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Earth is moving faster than Mars and so we overtake Mars and pass it. Mars appears to be moving the opposite direction, a motion called retrograde motion. When Mars displays retrograde motion, it appears to etch out a looped path.
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starryskies.com/The_sky/events/mars/opposition05.html
starryskies.com/The_sky/events/mars/opposition05.html
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This image shows the apparent pattern made by the planet Mars while in 'retrograde motion' during 2003. The middle of the yellow line bends in a loop, giving the illusion that Mars' movement is erratic.
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marsprogram.jpl.nasa.gov/allabout/nightsky/nightsky04.h...
marsprogram.jpl.nasa.gov/allabout/nightsky/nightsky04.html
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Retrograde motion of Mars. Under normal circumstances, the planet appears to move to the East (upwards, in the diagram), but when it is being overtaken by the Earth, our faster motion makes Mars appear to be going backwards (downwards, in the diagram).
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cseligman.com/text/sky/retrograde.htm
cseligman.com/text/sky/retrograde.htm
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Retrograde Motion; Using This Interactive; Retrograde Motion Analysis Tool; Exercises; Solutions to Exercises;
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www.mhhe.com/physsci/astronomy/applets/Retro/frame.html
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The following animation shows a simplified helicentric model with three objects: the Sun (yellow) in the centre with the Earth (blue) and Mars (red) in circular orbits around it. The phenomenon of ``retrograde motion'' occurs while Mars is at opposition and is overtaken by the Earth.
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www.astro.utoronto.ca/~zhu/ast210/helicentric.html
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The following animation shows both the helicentric model and geocentric model with three objects: the Sun (yellow), Earth (blue) and Mars (red). Both models produce the same effect as viewed from the Earth. ... You can stop the planet motion by clicking on the image at any time, and then press the mouse again to activate it.
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www.astro.utoronto.ca/~zhu/ast210/both.html
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From one time that the Earth and Mars are on a line through the Sun (called being in "opposition") to the next opposition is 2.135 Earth orbits. It is in a short period including the time of opposition when Mars exhibits its retrograde motion to an observer on the Earth.
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hyperphysics.phy-astr.gsu.edu/Hbase/solar/retromars.htm...
hyperphysics.phy-astr.gsu.edu/Hbase/solar/retromars.html
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This applet demonstrates retrograde motion. Watch Mars' apparent motion across the Earth's sky as the Earth passes Mars in their orbits around the Sun.
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www.astro.illinois.edu/projects/data/Retrograde/
www.astro.illinois.edu/projects/data/Retrograde/
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Also during this time, Mars appeared to move backwards in the sky, a phenomenon called retrograde motion. Pictured above is a series of images digitally stacked so that ... Near the top of the loop, Earth passed Mars and the retrograde motion was the highest. Retrograde motion can also be seen for other Solar System planets.
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apod.nasa.gov/apod/ap080511.html
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