Question at position 44 Which of the following was an important reason why most ancient Greeks rejected the notion that the Earth orbits the Sun?They weren't as smart as we are.They believed that the Sun is a God.They could not measure small changes in the positions of stars that occur as Earth orbits the Sun.They could not measure how big the Earth was.Nobody thought of that possibility until the Renaissance period.Clear my selection

Question

BlackTom AI · Accepted Answer

Stellar parallax was far too small to detect with ancient instruments, so the absence of observed parallax made heliocentrism seem implausible to most Greeks.

1) Relevant knowledge points and concepts
- Stellar parallax: the apparent shift in a nearby star’s position against more distant background stars as Earth moves around the Sun.
- Angular resolution of the naked eye and ancient instruments: roughly on the order of an arcminute (≈60 arcseconds) or worse.
- Historical context: Greek geocentric models (Aristotle, Ptolemy) dominated because observations matched a fixed celestial sphere; however, heliocentric ideas (e.g., Aristarchus) were known but not widely accepted.

2) Step-by-step reasoning
- If Earth orbited the Sun, nearby stars should appear to shift position over six months relative to farther stars (maximum angular shift = 2×parallax angle).
- The parallax angle p (radians) ≈ 1 AU / distance to the star. For even the nearest stars, this angle is a fraction of an arcsecond to a few arcseconds.
- Ancient observers could not measure angles that small. For example, Proxima Centauri’s parallax is ~0.77 arcseconds; many stars have parallax much smaller. Naked-eye resolution (~60 arcseconds) is orders of magnitude too coarse.

3) Intermediate/calculation illustration
- Convert conceptually: 1 arcsecond = 1/3600 degree; ancient precision ~ tens to hundreds of arcseconds. Expected stellar parallaxes (<<60 arcseconds) would therefore be invisible to them.

4) Why the correct answer is correct
- The main observational objection to Earth’s motion was the lack of detectable stellar parallax. Without this expected shifting, the geocentric model better matched available measurements.

5) Why other options are incorrect
- “They weren't as smart”: dismissive and false; Greek astronomers made sophisticated measurements and theories.
- “They believed the Sun is a God”: religious beliefs existed, but scientific rejection was based on observation, not primarily theology.
- “They could not measure how big the Earth was”: false—Eratosthenes measured Earth’s circumference (~3rd century BCE).
- “Nobody thought of that possibility until the Renaissance”: false—Aristarchus proposed heliocentrism in ancient Greece.

6) Conclusion
The correct answer is: “They could not measure small changes in the positions of stars that occur as Earth orbits the Sun.” This explanation confirms and matches the provided answer.

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