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Astronomy in the Middle Ages to the Modern Era. From Copernicus to Galileo to man on the moon. Copernicus. Began the process of disproving the geocentric theory A heliocentric model of the universe offers a much simpler explanation of the universe (remember Occam’s Razor). Heliocentric Model.
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Astronomy in the Middle Ages to the Modern Era From Copernicus to Galileo to man on the moon
Copernicus • Began the process of disproving the geocentric theory • A heliocentric model of the universe offers a much simpler explanation of the universe (remember Occam’s Razor)
Heliocentric Model • Explains retrograde motion • Planets will appear to change direction every time Earth overtakes their orbit • Could now determine the distance a planet is from the sun using geometry • There were still problems with his model because he said the orbits of the planets were circular • His views were slow to be accepted
Tycho and Kepler • Copernicus opened the door to new ideas • A cultural renaissance was taking place in Europe • The Protestant Reformation had begun • The new world was being settled • It was an environment ripe for intellectual stimulation
Tycho Brahe • Believed that God placed the planets in the heavens as a sign to humankind of events on Earth • Made precise measurements with instruments he constructed
Tycho Brahe • First to show the existence of heavenly bodies outside of our solar system • Suggested that the heavens were more complex than we first believed • He had Earth still as the center of the universe with the Sun orbiting around it and the other planets orbiting the Sun
Johannes Kepler • Explained Brahe’s precise observations in mathematical terms • Developed three laws that explained most aspects of planetary motion
Kepler’s Laws • Law of Ellipses • Law of Equal Areas • Law of Periods
Law of Ellipses • Each planet orbits the sun in an elliptical path • Each ellipse has two foci – one of which is the sun • This means the planet is not always the same distance from the sun
Law of Ellipses • Perihelion – the point where the planet’s orbit is closest to the sun • Aphelion – the point where the planet’s orbit is furthest from the sun • The distance given is usually the average of the perihelion and the aphelion
Law of Equal Areas • Describes the speed at which planets travel at different points in their orbits • Earth’s orbit is nearly a perfect circle with the sun off center • Earth moved faster when it was closer to the sun
Law of Periods • Describes the relationship between the average distance of a planet from the sun and the orbital period of the planet • Orbital period – the time it takes to make one revolution around the sun • The cube of the average distance of a planet from the sun (a) is always proportional to the square of the period (p)
The Mathematics K X a3 = p2 K is a mathematic constant If we measure distance in AU and use earth-years, K = 1 and therefore a3 = p2 a = distance in astronomical units (AU) p = orbital period
Kepler’s Three Laws • Describe the essential features of planetary motion around our Sun • Were the first laws to describe the heavens correctly • Kepler also gave us the word satellite
Galileo Galilei • Used the newly invented telescope to study the motions of the planets (Note: Galileo did not invent the telescope) • Proved that the heliocentric model was the correct one
Galileo Galilei • Was the first to use the telescope to study the heavens • Observed that the moon was a ball of rock • Observed sunspots and that they changed from day to day and deduced that the sun rotated • Discovered that Jupiter had moons • Examined the Milky Way and saw that it was made up of millions of stars • Observed that Venus went through phases just like the Moon
Galileo Galilei • That fact that Venus had phases left no doubt that it orbited the Sun and put an end to the Geocentric model of the universe • The originator of the scientific method still in use today • Was brought up on charges of heresy against the church (1992 the church admitted it made a mistake)
Newton’s Application of Kepler’s Laws • Newton wanted to know why the planets moved liked this • Newton said that a moving body will only change its motion if an outside force causes it to do so • An outside force must cause it to curve • This force he determined was gravity • The gravitational pull of the sun is what keeps the planets in orbit around it.
Isaac Newton and the Birth of Astrophysics • Some consider him to be the greatest scientist of all time • Studying the moon he came up with the laws of gravity • Invented Calculus • His laws of gravity and motion were totally accepted for 200 years
The Growth of Astrophysics • New Planets were discovered • Stars had companions that orbit with them • Irregularities in the orbit of Uranus led to the discovery of Neptune • Bigger telescopes – Telescopes in space • Applying photography • Space Exploration