FACTOID # 21: 15% of Army recruits from South Dakota are Native American, which is roughly the same percentage for female Army recruits in the state.
 
 Home   Encyclopedia   Statistics   States A-Z   Flags   Maps   FAQ   About 
   
 
WHAT'S NEW
 

SEARCH ALL

FACTS & STATISTICS    Advanced view

Search encyclopedia, statistics and forums:

 

 

(* = Graphable)

 

 


Encyclopedia > Celestial navigation

Celestial navigation, also known as astronavigation, is a position fixing technique that was devised to help sailors cross the featureless oceans without having to rely on dead reckoning to enable them to strike land. Celestial navigation uses angular measurements (sights) between the horizon and a common celestial object. The Sun is most often measured. Skilled navigators can use the Moon, planets or one of 57 navigational stars whose coordinates are tabulated in nautical almanacs. Celestial Navigation is the 15th episode of The West Wing. ... Position fixing is the branch of navigation concerned with the use of a variety of visual and electronic methods to determine the position of a ship, aircraft or person on the surface of the Earth. ... Dead reckoning (DR) is the process of estimating ones current position based upon a previously determined position, or fix, and advancing that position based upon measured velocity, time, heading, as well as the effect of currents or wind. ... Sol redirects here. ... This article is about Earths moon. ... This article is about the astronomical term. ... A nautical almanac is a publication describing the positions and movements of celestial bodies, including the sun, moon, planets, and 57 stars chosen for their ease of identification and wide spacing. ...

Contents

How it works

Celestial navigation is the process whereby angles between objects in the sky (celestial objects) and the horizon are used to locate one's position on the globe. At any given instant of time, any celestial object (e.g. the Moon, Jupiter, navigational star Spica) will be located directly over a particular geographic position on the Earth. This geographic position is known as the celestial object’s subpoint, and its location (e.g. its latitude and longitude) can be determined by referring to tables in a nautical or air almanac. This article is about Earths moon. ... Atmospheric characteristics Atmospheric pressure 70 kPa Hydrogen ~86% Helium ~14% Methane 0. ... Spica (α Vir / α Virginis / Alpha Virginis) is the brightest star in the constellation Virgo, and one of the brightest stars in the nighttime sky. ... This article is about the geographical term. ... Longitude is the east-west geographic coordinate measurement most commonly utilized in cartography and global navigation. ...


The measured angle between the celestial object and the horizon is directly related to the distance between the subpoint and the observer, and this measurement is used to define a circle on the surface of the Earth called a celestial line of position (LOP). The size and location of this circular line of position can be determined using mathematical or graphical methods (discussed below). The LOP is significant because the celestial object would be observed to be at the same angle above the horizon from any point along its circumference at that instant.


An example illustrating the concept behind the intercept method for determining one’s position is shown in the Figure below. (Two other common methods for determining one’s position using celestial navigation are the longitude by chronometer and ex-meridian methods.) In the image below, the two circles on the map represent lines of position for the Sun and Moon at 1200 GMT on October 29, 2005. At this time, a navigator on a ship at sea measured the Moon to be 56 degrees above the horizon using a sextant. Ten minutes later, the Sun was observed to be 40 degrees above the horizon. Lines of position were then calculated and plotted for each of these observations. Since both the Sun and Moon were observed at their respective angles from the same location, the navigator would have to be located at one of the two locations where the circles cross. The Intercept Method or Marc St. ... Longitude by Chronometer, known by mariners as Long by Chrom, is an astronomical navigation method of calculating an observers position on earth. ... Ex- Meridian, is an astronomical navigation method of calculating an observers position on earth. ... For alternate meanings of GMT, see GMT (disambiguation). ... is the 302nd day of the year (303rd in leap years) in the Gregorian calendar. ... Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ... A sextant is a measuring instrument generally used to measure the angle of elevation of a celestial object above the horizon. ...


In this case the navigator is either located on the Atlantic Ocean, about 350 nautical miles (650 km) west of Madeira, or in South America, about 90 nautical miles (170 km) southwest of Asunción, Paraguay. In most cases, determining which of the two intersections is the correct one is obvious to the observer because they are often thousands of miles apart. As it is unlikely that the ship is sailing across the Pampas, the position in the Atlantic is the correct one. Note that the lines of position in the figure are distorted because of the map’s projection; they would be circular if plotted on a globe.


Image File history File links Sun_Moon_(annotated). ...


Angular measurement

Using a marine sextant to measure the altitude of the sun above the horizon

Accurate angle measurement evolved over the years. One simple method is to hold the hand above the horizon with your arm stretched out. The width of a finger is an angle just over 1.5 degrees. The need for more accurate measurements led to the development of a number of increasingly accurate instruments, including the kamal, astrolabe, octant and sextant. The sextant and octant are most accurate because they measure angles from the horizon, eliminating errors caused by the placement of an instrument's pointers, and because their dual mirror system cancels relative motions of the instrument, showing a steady view of the object and horizon. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... A sextant is a measuring instrument generally used to measure the angle of elevation of a celestial object above the horizon. ... A kamal is a celestial navigation device that determines latitude. ... A 16th century astrolabe. ... Octant Octant is a measuring instrument similar to a sextant. ... A sextant is a measuring instrument generally used to measure the angle of elevation of a celestial object above the horizon. ...


Navigators measure distance on the globe in degrees, arcminutes and arcseconds. A nautical mile is defined as 1852 meters, but is also (not accidentally) one minute of angle along a meridian on the Earth. Sextants can be read accurately to within 0.2 arcminutes. So the observer's position can be determined within (theoretically) 0.2 miles, about 400 yards (370 m). Most ocean navigators, shooting from a moving platform, can achieve a practical accuracy of 1.5 miles (2.8 km), enough to navigate safely when out of sight of land. A nautical mile or sea mile is a unit of length. ...


Practical navigation

Practical celestial navigation usually requires a marine chronometer to measure time, a sextant to measure the angles, an almanac giving schedules of the coordinates of celestial objects, a set of sight reduction tables to help perform the height and azimuth computations, and a chart of the region. With sight reduction tables, the only math required is addition and subtraction. Small handheld computers, laptops and even scientific calculators enable modern navigators to "reduce" sextant sights in minutes, by automating all the calculation and/or data lookup steps. Most people can master simpler celestial navigation procedures after a day or two of instruction and practice, even using manual calculation methods. A marine chronometer is a timekeeper precise enough to be used as a portable time standard, used to determine longitude by means of celestial navigation. ... A sextant is a measuring instrument generally used to measure the angle of elevation of a celestial object above the horizon. ... Calendarium cracoviense, an almanac for the year 1474. ...


Modern practical navigators usually use celestial navigation in combination with satellite navigation to correct a dead reckoning track, that is, a course estimated from a vessel's position, angle and speed. Using multiple methods helps the navigator detect errors, and simplifies procedures. When used this way, a navigator will from time to time measure the sun's altitude with a sextant, then compare that with a precalculated altitude based on the exact time and estimated position of the observation. On the chart, one will use the straight edge of a plotter to mark each position line. If the position line shows one to be more than a few miles from the estimated position, one may take more observations to restart the dead-reckoning track. Satellite navigation systems use radio time signals transmitted by satellites to enable mobile receivers on the ground to determine their exact location. ... Dead reckoning (DR) is the process of estimating ones current position based upon a previously determined position, or fix, and advancing that position based upon measured velocity, time, heading, as well as the effect of currents or wind. ...


In the event of equipment or electrical failure, one can get to a port by simply taking sun lines a few times a day and advancing them by dead reckoning to get a crude running fix.


Latitude

Latitude was measured in the past either at noon (the "noon sight") or from Polaris, the north star. Polaris always stays within 1 degree of celestial north pole. If a navigator measures the angle to Polaris and finds it to be 10 degrees from the horizon, then he is on a circle at about North 10 degrees of geographic latitude. Angles are measured from the horizon because locating the point directly overhead, the zenith, is difficult. When haze obscures the horizon, navigators use artificial horizons, which are bubble levels reflected into a sextant. This article is about the geographical term. ... For other uses, see Polaris (disambiguation). ... In broad terms, the zenith is the direction pointing directly above a particular location (perpendicular, orthogonal). ... A spirit level A spirit level or bubble level is an instrument designed to indicate whether a surface is level or plumb. ... A sextant is a measuring instrument generally used to measure the angle of elevation of a celestial object above the horizon. ...


Latitude can also be determined by the direction in which the stars travel over time. If the stars rise out of the east and travel straight up you are at the equator, but if they drift south you are to the north of the equator. The same is true of the day-to-day drift of the stars due to the movement of the Earth in orbit around the Sun; each day a star will drift approximately one degree. In either case if the drift can be measured accurately, simple trigonometry will reveal the latitude. Wikibooks has a book on the topic of Trigonometry The Canadarm2 robotic manipulator on the International Space Station is operated by controlling the angles of its joints. ...


Longitude

Longitude can be measured in the same way. If one can accurately measure the angle to Polaris, a similar measurement to a star near the eastern or western horizons will provide the longitude. The problem is that the Earth turns about 15 degrees per hour, making such measurements dependent on time. A measure only a few minutes before or after the same measure the day before creates serious navigation errors. Before good chronometers were available, longitude measurements were based on the transit of the moon, or the positions of the moons of Jupiter. For the most part, these were too difficult to be used by anyone except professional astronomers. Longitude is the east-west geographic coordinate measurement most commonly utilized in cartography and global navigation. ...


The longitude problem took centuries to solve. Two useful methods evolved during the 1700s, and are still practiced today: lunar distance, which does not involve the use of a chronometer, and use of an accurate timepiece, or chronometer. Finding Greenwich time while at sea using a lunar distance. ...


Lunar distance

Main article: Lunar distance

The older method, called "lunar distances", was refined in the 18th century. It is only used today by sextant hobbyists and historians, but the method is sound, and can be used when a timepiece is not available or its accuracy is suspect during a long sea voyage. The navigator precisely measures the angle between the moon and a body like the sun or a selected group of stars lying along the ecliptic. That angle, after it is corrected for various errors, is the same at any place on the surface of the earth facing the moon at a unique instant of time. Old almanacs used to list angles in tables. The navigator could thumb through the almanac to find the angle he or she measured, and thus know the time at Greenwich. Modern handheld and laptop calculators can perform the calculation in minutes, allowing the navigator to use other acceptable celestial bodies than the old nine. Knowing Greenwich time, the navigator can work out longitude. Finding Greenwich time while at sea using a lunar distance. ...


Use of time

Main article: Marine chronometer Today

The considerably more popular method was (and still is) to use an accurate timepiece to directly measure the time of a sextant sight. The need for accurate navigation led to the development of progressively more accurate chronometers in the 18th century. Today, time is measured with a chronometer, a quartz watch, a shortwave radio time signal broadcast from an atomic clock, or the time displayed on a GPS. A quartz wristwatch normally keeps time within a half-second per day. If it is worn constantly, keeping it near body heat, its rate of drift can be measured with the radio, and by compensating for this drift, a navigator can keep time to better than a second per month. Traditionally, a navigator checked his chronometer from his sextant, at a geographic marker surveyed by a professional astronomer. This is now a rare skill, and most harbor masters cannot locate their harbor's marker. A marine chronometer is a timekeeper precise enough to be used as a portable time standard, used to determine longitude by means of celestial navigation. ... A quartz clock A quartz clock is a timepiece that uses an electronic oscillator which is made up by a quartz crystal to keep precise time. ... A time signal is a visible, audible, mechanical, or electronic signal used as a reference to determine the time of day. ... “Nuclear Clock” redirects here. ... Over fifty GPS satellites such as this NAVSTAR have been launched since 1978. ... For other uses, see Watch (disambiguation). ...


Traditionally, three chronometers were kept in gimbals in a dry room near the center of the ship. They were used to set a watch for the actual sight, so that no chronometers were ever risked to the wind and salt water on deck. Winding the chronometers was a crucial duty of the navigator, logged as "chron. wound." for checking by line officers. Navigators also set the ship's clocks and calendar.


Modern celestial navigation

The celestial line of position concept was discovered in 1837 by Thomas Hubbard Sumner when, after one observation he computed and plotted his longitude at more than one trial latitude in his vicinity – and noticed that the positions lay along a line. Using this method with two bodies, navigators were finally able cross two position lines and obtain their position – in effect determining both latitude and longitude. Later in the 19th century came the development of the modern (Marcq St. Hilaire) intercept method; with this method the body height and azimuth are calculated for a convenient trial position, and compared with the observed height. The difference in arcminutes is the nautical mile "intercept" distance that the position line needs to be shifted toward or away from the direction of the body's subpoint. (The intercept method uses the concept illustrated in the example in the “How it works” section above.) Two other methods of reducing sights are the longitude by chronometer and the ex-meridian method. Thomas Hubbard Sumner (20 March 1807 – 9 March 1876) was a sea captain during the 19th century. ... The Intercept Method or Marc St. ... Longitude by Chronometer, known by mariners as Long by Chrom, is an astronomical navigation method of calculating an observers position on earth. ... Ex- Meridian, is an astronomical navigation method of calculating an observers position on earth. ...


While celestial navigation is becoming increasingly redundant with the advent of inexpensive and highly accurate satellite navigation receivers (GPS), it was used extensively in aviation until 1960s, and marine navigation until quite recently. But since a prudent mariner never relies on any sole means of fixing his/her position, many national maritime authorities still require deck officers to show knowledge of celestial navigation in examinations, primarily as a back up for electronic navigation. One of the most common current usages of celestial navigation aboard large merchant vessels is for compass calibration and error checking at sea when no terrestrial references are available. Over fifty GPS satellites such as this NAVSTAR have been launched since 1978. ...


The U.S. Air Force and U.S. Navy continued instructing military aviators on its use until 1997, because: Seal of the Air Force. ... The United States Navy (USN) is the branch of the United States armed forces responsible for naval operations. ...

  • it can be used independently of ground aids
  • has global coverage
  • cannot be jammed (except by clouds)
  • does not give off any signals that could be detected by an enemy[1]

The US Naval Academy announced that it was discontinuing its course on celestial navigation, considered to be one of its most demanding courses, from the formal curriculum in the spring of 1998 stating that a sextant is accurate to a three-mile (5 km) radius, while a satellite-linked computer can pinpoint a ship within 60 feet (18 m). Presently, midshipmen continue to learn to use the sextant, but instead of performing a tedious 22-step mathematical calculation to plot a ship's course, midshipmen feed the raw data into a computer.[2] A sextant is a measuring instrument generally used to measure the angle of elevation of a celestial object above the horizon. ...


Likewise, celestial navigation was used in commercial aviation up until the early part of the jet age; it was only phased out in the 1960s with the advent of inertial navigation systems. An inertial navigation system measures the position and altitude of a vehicle by measuring the accelerations and rotations applied to the systems inertial frame. ...


Celestial navigation continues to be taught to cadets during their training in the British Merchant Navy and remains as a requirement for their certificate of competency. For the steam locomotives, see SR Merchant Navy Class. ...


A variation on terrestrial celestial navigation was used to help orient the Apollo spacecraft enroute to and from the Moon. To this day, space missions, such as the Mars Exploration Rover use star trackers to determine the attitude of the spacecraft. Apollo Spacecraft: Command Module, Service Module, Lunar Module. ... Artists Concept of Rover on Mars (credit: Maas Digital LLC) Marvin the Martian, Spirit rover Mission patch Duck Dodgers, Opportunity rover Mission patch NASAs Mars Exploration Rover (MER) Mission is an ongoing robotic mission of exploring Mars, that began in 2003 with the sending of two rovers â€” Spirit... In the context of spacecraft, attitude control is control of the angular position and rotation of the spacecraft, either relative to the object that it is orbiting, or relative to the celestial sphere. ...


As early as the mid-1960s, advanced electronic and computer systems had evolved enabling navigators to obtain automated celestial sight fixes. These systems were used aboard both ships as well as US Air Force aircraft, and were highly accurate, able to lock onto up to 11 stars (even in daytime) and resolve the craft's position to less than 300 feet (91 m). The SR-71 high-speed reconnaissance aircraft was one example of an aircraft that used automated celestial navigation. These rare systems were expensive, however, and the few that remain in use today are regarded as backups to more reliable satellite positioning systems. The Lockheed SR-71, unofficially known as the Blackbird, is a long-range, advanced, strategic reconnaissance aircraft developed from the Lockheed A-12 and YF-12A aircraft by Lockheeds Skunk works, which was also responsible for the U-2 and many other advanced aircraft. ... A military aircraft used for monitoring enemy activity, usually carrying no armament. ...


Celestial navigation continues to be used by private yachtsmen, and particularly by long-distance cruising yachts around the world. For small cruising boat crews, celestial navigation is generally considered an essential skill when venturing beyond visual range of land. Although GPS (Global Positioning System) technology is reliable, offshore yachtsmen use celestial navigation as either a primary navigational tool or as a backup.


Celestial navigation trainer

Celestial navigation trainers combine a simple flight simulator with a planetarium in order to train aircraft crews in celestial navigation. For flight simulator software from Microsoft, see Microsoft Flight Simulator. ... For the song by Ai Otsuka, see Planetarium (song) // A planetarium is a theatre built primarily for presenting educational and entertaining shows about astronomy and the night sky, or for training in celestial navigation. ...


An early example is the Link Celestial Navigation Trainer, used of the Second World War.[3][4] Housed in a 45 feet (14 m) high building, it featured a cockpit which accommodated a whole bomber crew (pilot, navigator and bomber). The cockpit offered a full array of instruments which the pilot used to fly the simulated aeroplane. Fixed to a dome above the cockpit was an arrangement of lights, some collimated, simulating constellations from which the navigator determined the plane's position. The dome's movement simulated the changing positions of the stars with the passage of time and the movement of the plane around the earth. The navigator also received simulated radio signals from various positions on the ground. Mushroom cloud from the nuclear explosion over Nagasaki rising 18 km into the air. ... Cockpit of a light aircraft, showing instrumentation dials and dual control yokes. ... For other uses, see Bomber (disambiguation). ... Captain Nemo and Professor Aronnax contemplating measuring instruments in Twenty Thousand Leagues Under the Sea In physics and engineering, measurement is the activity of comparing physical quantities of real-world objects and events. ... For other uses, see Aviator (disambiguation). ... Airplane and Aeroplane redirect here. ... Collimated light is light whose rays are parallel. ... This article is about the star grouping. ... This article is about Earth as a planet. ...


Below the cockpit moved "terrain plates" – large, movable aerial photographs of the land below, which gave the crew the impression of flight and enabled the bomber to practise lining up bombing targets.


A team of operators sat at a control booth on the ground below the machine, from which they could simulate weather conditions such as wind or cloud. This team also tracked the aeroplane's position by moving a "crab" (a marker) on a paper map. For the geological process, see Weathering or Erosion. ...


The Link Celestial Navigation Trainer was developed in response to a request made by the British Royal Air Force (RAF) in 1939. The RAF ordered 60 of these machines, and the first one was built in 1941. The RAF used only a few of these, leasing the rest back to the U.S., where eventually hundreds were in use. RAF redirects here. ... For other uses of terms redirecting here, see US (disambiguation), USA (disambiguation), and United States (disambiguation) Motto In God We Trust(since 1956) (From Many, One; Latin, traditional) Anthem The Star-Spangled Banner Capital Washington, D.C. Largest city New York City National language English (de facto)1 Demonym American...


See also

Nautical Portal

Image File history File links No higher resolution available. ... The principles of air navigation are the same for all aircraft, big or small. ... The American Practical Navigator , written by Nathaniel Bowditch, is an encyclopedia of navigation, a valuable handbook on oceanography and meteorology, and contains useful tables and a maritime glossary. ... This article is about determination of position and direction on or above the surface of the earth. ... A sextant is a measuring instrument generally used to measure the angle of elevation of a celestial object above the horizon. ... Radio navigation is the application of radio frequencies to determining a position on the earth. ... Satellite navigation systems use radio time signals transmitted by satellites to enable mobile receivers on the ground to determine their exact location. ... Spherical geometry is the geometry of the two-dimensional surface of a sphere. ... A nautical almanac is a publication describing the positions and movements of celestial bodies, including the sun, moon, planets, and 57 stars chosen for their ease of identification and wide spacing. ... An ephemeris (plural: ephemerides) (from the Greek word ephemeros = daily) is a device giving the positions of astronomical objects in the sky. ... A star clock is a method of using the stars to determine the time. ... Longitude by Chronometer, known by mariners as Long by Chrom, is an astronomical navigation method of calculating an observers position on earth. ... The history of longitude is a record of the effort, by navigators and scientists over several centuries, to discover a means of determining longitude. ... Meridian Altitude, is an astronomical navigation method of calculating an observers latitude. ... John Harrison John Harrison (March 24, 1693–March 24, 1776) was an English clockmaker, who designed and built the worlds first successful chronometer (maritime clock), one whose accuracy was great enough to allow the determination of longitude over long distances. ... In Norse Mythology, Sigi is a one of the sons of Odin. ...

References

  1. ^ U.S. Air Force Pamphlet (AFPAM) 11-216, Chapters 8-13
  2. ^ Navy Cadets Won't Discard Their Sextants, The New York Times By DAVID W. CHEN Published: May 29, 1998
  3. ^ World War II. A Brief History of Aircraft Flight Simulation. Retrieved on January 27, 2005.
  4. ^ Corporal Tomisita "Tommye" Flemming-Kelly-U.S.M.C.-Celestial Navigation Trainer -1943/45. World War II Memories. Retrieved on January 27, 2005.

Seal of the Air Force. ... The New York Times is a daily newspaper published in New York City and distributed internationally. ... Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ... Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ...

External links


  Results from FactBites:
 
Boating, Sailing, & Navigation DVDs (2347 words)
CELESTIAL NAVIGATION - The Air Almanac (H.O. After #D303, this program goes on to show how to shoot the 57 Navigational Stars, 4 Planets and Moon.
Buckley simply and clearly explains the theory and practice of Celestial Navigation and teaches the noon shot.
Includes clear demonstrations on the water and in a simulated navigator's station in a Coast Guard certified navigation school.
Celestial navigation Summary (0 words)
Celestial navigation, also known as astronavigation, is a position fixing technique that was the first system devised to help sailors cross the featureless oceans without having to rely on random chance to enable them to strike land.
Celestial navigation is the process whereby angles between objects in the sky (celestial objects) and the horizon are used to locate one’s position on the globe.
Modern practical navigators nearly always use celestial navigation in combination with satellite navigation to correct a dead-reckoning track, that is, a course estimated from a vessel's position, angle and speed.
  More results at FactBites »

 
 

COMMENTARY     


Share your thoughts, questions and commentary here
Your name
Your comments

Want to know more?
Search encyclopedia, statistics and forums:

 


Press Releases |  Feeds | Contact
The Wikipedia article included on this page is licensed under the GFDL.
Images may be subject to relevant owners' copyright.
All other elements are (c) copyright NationMaster.com 2003-5. All Rights Reserved.
Usage implies agreement with terms, 1022, m