What Causes the Apparent Retrograde Motion of the Planets

question 100

Multiple Choice

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

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