Planets are retrograde when _____.

Question

BlackTom AI · Accepted Answer

The question asks: Planets are retrograde when _____.
Option 1: 'they are hidden behind the moon' — This is incorrect. Being hidden by the Moon refers to conjunctions or new/full phases for observing alignment, not to retrograde motion. Retrograde is a motion issue of a planet’s apparent path, not about visibility by the Moon.
Option 2: 'their astrological influence is more primitive' — This is a misleading conflation of astrology with observational astronomy. Retrograde motion is an astronomical phenomenon describing apparent motion, not a statement about the primitive nature of influence. Therefore this option mischaracterizes the concept.
Option 3: 'they appear to move backward' — This is correct. Retrograde motion describes how, from Earth's viewpoint, a planet seems to reverse its usual eastward path and move westward for a time before resuming its normal direction.
Option 4: 'they move to the south of their normal position' — This is not a standard way to describe retrograde motion. Planets do not retrograde by shifting south or north relative to their usual celestial latitude as the defining feature; retrograde is about apparent reversal along the orbit, not a fixed directional shift.
Option 5: 'they pass another planet by in the heavens' — While planets do occasionally pass one another in the sky, retrograde motion is not defined by close conjunctions or passing events. The key feature of retrograde is the apparent backward motion, not the timing of a planetary pass.
Thus, after evaluating each option on the basis of what retrograde motion means in observational astronomy, option 3 best aligns with the definition and concept of planetary retrograde motion.

Planets are retrograde when _____.单项选择题

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