From Aristotle to Newton: A Revolution in Science

Setting the Scene: Philosophy of the Time The heavens represent perfection. The heavens are immutable. The circle is the perfect shape. All heavenly motions must be circular. The earth is at the center of the universe. These ideas originated with Aristotle.

“The astronomer must try his utmost to explain celestial motions by the simplest possible hypothesis; but if he fails to do so, he must choose whatever other hypotheses meet the case.” -Ptolemy of Alexandria (140 A.D.)

Wanderers in the Heavens Planets don’t maintain a fixed position in the sky. Their brightness varies depending on how far away they are from Earth at any time. Planets appear to speed up and slow down in their motion. Planets also appear at times to move backwards, which is known as retrograde motion (normal motion is to move west to east across celestial sphere). WestEastSouth

Ptolemy tried to crate a model that would account for retrograde motion. He placed the planets in orbits (deferents) on orbits (epicycles) all around the Earth. Epicycle Deferent Earth

Ptolemy’s Epicycles

Where is retrograde motion occurring? Planet’s Path

Ptolemy’s Epicycles Where is retrograde motion? Planet’s Path

“A system of this sort seemed neither sufficiently absolute nor sufficiently pleasing to the mind.” --Copernicus On the Ptolemaic system:

Why heliocentric NOW??? Renaissance: – art – literature – medicine – exploration

Copernicus (1473 – 1543 AD) is known for : 1.First observations of the sun 2.First sun centered model of the solar system or universe 3.The world’s best naked-eye astronomical observations in history 4.Creating first a theoretical model to explain planetary motions 5.Creating first a theoretical model for explaining gravity

Copernicus (1473 – 1543 AD) is known for - 1.First observations of the sun 2.First sun centered model of the solar system or universe 3.The world’s best naked-eye astronomical observations in history 4.Creating first theoretical model to explain planetary motions 5.Creating first a theoretical model for explaining gravity

Copernicus (1473 – 1543 AD) - 1.Probably died a virgin 2.Was a priest and Lawyer 3.Had artificial wooden and silver noses 4.Probably died of Mercury poising 5.Rumored to have died of a bladder burst 6.Was blind at the time of his death 7.Was labeled a heretic by the church

Copernicus (1473 – 1543 AD) - 1.Probably died a virgin 2.Was a priest and Lawyer 3.Had artificial wooden and silver noses 4.Probably died of Mercury poising 5.Rumored to have died of a bladder burst 6.Was blind at the time of his death 7.Was labeled a heretic by the church

Copernicus devised the first comprehensive heliocentric cosmogony to successfully explain retrograde motion Retrograde motion is an apparent motion caused when one planet moves from being behind another planet to being in front of the other planet.

“To demonstrate that the appearances are saved by assuming the Sun at the center and the Earth in the heavens is not the same thing as to demonstrate that in fact the Sun is in the center and the Earth in the heavens. I believe that the first demonstration may exist, but I have grave doubts about the second.” --Cardinal Bellarmine (1615)

Tycho Brahe ( ) - 1.Probably died a virgin 2.Was a priest and Lawyer 3.Had artificial wooden and silver noses 4.Probably died of Mercury poising 5.Rumored to have died when his bladder burst 6.Was blind at the time of his death 7.Was labeled a heretic by the church

Tycho Brahe ( ) - 1.Probably died a virgin 2.Was a priest and Lawyer 3.Had artificial wooden and silver noses 4.Probably died of Mercury poising 5.Rumored to have died when his bladder burst 6.Was blind at the time of his death 7.Was labeled a heretic by the church

Tycho Brahe ( ) is known for - 1.First telescope observations of the sun 2.First sun centered scientific model of the solar system or universe 3.Being the world’s best naked-eye astronomer 4.Creating first theoretical model to explain planetary motions 5.Creating first a theoretical model for explaining gravity

Tycho Brahe ( ) is known for - 1.First telescope observations of the sun 2.First sun centered scientific model of the solar system or universe 3.Being the world’s best naked-eye astronomer 4.Creating first theoretical model to explain planetary motions 5.Creating first a theoretical model for explaining gravity

Tycho Brahe measured distances using parallax that disproved ancient ideas about the heavens He observed a supernova in 1572 and with this showed that the heavens were both changing and had a dimension of distance; this troubled scholars who previously thought the heavens were unchanging. He showed that comets were objects that occurred in the region of the planets, not in Earth’s atmosphere.

Johannes Kepler Probably died a virgin 2.Was a priest and Lawyer 3.Had artificial wooden and silver noses 4.Probably died of Mercury poising 5.Rumored to have died when his bladder burst 6.Was blind at the time of his death 7.Was labeled a heretic by the church

Johannes Kepler None of these. He was a deeply religious man and a family man. He was rumored to have hated Tycho Brahe and was in the relationship for the data. With that data he changed the understanding of motion of heavenly bodies forever. He was also a writer, who wrote children stories about the heavens.

Johannes Kepler is Known for - 1.First telescope observations of the sun 2.First sun centered scientific model of the solar system or universe 3.Being the world’s best naked-eye astronomer 4.Creating first theoretical model to explain planetary motions 5.Creating first a theoretical model for explaining gravity

Johannes Kepler is Known for - 1.First telescope observations of the sun 2.First sun centered scientific model of the solar system or universe 3.Being the world’s best naked-eye astronomer 4.Creating first theoretical model to explain planetary motions 5.Creating first a theoretical model for explaining gravity

Kepler’s First Law: The orbit of a planet about the Sun is an ellipse with the Sun at one focus.

Eccentricity, e how squashed or out of round the ellipse is a number ranging from 0 for a circle to 1 for a straight line e = 0.02 e = 0.7 e = 0.9

What is the shape of Earth’s orbit around the Sun? Earth, e = 0.016

Kepler’s Second Law: A line joining a planet and the Sun sweeps out equal areas in equal intervals of time.

Second Law Facts A line drawn from the planet to the Sun sweeps out equal areas in equal times orbital speed is not constant for an ellipse only for a circle planets move faster when near the Sun (perihelion) planets move slower when they are far from the Sun (aphelion)

Third Law The size of the orbit determines the orbital period –planets that orbit near the Sun have shorter periods than planets that are far from the Sun. a 3 AU = P 2 years

Kepler’s Laws - Lecture Tutorials: Kepler’s Second Law (p. 21) Work with a partner! Read the instructions and questions carefully. Discuss the concepts and your answers with one another. Come to a consensus answer you both agree on. If you get stuck or are not sure of your answer, ask another group. If you get really stuck or don’t understand what the Lecture Tutorial is asking, ask one for help.

According to Kepler’s second law, a planet with an orbit like Earth’s would: A. move faster when further from the Sun. B. move slower when closer to the Sun. C. experience a dramatic change in orbital speed from month to month. D. experience very little change in orbital speed over the course of the year. E. none of the above.

Which of the following best describes what would happen to a planet’s orbital speed if it’s mass were doubled but it stayed at the same orbital distance? A. It would orbit half as fast. B. It would orbit less that half as fast. C. It would orbit twice as fast. D. It would orbit more than twice as fast. E. It would orbit with the same speed.

Kepler’s second law says “a line joining a planet and the Sun sweeps out equal areas in equal amounts of time.” Which of the following statements means nearly the same thing? A. Planets move fastest when they are moving toward the Sun. B. Planets move equal distances throughout their orbit of the Sun. C. Planets move slowest when they are moving away from the Sun. D. Planets travel farther in a given time when they are closer to the Sun. E. Planets move the same speed at all points during their orbit of the Sun.

If a small weather satellite and the large International Space Station are orbiting Earth at the same altitude above Earth’s surface, which of the following is true? A. The large space station has a longer orbital period. B. The small weather satellite has a longer orbital period. C. Each has the same orbital period.

Galileo Probably died a virgin 2.Was a priest and Lawyer 3.Had artificial wooden and silver noses 4.Probably died of Mercury poisoning 5.Rumored to have died when his bladder burst 6.Was blind at the time of his death 7.Was labeled a heretic by the church

Galileo Probably died a virgin 2.Was a priest and Lawyer 3.Had artificial wooden and silver noses 4.Probably died of Mercury poisoning 5.Rumored to have died when his bladder burst 6.Was blind at the time of his death 7.Was labeled a heretic by the church

Galileo ( ) is known for - 1.First observations of the sun 2.First sun centered scientific model of the solar system or universe 3.Being the world’s best naked-eye astronomer 4.Creating first theoretical model to explain planetary motions 5.Creating first theoretical model for explaining gravity

Galileo ( ) is known for - 1.First observations of the sun 2.First sun centered scientific model of the solar system or universe 3.Being the world’s best naked-eye astronomer 4.Creating first theoretical model to explain planetary motions 5.Creating first theoretical model for explaining gravity

Galileo’s Observations

Milky Way There are thousands (billions) more stars in the Milky Way than are visible to the naked eye. Universe is bigger than imagined.

A Being with Ears The Bulge of Saturn Saturn is not a sphere. Circles and spheres do not dominate the heavens.

The Moon The moon has craters. The moon is not a perfect heavenly body.

Sunspots The Sun is not a perfect heavenly body. The Sun rotates about its own axis.

Galileo’s discoveries of the phases of Venus with his telescope showed that Venus must orbit the Sun and strongly supported a heliocentric model Venus is clearly smallest when it is in the full phase and largest when it is in the new phase. Then Venus must be very far from Earth when it is in the full phase and quite close to Earth when in the new phase – which supports the argument that Venus is orbiting the Sun not Earth.

Galileo’s telescope revealed phases of Venus which could only occur IF Venus orbits the Sun.

Galileo’s telescope revealed that Jupiter had moons which orbited Jupiter instead of Earth.

Isaac Newton (1642 – 1727) - 1.Probably died a virgin 2.Was a priest and Lawyer 3.Had artificial wooden and silver noses 4.Probably died of Mercury poisoning 5.Rumored to have died when his bladder burst 6.Was blind at the time of his death 7.Was labeled a heretic by the church

Isaac Newton (1642 – 1727) - 1.Probably died a virgin 2.Was a priest and Lawyer 3.Had artificial wooden and silver noses 4.Probably died of Mercury poisoning 5.Rumored to have died when his bladder burst 6.Was blind at the time of his death 7.Was labeled a heretic by the church

Isaac Newton (1642 – 1727) is known for - 1.First observations of the sun 2.First sun centered scientific model of the solar system or universe 3.Being the world’s best naked-eye astronomer 4.Creating first theoretical model to explain planetary motions 5.Creating first theoretical model for explaining gravity and …..

Isaac Newton (1642 – 1727) is known for - 1.First observations of the sun 2.First sun centered scientific model of the solar system or universe 3.Being the world’s best naked-eye astronomer 4.Creating first a theoretical model to explain planetary motions 5.Creating first theoretical model for explaining gravity and …..

Newton’s Three Laws of Motion First Law - A body remains at rest or moves in a straight line at a constant speed unless acted upon by an outside (net) force. Second Law - (net) Force = mass x acceleration Third Law - Whenever one body exerts a force on a second body, the second body exerts an equal and opposite force on the first body.

Newton’s Law of Gravitation Newton’s law of gravitation states: Two bodies attract each other with a force that is directly proportional to the product of their masses and is inversely proportional to the square of the distance between them.

Newton’s Laws and Kepler's Laws Newton’s law of gravitation and his three laws of motion prove all of Kepler’s laws.

Gravity and Newton's Laws – Lecture Tutorial (p. 29) Work with a partner! Read the instructions and questions carefully. Discuss the concepts and your answers with one another. Come to a consensus answer you both agree on. If you get stuck or are not sure of your answer, ask another group. If you get really stuck or don’t understand what the Lecture Tutorial is asking, ask for help.

Which of the following forces is strongest? A.The force you exert on the earth. B.The force the earth exerts on you. C.This is a trick question: the force you exert on the earth is identical in strength to the force the earth exerts on you.

The Circle of Scientific Progress The progression from the complex Ptolemaic model of the universe to Newton’s laws is an example of the scientific method in use (the model was changed until it met the observations and made correct predictions).