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Meridian Altitude
{{inline, date=June 2024 Meridian altitude is a method of celestial navigation to determine the latitude of an observer. It notes the altitude angle of an astronomical object above the horizon at culmination. Principle Meridian altitude is the simplest calculation of celestial navigation. An observer determines their latitude by measuring the altitude of an astronomical object at the time of its meridian transit. A meridian is the imaginary plane running north–south and through the zenith, nadir, and celestial poles. This is usually done with the equinox Sun at solar noon to determine the observer's latitude, but can be done with any celestial object. Solar noon is the time when the Sun crosses the meridian. For example, imagine that the equinox Sun is overhead (at the zenith) at a point on the Equator (latitude 0°), and Observer A is standing at this point – the subsolar point. If he were to measure the height of the Sun above the horizon with a sextant, he would find ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Celestial Navigation
Celestial navigation, also known as astronavigation, is the practice of position fixing using stars and other celestial bodies that enables a navigator to accurately determine their actual current physical position in space or on the surface of the Earth without relying solely on estimated positional calculations, commonly known as dead reckoning. Celestial navigation is performed without using satellite navigation or other similar modern electronic or digital positioning means. Celestial navigation uses "sights," or timed angular measurements, taken typically between a celestial body (e.g., the Sun, the Moon, a planet, or a star) and the visible horizon. Celestial navigation can also take advantage of measurements between celestial bodies without reference to the Earth's horizon, such as when the Moon and other selected bodies are used in the practice called "lunars" or the Lunar distance (navigation), lunar distance method, used for determining precise time when time is u ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Equator
The equator is the circle of latitude that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern Hemispheres of Earth, hemispheres. It is an imaginary line located at 0 degrees latitude, about in circumference, halfway between the North Pole, North and South Pole, South poles. The term can also be used for any other celestial body that is roughly spherical. In three-dimensional space, spatial (3D) geometry, as applied in astronomy, the equator of a rotating spheroid (such as a planet) is the parallel (circle of latitude) at which latitude is defined to be 0°. It is an imaginary line on the spheroid, equidistant from its geographical pole, poles, dividing it into northern and southern hemispheres. In other words, it is the intersection of the spheroid with the plane (geometry), plane perpendicular to its axis of rotation and midway between its geographical poles. On and near the equator (on Earth), noontime sunlight appears almost directly o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Intercept Method
In astronomical navigation, the intercept method, also known as Marcq St. Hilaire method, is a method of calculating an observer's position on Earth (geopositioning). It was originally called the ''azimuth intercept'' method because the process involves drawing a line which intercepts the azimuth line. This name was shortened to ''intercept'' method and the ''intercept distance'' was shortened to 'intercept'. The method yields a line of position (LOP) on which the observer is situated. The intersection of two or more such lines will define the observer's position, called a "fix". Sights may be taken at short intervals, usually during hours of twilight, or they may be taken at an interval of an hour or more (as in observing the Sun during the day). In either case, the lines of position, if taken at different times, must be advanced or retired to correct for the movement of the ship during the interval between observations. If observations are taken at short intervals, a few minut ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Haversine Formula
The haversine formula determines the great-circle distance between two points on a sphere given their longitudes and latitudes. Important in navigation, it is a special case of a more general formula in spherical trigonometry, the law of haversines, that relates the sides and angles of spherical triangles. The first table of haversines in English was published by James Andrew in 1805, but Florian Cajori credits an earlier use by José de Mendoza y Ríos in 1801. (NB. ISBN and link for reprint of second edition by Cosimo, Inc., New York, 2013.) The term ''haversine'' was coined in 1835 by James Inman. (Fourth edition) These names follow from the fact that they are customarily written in terms of the haversine function, given by . The formulas could equally be written in terms of any multiple of the haversine, such as the older versine function (twice the haversine). Prior to the advent of computers, the elimination of division and multiplication by factors of two proved convenient ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ex-meridian
Ex-meridian is a celestial navigation method of calculating an observer's position on Earth. The method gives the observer a position line on which the observer is situated. It is usually used when the Sun is obscured at noon, and as a result, a meridian altitude is not possible. The navigator measures the altitude of the Sun as close to noon as possible and then calculates where the position line lies. Methodology This method uses an assumed longitude and calculates the latitude that a position line crosses it. The position line obtained is actually part of a small circle, as opposed to great circle, where any observer can stand and the celestial object would have the same altitude in the sky. When plotting the small segment of this circle on a chart it is drawn as a straight line, the resulting tiny errors are too small to be significant. The assumed longitude is usually obtained from the DR or Dead Reckoning position run up from a morning sight taken at around 9.00 am. This is wo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Celestial Navigation
Celestial navigation, also known as astronavigation, is the practice of position fixing using stars and other celestial bodies that enables a navigator to accurately determine their actual current physical position in space or on the surface of the Earth without relying solely on estimated positional calculations, commonly known as dead reckoning. Celestial navigation is performed without using satellite navigation or other similar modern electronic or digital positioning means. Celestial navigation uses "sights," or timed angular measurements, taken typically between a celestial body (e.g., the Sun, the Moon, a planet, or a star) and the visible horizon. Celestial navigation can also take advantage of measurements between celestial bodies without reference to the Earth's horizon, such as when the Moon and other selected bodies are used in the practice called "lunars" or the Lunar distance (navigation), lunar distance method, used for determining precise time when time is u ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nautical Almanac
A nautical almanac is a publication describing the positions of a selection of celestial bodies for the purpose of enabling navigators to use celestial navigation to determine the position of their ship while at sea. The Almanac specifies for each whole hour of the year the position on the Earth's surface (in declination and Greenwich hour angle) at which the Sun, Moon, planets, and First Point of Aries is directly overhead. The positions of 57 selected stars are specified relative to the First Point of Aries. In Great Britain, ''The Nautical Almanac'' has been published annually by HM Nautical Almanac Office, ever since the first edition was published in 1767. In the United States, a nautical almanac has been published annually by the US Naval Observatory since 1852. It was originally titled ''American Ephemeris and Nautical Almanac''. Since 1958, the USNO and HMNAO have jointly published a unified nautical almanac, ''The Astronomical Almanac'' for use by the navies of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
20th Parallel North
Following are circles of latitude between the 15th parallel north and the 20th parallel north: 16th parallel north The 16th parallel north is a circle of latitude that is 16 degrees north of the Earth's equatorial plane. It crosses Africa, Asia, the Indian Ocean, the Pacific Ocean, Central America, the Caribbean, and the Atlantic Ocean. At this latitude the sun is visible for 13 hours, 5 minutes during the summer solstice and 11 hours, 11 minutes during the winter solstice. As a dividing line After World War II, the parallel divided Vietnam into Chinese military administration in the north and the British in the south (See Timeline of World War II (1945) and War in Vietnam (1945-1946)). In the Chadian–Libyan conflict, from 1984 the parallel, known as the "Red Line", delineated areas controlled by opposing combatants. Previously the Red Line had been the 15th parallel north. (See also Operation Manta.) Around the world Starting at the Prime Meridian and heading eastw ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
South Pole
The South Pole, also known as the Geographic South Pole or Terrestrial South Pole, is the point in the Southern Hemisphere where the Earth's rotation, Earth's axis of rotation meets its surface. It is called the True South Pole to distinguish from the south magnetic pole. The South Pole is by definition the southernmost point on the Earth, lying antipode (geography), antipodally to the North Pole. It defines geodetic latitude 90° South, as well as the direction of true south. At the South Pole all directions point North; all lines of longitude converge there, so its longitude can be defined as any degree value. No time zone has been assigned to the South Pole, so any time can be used as the local time. Along tight latitude circles, clockwise is east and counterclockwise is west. The South Pole is at the center of the Southern Hemisphere. Situated on the continent of Antarctica, it is the site of the United States Amundsen–Scott South Pole Station, which was established in 19 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
North Pole
The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is the point in the Northern Hemisphere where the Earth's rotation, Earth's axis of rotation meets its surface. It is called the True North Pole to distinguish from the North magnetic pole, Magnetic North Pole. The North Pole is by definition the northernmost point on the Earth, lying antipode (geography), antipodally to the South Pole. It defines geodetic latitude 90° North, as well as the direction of true north. At the North Pole all directions point south; all lines of longitude converge there, so its longitude can be defined as any degree value. No time zone has been assigned to the North Pole, so any time can be used as the local time. Along tight latitude circles, counterclockwise is east and clockwise is west. The North Pole is at the center of the Northern Hemisphere. The nearest land is usually said to be Kaffeklubben Island, off the northern coast of Greenland about away, though ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Geographical Pole
A geographical pole or geographic pole is either of the two points on Earth where its axis of rotation intersects its surface. The North Pole lies in the Arctic Ocean while the South Pole is in Antarctica. North and South poles are also defined for other planets or satellites in the Solar System, with a North pole being on the same side of the invariable plane as Earth's North pole. Relative to Earth's surface, the geographic poles move by a few metres over periods of a few years. This is a combination of Chandler wobble, a free oscillation with a period of about 433 days; an annual motion responding to seasonal movements of air and water masses; and an irregular drift towards the 80th west meridian (geography), meridian. As cartography requires exact and unchanging coordinates, the averaged locations of geographical poles are taken as fixed ''cartographic poles'' and become the points where the body's great circles of longitude intersect. See also * Earth's rotation * Polar mo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Solar Zenith Angle
The solar zenith angle is the zenith angle of the sun, i.e., the angle between the sun’s rays and the vertical direction. It is the complement to the solar altitude or solar elevation, which is the altitude angle or elevation angle between the sun’s rays and a horizontal plane. At solar noon, the altitude angle (complement of the solar angle) is at a minimum and is equal to latitude minus solar declination angle. This is the basis by which ancient mariners navigated the oceans. Solar zenith angle is normally used in combination with the solar azimuth angle to determine the position of the Sun as observed from a given location on the surface of the Earth. Formula \cos \theta_s = \sin \alpha_s = \sin \Phi \sin \delta + \cos \Phi \cos \delta \cos h where * \theta_s is the ''solar zenith angle'' * \alpha_s is the ''solar altitude angle'', \alpha_s = 90^\circ - \theta_s * h is the hour angle, in the local solar time. * \delta is the current declination of the Sun * \Phi is the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
