sextant

Home > Science and Technology > Astronomy and Space Exploration > Astronomy: General

sextant instrument for measuring the altitude of the sun or another celestial body; such measurements can then be used to determine the observer's geographical position or for other navigational, surveying, or astronomical applications. The term sextant is used generally to include related devices such as the quadrant, quintant, and octant. The sextant was invented independently in England and America in 1731. Its construction is based on the principle that a reflected ray of light leaves a plane surface at the same angle at which the direct ray strikes the surface. The sextant consists basically of a triangular frame, the bottom of which is a graduated arc of 60°; a telescope is attached horizontally to the plane of the frame. A small index mirror is mounted perpendicular to the frame at the top of a movable index arm or bar, which swings along the arc. In front of the telescope is the horizon glass, half transparent and half mirror. The image of the sun or other body is reflected from the index mirror to the mirror half of the horizon glass and then into the telescope. If the index (or image) arm is then adjusted so that the horizon is seen through the transparent half of the horizon glass, with the reflected image of the sun lined up with it, the sun's altitude can be read from the position of the index arm on the arc. By reference to navigational tables, the geographical position can then be determined. A sextant may be used on land with an "artificial horizon" —a small, shallow receptacle containing mercury, which gives a truly horizontal surface. In aerial navigation a bubble octant—sometimes called a bubble sextant—is used, in which a spirit level is reflected into the field of view in such a way that the center of the bubble indicates the true horizon.

SEXTANT, codename for the Allied Cairo conference held from 23 to 26 November and 3 to 7 December 1943 to discuss future strategy (see Grand Alliance). In between, Churchill and Roosevelt and the Combined Chiefs of Staff attended EUREKA, the Teheran conference. EUREKA had been arranged because a Chinese delegation, led by Chiang Kai-shek, was also attending SEXTANT and Stalin, who unlike China was not at war with Japan, had refused to send a representative or come himself.

In Cairo, both Allied leaders were accompanied by large delegations. As well as the Chinese, there was also a delegation led by Mountbatten, South-East Asia Command's supreme commander. Initial discussions centred on South-East Asia and Chiang Kai-shek's desire for amphibious warfare operations in the Bay of Bengal to coincide with a proposed Chinese intervention in the Burma campaign. Churchill called these discussions lengthy, complicated, and minor. Despite British reluctance, Roosevelt promised Chiang just such an operation. The consequences of EUREKA later forced him to retract, but the Cairo Declaration that was issued stated that all three powers were agreed upon future operations against Japan. It also stated that Japan would be stripped of all the territories it had acquired since 1914; that those taken from the Chinese would be returned to China, ‘such as Manchukuo and Formosa, and the Pescadores’, and that ‘in due course’ Korea would become free and independent.

Discussions during the second part of SEXTANT included those with President Inönü on the likelihood of Turkey entering the war on the Allies' side, and Roosevelt told Churchill that he had decided to appoint Eisenhower to command the Normandy landings (see OVERLORD). See also diplomacy.

sextant A navigational instrument for measuring the altitude of celestial objects above the horizon. It consists of a graduated 60° arc (one-sixth of a circle) with a movable arm and sighting devices. An index mirror attached to the movable arm reflects the chosen object to another mirror, silvered across half its width, so that its image can be seen alongside the horizon. The object's altitude can then be read off the scale. A telescope and dark filters are provided to improve accuracy and allow observation of the Sun. Because the objects observed are reflected, the range of angles which can be measured is 120°, double that of the graduated scale.

sextant (astron.) instrument resembling a quadrant having a graduated are equal to ⅙ of a circle. XVII. — modL. use of L. sextāns, -ant- sixth part (of an as, etc.), f. sextus SIXTH. sextet(te) XIX. alt. of SESTET after L. sex SIX. sextile (astrol.) pert. to the aspect of two heavenly bodies which are 60 or ⅙ of the zodiac distant. XVI. — L. sextīlis, f. sextus SIXTH. sextillion see BILLION. †sextodecimo size of a book in which the leaf is 1/16 of the sheet, †decimosexto; sixteenmo. XVII. sextuple sixfold. XVII.

sextant Optical instrument for finding latitude (angular distance n or s of the Equator). A sextant consists of a frame with a curved scale marked in degrees, a movable arm with a mirror at the pivot, a half-silvered glass and a telescope. The instrument measures the angle of a heavenly body above the horizon, which depends on the observer's latitude. A set of tables gives the corresponding latitude for various angles measured.

sex·tant / ˈsekstənt/ • n. an instrument with a graduated arc of 60° and a sighting mechanism, used for measuring the angular distances between objects and esp. for taking altitudes in navigation. ORIGIN: late 16th cent. (denoting the sixth part of a circle): from Latin sextans, sextant- ‘sixth part,’ from sextus ‘sixth.’

sextant ˈsekstənt n. an instrument with a graduated arc of 60° and a sighting mechanism, used for measuring the angular distances between objects and especially for taking altitudes in navigation and surveying.

sextant •abeyant, mayn't •ambient, circumambient •gradient, irradiant, radiant •expedient, ingredient, mediant, obedient •valiant • salient • resilient • emollient •defoliant • ebullient • suppliant •convenient, intervenient, lenient, prevenient •sapient •impercipient, incipient, percipient, recipient •recreant • variant • miscreant •Orient • nutrient •esurient, luxuriant, parturient, prurient •nescient, prescient •omniscient • insouciant • renunciant •officiant • negotiant • deviant •subservient • transient •affiant, Bryant, client, compliant, defiant, giant, pliant, reliant •buoyant, clairvoyant, flamboyant •fluent, pursuant, truant •affluent • effluent • mellifluent •confluent • circumfluent • congruent •issuant • continuant • constituent •lambent • absorbent •incumbent, recumbent •couchant • merchant • hadn't •ardent, guardant, regardant •pedant •appendant, ascendant, attendant, codependent, defendant, descendant, descendent, intendant, interdependent, pendant, pendent, splendent, superintendent, transcendent •antecedent, decedent, needn't, precedent •didn't • diffident • confident •accident • dissident •coincident, incident •oxidant • evident •improvident, provident •president, resident •strident, trident •co-respondent, correspondent, despondent, fondant, respondent •accordant, concordant, discordant, mordant, mordent •rodent •imprudent, jurisprudent, prudent, student •couldn't, shouldn't, wouldn't •impudent •abundant, redundant •decadent • verdant • infant • elephant •triumphant • sycophant • elegant •fumigant • congregant • litigant •termagant • arrogant • extravagant •pageant •cotangent, plangent, tangent •argent, Sargent, sergeant •agent • newsagent • regent •astringent, contingent, stringent •indigent • intelligent • negligent •diligent • intransigent • exigent •cogent •effulgent, fulgent, indulgent •pungent •convergent, detergent, divergent, emergent, insurgent, resurgent, urgent •bacchant • peccant • vacant • piquant •predicant • mendicant • significant •applicant • supplicant • communicant •lubricant • desiccant • intoxicant •gallant, talent •appellant, propellant, propellent, repellent, water-repellent •resemblant •assailant, inhalant •sealant • sibilant • jubilant •flagellant • vigilant • pestilent •silent •Solent, volant •coolant • virulent • purulent •ambulant, somnambulant •coagulant • crapulent • flatulent •feculent • esculent • petulant •stimulant • flocculent • opulent •postulant • fraudulent • corpulent •undulant •succulent, truculent •turbulent • violent • redolent •indolent • somnolent • excellent •insolent • nonchalant •benevolent, malevolent, prevalent •ambivalent, equivalent •garment • clement • segment •claimant, clamant, payment, raiment •ailment •figment, pigment •fitment • aliment • element •oddment •dormant, informant •moment • adamant • stagnant •lieutenant, pennant, subtenant, tenant •pregnant, regnant •remnant • complainant •benignant, indignant, malignant •recombinant • contaminant •eminent •discriminant, imminent •dominant, prominent •illuminant, ruminant •determinant • abstinent •continent, subcontinent •appurtenant, impertinent, pertinent •revenant •component, deponent, exponent, opponent, proponent •oppugnant, repugnant •immanent •impermanent, permanent •dissonant • consonant • alternant •covenant • resonant • rampant •discrepant • flippant • participant •occupant • serpent •apparent, arrant, transparent •Arendt •aberrant, deterrent, errant, inherent, knight-errant •entrant •declarant, parent •grandparent • step-parent •godparent •flagrant, fragrant, vagrant •registrant • celebrant • emigrant •immigrant • ministrant • aspirant •antiperspirant • recalcitrant •integrant • tyrant • vibrant • hydrant •migrant, transmigrant •abhorrent, torrent, warrant •quadrant • figurant • obscurant •blackcurrant, concurrent, currant, current, occurrent, redcurrant •white currant • cross-current •undercurrent •adherent, coherent, sederunt •exuberant, protuberant •reverberant • denaturant •preponderant • deodorant •different, vociferant •belligerent, refrigerant •accelerant • tolerant • cormorant •itinerant • ignorant • cooperant •expectorant • adulterant •irreverent, reverent •nascent, passant •absent •accent, relaxant •acquiescent, adolescent, albescent, Besant, coalescent, confessant, convalescent, crescent, depressant, effervescent, erubescent, evanescent, excrescent, flavescent, fluorescent, immunosuppressant, incandescent, incessant, iridescent, juvenescent, lactescent, liquescent, luminescent, nigrescent, obsolescent, opalescent, pearlescent, phosphorescent, pubescent, putrescent, quiescent, suppressant, tumescent, turgescent, virescent, viridescent •adjacent, complacent, obeisant •decent, recent •impuissant, reminiscent •Vincent • puissant •beneficent, maleficent •magnificent, munificent •Millicent • concupiscent • reticent •docent •lucent, translucent •discussant, mustn't •innocent •conversant, versant •consentient, sentient, trenchant •impatient, patient •ancient • outpatient •coefficient, deficient, efficient, proficient, sufficient •quotient • patent •interactant, reactant •disinfectant, expectant, protectant •repentant • acceptant •contestant, decongestant •sextant •blatant, latent •intermittent •assistant, coexistent, consistent, distant, equidistant, existent, insistent, persistent, resistant, subsistent, water-resistant •instant •cohabitant, habitant •exorbitant • militant • concomitant •impenitent, penitent •palpitant • crepitant • precipitant •competent, omnicompetent •irritant • incapacitant • Protestant •hesitant • visitant • mightn't • octant •remontant • constant •important, oughtn't •accountant • potent •mutant, pollutant •adjutant • executant • disputant •reluctant •consultant, exultant, resultant •combatant • omnipotent • impotent •inadvertent •Havant, haven't, savant, savante •advent •irrelevant, relevant •pursuivant • solvent • convent •adjuvant •fervent, observant, servant •manservant • maidservant •frequent, sequent •delinquent • consequent •subsequent • unguent • eloquent •grandiloquent, magniloquent •brilliant • poignant • hasn't •bezant, omnipresent, peasant, pheasant, pleasant, present •complaisant • malfeasant • isn't •cognizant • wasn't • recusant •doesn't