The Working Principle and Uses of a Sextant
The sextant is an instrument used in navigation for measuring the angle of elevation of the sun or stars. It consists essentially of a fixed glass B, silvered on a vertical half, and a silvered mirror O which can be rotated about a horizontal axis. A small fixed telescope T is directed towards B.
Suppose that the angle of elevation of the sun, S, is required. Looking through T, the unsilvered half, of B, and also the view of it, H, seen by successive reflection at O and the silvered half B, are coincident. The mirror O is then parallel to B in the position M1, and the ray HO is reflected along OB and BD to enter the telescope T. the mirror O is now rotated to a position M2 until the image of the sun, S, seen by successive reflections at O and B, is on the horizon H’, and the angle of rotation, Ө, of the mirror is noted.
The ray SO from the sun is now reflected in turn from O and B so that it travels along BD, the direction of the horizon, and the angle of deviation of the ray is thus angle SOH. But the angle between the mirrors M2 and B is Ө. Thus, from our result for successive reflections at two inclined mirrors, angle SOH = 2Ө. Now the angle of elevation of the sun S, is angle SOH. Hence the angle of elevation is twice the angle of rotation of the mirror O, and can thus be easily measured from a scale which measures the rotation of O.
Since the angle of deviation after two successive reflections is independent of the angle of incidence on the first mirror, the image of the suns through T will continue to be seen on the horizon once O is adjusted, no matter how the ship pitches or rolls. This is an advantage of the sextant.
You can read more on the design, use and principle behind the use of a sextant by following this link
A sextant is a device used to measure the altitude of celestial bodies. It is an important instrument in navigation and can be used to calculate latitude. It is also useful for determining longitude.
A sextant consists of a telescope, a half-silvered horizontal mirror that the telescope “looks” through and a moving arm. The sextant works on the principle of double reflection.
What is a Sextant?
A sextant is an instrument used for celestial navigation. It determines the angle a star, sun or moon makes with the horizon. This information, combined with the time and date, can give you a line of position. It was developed to replace the octant, an earlier device that only covered 45 degrees. The name derives from the Latin “sextus,” meaning one-sixth.
A sextant consists of two mirrors and an index arm. The first is called a horizon mirror and is partially silvered to allow light to pass through it. The other is called the index mirror and can be seen straight through. The index arm is a moving part of the sextant, and by manipulating it you can take sightings.
Taking sights using the sextant requires careful observation and practice. There are a few errors that can occur with the device, and these must be corrected before making accurate measurements. Correctable errors include index error and side error, while non-correctable errors include perpendicularity error and collimation error. To spot these errors, look for a step between the true and reflected horizon when viewing the horizon through the index mirror. If you notice this, use the index error screw to correct it.
How Does a Sextant Work?
A sextant works by measuring the angle of inclination between two objects. It uses a semi-silvered mirror that allows only half of the light through and reflects the other half. The reflected light is then measured by the index and horizon mirrors with an angle scale on the bottom of the instrument. Rotating the sextant enables you to align two objects, and then read off the angle. Typically, degrees are read on the graduated arc, minutes on the vernier and seconds on the micrometer drum.
Sextants can also be used to measure the altitude of a celestial body, such as the Sun or Moon. When using a sextant for this purpose, it is important to ensure that the lower limb of the celestial object touches the horizon. It is also important to use the shade glasses provided with a sextant to protect your eyes from the sun’s rays.
The sextant is a simple device that can be used by anyone with some basic training. However, the sextant does require some practice and skill to use correctly. It is particularly sensitive to small errors that can be difficult to detect. These include collimation error, centering error, horizon mirror distortion and prismatic error.
Uses of a Sextant
The sextant is an important navigation tool because it can measure the angle between a celestial body and the horizon, allowing it to be used to find one’s position on the map. In addition, the sextant can also be used to measure the distance between two landmarks, such as mountains or lighthouses.
It is also useful when a ship is chasing another, as it can be used to determine how much closer or further away the other vessel is by measuring the angle between them. This is a useful skill to have when at sea and can save a lot of time and frustration. In addition, the sextant is not affected by movement of the ship, unlike many modern electronic navigation devices.
The sextant works by using the principle of double reflection. It has a frame that holds a horizontal mirror, index mirror, shade glasses, telescope, and a graduated scale and micrometer drum gauge. A movable radial arm is pivoted at the center of the frame, which can be moved until a star in the telescope coincides with the horizon on the graduated arc of the sextant. The angular distance of the star above the horizon can then be read on the graduated arc.
Description of a Sextant
A sextant is an instrument used for astronomical navigation. It is also used for terrestrial surveying. The foundation of a sextant is a frame, which holds all of its components together. A sextant can be made of plastic or metal. The index arm, which is used for taking sight measurements, is attached to the frame. Quality sextants are very accurate. There are a few errors that can occur when using a sextant, however. These include perpendicularity error and side error. The first is caused when the index mirror is not aligned with the horizon mirror. The second is when the index arm is not lined up with the scale.
The sextant is a complex instrument that uses the double reflection principle to measure angles. The sextant has two mirrors and a vernier to make sightings. When the index mirror and horizon mirror are lined up, the sextant can read degrees on an arc of 60 degrees. Sextants can also be read a few degrees to the left or right of zero, which is called being “on the arc.” The instrument can also be used to determine latitude by using trigonometry. Although modern ships are equipped with GPS and other satellite navigation tools, celestial navigation is still a vital skill for long-distance cruising yachts.
Applications of a Sextant
A sextant is used to measure the altitude of celestial objects above the horizon. It is also used to determine the local time of day. This is done by watching the sun climb in the sky and noting the time at which it reached its highest point. This measurement is referred to as the dip and it is recorded in nautical almanacs and charts.
A traditional sextant has two mirrors that divide the view into two sections. One section shows a direct view of the horizon and the other shows a reflection of the celestial object being sighted. This type of sextant is superior at night and in haze, but it requires accurate sweeping of the celestial object to ensure that its lowest limb touches the horizon.
Another type of sextant is the box sextant, which is used in surveying. It is a simpler instrument than the marine sextant and can be used to check the angles measured by other instruments. It is especially useful for chain surveying, which involves measuring the distances of various points along a length of land or water. A box sextant can also be used as an optical square by setting the vernier to 90o.
Mathematical Calculations Involving Sextant
A sextant is a precision instrument for measuring angles. It is used to determine the position of heavenly bodies and charted objects. It can also be used to calculate celestial longitude. Its accuracy is limited by the weather and the skill of the navigator. In poor conditions, a sextant can be off by several minutes of arc.
The sextant’s scale measures one-sixth of a circle, hence its name, and is named after the Latin sextus, meaning “sixth.” It is a double-reflecting instrument that can measure angles to a small degree to the left or right of zero on the arc. The sextant can also be corrected for dip, which is an adjustment to account for the height of your eye above sea level. To correct for dip, divide the sum of H (height of your eye in meters) by 1.7725 and subtract it from the angle measured by your sextant.
Advantages of Using a Sextant for Navigation
The sextant is an invaluable tool for coastal navigation and can be used to find horizontal danger angles, as well as vertical ones. It is also independent of electronics, which makes it an ideal backup for safe navigation. However, there are some situations when the fine level of accuracy that a sextant provides is unnecessary. In these cases, other methods are faster and more accurate.
Repair and Maintenance of a Sextant
If you use a sextant for celestial navigation, it is important to maintain it properly. This will ensure that it is accurate and will last longer. For this reason, it is a good idea to carry out a few DIY checks and adjustments to make sure that the instrument is working correctly. These include detecting side and index errors.
To check for side error, first set the sextant to zero and look at the horizon through the telescope. If the horizon line appears displaced vertically or horizontally, there is a side error. You can fix this by turning the adjustment screw on the horizon mirror until the real and reflected images appear in one straight continuous line.
Similarly, to check for index error, set the sextant to zero and observe a heavenly body. If the reflected image passes to the left or right of the direct image, there is an index error. This can be corrected by turning the second adjustment screw on the horizon mirror until the true and reflected images are in one straight, continuous line. It is also a good idea to keep the sextant away from bright sunlight and store it in a cool, dry place.
