Copernicus and Heliocentric Model
Overview
This lecture discusses how Copernicus revived the heliocentric (Sun-centered) model during the Renaissance, explaining planetary motion and retrograde motion in a simpler way than previous geocentric models.
The Renaissance and Copernicus
- Copernicus was a Renaissance astronomer who proposed the Sun-centered (heliocentric) model of the solar system.
- At that time, only wealthy individuals could usually afford to be scientists.
- Spelling of names, including Copernicus, was inconsistent in historical times.
Heliocentric Model Details
- Copernicus placed the Sun at the center, with Earth and other planets orbiting around it.
- Mercury and Venus were closer to the Sun than Earth; Mars and others were farther out.
- The Moon was the only object Copernicus had orbiting the Earth.
- He believed orbits were perfect circles with the Sun exactly at the center.
- Planets, including Earth, moved at different speeds around the Sun.
Understanding Retrograde Motion
- Retrograde motion is when planets appear to move backward in the sky.
- Copernicus showed retrograde motion is an optical illusion caused by Earth passing another planet as both orbit the Sun.
- When Earth, moving faster, overtakes Mars, Mars appears to move backward temporarily.
- This explanation was simpler than the old geocentric system with complicated circles.
Planet Names and Knowledge
- Known planets at the time included Mercury, Venus, Mars, Jupiter, and Saturn.
- Uranus and Neptune were unknown until later and invisible to the naked eye.
- Even Copernicus thought planets were strange stars, not worlds like Earth.
Key Terms & Definitions
- Heliocentric Model — A model placing the Sun at the center of the solar system with planets orbiting it.
- Geocentric Model — A model with Earth at the center of the universe.
- Retrograde Motion — The apparent backward movement of planets as seen from Earth due to relative motion.
- Optical Illusion — Something that appears different from reality due to how it is observed.
Action Items / Next Steps
- Review Copernicus's heliocentric model and how it explains retrograde motion.
- Prepare for next class by considering why circular orbits didn't fully match observations.