Retrograde Motion: What is it & How Does it Work?

In summary, retrograde motion is the apparent backwards movement of a planet against the background of stars. This is due to the relative positions of the planet and Earth, and does not actually change the planet's orbit. Mercury and Venus experience retrograde motion more frequently due to their shorter orbital periods, while the outer planets experience it once a year as Earth orbits around them. The term "planet" comes from a Greek word meaning "wanderer" because of the way they appear to move in relation to the stars throughout the year.
  • #1
Sobi
19
0
What is retrograde motion? Can some one explain this movement while Earth is constant and the outer planet is moving with relative rotational speed.
 
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  • #2
The orbits of all the planets around the Sun is in the same direction ( counterclockwise when viewed from above the Sun's north pole).
However sometimes we observe a planet APPARENTLY is moving backwards against the background of stars.
In fact the planet's orbit has not changed at all, the 'retrograde' movement is because of the relative positions of the planet and Earth.

http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question46.html
This may help, it's old but I think it make a good job of explaining.
 
  • #3
good post rootone.

So Mercury and Venus have a shorter 'year' than Earth does, so they go through retrograde motion (the appearance of moving backwards) more than once a year. But the outer planets, with longer orbital periods go through it once a year as the Earth comes around.

If I remember correctly, the word 'planet' comes from a greek word which means 'wanderer'. Because of the path of the planets with relation to the path of the stars in the background (parallax) thought the year.
 

1. What is retrograde motion?

Retrograde motion is the apparent backwards motion of a celestial object in the sky. It is an optical illusion caused by the relative positions and movements of the Earth and the object in question.

2. What causes retrograde motion?

Retrograde motion is caused by the differences in orbital speeds and paths between the Earth and the object in question. As the Earth passes the object, it appears to be moving backwards in the sky.

3. How does retrograde motion affect the planets?

Retrograde motion affects the planets by altering their apparent positions in the sky. It can also affect the timing of events, such as the appearance and disappearance of certain planets in the night sky.

4. Is retrograde motion a common occurrence?

Yes, retrograde motion is a common occurrence in our solar system. It is observed in all of the planets, as well as in other celestial objects such as comets and asteroids.

5. How is retrograde motion studied?

Retrograde motion is studied through observations and calculations made by astronomers. They use telescopes and other instruments to track the movement of celestial objects and analyze their positions and paths in the sky.

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