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Right Ascension
Right ascension
Right ascension
(abbreviated RA; symbol α) is the angular distance measured eastward along the celestial equator from the Sun
Sun
at the March equinox to the hour circle of the point above the earth in question.[1] When paired with declination, these astronomical coordinates specify the direction of a point on the celestial sphere (traditionally called in English the skies or the sky) in the equatorial coordinate system. Right ascension
Right ascension
and declination as seen on the inside of the celestial sphere
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Celestial Navigation
Celestial navigation, also 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 (e.g. the Sun, the Moon, a planet, or a star) and the visible horizon. The Sun
Sun
is most commonly used, but navigators can also 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
Celestial navigation
is the use of angular measurements (sights) 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
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Perpendicular
In elementary geometry, the property of being perpendicular (perpendicularity) is the relationship between two lines which meet at a right angle (90 degrees). The property extends to other related geometric objects. A line is said to be perpendicular to another line if the two lines intersect at a right angle.[2] Explicitly, a first line is perpendicular to a second line if (1) the two lines meet; and (2) at the point of intersection the straight angle on one side of the first line is cut by the second line into two congruent angles. Perpendicularity can be shown to be symmetric, meaning if a first line is perpendicular to a second line, then the second line is also perpendicular to the first. For this reason, we may speak of two lines as being perpendicular (to each other) without specifying an order. Perpendicularity easily extends to segments and rays
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Degree Symbol
؋ ​₳ ​ ฿ ​₿ ​ ₵ ​¢ ​₡ ​₢ ​ $ ​₫ ​₯ ​֏ ​ ₠ ​€ ​ ƒ ​₣ ​ ₲ ​ ₴ ​ ₭ ​ ₺ ​₾ ​ ₼ ​ℳ ​₥ ​ ₦ ​ ₧ ​₱ ​₰ ​£ ​ 元 圆 圓 ​﷼ ​៛ ​₽ ​₹ ₨ ​ ₪ ​ ৳ ​₸ ​₮ ​ ₩ ​ ¥ 円Uncommon typographyasterism ⁂fleuron, hedera ❧index, fist ☞interrobang ‽irony punctuation ⸮lozenge ◊tie ⁀RelatedDiacritics Logic symbolsWhitespace charactersIn other scriptsChinese Hebrew Japanese Korean Category Portal Bookv t eThe degree symbol (°) is a typographical symbol that is used, among other things, to represent degrees of arc (e.g
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Celestial Equator
The celestial equator is the great circle of the imaginary celestial sphere on the same plane as the equator of Earth. This plane of reference bases the equatorial coordinate system. In other words, the celestial equator is an abstract projection of the terrestrial equator into outer space.[1] As a result of the planet's axial tilt, the celestial equator is currently inclined by about 23.44° with respect to the ecliptic plane. An observer standing on Earth's equator visualizes the celestial equator as a semicircle passing through the zenith, the point directly overhead. 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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Degree (angle)
A degree (in full, a degree of arc, arc degree, or arcdegree), usually denoted by ° (the degree symbol), is a measurement of a plane angle, defined so that a full rotation is 360 degrees. It is not an SI unit, as the SI unit
SI unit
of angular measure is the radian, but it is mentioned in the SI brochure as an accepted unit.[4] Because a full rotation equals 2π radians, one degree is equivalent to π/180 radians.Contents1 History 2 Subdivisions 3 Alternative units 4 See also 5 Notes 6 References 7 External linksHistory[edit] See also: DecansA circle with an equilateral chord (red). One sixtieth of this arc is a degree. Six such chords complete the circle.The original motivation for choosing the degree as a unit of rotations and angles is unknown
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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.[1] 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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Earth's Rotation
Earth's rotation
Earth's rotation
is the rotation of Planet Earth
Earth
around its own axis. Earth
Earth
rotates eastward, in prograde motion. As viewed from the north pole star Polaris, Earth
Earth
turns counterclockwise. The North Pole, also known as the Geographic North Pole
North Pole
or Terrestrial North Pole, is the point in the Northern Hemisphere
Northern Hemisphere
where Earth's axis of rotation meets its surface. This point is distinct from Earth's North Magnetic Pole. The South Pole
South Pole
is the other point where Earth's axis of rotation intersects its surface, in Antarctica. Earth
Earth
rotates once in about 24 hours with respect to the Sun, but once every 23 hours, 56 minutes, and 4 seconds with respect to the stars (see below)
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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.[1] 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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Oblique Angle
2D anglesRight Interior Exterior2D angle pairsAdjacent Vertical Complementary Supplementary Transversal3D anglesDihedralAn angle formed by two rays emanating from a vertex.In planar geometry, an angle is the figure formed by two rays, called the sides of the angle, sharing a common endpoint, called the vertex of the angle.[1] Angles formed by two rays lie in a plane, but this plane does not have to be a Euclidean plane. Angles are also formed by the intersection of two planes in Euclidean and other spaces. These are called dihedral angles. Angles formed by the intersection of two curves in a plane are defined as the angle determined by the tangent rays at the point of intersection. Similar statements hold in space, for example, the spherical angle formed by two great circles on a sphere is the dihedral angle between the planes determined by the great circles. Angle
Angle
is also used to designate the measure of an angle or of a rotation
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Latitude
In geography, latitude is a geographic coordinate that specifies the north–south position of a point on the Earth's surface. Latitude
Latitude
is an angle (defined below) which ranges from 0° at the Equator
Equator
to 90° ( North
North
or South) at the poles. Lines of constant latitude, or parallels, run east–west as circles parallel to the equator. Latitude
Latitude
is used together with longitude to specify the precise location of features on the surface of the Earth. Without qualification the term latitude should be taken to be the geodetic latitude as defined in the following sections
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Right Angle
In geometry and trigonometry, a right angle is an angle of exactly 90° (degrees),[1] corresponding to a quarter turn.[2] If a ray is placed so that its endpoint is on a line and the adjacent angles are equal, then they are right angles.[3] The term is a calque of Latin angulus rectus; here rectus means "upright", referring to the vertical perpendicular to a horizontal base line. Closely related and important geometrical concepts are perpendicular lines, meaning lines that form right angles at their point of intersection, and orthogonality, which is the property of forming right angles, usually applied to vectors. The presence of a right angle in a triangle is the defining factor for right triangles,[4] making the right angle basic to trigonometry.Contents1 In elementary geometry 2 Symbols 3 Euclid 4 Conversion to other units 5 Rule of 3-4-5 6 Thales' theorem 7 See also 8 ReferencesIn elementary geometry[edit] A rectangle is a quadrilateral with four right angles
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Sexagesimal
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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Horizon
The horizon or skyline is the apparent line that separates earth from sky, the line that divides all visible directions into two categories: those that intersect the Earth's surface, and those that do not. At many locations, the true horizon is obscured by trees, buildings, mountains, etc., and the resulting intersection of earth and sky is called the visible horizon
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Equator
An equator is the intersection of the surface of a rotating sphere (such as a planet) with the plane perpendicular to the axis of rotation and midway between its poles. On Earth, the Equator
Equator
is an imaginary line on the surface, equidistant from the North and South Poles, dividing the Earth
Earth
into Northern and Southern Hemispheres
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Earth
Earth
Earth
is the third planet from the Sun
Sun
and the only object in the Universe
Universe
known to harbor life. According to radiometric dating and other sources of evidence, Earth
Earth
formed over 4.5 billion years ago.[24][25][26] Earth's gravity interacts with other objects in space, especially the Sun
Sun
and the Moon, Earth's only natural satellite. Earth
Earth
revolves around the Sun
Sun
in 365.26 days, a period known as an Earth
Earth
year
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