Lesson 5 Astronomy in the Renaissance

Lesson 5: Astronomy in the Renaissance (1400 to 1650)

Motivation

Introduction What did Copernicus believe? How did Tycho Brahe contribute to our understanding of space? What are Kepler’s three laws? How did Galileo Galilei help us understand the solar system?

What did Copernicus believe? Nicolaus Copernicus (1473  1543) Had trouble with Ptolemy’s geocentric (Earth-centered) model. Believed in Aristarchus’s heliocentric model

What is retrograde motion? Heliocentric models explain retrograde motion as a natural result of two planets passing each other. To better understand, look at the diagram and following animations. QuickTime Movie

Retrograde Motion (revisited)

What is the heliocentric model? Heliocentric view – the sun is the center of the solar system This view plus the geometry yields the distances of the planets from the sun Problems: religious issues and accuracy But theory was simpler – and it was correct

Copernicus Arrested?

Observed planetary motion with accurate instruments Accurately measured planets’ locations Observed things that suggested heavens were changeable and complex Proposed different, but still incorrect, geocentric model What did Tycho Brahe do? (1546−1601)

Who was Johannes Kepler? (1571  1630) Young assistant to Tycho Brahe Used Brahe’s data Developed three key laws of planetary motion Monument of Tycho Brahe and Johannes Kepler in Prague, CzechiaTycho BraheJohannes KeplerPragueCzechia

What are Kepler’s three laws? Kepler's First Law: The Law of Ellipses -- How planets move around the sun Kepler's Second Law: The Equal-Areas Law -- How planets move when nearer to the Sun Kepler's Third Law: The Harmonic Law -- How planets move when farther from the Sun

The orbits of the planets are ellipses with the Sun at one of the foci. Kepler's First Law: The Law of Ellipses -- How planets move around the sun

Kepler's Second Law: The Equal-Areas Law -- How planets move when nearer to the Sun The line that connects the planet to the Sun sweeps out equal areas in equal times. A planet's speed changes with its distance from the sun.

Planet’s speed also depends on position in its orbit around the Sun Kepler's Second Law: The Equal-Areas Law -- How planets move when nearer to the Sun

Kepler's Third Law: The Harmonic Law -- How planets move when farther from the Sun The squares of the orbital periods of the planets around the sun are proportional to the cubes of the orbital semimajor axes. P2=a3 What Kepler's third law entails is that the larger the orbit of a planet, the slower the planet will travel in its orbit, and conversely, the smaller the orbit of a planet, the faster it will travel.

P2 A3

Galileo Galilei (1564  1642) First person to use a telescope to study the heavens Saw key features: What the Moon is made of Sun spots and appearance Jupiter’s moons Milky Way’s size and content Galileo GalileiGalileo Galilei, 2000 Itialian Lire (1973)

Were Galileo’s ideas accepted? No: house arrest for rest of his life. Why? Trial by Inquisition

Summary Which key people changed the way we understand the Earth, Sun, and planets? Copernicus, Brahe, Kepler, and Galileo What idea did Copernicus develop and promote? Believed in Sun-centered (heliocentric) solar system Measured relative distances of planets from the Sun

Summary (cont’d) What is a heliocentric model? Sun at center of solar system and planets revolving How did Tycho Brahe contribute to our understanding of space? Observed and recorded planets’ locations Still supported geocentric theory

Summary (cont’d) What are Kepler’s three laws? 1. The Law of Ellipses (planets’ movement around sun) 2. The Equal-Areas Law (closer to Sun = faster) 3. The Harmonic Law (farther from Sun = longer) How did Galileo Galilei help us understand the solar system? Observed moon, sun, three planets Developed theories to support heliocentric solar system