1. ASTRONOMY

2. Astronomy? Impossible to understand and madness to investigate.
WHAT IS ASTRONOMY?
Astronomy – the study of the universe
Astronomy? Impossible to understand and madness to investigate.
— Sophocles, c. 420 BCE

3. Rotation: The turning of the Earth on its own axis
Day and Night
24 hours
Revolution: The orbit of the Earth (or planets) around the sun
Year
days

4. Year – the time it takes the earth to orbit once around the sun
Month – the time it takes the moon to orbit once around the earth
Day – the time it takes the earth to rotate once around its axis

5. Historical figures in the Copernican Revolution
Ptolemy – Greek Astronomer
-- 85 – 164 AD
--Proposed the Geocentric model of the universe; that the Earth was the center of the universe/solar system
-- Idea accepted for 1400 years
-- 1st person to use latitude and longitude to identify places on Earth
How was this knowledge of the solar system discovered?
It is a dramatic story in the History of Science. So today’s lecture is mainly historical. Then next time we’ll see how Isaac Newton explained the motion of the planets with his theories of motion and gravity.
The slide lists the famous names in the Copernican Revolution.
Ptolemy was a Greek astronomer who lived in Egypt during the time of the Roman Empire. He was born about 85 AD – 85 years after the birth of Jesus of Nazareth. He wrote a famous book on astronomy, which tried to show that the Earth is at the center of the universe, based on astronomical observations of his time. In the Ptolemaic model, all heavenly bodies revolve around the Earth -- stars, the sun, the moon, and the planets.
However, Ptolemy and others knew that the geocentric model was really not very accurate; so they tried to fix it up in various ways to agree with the observations. They had to postulate complicated orbits around the Earth, with cycles and epicycles, to agree with the observations on planetary motions. The Ptolemaic theory – the geocentric model -- survived for 1,400 years, in spite of its weaknesses. {READ}
Copernicus was trained to be a priest, and held an office in the Roman Catholic Church in Poland. But he spent his life in astronomical studies. At the end of his life he published the theory that the Earth and planets revolve around the sun. {READ}
Galileo and Kepler lived some years after Copernicus. They never met in person but they did correspond and they respected each other. Their work proved that Copernicus was right. {READ}
Finally, Newton developed a complete theory of planetary orbits. It is still used today.

6. Historical figures in the Copernican Revolution
Copernicus – Polish Astronomer
– 1543
-- Proposed the Heliocentric Model of the universe; that the Sun was the center of the solar system
--He thought the planets orbited the sun in circles

7. Historical figures in the Copernican Revolution
Brahe– Danish inventor, astronomer
– 1601
-- Invented/Improved instruments for observing the universe
-- Kepler worked for Brahe to observe the motion of the planets
--Modified the Geocentric Model
-- Thought the moon and sun orbited the Earth
-- All other planets orbited the sun

8. Historical figures in the Copernican Revolution
Kepler – German mathematician
--Began studying the orbits of planets with Brahe
--Discovered the orbits were not circles, but were really ellipses (ovals)
--stated that the planets move at different speeds around the sun
-- closer planets move faster than planets further out

9. Historical figures in the Copernican Revolution
Galileo –Italian Astronomer
– 1642
--1st to prove Copernicus’ Heliocentric Model with a telescope
--Used the phases of Venus with explained that Venus in fact revolved around the sun
--Spent the last years of his life under house arrest
--discovered the 4 moons of Jupiter
-- invented the thermometer
-- built compasses for surveying land

10. Historical figures in the Copernican Revolution
Newton – English scientist, astronomer, mathematician
--1st to describe the concept of gravity
--Stated the force that holds us to the Earth is the same thing that keeps the planets in orbit.
-- Three laws of motion
-- Law of Universal Gravitation
-- Developed Calculus

11. The observed solar system at the time of Newton
Sun
Mercury
Venus
Earth
Mars
Jupiter
Saturn
(all except Earth are named after Roman gods, because astrology was practiced in ancient Rome)
This was the solar system known at the time of Newton.
[[Clyde Tombaugh; b. Illinois 1906; grew up on a farm in Kansas; astronomer in New Mexico.]]
Three outer planets discovered later…
Uranus (1781, Wm Herschel)
Neptune (1846 Adams; LeVerrier)
Pluto (1930, Tombaugh)

12. Historical figures in the Copernican Revolution
Hubble – American Astronomer
--in 1929 formulated Hubble's Law, which determined the age of the universe and that it is expanding
--demonstrated that other galaxies besides our own Milky Way existed
--In the same year Edwin Hubble introduced his Hubble telescope.
-- The Hubble Space Telescope was launched on April 25th, 1990 on the space shuttle.

13. Edwin Hubble

14. Geocentric vs Heliocentric Theories

15. Earth or Sun Centered?
Geocentric Theory (Earth-centered) – Ptolemy’s theory that the earth was the center of the universe
Heliocentric Theory (Sun-centered) – Copernicus’ theory that the sun was the center of the universe

16. Claudius Ptolemy A geographer, mathematician, and astronomer
Developed the theory that the Earth was the center of the solar system
…“the natural motion of the Earth ….is towards the center of the universe; that is the reason it is now lying at the center.” Aristotle, On the Heavens

17. The Geocentric Theory
The earth is located at the center of the universe and all the planets revolve around the earth.

18. Nicolaus Copernicus 1473 -1543 A mathematician, and astronomer
Developed the theory that the sun was the center of the solar system
To know that we know what we know, and to know that we do not know what we do not know, that is true knowledge.

19. Galileo Galilei
By using the telescope, Galileo noted that Venus had “phases” like the moon, so it could not orbit Earth, but must orbit the Sun….
So, these observations supported Copernicus’ theory!
Part 3 -- Galileo (15 minutes)

20. The Heliocentric Theory
The Sun is the center of our solar system

21. The heliocentric model
Copernicus believed that the Earth rotates once per day, and revolves around the Sun once per year, as shown in the figure.
Do you think these motions of the Earth affect you? Well, they produce day and night; and they produce the seasons. {READ reasons for seasons}
The axis of rotation of the Earth is constant (points always in the same direction) and is at an angle to the plane of the orbit. Therefore the solar illumination in the northern or southern hemisphere varies throughout the year as the Earth goes around the sun. Solar illumination is greatest during the summer and least during the winter.
A common misconception is that the Earth is closer to the sun during the summer (so that the summer is hotter). That’s false! The distance to the sun has nothing to do with the seasons. Perihelion occurs in December. In any case, summer in the northern hemisphere is winter in the southern hemisphere; and vice versa. If the distance to the sun were relevant, then the two hemispheres would have the same seasons. But, on the contrary, their seasons are out of phase by 6 months. Right now – today -- it is winter in Australia and South America.
The figure shows the solstices and equinoxes (A, B, C, D).
At winter solstice (for the N hemisphere) the axis of rotation points away from the sun, so that the N hemisphere gets the least solar radiation. At summer solstice (for the N hemisphere) the axis points toward the sun, so that the N hemisphere gets the most solar radiation.
The reasons for seasons – the Earth travels around the sun, and its axis of rotation is tilted by 23.5 degrees to the plane of the orbit. In July, the northern hemisphere is getting more sunlight than in January.
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22. Comparing and Contrasting Historical Theories of the Solar System
Geocentric Model
Heliocentric Model

24. HEAVEN HELL Before the scientific revolution …
… people regarded the Earth as a very large object at the center of the universe. It is so large it seems to be a flat surface. The heavenly bodies – sun, moon, stars, planets – were thought to be small objects above the Earth.
And of course “heaven” was somewhere above; and “hell” was down below.
HELL

25. Timeline Galileo 1564-1642 Newton 1642-1727 Brahe 1546-1601 Copernicus
Kepler

26. The Copernican Revolution
This timeline shows the life spans of the four most important scientists in the Copernican Revolution. This advance in science was at the core of the Scientific Revolution.
Copernicus lived at the same time as Christopher Columbus. Galileo and Kepler were contemporaries, a generation after Copernicus. Then Newton completed the work in the next generation. Newton lived at the time of the first English colonies in America.
[Copernicus 1473 to 1543; Galileo 1564 to 1642; Kepler 1571 to 1630; Newton 1643 to 1727]
The idea that the sun and not the Earth is the center of the universe -- or at least at the center of the solar system -- started with Nicolas Copernicus.
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27. Nicolaus Copernicus The Earth moves, in two ways.
It rotates on an axis (period = 1 day).
It revolves around the sun (period = 1 year).
Part 2 -- Copernicus (15 minutes)
The Copernican model was based on the hypothesis that the Earth moves, in two ways.
{READ}
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28. Tycho Brahe 1546 – 1601 Adjusted the Geocentric Theory
Brahe’s precise observations of planet movement lead him to believe that the moon and sun orbited the sun, and the other planets orbited the sun

29. Through Brahe’s observations with instruments that lead to the invention of the telescope he developed mathematical calculations of the orbits of the planets, sun, and moon,
These calculations helped Kepler determine the equations for planetary motion

30. Johannes Kepler (1571 – 1630)
Developed the laws that describe how the planets move in the solar system
Planets move in elliptical orbits
Mrs. Scasny’s
Part 4 – Kepler (20 minutes)
{READ first part}
Johannes Kepler was a contemporary of Galileo. Galileo lived in Italy, Kepler in Northern Europe, mostly Germany. Galileo was a Catholic; Kepler a Lutheran.
Kepler held the position of Mathematician to the Holy Roman Emperor. His most important work was to study planetary observations, and to relate them to the heliocentric model of Copernicus.
The result of years of arduous mathematical work was summarized in three empirical laws of planetary orbits.
{READ the three laws}
So Kepler discovered the true behavior of the planets in the Solar System.
Kepler lived at a time of great turmoil in Europe. The Reformation and the Counter-Reformation led to terrible wars between Protestants and Catholics. Some rulers persecuted people for religion. While the man-made chaos was occurring all around him – sometimes even affecting Kepler himself – Kepler was discovering the natural order in the heavens.

31. Galileo’s discoveries in Astronomy
Galileo did not invent the telescope, but when he heard about the invention he figured out how to build telescopes. He had the best telescopes of his time. He was the first person to use telescopes to look at the heavenly bodies. He was first, so he made the discoveries.
 Craters and mountains on the moon
 4 Moons of Jupiter
 Phases of Venus
 The Milky Way consists of innumerable stars.
 Sunspots (dark spots) move across the sun’s face.
All of these favored the Copernican (heliocentric) model.
Galileo was professor of mathematics, but also interested in the physical world. His believed that observations and experiments are the only way to know nature.
We have seen that his discoveries in physics came from observations and measurements. His discoveries in astronomy came from telescopes.
{READ the slide}

32. Galileo’s sketch of the moon as seen from his telescope
Here are a couple of pictures of the moon.
The first is Galileo’s sketch…{READ}
The second is a modern photograph…{READ}
So Galileo could see that the moon is not some ideal heavenly disk, but a real material sphere with craters and mountains. It was like another little world. However, as was often the case with Galileo, many philosophers did not want to accept his new knowledge. They just couldn’t bring themselves to admit that their whole world view was based on errors.
In a letter to Kepler, Galileo wrote… “{READ the quote}
A photograph of the moon
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33. These ideas could be dangerous.
Galileo made many specific discoveries in astronomy, through observations by telescope.
The general implications…
● The planets are objects like the Earth – masses – rather than some kind of special heavenly objects. Or, to put it another way, the Earth is just another planet.
● The planets, including Earth, travel around the sun.
● The Universe is a lot bigger than we can see by the naked eye.
{READ first line}
Galileo also asked what his discoveries would imply about the universe in general.
The general implications of his discoveries were significant evidence for the Copernican Model.
{READ the rest}
These ideas could be dangerous.

34. The Trial of Galileo
The Church decided that the heliocentric model was a heresy.
But Galileo continued to argue in favor of the theory, and published his reasoning. The Inquisition in Rome accused him of heresy, and required him to answer.
He was put under arrest and sentenced to prison. But because of his fame and age (70 years old at that time) he was allowed to serve under house arrest in Florence, for the remaining years of his life.
A dramatic event in the history of Europe was the Trial of Galileo, in the year 1633.
{READ up to “Found guilty”}
To comprehend this event, you must realize that Galileo was a good Catholic. He was educated in a monastery. His two daughters both became nuns. He wanted to obey the Church. He thought he had followed all their rules to get his book published; and the evidence of history is that he had indeed followed their rules. Nevertheless he was accused of heresy.
{READ rest}
For the final 8 years of his life, Galileo was not allowed to travel or meet people or speak about his discoveries in astronomy. During that period, even at such an advanced age, he continued to work on physics; physics was not so controversial as cosmology.
Did Galileo know that his ideas about cosmology would eventually be accepted, although not in his lifetime? [[etc]] Of course he knew.

35. Isaac Newton 1642 - 1727 Part 5 -- Newton (15 minutes)
Finally, in this historical lecture, Isaac Newton.

36. To explain the motion of the planets, Newton developed three ideas:
Isaac Newton
Newton solved the premier scientific problem of his time --- to explain the motion of the planets.
To explain the motion of the planets, Newton developed three ideas:
The laws of motion
The theory of universal gravitation
All objects in the universe attract each other through gravity
Heavy objects and those that are close together have the strongest gravitational force
Calculus, a new branch of mathematics (oh what fun!!)
{READ to quotation}
Newton based his work on the discoveries of his predecessors. This Newton quotation is taken from a letter to Robert Hooke, another physicist of the time of Newton. {READ quotation}
“If I have been able to see farther than others it is because I stood on the shoulders of giants.”
--- Newton’s letter to Robert Hooke,
perhaps referring to Galileo and Kepler

37. Newton’s Theory of Universal Gravitation
Newton and the Apple
Newton asked good questions  the key to his success.
Observing Earth’s gravity acting on an apple, and seeing the moon, Newton asked whether the Earth’s gravity extends as far as the moon.
{READ}
(The apple never fell on his head, but sometimes a stupid person will say that, trying to be funny.)
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38. Warm Up How much time passes when…
…..the moon goes around the earth 3 times?
…..the earth goes around the sun 50 times?
…..the Earth rotates 360 degrees?
…..there are 12 full moons?
…..the Earth rotates halfway around?

39. Warm Up What causes the Earth’s seasons?
Draw the diagram below and label which season we would be having:

40. Warm Up What causes the Earth’s seasons?
Draw the diagram below and label which season we would be having:
SUN