus of about sixty species, and the natural order ( Sapotace[ae]) to which it belongs is called the Star-apple family. Star conner, one who cons, or studies, the stars; an astronomer or an astrologer. --Gascoigne. Star coral (Zo["o]l.), any one of numerous species of stony corals belonging to Astr[ae]a, Orbicella, and allied genera, in which the calicles are round or polygonal and contain conspicuous radiating septa. Star cucumber. (Bot.) See under Cucumber. Star flower. (Bot.)

   1. A plant of the genus Ornithogalum; star-of-Bethlehem.

   2. See Starwort (b) .

   3. An American plant of the genus Trientalis ( Trientalis Americana). --Gray. Star fort (Fort.), a fort surrounded on the exterior with projecting angles; -- whence the name. Star gauge (Ordnance), a long rod, with adjustable points projecting radially at its end, for measuring the size of different parts of the bore of a gun. Star grass. (Bot.)

      1. A small grasslike plant ( Hypoxis erecta) having star-shaped yellow flowers.

      2. The colicroot. See Colicroot.

         Star hyacinth (Bot.), a bulbous plant of the genus Scilla ( S. autumnalis); -- called also star-headed hyacinth.

         Star jelly (Bot.), any one of several gelatinous plants ( Nostoc commune, N. edule, etc.). See Nostoc.

         Star lizard. (Zo["o]l.) Same as Stellion.

         Star-of-Bethlehem (Bot.), a bulbous liliaceous plant ( Ornithogalum umbellatum) having a small white starlike flower.

         Star-of-the-earth (Bot.), a plant of the genus P ( Plantago coronopus), growing upon the seashore.

         Star polygon (Geom.), a polygon whose sides cut each other so as to form a star-shaped figure.

         Stars and Stripes, a popular name for the flag of the United States, which consists of thirteen horizontal stripes, alternately red and white, and a union having, in a blue field, white stars to represent the several States, one for each.

         With the old flag, the true American flag, the Eagle, and the Stars and Stripes, waving over the chamber in which we sit.
         --D. Webster.

         Star showers. See Shooting star, under Shooting.

         Star thistle (Bot.), an annual composite plant ( Centaurea solstitialis) having the involucre armed with stout radiating spines.

         Star wheel (Mach.), a star-shaped disk, used as a kind of ratchet wheel, in repeating watches and the feed motions of some machines.

         Star worm (Zo["o]l.), a gephyrean.

         Temporary star (Astron.), a star which appears suddenly, shines for a period, and then nearly or quite disappears. These stars were supposed by some astronomers to be variable stars of long and undetermined periods. More recently, variations star in start intensity are classified more specifically, and this term is now obsolescent. See also nova. [Obsolescent]

         Variable star (Astron.), a star whose brilliancy varies periodically, generally with regularity, but sometimes irregularly; -- called periodical star when its changes occur at fixed periods.

         Water star grass (Bot.), an aquatic plant ( Schollera graminea) with small yellow starlike blossoms.

n. 1 (context star English) Two stars which form a stellar system, such that they orbit the point of equilibrium of their gravitational fields; a binary star. 2 (context star English) Two stars that appear to be one when seen with the naked eye, either because they orbit one another (binary stars) or happen to be in the same line of sight even though they are separated by a great distance (optical double).

n. a system of two stars that revolve around each other under their mutual gravitation [syn: binary star, binary]

Double Star is a joint satellite based space mission by the China National Space Administration (CNSA) and the European Space Agency (ESA). It is the first space mission launched by China to investigate Earth's magnetosphere. It consists of two satellites: an Equatorial satellite (TC-1) and Polar satellite (TC-2). Double Star follows in the footsteps of ESA's Cluster mission by studying the effects of the Sun on the Earth's environment. After a nominal mission of one year (from the launch of TC-2 in July 2004), the Double Star mission was extended twice by both agencies till the end of September 2007.

Double star may refer to:

• Double Star, a novel by Robert Heinlein
• Double star, a pair of stars that appear close to each other in the sky
• Double Star Mission, a joint Chinese/European satellite effort
• Qingdao DoubleStar, a team in the Chinese Basketball Association

Two stars that orbit close to each other are called binary star.

In observational astronomy, a double star is a pair of stars that appear close to each other in the sky as seen from Earth when viewed through an optical telescope.

This can happen either because the pair forms a binary star, i.e. a binary system of stars in mutual orbit, gravitationally bound to each other, or because it is an optical double, a chance alignment of two stars in the sky that lie at different distances. Binary stars are important to stellar astronomers as knowledge of their motions allows direct calculation of stellar mass and other stellar parameters.

Since the beginning of the 1780s, both professional and amateur double star observers have telescopically measured the distances and angles between double stars to determine the relative motions of the pairs. If the relative motion of a pair determines a curved arc of an orbit, or if the relative motion is small compared to the common proper motion of both stars, it may be concluded that the pair is in mutual orbit as a binary star. Otherwise, the pair is optical. Multiple stars are also studied in this way, although the dynamics of multiple stellar systems are more complex than those of binary stars.

There are three types of paired stars:

• Optical Doubles are unrelated stars that appear close together through chance alignment with Earth.
• Visual Doubles are stars whose binary status was deduced through more esoteric means, such as occultation ( eclipsing binaries), spectroscopy ( spectroscopic binaries), or anomalies in proper motion. ( astrometric binaries).
• Visual Binaries are gravitationally-bound stars that are separately visible with a telescope.

Conceptually, there is no difference between the two visual categories, and improvements in telescopes can shift previously double stars into visual binaries, as happened with Polaris in 2006. Thus it is only the inability to telescopically observe or detect orbital motion in the visual double stars that differentiates these two groups.