[求教]哪位介绍一下四六分仪

在维基百科上六分仪找到中文介绍，四分仪只找到英文介绍： 六分仪： 六分仪（sextant），在测绘和船舶通信导航中，是由分度弧、指标臂、动镜、定镜、望远镜和测微轮组成，弧长约为圆周的六分之一，用以观察天体高度和目标的水平角与垂直角的反射镜类型的手持测角仪器。广泛用于航海和航空中，用来确定观测者的自身位置。 用六分仪测量太阳高度的动画 历史 六分仪的原理由伊萨克·牛顿提出，1732年，英国海军开始将原始仪器安装在船艇上，因为当时最大测量角度是90度，因此被称为八分仪。1757年，约翰·坎贝尔船长将八分仪的测量夹角提高到120度，发展成为六分仪。其后六分仪的测量夹角虽然逐渐提升到144度，但是其名称却一直保持不变。 六分仪图解 Sextant From Wikipedia, the free encyclopedia Jump to: navigation, search This article is about the Sextant as used for navigation. For the astronomer's sextant, see Sextant (astronomical). For the history and development of the sextant see Reflecting instruments For other uses, see Sextant (disambiguation). A sextant. A sextant. A sextant is an instrument generally used to measure the angle of elevation of a celestial object above the horizon. Making this measurement is known as sighting the object, shooting the object, or taking a sight. The angle, and the time when it was measured, can be used to calculate a position line on a nautical or aeronautical chart. A common use of the sextant is to sight the sun at noon to find one's latitude. See celestial navigation for more discussion. Held horizontally, the sextant can be used to measure the angle between any two objects, such as between two lighthouses, which will, similarly, allow for calculation of a line of position on a chart. The scale of a sextant has a length of 1⁄6 of a full circle (60°); hence the sextant's name (sextāns, -antis is the Latin word for "one sixth"). An octant is a similar device with a shorter scale (1⁄8 of a circle, or 45°), whereas a quintant (1⁄5, or 72°) and a quadrant (1⁄4, or 90°) have longer scales. Sir Isaac Newton (1643-1727) invented the principle of the doubly reflecting navigation instrument (a reflecting quadrant - see Octant (instrument)), but never published it. Two men independently developed the octant around 1730: John Hadley (1682-1744), an English mathematician, and Thomas Godfrey (1704-1749), a glazier in Philadelphia. The octant and later the sextant, replaced the Davis quadrant as the main instrument for navigation. Octant and logbook on board the frigate Grand Turk Octant and logbook on board the frigate Grand Turk Contents [hide] * 1 Navigational Sextants o 1.1 Advantages o 1.2 Anatomy of a sextant o 1.3 Care o 1.4 Adjustment * 2 See also * 3 Notes * 4 References * 5 External links [edit] Navigational Sextants This section discusses navigator's sextants. Most of what is said about these specific sextants applies equally to other types of sextants. Navigator's sextants were primarily used for celestial navigation. [edit] Advantages Like the Davis quadrant (also called backstaff), the sextant allows celestial objects to be measured relative to the horizon, rather than relative to the instrument. This allows excellent precision. However, unlike the backstaff, the sextant allows direct observations of stars. This permits the use of the sextant at night when a backstaff is difficult to use. For solar observations, filters allow direct observation of the sun. Since the measurement is relative to the horizon, the measuring pointer is a beam of light that reaches to the horizon. The measurement is thus limited by the angular accuracy of the instrument and not the sine error of the length of an alidade, as it is in a mariner's astrolabe or similar older instrument. The horizon and celestial object remain steady when viewed through a sextant, even when the user is on a moving ship. This occurs because the sextant views the (unmoving) horizon directly, and views the celestial object through two opposed mirrors that subtract the motion of the sextant from the reflection. The sextant is not dependent upon electricity (unlike many forms of modern navigation) or anything human-controlled (like GPS satellites). For these reasons, it is considered an eminently practical back-up navigation tool for ships. [edit] Anatomy of a sextant Marine Sextant Marine Sextant Using the sextant to measure the altitude of the Sun above the horizon Using the sextant to measure the altitude of the Sun above the horizon The index arm moves the index mirror. The indicator points at the arc to show the measurement. The body ties everything together. There are two types of sextants. Both types can give good results, and the choice between them is personal. Traditional sextants have a half-horizon mirror. It divides the field of view in two. On one side, there is a view of the horizon; on the other side, a view of the celestial object. The advantage of this type is that both the horizon and celestial object are bright, and as clear as possible. This is superior at night and in haze, where the horizon can be difficult to see. However, one has to sweep the celestial object to assure that the lowest limb of the celestial object touches the horizon. Whole-horizon sextants use a half-silvered horizon mirror to provide a full view of the horizon. This makes it easy to see when the bottom limb of a celestial object touches the horizon. Since most sights are of the sun or moon, and haze is rare without overcast, the low-light advantages of the half-horizon mirror are rarely important in practice. In both types, larger mirrors give a larger field of view, and thus make it easier to find a celestial object. Modern sextants often have 5 cm or larger mirrors, while 19th century sextants rarely had a mirror larger than 2.5 cm (one inch). In large part this is because precision flat mirrors have grown less expensive to manufacture and to silver. An artificial horizon is useful when the horizon is invisible. This occurs in fog, on moonless nights, in a calm, when sighting through a window, or on land surrounded by trees or buildings. Professional sextants can mount an artificial horizon in place of the horizon-mirror assembly. An artificial horizon is usually a mirror that views a fluid-filled tube with a bubble. Most sextants also have filters for use when viewing the sun, and reducing the effects of haze. Most sextants mount a 1 or 3 power monocular for viewing. Many users prefer a simple sighting tube, which has a wider, brighter field of view and is easier to use at night. Some navigators mount a light-amplifying monocular to help see the horizon on moonless nights. Others prefer to use a lighted artificial horizon. Professional sextants use a click-stop degree measure, and a worm adjustment that reads to a minute, 1/60 of a degree. Most sextants also include a vernier on the worm dial that reads to 0.2 minute. Since 1 minute of error is about a nautical mile, the best possible accuracy of celestial navigation is about 0.1 nautical miles (200 m). At sea, results within several nautical miles, well within visual range, are acceptable. A highly skilled and experienced navigator can determine position to an accuracy of about 0.25-nautical-mile (460 m).[1] A change in temperature can warp the arc, creating inaccuracies. Many navigators purchase weatherproof cases so their sextant can be placed outside the cabin to come to equilibrium with outside temperatures. The standard frame designs (see illustration) are supposed to equalize differential angular error from temperature changes. The handle is separated from the arc and frame so body heat does not warp the frame. Sextants for tropical use are often painted white to reflect sunlight and remain relatively cool. High-precision sextants have an invar (a special low-expansion steel) frame and arc. Some scientific sextants have been constructed of quartz or ceramics with even lower expansions. Many commercial sextants use low expansion brass or aluminum. Brass is lower-expansion than aluminum, but aluminum sextants are lighter and less tiring to use. Some say they are more accurate because one's hand trembles less. Aircraft sextants are now out of production, but had special features. Most had artificial horizons to permit taking a sight through a flush overhead window. Some also had mechanical averagers to make hundreds of measurements per sight, to compensate for random accelerations in the artificial horizon's fluid. Older aircraft sextants had two visual paths, one standard, another designed for use in open-cockpit aircraft that let one view from directly over the sextant in one's lap. More modern aircraft sextants were periscopic with only a small projection above the fuselage. With these, the navigator pre-computed his sight and then noted the difference in observed versus predicted height of the body to determine his position. After a sight is taken, it is reduced to a position by following any of several mathematical procedures. The simplest sight reduction is to draw the equal-elevation circle of the sighted celestial object on a globe. The intersection of that circle with a dead-reckoning track, or another sighting gives a more precise location. [edit] Care A sextant is a delicate instrument. If dropped, the arc might bend. After one has been dropped, its accuracy is suspect. Recertification is possible with surveying instruments and a large field, or with precision optical instruments. Repair is not possible. To avoid worries about bent arcs, serious navigators traditionally buy their sextants new. Common wisdom is that a used sextant is probably bent. Many navigators refuse to share their sextant, to assure that its integrity is traceable. A used sextant lacking a case is very likely to have a bent arc. Most sextants come with a neck-lanyard, and all but the cheapest come with a case. Traditional care is to put on the neck lanyard before removing the sextant from its case, and to always case the sextant between sights. [edit] Adjustment Due to the sensitivity of the instrument it is easy to knock the mirrors out of adjustment. For this reason a sextant should be checked frequently for errors and adjusted accordingly. There are four errors that can be adjusted by the navigator and they should be removed in the following order. Perpendicularity error This is when the index mirror is not perpendicular to the frame of the sextant. To test for this, place the index arm at about 60° on the arc and hold the sextant horizontally with the arc away from you at arms length and look into the index mirror. The arc of the sextant should appear to continue unbroken into the mirror. If there is an error then the two views will appear to be broken. Adjust the mirror until the reflection and direct view of the arc appear to be continuous. Side error This occurs when the horizon glass/mirror is not perpendicular to the plane of the instrument. To test for this, first zero the index arm then observe a star through the sextant. Then rotate the tangent screw back and forth so that the reflected image passes alternately above and below the direct view. If in changing from one position to another the reflected image passes directly over the unreflected image, no side error exists. If it passes to one side, side error exists. The user can hold the sextant on its side and observe the horizon to check the sextant during the day. If there are two horizons there is side error; adjust the horizon glass/mirror until the stars merge into one image or the horizons are merged into one. Collimation error This is when the telescope or monocular is not parallel to the plane of the sextant. To check for this you need to observe two stars 90° or more apart. Bring the two stars into coincidence either to the left or the right of the field of view. Move the sextant slightly so that the stars move to the other side of the field of view. If they separate there is collimation error. Index error This occurs when the index and horizon mirrors are not parallel to each other when the index arm is set to zero. To test for index error, zero the index arm and observe the horizon. If the reflected and direct image of the horizon are in line there is no index error. If one is above the other adjust the index mirror until the two horizons merge. This can be done at night with a star or with the moon. [edit] See also Wikimedia Commons has media related to: Sextant Look up Sextant in Wiktionary, the free dictionary. * Mariner's astrolabe * Davis quadrant * Octant (instrument) * Sextant (astronomical) * Celestial navigation * Gago Coutinho * Intercept method * Latitude * Longitude * History of longitude * Navigation * Bris sextant [edit] Notes 1. ^ Dutton's Navigation and Piloting, 12th edition. G.D. Dunlap and H.H. Shufeldt, eds. Naval Institute Press 1972, ISBN 0-87021-163-3 [edit] References * Bowditch, Nathaniel (2002). The American Practical Navigator. Bethesda, MD: National Imagery and Mapping Agency. ISBN 0939837544. * Cutler, Thomas J. (December 2003). Dutton's Nautical Navigation, 15th, Annapolis, MD: Naval Institute Press. ISBN 978-1557502483. * Department of the Air Force (March 2001). Air Navigation (PDF), Department of the Air Force. Retrieved on 2007-04-17. * Great Britain Ministry of Defence (Navy) (1995). Admiralty Manual of Seamanship. The Stationery Office. ISBN 0117726966. * Encyclopædia Britannica (1911). "Navigation". Encyclopædia Britannica (11th edition) 19. Ed. Chisholm, Hugh. Retrieved on 2007-04-17. * Encyclopædia Britannica (1911). "Sextant". Encyclopædia Britannica (11th edition) 24. Ed. Chisholm, Hugh. 749-751. Retrieved on 2007-04-17. * Maloney, Elbert S. (December 2003). Chapman Piloting and Seamanship, 64th, New York, NY: Hearst Communications Inc.. ISBN 1-58816-098-0. [edit] External links * Her Majesty's Nautical Almanac Office: http://www.nao.rl.ac.uk/ * The History of HM Nautical Almanac Office: http://www.nao.rl.ac.uk/nao/history/ * Instruments for Celestial NavigationPDF (361 KiB) Chapter from the online edition of Nathaniel Bowditch's American Practical Navigator * CD-Sextant - Build your own sextant Simple do-it-yourself project. * Lunars web site. online calculation * Complete celnav theory book, including Lunars

四分仪： Quadrant (instrument) From Wikipedia, the free encyclopedia Jump to: navigation, search A quadrant is an instrument that is used to measure angles up to 90°. Contents [hide] * 1 Types of quadrants * 2 The Geometric Quadrant o 2.1 Solar observations o 2.2 Back observation quadrant * 3 Framed quadrant * 4 See also * 5 References * 6 External links [edit] Types of quadrants There are several types of quadrants: * Mural quadrants used for measuring the altitudes of astronomical objects. * Large frame-based instruments used for measuring angular distances between astronomical objects. * Geometric quadrant used by surveyors and navigators. * Davis quadrant a compact, framed instrument used by navigators for measuring the altitude of an astronomical object. They can also be classified as[1] * Altitude - The plain quadrant with plumb line, used to take the altitude of an object. * Gunner's - The quadrant used by an artillery officer to set the angle of a gun barrel. * Gunter's - A quadrant used for time determination. Invented by Edmund Gunter in 1623. * Horary - A time telling quadrant. * Islamic - King identified four types of quadrants that were produced by Muslim astronomers.[2] 1. The sine quadrant – used for solving trigonometric problems: These quadrants, developed in Baghdad in the ninth century and prevalent until the nineteenth century, consisted of a graph-paper like grid on one side used for solving complex trigonometric problems. A cord was attached to the centre of the quadrant with a bead at the end of it. They were also sometimes drawn on the back of astrolabes. 2. The universal (shakkāzīya) quadrant – used for solving astronomical problems for any latitude: These quadrants had either one or two sets of shakkāzīya grids and were developed in the fourteenth century in Syria. Some astrolabes are also printed on the back with the universal quadrant like an astrolabe created by Ibn al-Sarrāj. 3. The horary quadrant – used for finding the time with the sun: The horary quadrant could be used to find the time either in equal or unequal (length of the day divided by twelve) hours. Different sets of markings were created for either equal or unequal hours. For measuring the time in equal hours, the horary quadrant could only be used for one specific latitude while a quadrant for unequal hours could be used anywhere based on an approximate formula. One edge of the quadrant had to be aligned with the sun, and once aligned, a bead on the end of a plumbline attached to the centre of the quadrant showed the time of the day. 4. The astrolabe/almucantar quadrant – a quadrant developed from the astrolabe: This quadrant was marked with one half of a typical astrolabe plate as astrolabe plates are symmetrical. A cord attached from the centre of the quadrant with a bead at the other end was moved to represent the position of a celestial body (sun or a star). The ecliptic and star positions were marked on the quadrant for the above. It is not known where and when the astrolabe quadrant was invented, existent astrolabe quadrants are either of Ottoman or Mamluk origin, while there have been discovered twelfth century Egyptian and fourteenth century Syrian treatises on the astrolabe quadrant. These quadrants proved to be very popular alternatives to astrolabes. [edit] The Geometric Quadrant Geometric quadrant with plumb bob. Geometric quadrant with plumb bob. The geometric quadrant is a quarter-circle panel usually of wood or brass. Markings on the surface might be printed on paper and pasted to the wood or painted directly on the surface. Brass instruments had their markings scribed directly into the brass. For marine navigation, the earliest examples were found around 1460. They were not graduated in degrees but rather had the latitudes of the most common destinations directly scribed on the limb. When in use, the navigator would sail north or south until the quadrant indicated he was at the destination's latitude, turn in the direction of the destination and sail to the destination maintaining a course of constant latitude. After 1480, more of the instruments were made with limbs graduated in degrees.[3] Along one edge there were two sights forming an alidade. A plumb bob was suspended by a line from the centre of the arc at the top. In order to measure the altitude of a star, the observer would view the star through the sights and hold the quadrant so that the plane of the instrument was vertical. The plumb bob was allowed to hang vertical and the line indicated the reading on the arc's graduations. It was not uncommon for a second person to take the reading while the first concentrated on observing and holding the instrument in proper position. The accuracy of the instrument was limited by its size and by the effect the wind or observer's motion would have on the plumb bob. For navigators on the deck of a moving ship, these limitations could be difficult to overcome. [edit] Solar observations Drawing of a back observation quadrant. This instrument was used in the manner of a backstaff to measure the altitude of the sun by observing the position of a shadow on the instrument. Drawing of a back observation quadrant. This instrument was used in the manner of a backstaff to measure the altitude of the sun by observing the position of a shadow on the instrument. In order to avoid staring into the sun to measure its altitude, navigators could hold the instrument in front of them with the sun to their side. By having the sunward sighting vane cast its shadow on the lower sighting vane, it was possible to align the instrument to the sun. Care would have to be taken to ensure that the altitude of the centre of the sun was determined. This could be done by averaging the elevations of the upper and lower umbra in the shadow. [edit] Back observation quadrant In order to perform measurements of the altitude of the sun, a back observation quadrant was developed.[3] With such a quadrant, the observer viewed the horizon from a sight vane (C in the figure on the right) through a slit in the horizon vane (B). This ensured the instrument was level. The observer moved the shadow vane (A) to a position on the graduated scale so as to cause its shadow to appear coincident with the level of the horizon on the horizon vane. This angle was the elevation of the sun. [edit] Framed quadrant A large frame quadrant at the ancient Beijing Observatory. It was constructed in 1673. A large frame quadrant at the ancient Beijing Observatory. It was constructed in 1673. Large frame quadrants were used for astronomical measurements, notably determining the altitude of celestial objects. They could be permanent installations, such as mural quadrants. Smaller quadrants could be moved. Like the similar astronomical sextants, they could be used in a vertical plane or made adjustable for any plane. When set on a pedestal or other mount, they could be used to measure the angular distance between any two celestial objects. The details on their construction and use are essentially the same as those of the astronomical sextants; refer to that article for details. [edit] See also * Mural instrument * Davis quadrant [edit] References 1. ^ Gerard L'E. Turner, Antique Scientific Instruments, Blandford Press Ltd. 1980 ISBN 0-7137-1068-3 2. ^ King, D. (1987), ‘Islamic Astronomical Instruments’, Variorum, London, repr. Aldershot: Variorum, 1995. 3. ^ a b May, William Edward, A History of Marine Navigation, G. T. Foulis & Co. Ltd., Henley-on-Thames, Oxfordshire, 1973, ISBN 0 85429 143 1 * Maurice Daumas, Scientific Instruments of the Seventeenth and Eighteenth Centuries and Their Makers, Portman Books, London 1989 ISBN 978-0713407273

2楼的图片是建国门的古观象台吧

【 在 aressong 的大作中提到: 】 : 在维基百科上六分仪找到中文介绍，四分仪只找到英文介绍： : 六分仪： : 六分仪（sextant），在测绘和船舶通信导航中，是由分度弧、指标臂、动镜、定镜、望远镜和测微轮组成，弧长约为圆周的六分之一，用以观察天体高度和目标的水平角与垂直角的反射镜类型的手持测角仪器。广泛用于航海和航空中，用来确定观测者的自身位置。 : ................... 整一堆英文想累死人啊 百度百科搜象限仪和六分仪，简洁多了

想起了大航海里的六分仪.. 【 在 aressong 的大作中提到: 】 : 在维基百科上六分仪找到中文介绍，四分仪只找到英文介绍： : 六分仪： : 六分仪（sextant），在测绘和船舶通信导航中，是由分度弧、指标臂、动镜、定镜、望远镜和测微轮组成，弧长约为圆周的六分之一，用以观察天体高度和目标的水平角与垂直角的反射镜类型的手持测角仪器。广泛用于航海和航空中，用来确定观测者的自身位置。 : ...................

【 在 aressong 的大作中提到: 】 : 在维基百科上六分仪找到中文介绍，四分仪只找到英文介绍： : 六分仪： : 六分仪（sextant），在测绘和船舶通信导航中，是由分度弧、指标臂、动镜、定镜、望远镜和测微轮组成，弧长约为圆周的六分之一，用以观察天体高度和目标的水平角与垂直角的反射镜类型的手持测角仪器。广泛用于航海和航空中，用来确定观测者的自身位置。 : ................... 多谢。。。可惜没耐心读完E文。。。

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