medium · Enhanced ACT english
Early astronomers observed that certain 'wandering stars' did not follow the same fixed paths as other celestial bodies. These planets moved in complex loops across the night sky, a phenomenon known as retrograde motion.
[Which choice best concludes the paragraph by emphasizing the mystery this phenomenon presented to ancient observers?]
- Retrograde motion is actually an optical illusion caused by the differing orbital speeds of Earth and the other planets.
- Mars and Jupiter are the most common planets that display this visible backward movement during certain times of the year.
- Astronomers eventually developed the Copernican model to explain that all planets in the solar system revolve around the Sun.
- These erratic movements defied the prevailing belief in a simple, geocentric universe, leaving early scholars deeply perplexed.
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