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## Astronomy and the Renaissance

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**Astronomy and the Renaissance**• Know about Copernicus and the Sun-Centered Model • Know Kepler’s Laws of Planetary Motion**Ptolemy’s Model**• Claudius Ptolemy – AD 150 • Ptolemy believed that heavenly bodies (planets and stars) were perfect, in contrast to earthbound objects • For 1,300 years, his model was the conventional wisdom of the scientific world • The universe was based on perfect circles • An epicycle is the circular orbit of a planet, the center of which revolves around the Earth in another circle**Lesson Overview**• Copernicus and the Sun-Centered Model • Kepler’s Laws of Planetary Motion**Why Copernicus Searched for a Better Model**• Ptolemy’s model designed to predict planetary movements were off (by as much as 2 degrees)… • Hence calendars, largely based on astronomical bodies were not accurate. More accurate data was needed for the Roman Catholic Church in order to correctly observe religious events. • In addition, Ptolemy’s theory of epicycles didn’t adequately explain changes in Mars’ brightness**Copernicus’ Heliocentric System**• Earth, one of several planets revolving around the Sun • Plane of Earth’s equator tilted • Moon revolves around Earth • Earth’s atmosphere simply follows Earth as it rotates**Tycho Brahe**Tycho Brahe’s (1571-1630) • Danish astronomer and fierce mathematician • Tycho’s observations didn’t confirm the more recent Copernican model. • Trying to bridge the two Tycho developed a hybrid model that put Earth at the center of Sun’s orbit • Other planets orbiting Sun • Wrong conclusion for a good reason**Tycho Brahe**• Tycho Brahe's contributions to astronomy were atill enormous. • Supernova (1572) • He not only designed and built instruments, he also calibrated them and checked their accuracy periodically….thus he revolutionized astronomical instrumentation. • He also gave a young mathematician, Johannes Kepler a break…..well sort of**Kepler’s First Law: The Significance of the Ellipse**• Ellipse – a geometrical shape of which every point is same total distance from two fixed points • Each planet’s path around the Sun is an ellipse • The Sun is at one focal point**Kepler’s Second Law: The Planets’ Changing Speeds**• A planet speeds up when it is closer to the Sun, and slows down when it is farther away**How Kepler’s Third Law Implied the Force of Gravity**• Kepler hypothesized that a force held the planets near the Sun—gravity • His 3rd Law states that the square of a planet's orbital period is proportional to the cube of its average distance from the Sun. (period)2 = (constant) x (average distance)3 • Harmonic Law: expresses a relationship between the time a planet takes to orbit the Sun and its distance from the Sun Longer distance from sun, longer time to orbit, more distance traveled thus slower speed in its orbit**Extra Credit: This Saturday**http://www.redbullflugtagusa.com/?utm_source=google&utm_medium=cpc&utm_campaign=Red+Bull+-+Flugtag+Philadelphia+Spectator+-+Branded&utm_group=Branded+-+Phrase&utm_term=red+bull+flugtag#/event/philadelphia-2012**Astronomy and the Renaissance**• Know about Copernicus and the Sun-Centered Model • Know Kepler’s Laws of Planetary Motion**Next…**Done – Astronomy and the Renaissance Next – The Enlightenment and Modern Astronomy