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Topic: Prograde and retrograde motion

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	Prograde and retrograde motion - Wikipedia, the free encyclopedia
		Prograde motion is the rotational or orbital motion of a body in a direction similar to that of other bodies within a given system, and is sometimes called direct motion.
		Retrograde motion is the apparent 'backwards' motion of the outer planets (Mars, Jupiter, Saturn, Neptune, Uranus, and Pluto) observed from Earth with respect to the background stars.
		Most planets, including Earth, spin in the prograde sense: They spin in the same direction as they orbit the Sun (that is, their north rotational pole and north orbital pole point in similar directions, more or less in the direction of the Solar north pole).
	en.wikipedia.org /wiki/Prograde_and_retrograde_motion (978 words)

	Prograde and retrograde motion (Site not responding. Last check: 2007-08-19)
		Retrograde motion is the orbital motion of a body in a direction opposite that which is normal to spatial bodies within a given system.
		This is retrogradation, since the planet seems to be moving in a direction opposite to that which is typical for planets.
		In modern astronomy, the term retrograde motion refers to objects which are actually moving in a direction opposite that which is normal to spatial bodies within a given system, as opposed to merely observed phenomena (retrogradation) such as that described above.
	hallencyclopedia.com /Prograde_and_retrograde_motion (994 words)

	Kids.net.au - Encyclopedia Prograde and retrograde motion -
		The moons Ananke, Carme, Pasiphae and Sinope all orbit Jupiter in a retrograde direction, and are thought to be fragments of a single body that Jupiter captured long ago.
		The moon Phoebe orbits Saturn in a retrograde direction, and is thought to be a captured asteroid.
		The moon Triton orbits Neptune in a retrograde direction, and is thought to be a captured Kuiper belt object.
	www.kids.net.au /encyclopedia-wiki/re/Retrograde_orbit (767 words)

	Prograde And Retrograde Motion (Site not responding. Last check: 2007-08-19)
		Retrograde motion is the orbital motion of a body in a direction opposite that which is normal to...
		Prograde and retrograde motion : Retrograde motion Retrograde motion is the orbital motion of a body in a direction opposite that which is normal...
		prograde and retrograde satellite orbits: Satellite orbits in which motion is in the same or opposite direction, respectively, as the planet's rotation.
	www.signastrology.info /prograde_and_retrograde_motion.html (349 words)

	Reference.com/Encyclopedia/Retrogradation
		Retrogradation refers to the motion of the outer planets (Mars, Jupiter, Saturn and so forth) when they move from east to west relative to the background stars (most of the time the planets move from west to east).
		Retrogradation was quite a puzzle for ancient astronomers who used the geocentric model.
		In the heliocentric model, retrogradation is a natural result of the combined motion of the Earth and the planet observed.
	www.reference.com /browse/wiki/Retrogradation (116 words)

	Retrograde Motion (Site not responding. Last check: 2007-08-19)
		This is a phenomenon called retrograde motion, which is brought about by the relative speeds of the planets as they revolve around the sun.
		Direct motion Objects moving around the Sun in the same direction as the Earth are moving in direct motion, objects moving in the opposite direction are moving in retrograde motion.
		Retrogression (or Retrograde Motion) Movement of a weather system in a direction opposite to that of the basic flow in which it is embedded, usually referring to a closed low or a longwave trough...
	lowellfive.mesalowell.com /retrogrademotion (1113 words)

	iqexpand.com (Site not responding. Last check: 2007-08-19)
		Retrograde Motion One phenomenon that aincient astronomers had difficulty explaining was the...
		An explanation of the retrograde motion of some planets: why they seem to go back on their tracks, as viewed from Earth.
		Retrograde Motion and Varying Brightness of the Planets The Copernican system by banishing the idea that the Earth was the center of the Solar System, immediately led to a simple explanation of both...
	retrograde_motion.iqexpand.com (1034 words)

	Retrograde motion of the planets
		To examine the smooth motion of the planet on the field of stars, each image has been rotated and oriented so that the stars and asterisms appear at the same orientation on each image.
		The planet is moving in retrograde (backwards) motion toward the celestial west.
		The planet is moving in retrograde (backwards) motion toward the celestial west, but at a slower rate.
	www.warren-wilson.edu /~physics/Contemp-Astronomy/PlanetTracking/PlanetTrack2.htm (1241 words)

	Discussion about Earth orientation parameters definitions (Site not responding. Last check: 2007-08-19)
		Prograde polar motion is a component of the Earth rotation which is parameterized as...
		Prograde nutation is a component of the Earth rotation which is parameterized as...
		I propose to include definition prograde polar motion and retrograde polar motion as well as prograde and retrograde nutations in the terms of canonical EOP in order to allow to authors to refer to this recommendation.
	gemini.gsfc.nasa.gov /pet/discussion/eop.html (1268 words)

	Astronomy Course Notes
		Because the Earth is in motion, we perceive odd motions of the planets.
		This short-lived, periodic westward motion is called "backward", or "retrograde motion", or sometimes "retrogradation".
		This motion is not real, but is an effect caused by our perspective on a moving Earth.
	astro.wsu.edu /allen/courses/notes/orbits.html (1060 words)

	prograde and retrograde motion (Site not responding. Last check: 2007-08-19)
		Venus and Uranus spin clockwise, so they have a retrograde rotation.
		When we observe the sky, we expect most objects to appear to move in a particular direction with the passing of time.
		However it is possible to observe a body moving west to east, such as an artificial satellite or Space Shuttle that is orbiting eastward.
	www.yourencyclopedia.net /prograde_and_retrograde_motion.html (796 words)

	Retrograde Motion (Site not responding. Last check: 2007-08-19)
		Retrograde Motion Retrograde motion, in astronomy, real or apparent movement of a planet, moon, asteroid, or comet from east to west relative to the fixed stars.
		The most common direction of motion in the solar system, both for orbital revolution and axial rotation, is from west to east (counterclockwise as seen from the north celestial pole): revolution or rotation in the opposite direction is actual retrograde motion.
		Retrograde Motion The animation on the left shows the Sun, Earth, and Mars seen from a Sun-centered point of view, whereas the animation on the right shows the three bodies seen from an Earth-centered point of view.
	www.aerospace-reference.com /directory/planet-pluto/retrograde-motion.html (719 words)

	Chapter 1: The Copernican Revolution
		According to Ptolemy's geocentric theory, this is explained by having each planet moving on a small circle (an epicycle) while at the same time the center of the small circle moves around the earth in a larger circle (the deferent).
		Thus the diurnal motions of the celestial objects are merely an optical illusion.
		During retrograde motion, the planet reverses its normal motion and moves for a short time from east to west among the zodiac stars before again resuming its normal motion.
	www.pbcc.cc.fl.us /faculty/sundquij/ast1002/history.htm (1604 words)

	General Science 2310 and General Science 2330
		The motion of Mercury in its orbit is determined by the digit third from the right (in this case 7), if the number is 4 or less the motion is prograde, otherwise the motion is retrograde (in the example, the right ascension of Mercury is 4 hours and its motion is retrograde).
		For the inner planets, the regions of prograde or retrograde motion are determined by drawing tangents from the Earth to the planet's orbit, thus cutting the orbit into prograde and retrograde sections.
		Notice that Mars is right on the border between prograde and retrograde, it is neither moving forwards or backwards on the right ascension wheel.
	www.lakeheadu.ca /~physwww/courses/Astro/2310/Godseye/hscope-tut.htm (1111 words)

	Ecliptic (Site not responding. Last check: 2007-08-19)
		As a consequence the majority of the planets and moons revolve around the Sun roughly on a single plane, called the plane of the ecliptic, and in a single direction, referred to as prograde.
		Seen from above Earth's north pole, prograde motion is anticlockwise.
		Bodies which orbit in the opposite direction are said to have retrograde motion.
	www.inconstantmoon.com /not_motn.htm (78 words)

	Prograde and Retrograde Motion (Site not responding. Last check: 2007-08-19)
		In doing this, the direction of motion of, planet / moon, is ignored because: i) all planets are orbiting the Sun in the same direction - that is all planets of our solar system are prograde in nature and ii) as our Earth has only one moon and that too is prograde in nature.
		There is nothing special about prograde motion except it happens to be the direction of the earth's orbit.
		(Jupiter's orbital period is ~12 years.) The difference between Jupiter's motion and a straight line, over the seven-day orbit of Ganymede, is negligible, and this means that the difference between prograde motion and retrograde motion is also negligible.
	www.newton.dep.anl.gov /askasci/phy00/phy00572.htm (501 words)

	Planetary Motions (Site not responding. Last check: 2007-08-19)
		The motions of the planets are roughly confined to the ecliptic.
		This motion is harder to understand in the context of an Earth-centered (geo-centric) model.
		The explanation for retrograde motion in a helio-centric model is that retrograde occurs roughly when a faster moving planet catches up to and passes a slower moving planet (Copernicus circa 1500).
	zebu.uoregon.edu /~imamura/121/oct6/planet.html (486 words)

	Celestial sphere
		In this sense, the celestial sphere model is a very practical tool for positional astronomy.
		For example, over the course of a year the Sun, relative to the background stars, will follow a bisecting great circle (known as the ecliptic).
		See also: prograde and retrograde motion The celestial sphere is divided by projecting the equator into space.
	encyclopedia.codeboy.net /wikipedia/c/ce/celestial_sphere.html (412 words)

	What does it mean for Mercury to be in retrograde?
		Retrograde motion is an APPARENT change in the movement of the planet through the sky.
		The retrograde motion continues for a short time and then the motion switches back to prograde.
		The explanation for retrograde motion in a heliocentric model is that retrograde occurs roughly when a faster moving planet catches up to and passes a slower moving planet.
	starchild.gsfc.nasa.gov /docs/StarChild/questions/question46.html (344 words)

	A RE-EVALUATION OF THE EXTRATERRESTRIAL ORIGIN OF THE CAROLINA BAYS
		The probabilities of collision with a retrograde object are somewhat higher than the prograde or directly moving object, because an object perturbed out of a direct orbit will, when crossing planetary orbits, spend more time in the vicinity of the planets which are moving in the same general direction as the perturbed body.
		If the object exhibits retrograde motion, the impact velocity on Earth will be additive, equal to the velocity of that body plus the velocity of the Earth as it moves in orbit about the sun (30km/sec).
		Observations of the motion of the object across the sky indicated that it was traveling toward the earth probably in retrograde motion at a very high velocity, perhaps 50 km/sec, which would be typical of a comet but not of ordinary meteorites.
	abob.libs.uga.edu /bobk/cbayint.html (8384 words)

	Celestial sphere: Definition and Links by Encyclopedian.com (Site not responding. Last check: 2007-08-19)
		As the Earth rotates on its axis, the objects on the celestial sphere will appear to rotate around the celestial poles every 24 hours, this is diurnal motion.
		For example the Sun will typically appear to rise in the east and set in the west, as will the stars, planets and moon.
		Superimposed on diurnal motion is; intrinsic motion[?] as the objects change their relative positions, with respect to Earth.
	www.encyclopedian.com /ce/Celestial-sphere.html (382 words)

	iqexpand.com (Site not responding. Last check: 2007-08-19)
		The highest known inclination of an asteroid orbit is around 55 degrees (retrogade orbits have inclinations exceeding 90 degrees).
		retrograde - definition of retrograde in the Medical dictionary - by...
		The most well-known celestial body with retrogade motion is Comet...
	retrogade_orbit.iqexpand.com /index.php?...&action=edit (1022 words)

	hw8 (Site not responding. Last check: 2007-08-19)
		On the other hand, since the moon is much smaller than the Earth, as the Earth enters the moon's shadow, only a tiny portion of the earth's surface will actually be covered by the moon's shadow and only the people in that tiny portion, weather permitting, will see the solar eclipse.
		So by observing a planet at the same time night after night and determining which direction a planet is moving relative to the fixed stars, you can tell whether or not it is in retrograde motion.
		Mars undergoes retrograde motion when the Earth passes mars as the Earth orbits the Sun.
	www.astro.indiana.edu /~classweb/a100s0489/hw/hw8.html (404 words)

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