SUMMARY / RELATED TOPICS

Celestial navigation

Celestial navigation known as astronavigation, is the ancient and modern practice of position fixing that enables a navigator to transition through a space without having to rely on estimated calculations, or dead reckoning, to know their position. Celestial navigation uses "sights", or angular measurements taken between a celestial body and the visible horizon; the Sun is most used, but navigators can use the Moon, a planet, Polaris, or one of 57 other navigational stars whose coordinates are tabulated in the nautical almanac and air almanacs. Celestial navigation is the use of angular measurements between celestial bodies and the visible horizon to locate one's position in the world, on land as well as at sea. At a given time, any celestial body is located directly over one point on the Earth's surface; the latitude and longitude of that point is known as the celestial body's geographic position, the location of which can be determined from tables in the nautical or air almanac for that year.

The measured angle between the celestial body and the visible horizon is directly related to the distance between the celestial body's GP and the observer's position. After some computations, referred to as sight reduction, this measurement is used to plot a line of position on a navigational chart or plotting worksheet, the observer's position being somewhere on that line. Sights on two celestial bodies give two such lines on the chart, intersecting at the observer's position. Most navigators will use sights of three to five stars, if available, since that will result in only one common intersection and minimizes the chance of error; that premise is the basis for the most used method of celestial navigation, referred to as the'altitude-intercept method'. At least three points must be plotted; the plot intersection will provide a triangle where the exact position is inside of it. Accuracy of the sights is indicated by the size of the triangle. There are several other methods of celestial navigation that will provide position-finding using sextant observations, such as the noon sight, the more archaic lunar distance method.

Joshua Slocum used the lunar distance method during the first recorded single-handed circumnavigation of the world. Unlike the altitude-intercept method, the noon sight and lunar distance methods do not require accurate knowledge of time; the altitude-intercept method of celestial navigation requires that the observer know exact Greenwich Mean Time at the moment of their observation of the celestial body, to the second—since for every four seconds that the time source is in error, the position will be off by one nautical mile. An example illustrating the concept behind the intercept method for determining one's position is shown to the right. In the adjacent image, 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 the Sun was observed to be 40 degrees above the horizon. Lines of position were 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. In this case the navigator is either located on the Atlantic Ocean, about 350 nautical miles west of Madeira, or in South America, about 90 nautical miles 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 thousands of miles apart; as it is unlikely that the ship is sailing across South America, 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. An observer at the Gran Chaco point would see the Moon at the left of the Sun, an observer in the Madeira point would see the Moon at the right of the Sun. Accurate angle measurement evolved over the years. One simple method is to hold the hand above the horizon with one's arm stretched out.

The width of the little finger is an angle just over 1.5 degrees elevation at extended arm's length and can be used to estimate the elevation of the sun from the horizon plane and therefore estimate the time until sunset. The need for more accurate measurements led to the development of a number of accurate instruments, including the kamal, astrolabe 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, because their dual mirror system cancels relative motions of the instrument, showing a steady view of the object and horizon. Navigators measure distance on the globe in degrees and arcseconds. A nautical mile

André Hennebicq

André Hennebicq was a Belgian painter, specialising in historical pictures and murals. He trained under Joseph Stallaert in Tournai, his native town, Jan Frans Portaels in the Académie Royale des Beaux-Arts in Brussels, he won the Prix de Rome in 1865. Hennebicq, Leon, 1937: La vie d’André Hennebicq. Peintre. Brussel: Ferdinand Larcier Hermans, C. 1923: Annuaire de l’Académie Royale des Sciences, des Lettres et des Beaux-Arts de Belgique: Notice sur André Hennebicq 89, 101-114 online edition Masson, P. Van Grieken. J. & Vandekerckhove, V. 2004: In eer hersteld. De monumentale schilderijenreeks van André Hennebicq in het Leuvense stadhuis. Leuven: Stad Leuven

Gmina Kluczbork

Gmina Kluczbork is an urban-rural gmina in Kluczbork County, Opole Voivodeship, in south-western Poland. Its seat is the town of Kluczbork, which lies 41 kilometres north-east of the regional capital Opole; the gmina covers an area of 217 square kilometres, as of 2006 its total population is 38,618. The gmina contains part of the protected area called Stobrawa Landscape Park. Apart from the town of Kluczbork, Gmina Kluczbork contains the villages and settlements of Bąków, Bażany, Bogacica, Bogacka Szklarnia, Bogdańczowice, Czaple Wolne, Gotartów, Krasków, Kujakowice Dolne, Kujakowice Górne, Kuniów, Ligota Dolna, Ligota Górna, Ligota Zamecka, Łowkowice, Maciejów, Nowa Bogacica, Smardy Dolne, Smardy Górne, Stare Czaple, Unieszów and Żabiniec. Gmina Kluczbork is bordered by the gminas of Byczyna, Gorzów Śląski, Lasowice Wielkie, Murów, Olesno and Wołczyn. Polish official population figures 2006