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Topic: Retrograde motion

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  Prograde and retrograde motion - Wikipedia, the free encyclopedia   (Site not responding. Last check: 2007-11-06)
Retrograde motion is the orbital motion of a body in a direction opposite that which is normal to spatial bodies within a given system.
However it is possible to observe a body moving west to east, such as an artificial satellite or Space Shuttle that is orbiting eastward (the preferred direction, because the rotation of the Earth assists in acquiring the required orbital speed).
This is retrogradation, since the planet seems to be moving in a direction opposite to that which is typical for planets.
en.wikipedia.org /wiki/Retrograde   (799 words)

 AllRefer.com - retrograde motion (Astronomy, General) - Encyclopedia
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.
With the exception of the rotation of Venus, there is no real retrograde motion among the planets, although the plane in which Uranus rotates and its five satellites revolve is tilted slightly more than 90° to the plane of the ecliptic, so that these motions are technically retrograde.
In the geocentric Ptolemaic system, the retrograde motion of the planets was explained, using epicycles, as real retrograde motion; the modern heliocentric theory satisfactorily explains these motions as apparent, due to the relative speeds of the planets in their orbits about the sun.
reference.allrefer.com /encyclopedia/R/retrogra.html   (451 words)

 Models of Planetary Motion -- McConnell
This motion is uniform in every way--the speed of the yellow object along the circle is uniform, the circle shares a center with the earth, the object sweeps out equal angles in equal times.
The motion of the green object is perfectly uniform, though it will appear nonuniform to an observer on earth because the earth does not coincide with the center of the motion.
For Copernicus, the apparent retrograde motion of the planets is a result of the relative speeds of the earth and the planets as observed from the earth:
faculty.fullerton.edu /cmcconnell/Planets.html   (1465 words)

 Retrograde Motion   (Site not responding. Last check: 2007-11-06)
Other aspects of the sun's activity are its southerly motion in the winter and returning more nearly overhead in the summer, and the length of day at these extremes.
Ptolemy's was the dominant view of planetary motion for nearly 1500 years, until Copernicus' observations led once again to a heliocentric (or sun centered) formulation.
That this view can account for "retrograde motion" can be demonstrated by making a series of observations from one moving planet to another when both are in opposition to the sun.
www.iit.edu /~smile/ph8910.html   (514 words)

 The Apparent Motion of Planets on the Celestial Sphere   (Site not responding. Last check: 2007-11-06)
As part of this philosophy, it was believed that the only motion permitted objects in the heavens was uniform circular motion (motion at constant angular speed on a circle), because such motion brought one back cyclically to the starting point and therefore was (in a sense) unchanging.
This philosophy had no problem with the direct motion of the planets, since that could be explained by uniform circular motion of the planets about the Earth (which, as any fool who looked at the sky could see, was clearly the center of the Universe).
However, neither the varying brightness of the planets, nor the occasional retrograde motion of the planets on the celestial sphere, were easily reconciled with this idea of unchanging objects executing uniform circular motion in the heavens.
csep10.phys.utk.edu /astr161/lect/retrograde/retrograde.html   (277 words)

 Retrograde Motion of planets (Science U)
The simplest model to explain the motion of the planets has them, along with the Moon and the Sun (the other two wandering objects in the sky), moving in circles, centered around a fixed Earth.
This model worked well as far as retrograde motion was concerned, since when the planet is in the lower part of the epicycle it is moving in the opposite direction as viewed from the earth.
Retrograde motions arise from the combined motions of the planets and the Earth.
www.scienceu.com /observatory/articles/retro/retro.html   (697 words)

 Venus Retrograde: Astrology on the Web
On top of that, the effects of the retrograde period will continue to be felt until she returns in direct motion on March 7 to the degree where she first made her station (1° Aquarius 27').
A retrograde period is best seen as a cycle, beginning when the planet begins to slow to a halt before travelling backwards through the zodiac and ending when the planet returns to the point where it first paused.
When Venus is retrograde, everyone's emotional state is more introspective and we tend to react emotionally to the issues and concerns that relate to the sign involved.
www.astrologycom.com /venusret.html   (904 words)

 Retrograde · Astrological definition of Retrograde · Astrology Encyclopedia
Retrograde planets in a birth map were anciently said to be weak or debilitated, but a more logical interpretation would seem to indicate that the influence is rendered stronger, which in the case of a malefic planet is definitely unfortunate.
To be able to visualize and thus thoroughly understand the phenomenon of retrograde motion it is advisable to study the cycles of two groups of planets: the minor planets, those between the Earth and the Sun; and the major planets, those whose orbits lie outside that of the Earth.
Figure 2, a comparative illustration of the motion of Venus as an inside planet and Mars as an outside planet, in reference to the motion of the Earth, facilitates a ready understanding of the relationship of the orbits which produces the phenomenon known as retrograde motion.
www.astrologyweekly.com /dictionary/retrograde.php   (1990 words)

 Burn Rate: The Retrograde Phenomenon
After a time of retrograde motion, it once again comes to a halt and starts again in a direct or forward motion.
In particular, it is considered significant if the retrograde loop occurs at a sensitive point in one's horoscope, such as the position of a natal planet.
After all, the entire retrograde phenomenon is little more than a reflection of the Earth's motion around the Sun in relation to the planet in question -- "through a glass darkly," so to speak.
astrologysoftware.com /resources/articles/burnrate.asp?orig=00034-0000   (2376 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)

 Open Course : Astronomy : Introduction : Lecture 5 : Motion of the Planets
The former produces the retrograde motion, while the latter is primarily responsible for the direct motion.
The heliocentric cosmology also explains retrograde motion, by relying on the fact that the planets move at different speeds; in particular, inner planets move faster and outer planets move more slowly.
The retrograde motion, Venus phase, and Galilean satellite animations, and star charts, were produced on a Macintosh with the Voyager II program, and are ©1988-93 Carina Software, 830 Williams St., San Leandro, CA 94577, (510) 352-7328.
www.opencourse.info /astronomy/introduction/05.motion_planets   (3294 words)

 The Copernican Model: A Sun-Centered Solar System
Retrograde Motion and Varying Brightness of the Planets
The retrograde motion could be explained in terms of geometry and a faster motion for planets with smaller orbits, as illustrated in the following animation.
A similar construction can be made to illustrate retrograde motion for a planet inside the orbit of the Earth.
csep10.phys.utk.edu /astr161/lect/retrograde/copernican.html   (863 words)

 Geocentric (Ptolemaic) Perspective - Retrograde Epicyclic Motion - Scientific Revolution - Professor Robert A. Hatch
Viewed from earth, the planet would appear to undergo a 'looping' retrograde motion against the backdrop of the 'fixed stars.' To all appearances, the planet would move in its direct order, gradually slow down and finally appear to stop (stationary point one).
In sum, from a geocentric perspective, retrograde motion was one of the major astronomical problems requiring attention in order to 'save the appearances.' To this end, Ptolemy's model was unsurpassed for simplicity, accuracy, and elegance until Copernicus some 1400 years later.
And most importantly, for present purposes, the Copernican system explained away retrograde motion, it was not a real motion, Copernicus argued, but an illusion resulting from the very structure of the planetary system.
www.clas.ufl.edu /users/rhatch/pages/03-Sci-Rev/SCI-REV-Home/resource-ref-read/chief-systems/08-0retro-2.htm   (691 words)

 Vedic astrology truth
Retrograde motion has been a subject of discussion in modern and ancient astronomy.
This type of motion observed from earth, is due to the rotation and revolution of the earth.
Retrograde motion of the planets beginning with Mars (Mars, Mercury, Jupiter, Venus, Saturn) commences when the sighrochakendras (apogees) are respectively 163, 145, 125.
www.geocities.com /jyothishkerala/astrology12.htm   (1118 words)

 Science 122 Lab: Retrograde
Retrograde motion refers to the change of direction of the planets as they wander through the fixed background of the stars.
The retrograde motion of the planets is much more difficult to explain, especially if one is locked into a paradigm that insistst that all heavenly motiion must be circular.
In this exercise you to plot and graphically observe the retrograde motion of Mars during the period from October 1970 to May 1971, and it will allow you to see how it can be explained by both a geogentric and a heliocentric model.
honolulu.hawaii.edu /distance/sci122/SciLab/L2/L2.html   (1478 words)

 Retrograde Planets - Mercury Retrograde
An apparent backward motion of the planets is called a "retrograde" motion.
A retrograde planet prolongs the influence of that planet in its sign and house of a horoscope.
Mercury is Retrograde in different signs at various times of the year, but does not occur on the same dates from year to year.
www.crystalinks.com /retrogrades.html   (1296 words)

 Planetary Motions   (Site not responding. Last check: 2007-11-06)
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)

 Heliocentric (Copernican) - Planetary Retrograde Motion
Put differently, when a superior planet 'retrogrades' it appears first to move in its direct order, it then slows down and appears to stop (stationary point one).
The motion of the earth is not at all obvious to the observer.
In retrospect, the solution to the problem of retrograde motion was not simply to describe the motion by means of geometry but to explain it by means of cosmology.
www.clas.ufl.edu /users/rhatch/pages/03-Sci-Rev/SCI-REV-Home/resource-ref-read/chief-systems/08-0retro-1.htm   (340 words)

 The Universe of Aristotle and Ptolemy
However, the troubling observations of varying planetary brightness and retrograde motion could not be accommodated: the spheres moved with constant angular velocity, and the objects attached to them were always the same distance from the earth because they moved on spheres with the earth at the center.
Then, the centers of the epicycles executed uniform circular motion as they went around the deferent at uniform angular velocity, and at the same time the epicyles (to which the planets were attached) executed their own uniform circular motion.
Thus, the idea of uniform circular motion is saved (at least in some sense) by this scheme, and it allows a description of retrograde motion and varying planetary brightness.
csep10.phys.utk.edu /astr161/lect/retrograde/aristotle.html   (757 words)

 Retrograde motion was a great mystery to ancient astronomers.   (Site not responding. Last check: 2007-11-06)
Retrograde motion was a great mystery to ancient astronomers.
They believed the earth was stationary at the center of the universe, and the stars and planets all revolved around the earth.
In this ancient “geocentric” view of the universe, complicated models with planets moving on circles upon other circles were required to explain retrograde motion.
antoine.frostburg.edu /phys/luzader/cac/planets_2/tsld008.htm   (64 words)

 Retrograde Motion
One phenomenon that aincient astronomers had difficulty explaining was the retrograde motion of the planets.
To account for the observed retrograde motion of the planets, it was necessary to resort to a system of epicycles, whereby the planets moved around small circular paths that in turn moved around larger circular orbits around the Earth.
The explanation for retrograde motion in this system arises from the fact that the planets further from the sun are moving more slowly in their orbits than those closer to the sun.
alpha.lasalle.edu /~smithsc/Astronomy/retrograd.html   (696 words)

 Retrograde Motion of Planets and Planetoids   (Site not responding. Last check: 2007-11-06)
This views shows the motion of the Earth and a planet relative to the Sun - Both move anti-clockwize as seen from the north.
This animation draws a line from the sun to the planet to show the helocentric longitude p lus the line of sight to the planet from the Earth.
This view show the projection of the image of the planet motion on the sky and illustrates the retrograde motion near opposition
www.go.ednet.ns.ca /~larry/orbits/retrogrd.html   (226 words)

 Kepler's Laws (Lab 3) Retrograde Motion
This westerly motion, a motion counter to the typical easterly motion, is called retrograde motion.
This retrograde motion was very difficult for early astronomers to explain.
The explanation for retrograde motion in this system is much simpler and more natural arising from the fact that the planets further from the sun are moving more slowly in their orbits than those closer to the sun.
www.unm.edu /~astro1/101lab/lab3/lab3_D.html   (612 words)

 Mars Exploration: All About Mars
An "overhead" view of the two planets' orbits is shown in the bottom half of the animation.
This apparent backwards movement is called "retrograde motion." The illusion also happens with Jupiter and the other planets that orbit farther from the sun.
Suppose you were to draw a dot on a sky map each night to show where Mars appears as it moves forward, goes through retrograde, and then resumes its forward motion.
mars.jpl.nasa.gov /allabout/nightsky/nightsky04.html   (441 words)

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