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Right Ascension
RIGHT ASCENSION (abbreviated RA; symbol α) is the angular distance measured eastward along the celestial equator from the vernal equinox to the hour circle of the point in question. When combined with declination , these astronomical coordinates specify the direction of a point on the celestial sphere in the equatorial coordinate system . RIGHT ASCENSION and declination as seen on the inside of the celestial sphere . The primary direction of the system is the vernal equinox , the ascending node of the ecliptic (red) on the celestial equator (blue). Right ascension
Right ascension
is measured eastward along the celestial equator from the primary direction. An old term, right ascension (Latin, ascensio recta ) refers to the ascension, or the point on the celestial equator which rises with any celestial object, as seen from the Earth
Earth
's equator , where the celestial equator intersects the horizon at a right angle
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Epoch (astronomy)
In astronomy , an EPOCH is a moment in time used as a reference point for some time-varying astronomical quantity, such as the celestial coordinates or elliptical orbital elements of a celestial body , because these are subject to perturbations and vary with time. These time-varying astronomical quantities might include, for example, the mean longitude or mean anomaly of a body, the node of its orbit relative to a reference plane , the direction of the apogee or aphelion of its orbit, or the size of the major axis of its orbit. The main use of astronomical quantities specified in this way is to calculate other relevant parameters of motion, in order to predict future positions and velocities
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Axial Precession
In astronomy , AXIAL PRECESSION is a gravity-induced, slow, and continuous change in the orientation of an astronomical body's rotational axis . In particular, it can refer to the gradual shift in the orientation of Earth
Earth
's axis of rotation, which, similar to a wobbling top, traces out a pair of cones joined at their apices in a cycle of approximately 26,000 years. The term "precession" typically refers only to this largest part of the motion; other changes in the alignment of Earth's axis—nutation and polar motion —are much smaller in magnitude. Earth's precession was historically called the PRECESSION OF THE EQUINOXES, because the equinoxes moved westward along the ecliptic relative to the fixed stars , opposite to the yearly motion of the Sun along the ecliptic
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North Ecliptic Pole
An ORBITAL POLE is either point at the ends of an imaginary line segment that runs through the center of an orbit (of a revolving body like a planet ) and is perpendicular to the orbital plane . Projected onto the celestial sphere , orbital poles are similar in concept to celestial poles , but are based on the body's orbit instead of its equator . The north orbital pole of a revolving body is defined by the right-hand rule . If the fingers of the right hand are curved along the direction of orbital motion , with the thumb extended and oriented to be parallel to the orbital axis , then the direction the thumb points is defined to be the orbital north. The orbital poles of Earth
Earth
are referred to as the ECLIPTIC POLES. ECLIPTIC POLEThe ECLIPTIC POLES are the two points where an imaginary line (the ECLIPTIC AXIS) perpendicular to the ecliptic plane, on which Earth orbits the Sun
Sun
, intersects the celestial sphere
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Draco (constellation)
DRACO is a constellation in the far northern sky. Its name is Latin for dragon . It was one of the 48 constellations listed by the 2nd century astronomer Ptolemy
Ptolemy
, and remains one of the 88 modern constellations today. The north pole of the ecliptic is in Draco. Draco is circumpolar (that is, never setting), and can be seen all year from northern latitudes. CONTENTS* 1 Features * 1.1 Stars * 1.2 Deep-sky objects * 1.3 Mythology * 1.4 Meteor showers * 2 Namesakes * 3 See also * 4 References * 5 External links FEATURES The constellation Draco as it can be seen by the naked eye STARS Main article: List of stars in Draco Thuban (α Draconis) was the northern pole star from 3942 BC, when it moved farther north than Theta Boötis, until 1793 BC
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South Ecliptic Pole
An ORBITAL POLE is either point at the ends of an imaginary line segment that runs through the center of an orbit (of a revolving body like a planet ) and is perpendicular to the orbital plane . Projected onto the celestial sphere , orbital poles are similar in concept to celestial poles , but are based on the body's orbit instead of its equator . The north orbital pole of a revolving body is defined by the right-hand rule . If the fingers of the right hand are curved along the direction of orbital motion , with the thumb extended and oriented to be parallel to the orbital axis , then the direction the thumb points is defined to be the orbital north. The orbital poles of Earth
Earth
are referred to as the ECLIPTIC POLES. ECLIPTIC POLEThe ECLIPTIC POLES are the two points where an imaginary line (the ECLIPTIC AXIS) perpendicular to the ecliptic plane, on which Earth orbits the Sun
Sun
, intersects the celestial sphere
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Second Of Arc
A MINUTE OF ARC, ARCMINUTE (arcmin), ARC MINUTE, or MINUTE ARC is a unit of angular measurement equal to 1/60 of one degree . Since one degree is 1/360 of a turn (or complete rotation), one minute of arc is 1/7004216000000000000♠21600 of a turn (or, in radians , π/7004108000000000000♠10800). A SECOND OF ARC, ARCSECOND (arcsec), or ARC SECOND is 1/60 of an arcminute, 1/7003360000000000000♠3600 of a degree, 1/7006129600000000000♠1296000 of a turn, and π/7005648000000000000♠648000 (about 1/7005206265000000000♠206265) of a radian. These units originated in Babylonian astronomy as sexagesimal subdivisions of the degree; they are used in fields that involve very small angles, such as astronomy , optometry , ophthalmology , optics , navigation , land surveying and marksmanship . To express even smaller angles, standard SI prefixes can be employed; the MILLIARCSECOND (mas) and MICROARCSECOND (μas), for instance, are commonly used in astronomy
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Minute Of Arc
A MINUTE OF ARC, ARCMINUTE (arcmin), ARC MINUTE, or MINUTE ARC is a unit of angular measurement equal to 1/60 of one degree . Since one degree is 1/360 of a turn (or complete rotation), one minute of arc is 1/7004216000000000000♠21600 of a turn (or, in radians , π/7004108000000000000♠10800). A SECOND OF ARC, ARCSECOND (arcsec), or ARC SECOND is 1/60 of an arcminute, 1/7003360000000000000♠3600 of a degree, 1/7006129600000000000♠1296000 of a turn, and π/7005648000000000000♠648000 (about 1/7005206265000000000♠206265) of a radian. These units originated in Babylonian astronomy as sexagesimal subdivisions of the degree; they are used in fields that involve very small angles, such as astronomy , optometry , ophthalmology , optics , navigation , land surveying and marksmanship . To express even smaller angles, standard SI prefixes can be employed; the MILLIARCSECOND (mas) and MICROARCSECOND (μas), for instance, are commonly used in astronomy
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Celestial Equator
The CELESTIAL EQUATOR is a great circle on the imaginary celestial sphere , in the same plane as the Earth
Earth
's equator . In other words, it is a projection of the terrestrial equator out into space. As a result of the Earth's axial tilt , the celestial equator is inclined by 23.4° with respect to the ecliptic plane . An observer standing on the Earth's equator visualizes the celestial equator as a semicircle passing directly overhead through the zenith . As the observer moves north (or south), the celestial equator tilts towards the opposite horizon. The celestial equator is defined to be infinitely distant (since it is on the celestial sphere); thus the observer always sees the ends of the semicircle disappear over the horizon exactly due east and due west, regardless of the observer's position on Earth
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Celestial Navigation
CELESTIAL NAVIGATION, also known as ASTRONAVIGATION, is the ancient science 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
Celestial navigation
uses "sights," or angular measurements taken between a celestial body (the sun, the moon, a planet or a star) and the visible horizon. The sun is most commonly used, but navigators can also use the moon, a planet, Polaris
Polaris
, or one of 57 other navigational stars whose coordinates are tabulated in the nautical almanac and air almanacs. Celestial navigation
Celestial navigation
is the use of angular measurements (sights) between celestial bodies and the visible horizon to locate one's position on the globe, 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
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Sexagesimal
SEXAGESIMAL (BASE 60) is a numeral system with sixty as its base . It originated with the ancient Sumerians in the 3rd millennium BC, was passed down to the ancient Babylonians , and is still used—in a modified form—for measuring time , angles , and geographic coordinates . The number 60, a superior highly composite number , has twelve factors , namely 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30, and 60, of which 2, 3, and 5 are prime numbers . With so many factors, many fractions involving sexagesimal numbers are simplified. For example, one hour can be divided evenly into sections of 30 minutes, 20 minutes, 15 minutes, 12 minutes, 10 minutes, 6 minutes, 5 minutes, 4 minutes, 3 minutes, 2 minutes, and 1 minute. 60 is the smallest number that is divisible by every number from 1 to 6; that is, it is the lowest common multiple of 1, 2, 3, 4, 5, and 6. In this article, all sexagesimal digits are represented as decimal numbers, except where otherwise noted
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Degree Symbol
؋ ​₳ ​ ฿ ​₿ ​ ₵ ​¢ ​₡ ​₢ ​ $ ​₫ ​₯ ​֏ ​ ₠ ​€ ​ ƒ ​₣ ​ ₲ ​ ₴ ​ ₭ ​ ₺ ​₾ ​ ₼ ​ℳ ​₥ ​ ₦ ​ ₧ ​₱ ​₰ ​£ ​ 元 圆 圓 ​﷼ ​៛ ​₽ ​₹ ₨ ​ ₪ ​ ৳ ​₸ ​₮ ​ ₩ ​ ¥ 円 UNCOMMON TYPOGRAPHY asterism ⁂ hedera ❧ index, fist ☞ interrobang ‽ irony punctuation ⸮ lozenge ◊ tie ⁀ RELATED* * Diacritics * Logic symbols * Whitespace characters IN OTHER SCRIPTS * Chinese * Hebrew * Japanese * Korean * Category
Category
* Portal
Portal
* Book
Book
* v * t * e The DEGREE SYMBOL (°) is a typographical symbol that is used, among other things, to represent degrees of arc (e.g
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J2000.0
In astronomy , an EPOCH is a moment in time used as a reference point for some time-varying astronomical quantity, such as the celestial coordinates or elliptical orbital elements of a celestial body , because these are subject to perturbations and vary with time. These time-varying astronomical quantities might include, for example, the mean longitude or mean anomaly of a body, the node of its orbit relative to a reference plane , the direction of the apogee or aphelion of its orbit, or the size of the major axis of its orbit. The main use of astronomical quantities specified in this way is to calculate other relevant parameters of motion, in order to predict future positions and velocities
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Terrestrial Time
TERRESTRIAL TIME (TT) is a modern astronomical time standard defined by the International Astronomical Union
International Astronomical Union
, primarily for time-measurements of astronomical observations made from the surface of Earth. For example, the Astronomical Almanac uses TT for its tables of positions (ephemerides ) of the Sun, Moon and planets as seen from Earth. In this role, TT continues TERRESTRIAL DYNAMICAL TIME (TDT or TD), which in turn succeeded ephemeris time (ET) . TT shares the original purpose for which ET was designed, to be free of the irregularities in the rotation of Earth . The unit of TT is the SI second , the definition of which is currently based on the caesium atomic clock , but TT is not itself defined by atomic clocks. It is a theoretical ideal, and real clocks can only approximate it
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Equatorial Mount
An EQUATORIAL MOUNT is a mount for instruments that compensate Earth\'s rotation by having one rotational axis parallel to the Earth's axis of rotation. This type of mount is used for astronomical telescopes and cameras . The advantage of an equatorial mount lies in its ability to allow the instrument attached to it to stay fixed on any celestial object with diurnal motion by driving one axis at a constant speed. Such an arrangement is called a sidereal or clock drive . The green equatorially mounted telescope rotates at the same rate as the earth but in the opposite direction, while the red telescope is not driven
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John Flamsteed
JOHN FLAMSTEED FRS (19 August 1646 – 31 December 1719) was an English astronomer and the first Astronomer Royal . He catalogued over 3000 stars. CONTENTS * 1 Life * 2 Scientific work * 3 Honours * 4 See also * 5 References * 6 Further reading * 7 External links LIFEFlamsteed was born in Denby
Denby
, Derbyshire
Derbyshire
, England, the only son of Stephen Flamsteed and his first wife, Mary Spadman. He was educated at the free school of Derby, and was educated at Derby School , in St Peter's Churchyard, Derby
Derby
, near where his father carried on a malting business . At that time, most masters of the school were Puritans . Flamsteed had a solid knowledge of Latin , essential for reading the scientific literature of the day, and a love of history , leaving the school in May, 1662
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