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As beginner, I would like to understand how planets exhibit retrograde motion.

When does the retrograde motion start for a planet like Mars and how long (time limit) planets will appear to be in such motion?

Any good URL or simple explanation will be helpful.

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The Wikipedia article on apparent retrograde motion seems to have a table containing exactly what you are looking for:

retrograde motion table

The apparent motion is observed when the projection of a planet is compared to the star background. There are no real change in the planetary orbits, but when for example the Earth catches up with Mars, it seems to move retrograde relative to the background because of our own change of view. (Like how it appears that you are scrolling further down on this page when the background moves upwards.)

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  • $\begingroup$ Thanks. Are the no of 'days in retrograde' fixed for any year? If not, provide me some good URL where in I can get some info $\endgroup$ Apr 8 '16 at 19:27
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    $\begingroup$ @SathishKumar The period of days in retrograde repeats for every synodic period. $\endgroup$ Apr 8 '16 at 19:39
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Here's a nice animation from the Washington Post:

enter image description here

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Retrograde is in fact an illusion. The earth revolves around the sun faster than the planets farther from the sun. And if the Earth passes one of those distant planets on its journey around the Sun, for us who are on Earth, you think if you can choose it, but it's just an illusion. The planet is moving in the same direction as it always has, but our perspective is different. The Earth's rotation around the Sun takes 365 days. Mars needs 687 Earth days to create a complete orbit. We are both moving, but Mars is far away and wants to move it around. Every 26 months, the Earth goes to Mars and passes by it. As our orbital path passes by the Red Planet, we experience the illusion that Mars is moving away from us, not the fact that the Earth is moving away from Mars. Two months ago, our perception hit the reset button using our Sirat move, and it looks like it will resume moving forward if Mars moves.

If the Earth and Mars are rotating at the same speed and are in a constant position throughout their orbit relative to if, Mars always looks to you if it moves in a direction from east to west. Because it is not, every two years, Mars normally lags behind. This is an illusion, which is one of the ways that Earth and Mars revolve around the Sun.

Every two years or more, there are a few months that I think can change Mars's position from night to night and move from east to west. This strange behavior was very confusing for the celestial observers. Did the planet really stop, back up, change its mind, and then keep moving? Did it have a weird meaning?

Today we know what is going on. This is an illusion, which is one of the ways that Earth and Mars revolve around the Sun.

Mars Retrograde occurs every two years

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    $\begingroup$ Hi Roham. This isn't a bad answer, but it has suffered at the hands of Autocorrect! I've fixed some, but you can proofread to see if there are any others like "Sirat" $\endgroup$
    – James K
    Apr 14 at 6:41

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