Astronomy Lesson Aristotle 384 ‐ 322 BCE
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8 Astronomers.notebook Astronomy Lesson 8.1 Astronomy’s Movers and Shakers 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 384 ‐ 322 BCE Aristotle 384 ‐ 322 BCE
Transcript of Astronomy Lesson Aristotle 384 ‐ 322 BCE
8 Astronomers.notebook
Astronomy Lesson
8.1 Astronomy’s Movers and Shakers
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 384 ‐ 322 BCE
Aristotle 384 ‐ 322 BCE
8 Astronomers.notebook
Aristarchus 310 ‐ 230 BCE
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 100 ‐ 165 CE
Claudius Ptolemy 100 ‐ 165 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.
8 Astronomers.notebook
• Copernicus’ model was simple compared to the epicycles in Ptolemy’s model.
Nicolas Copernicus 14731553Astronomy Lesson
8.2 Astronomy Giants
Giants of early Astronomy
Tycho Brahe Johannes Kepler Galileo Galilei Isaac Newton 15461601 15711630 15641642 16421727
tycho brahe 1546 - 1601
8 Astronomers.notebook
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.
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 abouthis discovery.
Tycho Brahe 1546 1601
X ray image of Tycho’s supernova today – Chandra Observatory
• 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.
Tycho Brahe 1546 1601
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 1600.
It was in Prague that he lost his nose in a duel.
Tycho Brahe 1546 1601
8 Astronomers.notebook
Tycho’s Gold nose Johannes Kepler 1571‐1630
The orbits of the planets around the Sun are ellipses with the Sun at one focus.
Kepler’s First Law 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...)
Kepler’s Three Laws of Planetary Motion
8 Astronomers.notebook
Kepler’s Second Law of Planetary Motion
• 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 Second Law
A planet’s orbital period (T) and distance from Sun (d), are related:
T2=d3
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.
Kepler’s Third Law of Planetary MotionGalileo Galilei 1564‐1642
The Father of Modern Observational Astronomy
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.
4. 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
Galileo’s Telescopic Observations
of Jupiter’s moons in 1610
Telescopic Observations of Venus
When Galileo saw that Venus showed phases that were bigger than a crescent, he realized that it must orbit the Sun.
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.
8 Astronomers.notebook
Apollo 15 Gravity Experiment
“If I have seen further, it is by standing on the shoulders of giants.”
Isaac Newton 1642‐1727
Newton’s Three Laws of Motion
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Astronomy Lesson
8.3 Modern Astronomy
“The only reason for time is so that everything doesn't happen at once.”
Einstein and Spacetime
Describe light particle on....
Flat surface:
Massive object:
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
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. So black holes are black because not even light can escape from them. And…they are not holes.
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.
LIGO detects Gravitational Waves 2015
The LIGO (Laser Interferometer Gravitationalwave Observatory) made its first detection of gravitational waves in September, 2015.
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 forcesGluons transmit the strong nuclear forceW 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.
