Astronomy Lesson 8.1 Astronomy s Movers and Shakers

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8 Astronomers.notebook Astronomy Lesson 8.

322 BCE Heavenly objects must move on circular

Earth is motionless at the center of the

Postulated that there were only 5 elements:

1 8 Astronomers.notebook Astronomy Lesson 8.1 Astronomy s Movers and Shakers Aristotle BCE Heavenly objects must move on circular paths at constant speeds. Earth is motionless at the center of the universe. Postulated that there were only 5 elements: fire, air, water, earth, aether. Motions were the result of each element taking its natural place. Aristotle BCE

to explain retrograde (backwards) planetary

It involved the use of epicycles (circles on

Claudius Ptolemy 100 165 CE Developed the

2 8 Astronomers.notebook Aristarchus BCE Claudius Ptolemy CE Ptolemy created an elaborate geometrical and mathematical model to explain retrograde (backwards) planetary motion. It involved the use of epicycles (circles on circles). Claudius Ptolemy CE Developed the heliocentric model of the universe. Used the idea that the Earth rotated on an axis to explain daily motion. He still believed that stars orbited the Sun.

3 8 Astronomers.notebook Nicolas Copernicus Copernicus model was simple compared to the epicycles in Ptolemy s model. Astronomy Lesson 8.2 Astronomy Giants Giants of early Astronomy Tycho Brahe Johannes Kepler Galileo Galilei Isaac Newton tycho brahe

Aristotle had argued that the heavens were perfect, and therefore unchanging. Tycho wrote a book about his discovery.

Tycho believed the Earth was too sluggish to orbit around anything.

island, Hveen. Tycho constructed a state of the art observatory, and made 20 years of extremely accurate planetary measurements.

4 8 Astronomers.notebook Tycho Brahe In 1572, astronomers were startled to see a new star now called Tycho s supernova appear in the sky. Aristotle had argued that the heavens were perfect, and therefore unchanging. Tycho wrote a book about his discovery. Tychonian System The Tychonian System shows the Moon and the Sun revolving around the Earth. Tycho believed the Earth was too sluggish to orbit around anything. Tycho Brahe When Tycho wrote a book about his discovery, the king of Denmark honored him with a generous income and the gift of an island, Hveen. Tycho constructed a state of the art observatory, and made 20 years of extremely accurate planetary measurements. X ray image of Tycho s supernova today Chandra Observatory Tycho Brahe What most bothered Tycho until the time he lost his job at the observatory was that he very precise measurements did not perfectly predict the motions of the planets. He went to work as the mathematician for the Holy Roman Emperor Rudolff II. in Prague and hired Johannes Kepler as his assistant in It was in Prague that he lost his nose in a duel.

orbits of the planets around the Sun are ellipses with the Sun at one focus.

string. First, press the thumbtacks into a board. Then, loop the string about the tacks.

5 8 Astronomers.notebook Tycho s Gold nose Johannes Kepler Kepler s First Law of Planetary Motion The orbits of the planets around the Sun are ellipses with the Sun at one focus. Kepler s Three Laws of Planetary Motion It s easy to draw ellipses with two thumbtacks and a loop of string. First, press the thumbtacks into a board. Then, loop the string about the tacks. Next, place a pencil in the loop. If you keep the string taut as you move the pencil, it traces out an ellipse. What do the two focus points represent in our solar system? The Sun and a orbiting body (planet,comet, asteroid...)

8 Astronomers.notebook Kepler s Second Law of Planetary Motion Kepler s Second Law A line drawn from a planet to the sun sweeps out equal areas in equal amounts of time.

6 8 Astronomers.notebook Kepler s Second Law of Planetary Motion Kepler s Second Law A line drawn from a planet to the sun sweeps out equal areas in equal amounts of time. This happens because elliptical orbits have acceleration. A planet moves faster when closer to the Sun. Kepler s Third Law of Planetary Motion Galileo Galilei The Father of Modern Observational Astronomy A planet s orbital period (T) and distance from Sun (d), are related: T 2 =d 3 Where T measured in years and d measured in AU 1 Astronomical Unit (AU) = the average distance between Earth and Sun, about 93 million miles.

8 Astronomers.notebook Galileo s contributions to Astronomy 1. Made telescopes with up to 30x magnification. 2. Discovered 4 of Jupiter s moons.* 3. One of the first Europeans to witness sunspots.

Was the first to observe Neptune, but did not realize it was a planet.

7 8 Astronomers.notebook Galileo s contributions to Astronomy 1. Made telescopes with up to 30x magnification. 2. Discovered 4 of Jupiter s moons.* 3. One of the first Europeans to witness sunspots. Galileo s Telescopic Observations of Jupiter s moons in Observed phases of Venus.* 5. Observed Saturn s rings ( ears )*. 6. Was the first to observe Neptune, but did not realize it was a planet. * discredits geocentric model Telescopic Observations of Venus Galileo and Gravity Galileo formulated a new idea about free falling objects: All objects regardless of their mass, fall at the same rate. This contradicted the ideas of Aristotle, who said that heavier objects must fall faster than lighter ones. A version of this experiment was repeated on the Moon by the Apollo 15 astronauts. When Galileo saw that Venus showed phases that were bigger than a crescent, he realized that it must orbit the Sun.

8 8 Astronomers.notebook Apollo 15 Gravity Experiment Isaac Newton If I have seen further, it is by standing on the shoulders of giants. Newton s Three Laws of Motion

9 8 Astronomers.notebook Astronomy Lesson 8.3 Modern Astronomy The only reason for time is so that everything doesn't happen at once. Einstein and Spacetime Eddington proves starlight bends in spacetime In 1919, Sir Arthur Eddington observed the exact positions of stars in the Hyades cluster during a total solar eclipse. He found that their positions were shifted as Einstein had predicted. Hyades star cluster Describe light particle on... Flat surface: Massive object:

8 Astronomers.notebook Einstein, Schwarzschild, and Black Holes Einstein s Theory of General Relativity predicted that black holes should exist, and Kurt Schwarzschild worked out the math.

So black holes are black because not even light can escape from them. And they are not holes.

Quantum Theory and the Four Fundamental Forces There are 4 known types of forces in the universe, and according to quantum theory, they should all arise as a result of messenger particles: Photons

10 8 Astronomers.notebook Einstein, Schwarzschild, and Black Holes Einstein s Theory of General Relativity predicted that black holes should exist, and Kurt Schwarzschild worked out the math. Since gravity depends on only mass and distance, he reasoned that if an object collapsed to a small enough radius, then the force of gravity would be so great that the escape velocity from the object would exceed the speed of light. Einstein and Gravitational Waves Einstein also predicted that energetic events in space would cause disturbances in spacetime called gravitational waves, like a rock thrown into a pond causes ripples. So black holes are black because not even light can escape from them. And they are not holes. LIGO detects Gravitational Waves 2015 The LIGO (Laser Interferometer Gravitational wave Observatory) made its first detection of gravitational waves in September, Quantum Theory and the Four Fundamental Forces There are 4 known types of forces in the universe, and according to quantum theory, they should all arise as a result of messenger particles: Photons convey electromagnetic forces Gluons transmit the strong nuclear force W and Z bosons create the weak nuclear force when they move All of the above are documented and there is observational evidence to support their existence. All three of the above are forces that dominate across small distances. But, what about gravity? Gravity dominates only when a large distance is involved and is weaker than the other 3 fundamental forces. If it is like the other three forces, there should be a messenger particle that creates it. This hypothetical particle is called the graviton. It has been described in theory but has not been found. Part of the problem may be due to the fact that gravity is a very weak force.

PHYS 155 Introductory Astronomy

PHYS 155 Introductory Astronomy - observing sessions: Sunday Thursday, 9pm, weather permitting http://www.phys.uconn.edu/observatory - Exam - Tuesday March 20, - Review Monday 6:30-9pm, PB 38 Marek Krasnansky