medium · 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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