
Review of Short Phrases and Links 
This Review contains major "Celestial Sphere" related terms, short phrases and links grouped together in the form of Encyclopedia article.
Definitions
 The celestial sphere is an imaginary projection of the Sun, Moon, planets, stars, and all astronomical bodies upon an imaginary sphere surrounding Earth.
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 The Celestial sphere is an imaginary sphere around the Earth on which the stars in the sky are projected.
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 The celestial sphere (Article 1501) is an imaginary sphere of infinite radius with the Earth at its center (Figure 1524a).
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 The celestial sphere is assumed to be fixed, so as the Earth rotates the celestial sphere appears to rotate in the opposite direction once per day.
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 The celestial sphere is divided by projecting the equator into space.
 Angles on the celestial sphere, measured in degrees, minutes and seconds.
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 Solving any of these problems involves finding the unknown sides or angles of a triangle on the celestial sphere from the known sides and angles.
 The zenith is the point on the celestial sphere where the direction of the gravity vector in a point, extended upwards, intersects it.
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 The latter depends on the direction in which an observer looks, so one has to be careful when comparing stars in different regions of the celestial sphere.
 The nadir is the opposite point (or rather, direction), where the direction of gravity extended downward intersects the (invisible) celestial sphere.
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 Angular distance on the celestial sphere measured along the great circle from the zenith to the celestial object.
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 Return the angular distance between two points (ra1, dec1) and (ra2, dec2) of celestial sphere.
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 This motion is from west to east, in opposition to the apparent eastwest movement of the celestial sphere.
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 Even though the planets move on the celestial sphere, they do not wander all over it but are confined to a narrow strip, dividing it in half.
 East and West on the Celestial Sphere It is useful to define east and west directions on the celestial sphere, as illustrated in the following figure.
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 As the Earth rotates within the celestial sphere, stars will rise in the East and will travel across our sky from East to West.
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 They thought the stars rose and set because the celestial sphere (the sky) rotated, carrying the stars from east to west.
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 The result is that, in a period of 25,800 years, the pole of the heavens moves as a circle on the celestial sphere on a radius of 23°4.
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 Therefore, they do not coincide exactly with that half of the celestial sphere above the horizon at any one time or place.
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 This designation is convenient because it represents the sidereal day, the time it takes for the Earth to make one rotation relative to the celestial sphere.
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 We can imagine that at any given time, half of the stars in the celestial sphere will be visible while the other half will be on the daytime side of the sky.
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 Declination  One of the two angles uses to specify location on the celestial sphere.
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 As circumstances require, the celestial sphere may be centered at the observer, at the Earth's center, or at any other location.
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 The satellite was able to observe the entire celestial sphere from its location in space.
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 Since the Sun travels an apparent path around the celestial sphere once per year, eclipses are possible only at roughly sixmonth intervals.
 The Sun spends half the year in the southern half of the celestial sphere and the other half in the northern.
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 If you plot the exact spots the Sun appears in front of in the course of a year, you get a line on the celestial sphere called the ecliptic.
 At any time, the Sun is also somewhere on the celestial sphere, and as the Earth turns, it rises and sets the same way as stars do.
 You may find the celestial equator in the same way; it is where the plane of the Earth's equator `intersects' the celestial sphere.
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 He designed the first portable celestial sphere to explain and measure the movements of celestial objects and led the way for spherical trigonometry.
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 Crux is exactly opposite to Cassiopeia on the celestial sphere, and therefore it cannot be in the sky with the latter at the same time.
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 So the celestial sphere, with its coordinate grid permanently printed on it, appears to take about 24 hours to complete one turn around Earth.
 Hence the equinoxes move westwards on the celestial sphere by 1 ° in about 72 years, and take 25 800 years to complete one circuit.
 Another important part of the celestial sphere is the line that marks the movement of the Sun with respect to the stars throughout the year.
 The equatorial coordinate system designates an object's location with respect to Earth's entire night sky, or the celestial sphere.
 These numbers are with respect to the celestial sphere and do not change.
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 This marks the point on the celestial sphere opposite the location of the galactic core.
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 Point on the celestial sphere vertically below the observer and hence diametrically opposite the zenith.
 Because the Earth's spin axis is tilted and the Earth orbits around the Sun, the Sun appears to be further north or south of the celestial sphere.
 However, this is not now since the tilt of earth is itself changing its direction, tracing a circle on the celestial sphere.
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 Over the course of a year, the Sun moves through a great circle on the celestial sphere, tracing out the same path year after year.
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 This great circle is the path of the Sun on the celestial sphere as it travels around the Earth in a year.
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 The path that the Sun traces on the celestial sphere is called the ecliptic.
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 It is a zone of the celestial sphere that extends from 8.5 degrees on either side if the path of the sun.
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 Since right ascension coordinates are fixed to the celestial sphere the RA disk is usually driven by a clock mechanism in sync with sidereal time.
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 M [ top] Meridian (astronomy)  In the sky, a meridian is an imaginary great circle on the celestial sphere.
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 Lacerta is located between Cygnus, Cassiopeia and Andromeda on the northern celestial sphere.
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 The imaginary line dividing the northern and southern hemispheres of the celestial sphere.
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 Celestial Equator An imaginary line that divides the celestial sphere into a northern and southern hemisphere.
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 The Northern Hemisphere is the half of a planet's surface (or celestial sphere) that is north of the equator.
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 Ecliptic  A line around the middle of the celestial sphere, connecting the points occupied by the Sun over the year.
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 The term is also used for each of the two points on the celestial sphere at which the ecliptic and the celestial equator intersect, i.e.
 Equinoxes and Solstices The points where the ecliptic crosses the equatorial plane of the celestial sphere are called equinoxes.
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 A constellation is any one of the sections of the sky (or celestial sphere) that is divided in appearance.
 A constellation is any one of the 88 areas into which the sky  or the celestial sphere  is divided.
 The constellation is located between 0° and +60° declination, 13 and 16 hours of right ascension on the celestial sphere.
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 However, it was observed that at times the planets moved westward for some period on the celestial sphere; this was termed "Retrograde Motion".
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 Instead of following the Sun on the celestial sphere, you can follow the Earth in its orbit about the Sun and see things from a Suncentered perspective.
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 Node: either of the points on the celestial sphere at which the plane of an orbit intersects a reference plane.
 Since the orbit is precessing, this will be slightly different from the sidereal period  relative to a fixed point on the celestial sphere.
 The fixed stars were part of this celestial sphere, all at the same fixed distance from the immobile earth at the center of the sphere.
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 Unlike celestial meridians, which remain fixed with respect to the earth, hour circles move with the celestial sphere as it rotates about the earth.
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 This fourminute lag is a typical an astronomical sidereal day, the time it takes any "fixed" object located on the celestial sphere to pass overhead twice.
 As illustrated in Figure 1.13(a), the ecliptic forms a great circle on the celestial sphere, inclined at an angle of 23.5° to the celestial equator.
 Just as the angle between the pole and the equator on Earth is a right angle, the same is true of the celestial sphere.
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 The ecliptic is a great circle of the celestial sphere inclined at an angle of about 23° 27' to the celestial equator.
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 The sidereal year is the length of time that the Sun takes to return to the same position with respect to the stars of the celestial sphere.
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 The first observation of light deflection was performed by noting the change in position of stars as they passed near the Sun on the celestial sphere.
 Set of numbers used to pinpoint the position in the sky (see celestial sphere) of a celestial object.
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 This gives the positions of these objects on the celestial sphere at a particular date and time, which can then be converted into suitable coordinates.
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 As seen by an observer on Earth on the imaginary celestial sphere, the Moon crosses the ecliptic every orbit at positions called nodes twice every month.
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 A component of the coordinate system used to designate positions on the celestial sphere.
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 A useful construct for describing locations of objects in the sky is the celestial sphere, which is considered to have an infinite radius.
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 The branch of astronomy that deals with precisely measuring the positions of objects on the celestial sphere.
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 The Celestial Sphere Imagine objects to be attached to a sphere surrounding the earth.
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 One of these is the visualization of the night sky as a celestial sphere which contains the stars and rotates about the Earth.
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 Dividing the night sky into two roughly equal hemispheres, the Milky Way appears as a hazy band of white light arching across the entire celestial sphere.
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 The author considers the night sky as the celestial sphere and powerfully exploits the methods of spherical geometry.
 Nadir The point on the celestial sphere opposite the zenith or directly below the observer.
 Nadir That point on the celestial sphere vertically below the observer, or 180 degrees from the zenith.
 Nadir The point on the celestial sphere 180 degrees from the zenith.
 RA; symbol α) is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system.
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 Right ascension is a celestial coordinate that is used to measure the degree s of longitude on the on the celestial sphere.
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 In astronomy, coordinate on the celestial sphere that corresponds to longitude on the surface of the Earth.
 On the celestial sphere, positions are located by latitude and longitude.
 The line of intersection of these planes defines two points on the celestial sphere: the ascending and descending nodes.
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 In astronomical terms it refers to the intersection on the celestial sphere between the celestial equator and the plane of the ecliptic.
 The ecliptic is the intersection of the ecliptic plane and the celestial sphere.
 The North Pole is the point where the Earth's axis intersects the Celestial sphere in the Northern hemisphere.
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 This gives us different pole stars as the north pole of the Earth sweeps out a circle on the celestial sphere.
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 Imagine that an observer accelerates (with constant magnitude of acceleration) in the direction of the North pole on his celestial sphere.
 Locating an object on the celestial sphere with settings circles is similar to finding a location on a terrestrial map using latitude and longitude.
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 Declination is the celestial equivalent of latitude, and is simply the Earth's latitude lines projected onto the celestial sphere.
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 Rotate the celestial sphere around while it is rectified for our latitude and notice that the ecliptic is never overhead.
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 If time passes by, then the celestial sphere moves.
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 Note how the sky serves as a clock  except that the clockface (celestial sphere) moves while the clock "hand" (meridian) stays fixed.
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 Revolution in Orbit The Moon appears to move completely around the celestial sphere once in about 27.3 days as observed from the Earth.
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 Also, the band where the ecliptic runs centrally through the celestial sphere and contains the sun, the moon, and all the planets except Venus and Pluto.
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 The Greeks did not consider the Sun, the Moon, and the planets to be part of the celestial sphere, however.
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 Think of oneself in a planetarium, where the stars are projected by lights onto the walls and ceiling; this is the celestial sphere.
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 A visit to a planetarium or a session under the night sky can be very helpful to you in developing a conceptual understanding of the celestial sphere.
 The North Star is a star located close to the North Pole of the celestial sphere, i.e., the projection of the North Pole onto the sky.
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 Right ascension and declination  Two angles marking the position of a star on the celestial sphere.
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 It can also be described as the apparent change of the star on the celestial sphere, and is measured in seconds of arc per year.
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 Firmament  The celestial sphere and the collection of stars whose position is fixed on it.
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 They are mentioned in Ptolemy 's Almagest, where precession is explained as the rotation of the celestial sphere around a motionless Earth.
 The classical astronomers called these planets wandering stars to differentiate them from the fixed stars of the celestial sphere (Ptolemy).
 The celestial sphere is a useful mapping and tracking remnant of the geocentric theory of the ancient Greek astronomers.
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 In physics, the identity component of the Lorentz group acts on the celestial sphere in the same way that the Möbius group acts on the Riemann sphere.
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Categories
 Information > Science > Astronomy > Celestial Equator
 Ecliptic
 Observer
 Projection
 Information > Science > Astronomy > Zenith
Related Keywords
* Apparent Motion
* Apparent Path
* Apparent Position
* Astronomers
* Astronomy
* Axis
* Celestial Bodies
* Celestial Coordinate System
* Celestial Equator
* Celestial Meridian
* Celestial Pole
* Celestial Poles
* Circle
* Circles
* CoOrdinates
* Complete Rotation
* Constellations
* Constellation Draco
* Coordinate System
* Coordinate Systems
* Daily Rotation
* Declination
* Degree
* Degrees
* Earth
* Ecliptic
* Equator
* Equatorial Coordinate System
* Equinox
* Equinoxes
* Galactic Equator
* Great Circle
* Great Circles
* Horizon
* Hour Angle
* Hour Circle
* Lie Close
* North
* North Celestial Pole
* Observer
* Origin
* Plane
* Planets
* Point
* Poles
* Practical Tool
* Project
* Projected
* Projection
* Projections
* Right Ascension
* Rotation
* Sky
* South Celestial Poles
* South Poles
* Sphere
* Star Chart
* Sun
* Vernal Equinox
* Vertical Circle
* Zenith
* Zodiac

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