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Topic: Celestial coordinate system

	NationMaster - Encyclopedia: Right ascension
		The celestial sphere is divided by the celestial equator.
		RA is the celestial equivalent of terrestrial longitude.
		The ecliptic coordinate system is a celestial coordinate system that uses the ecliptic for its fundamental plane.
	www.nationmaster.com /encyclopedia/Right-ascension (1321 words)

	Basic Astronomical Terms
		Celestial coordinate corresponding to latitude in the equatorial celestial coordinate system.
		Celestial coordinate corresponding to longitude in the equatorial celestial coordinate system.
		The celestial coordinate corresponding to latitude is the Declination.
	www.seds.org /MESSIER/xtra/Terms/terms.html (939 words)

	Astronomical Leage - Astro Note 11: Celestial Coordinate Systems
		Since all objects on the celestial sphere appear to be at the same, arbitrarily large distance from the observer, it is usually not necessary to know the object's true distance.
		Coordinates are then specified by angular measure around the great circle from the reference point and by angular distance from the reference plane along another great circle perpendicular to that plane.
		That intersection where the Sun appears to cross the celestial equator from south to north is chosen as the reference point and is known as the vernal equinox.
	www.astroleague.org /al/astrnote/astnot11.html (607 words)

	Celestial Coordinate System
		It is useful to impose on the celestial sphere a coordinate system that is analogous to the latitude-longitude system employed for the surface of the Earth.
		This coordinate system is illustrated in the following figure (for which you should imagine the earth to be a point at the center of the sphere).
		In the celestial coordinate system the North and South Celestial Poles are determined by projecting the rotation axis of the Earth to intersect the celestial sphere, which in turn defines a Celestial Equator.
	csep10.phys.utk.edu /astr161/lect/time/coordinates.html (700 words)

	Spartanburg SC \| GoUpstate.com \| Spartanburg Herald-Journal
		There are different celestial coordinate systems each using a coordinate grid projected on the celestial sphere, in analogy to the geographic coordinate system used on the surface of the Earth.
		The coordinate systems differ only in their choice of the fundamental plane, which divides the sky into two equal hemispheres along a great circle.
		Popular choices of pole and equator are the older B1950 and the modern J2000 systems, but a pole and equator "of date" can also be used, meaning one appropriate to the date under consideration, such as that at which a measurement of the position of a planet or spacecraft is made.
	www.goupstate.com /apps/pbcs.dll/section?category=NEWS&template=wiki&text=celestial_coordinate_system (386 words)

	Conversion to Standard Celestial Coordinates
		In the original AIPS convention, the native system was required to be locally parallel to the standard celestial coordinate system at the tangent point.
		The axes of the native sky coordinate system derived by deprojection need not be in the same direction as those of the standard celestial coordinate system.
		Galactic coordinates as defined above are in the ``new'' system adopted by the IAU in 1950, where the origin, 0° latitude and 0° longitude, is in the direction of the galactic center.
	archive.stsci.edu /fits/users_guide/node59.html (353 words)

	Coordinate Systems
		A coordinate of -90 degrees declination indicates that the point is on the south celestial pole while +90 degrees indicates that it is on the north celestial pole.
		The horizon (sometimes called horizontal) coordinate system is easier to visualize than the equatorial coordinate system, but harder to work with because positions are measured in relation to the zenith which is always changing position.
		The coordinates in the horizon coordinate system are the altitude and azimuth of a point.
	library.thinkquest.org /29033/begin/coordinate.htm (1957 words)

	Meade Instruments Corporation - Understanding Celestial Movements and Coordinates
		Understanding celestial coordinates: Celestial objects are mapped according to the R.A. and Dec. coordinate system on the "celestial sphere," the imaginary sphere on which all stars appear to be placed.
		The Poles of the celestial coordinate system are defined as those 2 points where the Earth's rotational axis, if extended to infinity, North and South, intersect the celestial sphere.
		With all celestial objects therefore capable of being specified in position by their celestial coordinates of Right Ascension and Declination, the task of finding objects (in particular, faint objects) in the telescope can be simplified.
	www.meade.com /manuals/m395/celest.html (892 words)

	Celestron -- Telescope Basics
		The celestial coordinate system is an imaginary projection of the Earth's geographical coordinate system onto the celestial sphere which seems to turn overhead at night.
		The celestial parallels of latitude are called "coordinates of declination (Dec.)," and like the Earth's latitudes they are named for their angular distances from the equator.
		Declinations north of the celestial equator are "+" and declinations south are "-".
	www.celestron.com /tb-gen.htm (1029 words)

	Wall Clock, Station & unusual large repro antique clocks by Thomas Kent & Newgate
		Ecliptical coordinates were used by Hipparchos and Ptolemy in their star catalogues, and were the standard of celestial measurement until the Renaissance, when they were replaced by the equatorial coordinate system.
		The equatorial coordinate system is identical to the ecliptical system, except that it uses the celestial equator for horizontal measurement instead of the ecliptic.
		Because the celestial equator is simply a projection of the earth's equator, the equatorial coordinate system is analogous to terrestrial longitude and latitude, and provides a more accurate system of measurement.
	www.curioshop.co.uk (3040 words)

	Glossary for Planetary Science Research Discoveries \| PSRD
		Celestial sphere:- An imaginary sphere centered on the Earth, or arbitrary large radius on the surface of which the stars are considered to be fixed.
		Declination: Celestial coordinate which is equivalent to the latitude of an object on Earth.
		The two great circles defined by the celestial equator and the ecliptic, which is defined as the plane of the solar system, cross each other at 2 points: at the vernal equinox (first day of spring) and the autumnal equinox (first day of autumn).
	www.psrd.hawaii.edu /PSRDglossary.html (8957 words)

	KidsAstronomy.com - Virtual Explorer
		The Z axis of the celestial coordinate system coincides with the Earth's axis of rotation; the positive end of the Z axis lies in the direction of the Earth's north pole.
		When the program starts, the origin and axes of the ship's coordinate system coincide with those of the celestial coordinate system; that is, your ship is aligned with Earth's north pole, and the first point in Aries is to your right.
		These are expressed as the distance of the viewpoint from the Sun in light years, along the axes of the celestial coordinate system.
	www.kidsastronomy.com /virtual_explorer/index.html (1306 words)

	Lecture 2:Sunrise and Sunset: Apparent Solar Motion
		Be able to identify the North Celestial Pole, Zenith, and the Celestial Equator.
		For an Observer on the Equator, the Celestial Equator is Directly Above the Ob Slide # 30: Between the Equator and the North Pole
		Neither the Celestial Equator or the North Celestial Pole is Overhead
	astro.gmu.edu /classes/a10594/notes/l02/l02.html (755 words)

	6.9 Celestial Coordinate System Subroutines
		The FITS community has adopted a set of keyword conventions that define the transformations needed to convert between pixel locations in an image and the corresponding celestial coordinates on the sky, or more generally, that define world coordinates that are to be associated with any pixel location in an n-dimensional FITS array.
		Get the values of all the standard FITS celestial coordinate system keywords from the header of a FITS table where the X and Y (or RA and DEC coordinates are stored in 2 separate columns of the table.
		Calculate the celestial coordinate corresponding to the input X and Y pixel location in the image.
	heasarc.gsfc.nasa.gov /docs/software/fitsio/c/f_user/node57.html (497 words)

	Celestial Coordinates
		Measurement of "celestial latitude" is given the name declination (DEC), but is otherwise identical to the measurement of latitude on the Earth: the declination at the celestial equator is 0 deg and extends to ±90 deg at the celestial poles.
		The Earth's equator is tilted 23.5 deg from the plane of its orbital motion, or in terms of the celestial sphere, the ecliptic is inclined 23.5 deg from the celestial equator.
		Altitude of the intersection of the celestial equator with the meridian = 90 deg - Latitude
	lyra.colorado.edu /sbo/astroinfo/coords/coordinates.html (2585 words)

	Astronomy Hypertext: Astronomical Coordinate Systems
		However, the celestial sphere, which is the apparent sphere of the sky, is not a plane: It is the inside of a sphere, and one that rotates relative to Earth's surface.
		The two most frequently used coordinate systems are the horizon system and the equatorial system, and they are analogous in principle to the grid lines of geographic longitude and latitude.
		In the horizon system, the horizon and vertical circles remain fixed relative to an observer with the celestial sphere moving relative to them, whereas in this system, the celestial meridian and hour circles are on the celestial sphere and thus rotate with it relative to an observer.
	physics.gmu.edu /~jevans/astr103/CourseNotes/earthSky_coordinateSystems.html (1047 words)

	ccfind
		xrotation and yrotation are interpreted as the rotation of the ra / longitude and dec / latitude coordinates with respect to the x and y axes, and default 0.0 and 0.0 degrees respectively.
		CCFIND computes the pixel coordinates of each object by, 1) transforming the input celestial coordinates to image celestial coordinate system, 2) using the image celestial coordinate system to compute the initial pixel coordinates, and 3) computing the final pixel coordinates using a centroiding algorithm.
		In both the above examples, x and y are the pixel coordinates, xi and eta are the usual projected (standard) coordinates, lng and lat are the celestial coordinates, and PROJ stands for the projection function, usually the tangent plane projection function.
	stsdas.stsci.edu /cgi-bin/gethelp.cgi?ccfind (2531 words)

	ICRS Narrative
		For each solar system body involved, an ephemeris (pl. ephemerides) is used, which is simply a table of the celestial coordinates of the body as a function of time (or an algorithm that yields such a table).
		Descriptions of reference frames and reference systems often refer to three coordinate axes, which are simply the set of right-handed cartesian axes that correspond to the usual celestial spherical coordinate system.
		The previous astronomical reference system was based on the equator and equinox of J2000.0 determined from observations of planetary motions, together with the IAU (1976) System of Astronomical Constants and related algorithms [1].
	aa.usno.navy.mil /faq/docs/ICRS_doc.html (4516 words)

	Zodiac at AllExperts
		One reason this system of coordinates was particularly useful in antiquity is that writing large numbers was difficult before the introduction of arabic numbers.
		The key disadvantage of a zodiac system of coordinates is if the nodal stars that serve as the fixed reference points for the system exhibit significant proper motion so that within the system of coordinates every other star appears to move dramatically in unison.
		Because of the division of the zodiac into 12 signs of 30Â° each; due to various specifications for the boundaries of the constellations and signs; and especially due to the precession of the equinoxes for the tropical system of coordinates, the zodiacal signs should not be confused with the constellations of the zodiac.
	en.allexperts.com /e/z/zo/zodiac.htm (3923 words)

	LIBRA SIGN OF THE ZODIAC HOROSCOPE FORETELL YOUR FUTURE FORTUNE TELLER
		To use the zodiac coordinate system all one has to know is where to find one of the nodal constellations that include the fixed reference points for the system: Taurus and Scorpio.
		Finally, since the zodiac system uses the ecliptic rather than the terrestrial equator for its equatorial plane it is not susceptible to the drifting of stars across the celestial equator as in the commonly used equatorial coordinate system (right ascension, declination).
		The key disadvantage of a zodiac system of coordinates will manifest as a problem, if the nodal stars that serve as its fixed reference points for the system exhibit significant proper motion so that within the system of coordinates every other star appears to move dramatically in unison.
	www.solarnavigator.net /history/astrology/libra.htm (4176 words)

	Observation - Coordinates and Direction (Site not responding. Last check: )
		This system is difficult to use in Astronomy for two reasons: the celestial sphere does not rotate this way, and the coordinates of stars, planets, and galaxies are given based on the equatorial system.
		The coordinates of celestial objects given in the equatorial system are universal.
		This coordinate system is useful when plotting the positions of the other planets as well as asteroids and comets.
	astronomyonline.org /Observation/Coordinates.asp (439 words)

	Spherical Coordinate System Lab
		This coordinate system is based upon the physical fact that we live on the earth and gravity pulls us to the earth establishing and up and a down locally.
		The declination of the celestial equator is 0.
		This coordinate system is based upon the physical fact that we live in a flattened disk of stars that the solar system revolves about in approximately 250 million years.
	www.mc.cc.md.us /Departments/planet/planet/Coordinate_Systems_Lab.htm (1626 words)

	IRAF Help page for "skyctran" (V2.10.4p2)
		The default ilngunits and ilatunits values are hours and degrees for the equatorial coordinate systems and degrees and degrees for the remaining sky coordinate systems.
		This coordinate system is the one used by the image input/output routines to access the image on disk.
		Using an image whose header coordinate system is equatorial FK5 equinox 2000.0 and a different image of the same region whose coordinate system is galactic use the image display and cursor to create a list of tie points in logical pixel coordinates that can be used as input to the registration tasks geomap and geotran.
	ecf.hq.eso.org /scripts/irafhelp?skyctran (2779 words)

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