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Early Astronomers

Explore the evolution of astronomical models from Ptolemy's geocentric view to Copernicus's heliocentric revolution. Learn about retrograde motion, epicycles, and the pioneering astronomers who shaped our understanding of the universe.

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Early Astronomers

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  1. UNIT 1 – HISTORY OF ASTRONOMY PP3 ASTRONOMY MR. THOMPSON Early Astronomers

  2. Ptolemy • 1st person to write a detailed description of a geocentric model of the universe, using observations of ancient astronomers. • Geocentric: A model of the universe that has the Earth in the center. • This model was accepted for 15 centuries because it did not conflict with religious or philosophical issues.

  3. Ptolemy’s Model – Geocentric Used retrograde motion and epicycles when describing his models of the universe.

  4. Retrograde Motion and Epicycles • Retrograde motion– when the position of a planet in the night sky spears to move back and forth over a period of time. • Apparent “backwards” motion of a planet when viewed from Earth. • Epicycles – in early models of the universe, the planets had circular orbits and were described to move in smaller circles within their orbits. Used by early astronomers to account for retrograde motion.

  5. Retrograde Motion example

  6. Nicolaus Copernicus • 1st person to develop a heliocentric model of the universe. • Believed that a simpler model of the universe would make more sense and suggested that the Sun was at the center and not the Earth. • Heliocentric: A model of the universe that has the Sun in the center

  7. Copernicus’ Model - Heliocentric Planets orbited in circles around the sun. Used retrograde motion model. Due to some minor irregularities, added some epicycles to explain the data.

  8. Nicolaus Copernicus • Did not publish his ideas until he was on his deathbed, to avoid the criticism and ridicule of the Catholic church. • The church did not take his work seriously when it was first published and did not take much notice of it.

  9. Retrograde Motion and Copernicus’ Model

  10. Galileo Galilei • 1st astronomer to use a telescope to study celestial objects. • Some of Galileo’s discoveries: • Craters on the Moon • Spots on the Sun • 4 moons of Jupiter • Venus goes through phases • Sun rotated, not stationary

  11. Galileo Galilei • Defended the Copernican model of the universe; provided strong observational evidence for heliocentrism. • Publicly ridiculed the earlier geocentric view of the solar system. • He was sentenced to house arrest by the Catholic Church for his scientific work.

  12. Tycho Brahe • Astronomer who collected vast amounts of observational data without a telescope • Measured the position of the sun, moon and planets daily for almost 20 years. • Measured the position of 777 stars. • The data was later used to determine the shape of a planet’s orbit. • He created the “Tychonic” model that attempted to combine the mathematical logic of Coperincus’ heliocentric model and Ptolemy’s more widely accepted geocentric model.

  13. “Tychonic” Model • All planets, except Earth, orbit the sun. • Moon and the sun (with all other planets) orbit the Earth. • Stars are in a fixed sphere around the whole system.

  14. Tycho Brahe • The “Tychonic” models was used favorably for quite some time. • Explained all observational data. • Eliminated the need for confusing epicycles. • Avoided church conflict, appealing to all, by combining the geocentric and heliocentric models.

  15. Review • Terms – • Geocentric • Heliocentric • Retrograde motion • Epicycles • Astronomers (What did they do? Model?) – • Ptolemy • Copernicus • Galileo • Tycho

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