2.2 Copernican revolution and the heliocentric model

The Copernican Revolution shook up our view of the cosmos. It put the Sun at the center, not Earth, and explained planet movements more simply. This shift challenged old ideas and sparked conflict with religious authorities.

Galileo and Kepler built on Copernicus' work with key observations and laws. Their contributions strengthened the heliocentric model and set the stage for future scientific advances, reshaping our understanding of the universe.

The Copernican Revolution

Features of heliocentric model

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• Proposed the Sun, not the Earth, at the center of the universe
  • Planets, including Earth, orbit around the Sun in circular paths (Mercury, Venus, Mars, Jupiter, Saturn)
  • Moon orbits around the Earth
• Explained retrograde motion of planets more simply than geocentric model
  • Retrograde motion: apparent backward motion of planets in the sky (Mars, Jupiter)
  • Geocentric model required complex epicycles and deferents to explain
  • Heliocentric model: retrograde motion a natural consequence of Earth and other planets orbiting Sun at different speeds
• More mathematically elegant and simplified calculations compared to Ptolemaic system
• Still believed in circular orbits and required some epicycles to match observations

Contributions of Galileo and Kepler

• Galileo Galilei:
  • Used telescopic observations to support heliocentric model
    • Discovered four moons orbiting Jupiter (Io, Europa, Ganymede, Callisto), challenging idea that all celestial bodies must orbit Earth
    • Observed phases of Venus, consistent with planet orbiting Sun
  • Faced opposition from Catholic Church for supporting heliocentric model
• Johannes Kepler:
  • Introduced concept of elliptical orbits, replacing Copernicus' circular orbits
  • Developed three laws of planetary motion based on observations of Mars:
    1. Law of Ellipses: Planets move in elliptical orbits with Sun at one focus
    2. Law of Equal Areas: Line segment joining planet and Sun sweeps out equal areas during equal time intervals
    3. Law of Periods: Square of orbital period of planet proportional to cube of semi-major axis of its orbit
  • Kepler's laws provided more accurate description of planetary motion and further supported heliocentric model

Implications of Copernican revolution

• Challenged prevailing Aristotelian and Ptolemaic worldviews that placed Earth at center of universe
• Conflicted with literal interpretation of some biblical passages (Joshua 10:12-13, describing Sun standing still)
• Catholic Church initially resisted heliocentric model, seeing it as threat to authority and established theological understanding of universe
  • In 1616, Church banned Copernicus' book "De revolutionibus" and declared heliocentric theory heretical
  • Galileo faced Inquisition and forced to recant support for heliocentric model in 1633
• Contributed to shift in relationship between science and religion, as scientific observations began challenging traditional religious beliefs
• Acceptance of heliocentric model required reinterpretation of biblical passages and reassessment of humanity's place in universe

Impact on scientific understanding

• Marked significant paradigm shift in history of science, challenging long-held geocentric model
• Paved way for further advancements in astronomy and physics
  • Isaac Newton's laws of motion and universal gravitation
  • Development of modern celestial mechanics
• Provided more accurate and predictive framework for understanding planetary motion and celestial phenomena
• Demonstrated power of scientific observation, mathematical modeling, and empirical evidence in overturning established beliefs
• Inspired further scientific inquiry and contributed to Scientific Revolution of 16th and 17th centuries
• Had far-reaching consequences beyond astronomy, influencing philosophy, theology, and general perception of humanity's place in universe