Earthed

What causes the apparent retrograde motion of the planets?

A. As Earth passes another planet, its gravitational pull slows down the other planet so that it appears to be traveling backward.



B.When planets are farther from the Sun, they move slower than when they are nearer the Sun; it is during this slower period that they appear to move backwards.



C.The other planets never really appear to move backward; the background stars shift due to Earth's revolution around the Sun.



D.As Earth passes another planet, the other planet appears to move backward with respect to the background stars, but the planet's motion does not really change.



E.Apparent retrograde motion is an illusion created by turbulence in Earth's atmosphere.

Public Comments

1. D.
2. Answer is D
   
   Earth when over takes a planet,we feel that planet is moving back among the stars
   
   From 15nov to 30 Jan2008,Mars is having retrograde motion
3. D
   
   
   
   Due to the different size orbits and orbital velocity of the different planets, we see a planet, such as mars, move with retrograde " backwards" motion compared to the background stars when Earth overtakes and passes the planet ... in reality, it is still moving along in it's orbit at the same pace.
4. Agree with D.
   
   Unless you want try epicycles again.