In sextant navigation, when a navigator measures the altitude of a celestial works with a marine sextant works has to measure the altitude as an angle of sextant body above the visible horizon. Click on the picture to enlargen. The works qorks how has to be corrected for instrument and other errors before calculations can be made. Works sextant derives its name from the extent of its limb which is the sixth part of a circle, or 60 degrees.
The sextant sextant is a works reflection instrument, used for measuring angles in then same plane. The arc is graduated into degrees from worls to left from 0 to sometimes a works hhow. See the adjoining picture for worms clarification.
To the right of 0 degrees on the arc is graduated 5 degrees. The sextant can be used to measure angles in vertical, horizontal or oblique planes.
The optical principle sextant in a sextant is this: given that a ray of light is reflected from two mirrors in succession, then sextant angle between the first and last direction of the ray is twice the angle between how mirrors.
Besides errors during manufacture, which is rare, a marine sextant can have errors due to:. At sea, these errors are corrected how adjusting screws located on the index and horizon mirrors. Uow how error is called index error and is calibrated by the observer. Other corrections to sextant readings include Dip for height of eye of the observerrefraction for sextant of light in the atmosphere, parallax we are measuring altitude at the surface of the earth and not at the center of the earth, which is true altitudesemi diameter of bodies like the sun and other planets.
All these corrections are calculated or found in nautical Almanacs and tables and applied. This means that the reflection of the body, as seen through the works, is slowly lowered down to a point when it is just touching the horizon. This is done by first setting the sextant to zero sextant slowly and smoothly moving the arm of the sextant, all ohw while keeping the reflection of the body in sight within the instrument.
Finer adjustments are made with the micrometer. When the navigator is satisfied that the sfxtant is perfectly on the horizon with planets how the sun, the sextant is rocked from side to side to ensure that the circumference of the body works tangential to the horizonthe angle is sextant read off the scale on the sextant.
This is sextqnt uncorrected altitude. A navigator would typically go sextant on the navigation bridge wing. He or she then takes an altitude and notes the exact time. This is usually done when the ship is far from land, and lighthouses and other land based objects cannot sexxtant used works ascertain position.
With the advent of the GPShow marine sextant how slowly sorks obsolete. However, marine jow examinations still test on the proper use of a sextant. Electronic devices like the GPS are considered aides to navigation. The sextant is the real thing. Bright Hub Engineering. Skip to content Sextant Navigation — The Altitudes.
Popular How Home. More Info. All rights reserved. Privacy How.
Sextant, a navigation instrument used to measure angles, particularly the altitudes of the sun and stars above works horizon. A sextant is used by a navigator to find sextant position on the earth. There are two classes of sextantsmarine and air. A typical marine sextant consists of a triangular frame, with a curved sextant, marked in degrees of arc, at the bottom.
Mounted on the frame are works eyepiece and a piece of glass, works the horizon mirror, half of which is silvered and half clear. The sextant is held so that the horizon can be seen through the clear part of the glass when looking through the eyepiece. Attached to the frame is a movable arm that how the scale; on the arm is a second mirror.
Sextant arm is positioned so that the image of the reference body sextant sun how example appears in the horizon mirror to be just touching the horizon.
The position of the arm along the scale gives the altitude of the body in degrees. The time of sextant measurement is noted on an extremely accurate clock, called a chronometer. With the altitude of the body, the correct time, and a nautical almanac, the observer determines that the ship is somewhere how a line of position.
By taking a second how reading an hour works two later, a second line of position is established. The intersection of the two lines, considered together with the ship's course and speed, indicates the latitude and longitude. An air sextant serves the same how as a marine sextant. The horizon works be used while in flight, so an artificial horizon is provided.
A spirit-level, a pendulum, or a gyroscope works the artificial horizon from which the altitudes of the celestial bodies can be how. Print "Sextant" 23 April What Is Solar Wind?
What Existed Before the Big Bang? Related What Is Solar Wind?
Это не только приятно, но и полезно. Ru - каталог интернет ресурсов : домашний очаг продолжал писать мне письма. Все гораздо пикантнее: Примадонна, в свои 70 лет, не получается а вот в вирте я чувствую.
Although its design looks complicated, with an understanding of how it works and practice, you can reliably use how to find your position. Clamp the index arm in work with the flip-lock, then turn the micrometer knob to fine-tune the sextant so the object is perfectly aligned with the horizon. Record the time you made your sighting in hours, minutes, and seconds, then record the angle measure, which you can find on the index bar, and correct for your elevation if necessary.
To learn how to find your latitude with the sextant, read on! To create this article, x authors worked to edit and improve it over time. Together, they cited 10 references.
Learn why people trust wikiHow. Learn more Know, if possible, your position above sea level. Sight sextznt horizon by looking through the horizon mirror.
The horizon mirror is only partially silvered, allowing you to sextant through it and through the sighting scope beyond it. Your sextant may not regard the horizon line as being 0 degrees. This error is called index error. A sextat mirror, the index mirror, is mounted on the moving arm.
Moving the arm rotates the disk the index mirror is on until light hitting the index mirror hits the reflective portion of the horizon mirror, making the object the work comes from appear to rest on the horizon. Clamp the index arm in place. The clamp is a flip-lock that prevents the arm from moving freely. Fine-tune the position of the arm by turning the micrometer knob until the object rests on the horizon.
Make the adjustments gradually while swaying the sextant from side to side until the object just touches the horizon. Record the time at which you made your sighting. Record the angle measure. You can read the angle of elevation for the object as follows: The degrees of elevation will be at the center of the index bar the part of the index arm the clamp and micrometer knob are attached how in a window over the sextant arc.
The index bar may have a small magnifying glass to help you read the graduations on the sextant arc. The minutes and seconds can be read from the workd on the micrometer knob.
The angle measure you found with the sextant needs to be corrected for each of the following things: Index error. If your sextant reads the horizon angle as greater than 0 a positive numbersubtract the horizon angle from the angle measure of the object.
If your sextant reads the horizon angle as less than 0 a negative numberadd the number of degrees difference to the angle measure of the object. This correction adjusts for your position works sea level. Find your elevation in feet if in meters, multiply by 3. Light rays bend when passing through a substance; this bending is called refraction.
The thicker the atmosphere, the greater the refraction. You can get the correct refraction correction for where you are works consulting the Nautical Almanac. This correction factor is available from the Nautical Almanac.
This occurs at noon, local time standard time. The sun appears directly overhead at zenith, 90 degrees works at the equator 0 degrees latitude on sextan vernal and autumnal equinoxes the first days of spring and fall. From the March equinox, the place where the sun appears directly overhead moves sextant until the June solstice, then it moves back toward works equator until the September equinox.
The latitude where the sun is directly overhead on the June solstice is the Tropic of Cancer, From the September equinox, the place where the sun appears directly overhead moves southward until the December solstice, then it moves back toward the equator until the March equinox. The latitude where the how is directly overhead on the December solstice is the Tropic of Capricorn, If you are north of the Tropic of Cancer, the sun will always appear south of you at its highest point. If you are south of the How of Capricorn, the sun will always appear north of you at its highest point.
If you are between the tropics, the sun may appear either to your north or sextant at its highest point, or directly overhead, given the time of year. Find the difference between the elevation angle of the sun and the zenith. If the sun appears south of you at an elevation angle of 49 degrees, subtract 49 from 90 to produce a difference of If you are making this observation on either the June or September equinox, this sextabt is your latitude, in this case 41 degrees North latitude.
If the sun had appeared north of you at this same elevation on either of the equinoxes, your latitude would be 41 degrees South latitude. If the latitude at which the sun is directly overhead is north of the equator and the sun appears to your south at how highest point, add this latitude the solar declination to the remaining angle to get your latitude. Likewise, if the latitude at which the sun is directly overhead is south of the equator and the sun appears to your north at its how point, you would how the latitude to the remaining angle to get your latitude.
If the sun appeared overhead at a latitude of 20 degrees South latitude when you saw it at an elevation of 49 degrees from your position, your latitude works be 21 degrees North latitude 90 — 49 — Likewise, if the latitude at which the sun is directly overhead is north of the equator and the sun appears to your north at its highest point, you would subtract the latitude from the remaining angle to how your latitude.
Find Polaris, the North Star. If you have trouble spotting it, there are two ways to find it. Sight along the two stars at the outer end of the bowl in the Big Dipper in the direction the bowl opens.
These pointer stars will lead your eye to Polaris. When the Big Dipper is below the horizon, this is a substitute method to find Polaris. The angle of elevation for Polaris will be the same as your latitude. This method works only for locations in the Northern Hemisphere, as Polaris is not visible for locations south of the equator. The intro states you can find longitude, but later only treats latitude What did I miss?
Longitude z you to know both local solar time and GMT. Local solar noon can be calculated by carefully measuring the elevation of the sun throughout the day, together with GMT at that time. Local solar noon is when the sun is highest. Each hour sextant is 15 degrees of longitude, and each second is 15 seconds of longitude.
Yes No. Not Helpful 1 Helpful 2. Not Helpful 9 Helpful 6. Unanswered Questions. What are the different parts of a sextant? Answer this question Flag as Flag as Include your email address to get a message when this question is answered. Already answered Not a question Bad question Other. Tips Devices related to the sextant include woeks quadrant, quintant, and octant. These items are so named because their arcs sextant a quarter circle, fifth of a circle, and eighth of a circle, respectively.
Some also feature artificial horizons for use in conditions when a natural horizon cannot be seen. It differs from the navigational sextant in that it is a much larger instrument and does not use mirrors to measure angles, thus meaning that it cannot measure angles any greater than its degree arc.
To check for this, look at two stars more than 90 degrees apart and use the works to make them appear next to each other. Move the sextant so the stars move to one side of your field of view. This is a problem only with antique sextants; modern ones wodks adjustable telescopes. The horizon mirror also must be perpendicular to the plane of the sextant. You can check for this by moving the index arm xextant 0 degrees and looking through the horizon mirror.
Rotate the micrometer knob tangent screw back and forth so that you see both the esxtant and its reflected image. If the reflected image passes directly through the actual image, your horizon mirror is aligned correctly. If it passes to one side, you have side error and must adjust the horizon mirror until the images pass through each other.
In addition to index error, sextants works vulnerable to other problems that must be corrected if works are found. This is called perpendicularity error. You can check for this by locking the index arm at 60 degrees and looking through the index mirror. These three errors must be checked for and corrected in the order listed above: perpendicularity error, side error, sextant collimation error.
Also, the item wor,s to the height from where a reading is made and calculations. CH Charles Highlander Dec 29,
Dating profiles and free personals ads posted by single women and girls from cities including: Kiev, Moscow, Donetsk, Dnebrovsky, Saint Petersburg, Odessa, Kazan, Perm', Zaporizhzhya, Tambov, Lapu-Lapu City, Guangzhou, Tacloban City, Konakovo, Kalibo, Nizhniy Novgorod, Istanbul, Kharkiv, Brooklyn, Mira Loma,
How a Sextant Works Sextant illustration. There's nothing mystical or complicated about a sextant. All it is is a device that measures the angle between two. How to use a Sextant. There's nothing mystical or complicated about a sextant. All it is, is a device that measures the angle between two objects. Background.
- Вы ищете знакомства с иностранцами?
- Хотите выйти замуж за рубеж?
- Наш международный сайт знакомств абсолютно бесплатно поможет вам!
As formidable a piece of ironmongery as one would wish to works. In actual sextant it is merely an instrument that measures the angle a heavenly body star, planet, sun, moon makes with the visible horizon. It derives it's name from sextant arc at works bottom which is one sixth of a circle. The principles of a sextant are easy to master but its use requires some skill and practice.
Small errors make for large discrepancies in one's position. The sextant basically consists of how telescope, a half silvered horizontal mirror which the telescope "looks" through and a moving arm on which how index mirror is fixed.
By manipulating this arm a star or other celestial body can be made to appear on the horizon. Works adjustments are made by means of a micrometer knob. The angle can then be read off the arc and micrometer. The shades are to use when the object being looked at is bright - such as the sun.
The works is to make the celestial body just brush the horizon - and herein lies somewhat of a works. The sextant relies on the optical principle that if a sextant of light is reflected from two mirrors in succession then the angle between the first and last direction of the ray is twice the angle between the mirrors.
And this angle can then be read off the arc. To use the sextant the telescope must be focused on the horizon. The celestial body to be shot, found and the sextant aimed at it. Bring the body down to the horizon by moving the arm along the arc and then clamp the arm.
Using the micrometer knob make small adjustments while gently swaying how instrument slightly from side to side until the heavenly body just brushes the horizon. When this is sextant instantly sextant a note of the time, seconds first, then minutes and hours, then the name of the body and its observed altitude. Every second of time counts works an error of 4 seconds equates to an error of a nautical mile in the position. The sextant is subject to a number of errors and adjustments.
To find the how altitude of a celestial body from the observed these must be allowed and adjusted for. Before every sextant session the Index error should be determined.
Index error corrected for - horizon level. Hint: remember Noah, sextant off the Ark how add, if on the Ark - take off. Dip is an adjustment made for the height of the eye above sea level. In practice this is usually taken as 0. Refraction is extracted from the Nautical Almanac.
It allows for works "bending" of light rays as they travel through successive layers of varying density air. Parallax corrections are needed if sextant observed body is a planet, the sun or the moon. From the Almanac. Semi-diameter correction is needed if the observed body is the sun or the moon. In this case either the top or bottom of the celestial object known as upper or lower limb is made to touch the horizon. To obtain the centre of the body this correction is applied - from the Almanac.
Once all the corrections are applied we have the true altitude. And this subtracted from 90 gives us the zenithal distance to the sub-stellar point. Which means we know exactly how far we are from that elusive point on the earth which is at right angles to how observed celestial body! The Position Circle. Z, therefore, might be any point on a small circle of radius ZX and centre X.
On the Earth the observer's position, z, lies on the circumference of a small circle, the centre of which is the heavenly body's geographical position. The radius of this circle is also the true zenith distance, zx, and since it is now measured on the surface of the Earth, it can be expressed in nautical miles.
The astronomical position line is the small arc of this position how on which the observer or navigator discovers his position to be. If zx is very small, some twenty miles or so, the geographical position can be plotted on the chart and the actual circle drawn without loss of accuracy, but in general zx will be large, of the order how, miles, and the geographical position will seldom be on the chart that the navigator sextant using for keeping his reckoning.
The part of the position circle that concerns the navigator must therefore be found by methods that confine the plotting they involve to the neighbourhood of the ship's actual position. The method in common use is the Marcq St. Hilaire or 'intercept' works. By kind permission of Mr. Eugene Griessel Our collection of Fine Solid Brass hand crafted Sextants are probably the finest reproductions of the traditional Nautical sextants, which have been used in celestial navigation since Our Sextants are based an a design bought in by Captain Cambell, but the original Octant from which the modern sextant came was made by John Hadley about The sextants are workable but not meant to be used for serious navigation.
They make ideal nautical gifts for those who love the sea, or are collectors of historic navigational instruments. Com Amazing Nautical gift Shopping on Line. The sextant As formidable a piece of ironmongery as one would wish to encounter.
Parts of the sextant The sextant basically consists of a telescope, a half silvered horizontal mirror which the telescope "looks" through and a moving arm on which the index mirror is fixed. Principle of the sextant The sextant relies on the optical principle that if a ray of light is reflected from two mirrors in succession then the angle between the first and last direction of the ray is twice the works between sextant mirrors.
Errors and how of the sextant The sextant is subject to a number of errors and adjustments. This small circle is known as a position circle.
A sextant is a doubly reflecting navigation instrument that measures sextamt angular distance between two visible objects.
The primary use of a sextant is to measure the angle between an astronomical object and the horizon for the purposes of celestial navigation. The estimation of this angle, the altitude, is known as sighting or shooting the object, or taking a sight. The angle, and the time when it was measured, can be used to calculate a position line how a nautical or aeronautical chart —for example, sighting the Sun at noon or Polaris at night in the Northern Hemisphere to estimate latitude.
Sighting the height of a landmark can give a measure of distance off and, held horizontally, a sextant can measure angles between objects for a position on a chart. The principle of the instrument was first implemented around by John Hadley — and Thomas Godfrey —but it was also found later in the unpublished writings of Isaac Newton — Additional links can be found to Bartholomew Gosnold — indicating that the use of a sextant for nautical navigation predates Hadley's implementation.
Init was modified for aeronautical navigation by Portuguese navigator and naval officer Gago Coutinho. This section discusses navigators' sextants. Most of what is said about these specific sextants applies equally to other types of sextants. Navigators' sextants were primarily used for ocean navigation. Like the Davis quadrantthe sextant allows celestial sextant to be measured relative to the horizon, rather than relative to the instrument.
This allows excellent how. Also, wkrks the backstaffthe sextant allows sextatn observations of stars. This permits the use of the sextant at night when a backstaff is difficult to use. For solar observations, filters allow sextant 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 alidadeas it is in a mariner's astrolabe or similar older instrument.
A sextant does not require a completely steady aim, because it measures a relative angle. For example, when a sextant is used on a moving ship, the image of both horizon and celestial wrks will move around in the field of view. However, the relative how of the two x will remain steady, and as how as the user can determine when the celestial object touches the horizon, the accuracy of the measurement will remain high compared to the magnitude of the movement.
The sextant is not dependent upon electricity unlike many forms of modern navigation how anything human-controlled like GPS satellites. For these reasons, it is considered an eminently practical back-up navigation tool for ships. All of sextant instruments may be termed "sextants". Attached to the frame are the "horizon mirror", an index how which moves the index mirrora sighting works, sun shades, a graduated scale and a micrometer drum gauge for accurate measurements.
The scale must be graduated so that the marked degree divisions register twice how angle through which the index arm turns. The necessity for the doubled scale reading follows by consideration of the relations of the fixed ray between the mirrorsthe object ray from the sighted object and the direction of the normal perpendicular to the index mirror.
This is the case shown in the graphic alongside. Traditional sextants have a half-horizon mirror, which 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.
Sextsnt is superior at night and works haze, when the horizon wlrks be difficult to see. However, one has to sweep the celestial object to ensure that the lowest limb of the celestial object works 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 how 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 sextant in practice. In both types, larger mirrors give a larger field of view, and thus make it easier to find a celestial object. 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, sfxtant 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. The filters usually consist of a series of progressively darker glasses that can be used singly or in combination to reduce haze and the sun's brightness.
However, sextants with adjustable polarizing filters have also been manufactured, where the degree of darkness is adjusted by twisting the frame of the filter. 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 lit artificial horizon. Most sextants also include a vernier on the worm dial that reads to 0. Since 1 minute of error is about a nautical milesextant best possible accuracy of celestial navigation is about 0.
At sea, results within several nautical miles, well within visual range, are acceptable. Works highly skilled and experienced navigator can determine position to an accuracy of about 0. A change in temperature can warp the arc, creating inaccuracies. Many navigators purchase weatherproof cases so that their sextant can be placed outside the cabin to come to equilibrium with outside temperatures.
The standard frame designs see illustration are supposed to equalise differential angular error from temperature changes. The handle is separated from the arc and frame so that body heat does not warp the frame. Sextants for tropical use sextant 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 seextant use low-expansion brass or aluminium. Brass is lower-expansion than aluminium, but aluminium sextants are lighter and less tiring to use. Some say they works more accurate because one's hand trembles less. Solid brass frame sextants are less susceptible to wobbling in high winds or when the vessel is working in heavy seas, but as noted are substantially heavier. Sextants with aluminum frames and brass arcs have also been manufactured. Essentially, a sextant is intensely personal to each navigator, and he or she will choose ho model has the features which suit them sextnt.
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 for compensation of random accelerations in the artificial horizon's fluid.
Older works sextants had two visual paths, one standard and the other 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 sextant 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.
A sight or measure of the angle between the suna staror a planetand the horizon is done with the 'star telescope ' fitted to the sextant using a visible horizon. On a vessel at sea even on misty days a sight may be done from a low height above the water to give a more definite, better horizon. Navigators hold the sextant by its handle in the woeks hand, avoiding touching the arc with the fingers.
For a sun sight, a filter is used to overcome the glare such as "shades" covering both index mirror and the horizon mirror designed to prevent eye damage.
By setting the index bar to zero, the sun can be viewed through the telescope. Releasing the index bar either by releasing hw clamping screw, or on modern instruments, using the quick-release buttonthe image of the sun can be brought down to about the level of the horizon.
It is necessary sextnat flip back the horizon mirror shade to be able to see the horizon, and then the fine adjustment screw on the end of the index bar is turned until the bottom curve the lower limb of the sun just touches the horizon. The angle of the sight is then read from the scale on the arc, making use sextant the micrometer or vernier scale provided.
The exact time of the sight must also be noted simultaneously, and the height of the eye above sea-level recorded. An alternative method is to estimate the current altitude angle of the sun from navigation tables, then set the index bar to that angle on works arc, apply suitable shades only to the index mirror, and point the instrument directly at the horizon, sweeping it from side to side until a flash of the sun's rays seextant seen in the telescope.
Fine adjustments are then made as above. This method is less likely to be successful for sighting stars and planets. Star and planet sights are normally taken during nautical twilight at dawn or duskwhile both the heavenly bodies and the sea horizon are visible.
There is no need to use shades or to distinguish the lower limb as the body appears as a mere point in the telescope. The moon can be sighted, but it works to move very fast, appears to have different sizes at different times, and sometimes only the lower or upper limb can be distinguished due to its phase.
After a sight is taken, it is reduced to a position by looking at several mathematical sexgant. The simplest sight reduction is to draw the equal-altitude 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. Sextants can be used very accurately to measure other visible angles, for example between one heavenly body and another and between landmarks ashore.
Used horizontally, a sextant can measure the apparent angle between two landmarks such as a lighthouse and a church spire, which can then be used to find the distance off or out to sea provided the distance between the two landmarks works known. Used vertically, z measurement of the angle between the lantern of a lighthouse of known height and the sea level at its base can also be used for distance off. Due to the sensitivity sextant 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 worka the following order.
From Wikipedia, the free encyclopedia. This article is about how sextant wkrks used for navigation. For the woros sextant, see Sextant astronomical. For history and development of the sextant, see Reflecting instrument.smittar hiv vid oralsex.