The Copernican Revolution - Lecture Slides | ASTR 104, Study notes of Astronomy

Download The Copernican Revolution - Lecture Slides | ASTR 104 and more Study notes Astronomy in PDF only on Docsity! 3/4/09 1 The Copernican Revolution •  The Copernican Revolution is about astronomers struggling with two related problems –  Earth’s place in the cosmos –  The motion of the planets •  Copernicus revolutionized humanity’s view of Earth’s place in the Universe –  By placing the Sun at the center, Copernicus made Earth move along an orbit like the other planets •  The problem of planetary motion was partly solved by Kepler’s Laws –  Kepler figured out laws to describe how the planets move, but not the reasons why Kelper’s Three Laws •  1st: The orbit of a planet about the Sun is an ellipse with the Sun at one focus. •  2nd: A line drawn from the planet to the Sun sweeps out equal areas in equal times •  3rd: The size of the orbit determines the orbital period 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. The planet in the orbit shown below obeys Kepler’s Laws. During how many portions of the planet’s orbit (A, B, C and D) would the planet be speeding up the entire time? A.  Only during one of the portions shown. B.  During two of the portions shown. C.  During three of the portions shown. D.  During four of the portions shown. E.  None of the above. The planet in the orbit shown below obeys Kepler’s Laws. During which of the portions of the planet’s orbit would the planet experience an increase in speed for at least a moment? A.  Only during one of the portions shown. B.  During two of the portions shown. C.  During three of the portions shown. D.  During four of the portions shown. 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. 3/4/09 2 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 An asteroid orbits the Sun at an average distance a = 4 AU. How long does it take to orbit the Sun? A.  4 years B.  8 years C.  16 years D.  64 years The great scientist Galileo made discoveries that strongly supported a heliocentric cosmogony http://en.wikipedia.org/wiki/ Galileo_Galilei#Church_controv ersy Was blind at the time of his death Was labeled a heretic by the church Galileo is known for first observations of the Sun, the Moon, etc…with a telescope Galileo (1564-1642) was Italian How did Galileo solidify the Copernican revolution? •  Italian mathematician & scientist in early 17th century •  Misconception Alert: Galileo did not invent the telescope –  He did observe the heavens –  He applied his observations to the question of Earth’s place in the cosmos –  His discoveries supported Copernicus’ hypothesis Galileo and his telescope 3/4/09 5 Venus is clearly smallest when it 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 closes to Earth when in the new phase – which supports the argument that Venus is orbiting the Sun not Earth. Galileo’s discoveries of the phases of Venus with his telescope showed that Venus must orbit the Sun and strongly supported a heliocentric model Galileo’s observations of phases of Venus proved that it orbits the Sun and not Earth. Galileo’s telescope revealed that Jupiter had moons which orbited Jupiter instead of Earth. The moons of Jupiter supported the Copernican model •  Aristotle’s model was Earth-centered –  But, Jupiter's moons revolve around Jupiter –  There are centers of motion other than Earth •  Jupiter's innermost moon had the shortest orbital period and the moons further from Jupiter had longer periods –  The periods obeyed Kepler’s 3rd Law Galileo’s discoveries made him famous… and infamous Published “Dialogue Concerning the Two Chief World Systems” in 1632 –  Compared the Copernican system with the Ptolemaic system –  Directly challenged the Earth-centered view held by the authorities of the day In 1633, Galileo was brought before the Inquisition –  He was forced to recant his support of the Copernican system –  Placed under house arrest until his death in 1642 His book on the subject was removed from the Church’s index of banned books in 1824 Galileo was formally vindicated by the Church in 1992 3/4/09 6 How can we distinguish science from non-science? •  Defining science can be surprisingly difficult. •  Science from the Latin scientia, meaning “knowledge.” •  But not all knowledge comes from science… The idealized scientific method •  Based on proposing and testing hypotheses •  hypothesis = educated guess But science rarely proceeds in this idealized way… For example: •  Sometimes we start by “just looking” then coming up with possible explanations. •  Sometimes we follow our intuition rather than a particular line of evidence. Hallmarks of Science: #1 Modern science seeks explanations for observed phenomena that rely solely on natural causes. (A scientific model cannot include divine intervention) Hallmarks of Science: #2 Science progresses through the creation and testing of models of nature that explain the observations as simply as possible. (Simplicity = “Occam’s razor”) Hallmarks of Science: #3 A scientific model must make testable predictions about natural phenomena that would force us to revise or abandon the model if the predictions do not agree with observations. 3/4/09 7 Isaac Newton (1642 – 1727) was British Is known for creating first theoretical model for explaining gravity and ….. How did Newton change our view of the Universe? •  Realized the same physical laws that operate on Earth also operate in space –  One universe •  Worked out fundamental laws of motion and gravity •  Designed the reflecting telescope •  Discovered that white light is a mix of all colors •  Also invented calculus Isaac Newton formulated three laws of motion and the law of gravitation – these laws describe the motion of our physical world How do we describe motion? Precise definitions to describe motion: •  Speed: Rate at which object moves € speed = distancetime units of m s       example: speed of 10 m/s •  Velocity: Speed and direction example: 10 m/s, due east •  Acceleration: Any change in velocity units of speed/time (m/s2) What produces acceleration in a car? A. The gas pedal B. The brake C. The steering wheel D. A and B E. All of the above The Acceleration of Gravity •  All falling objects accelerate at the same rate (not counting friction of air resistance). •  On Earth, g ≈ 10 m/ s2: speed increases 10 m/s with each second of falling. 3/4/09 10 If a planet travels in a circular orbit without speeding up or slowing down, is it accelerating? A. Yes B.  No If a planet travels in a circular orbit without speeding up or slowing down, does it have a force on it? A. Yes B.  No What keeps a planet rotating and orbiting the Sun? Conservation of Angular Momentum •  The angular momentum of an object cannot change unless an external twisting force (torque) is acting on it •  Earth experiences no twisting force as it orbits the Sun, so its rotation and orbit will continue indefinitely angular momentum = mass x velocity x radius Conservation of Angular Momentum •  Angular momentum = m × v × r •  Orbital – Kepler’s 2nd law Angular momentum conservation also explains why objects rotate faster as they shrink in radius: 3/4/09 11 Conservation of Energy •  Energy can be neither created nor destroyed. •  It can change form or be exchanged between objects. •  The total energy content of the Universe was determined in the Big Bang and remains the same today. Where do objects get their energy? •  Energy makes matter move. •  Energy is conserved, but it can: – Transfer from one object to another – Change in form Basic Types of Energy •  Kinetic (motion) •  Radiative (light) •  Stored or potential Energy can change type but cannot be destroyed. Thermal Energy: the collective kinetic energy of many particles (for example, in a rock, in air, in water) Thermal energy is related to temperature but it is NOT the same. Temperature is the average kinetic energy of the many particles in a substance. Temperature Scales Thermal energy is a measure of the total kinetic energy of all the particles in a substance. It therefore depends both on temperature AND density Example: 3/4/09 12 Gravitational Potential Energy •  On Earth, depends on: –  object’s mass (m) –  strength of gravity (g) –  distance object could potentially fall Gravitational Potential Energy •  In space, an object or gas cloud has more gravitational energy when it is spread out than when it contracts. ⇒ A contracting cloud converts gravitational potential energy to thermal energy. Mass-Energy •  Mass itself is a form of potential energy •  A small amount of mass can release a great deal of energy •  Concentrated energy can spontaneously turn into particles (for example, in particle accelerators)