1. The first direct image of a planet belonging to a star similar to the Sun. Located just 500 light-years away toward the constellation Scorpius, this star is only slightly less massive and a little cooler than the Sun. But it is much younger, a few million years old compared to the middle-aged Sun's 5 billion years. This sharp infrared image shows the young star has a likely companion
positioned above and left - a hot planet with about 8 times the mass of Jupiter, orbiting a whopping 330 times the Earth-Sun distance from its parent star. The young planetary companion is still hot and relatively bright in infrared light due to the heat generated during its formation.

2. Homework #1 is due today, 8:00 pm
Homework #2 will be posted shortly
It will be due Monday, September 21, 8:00 pm

3. Johannes Kepler ( )
Hired by Tycho to analyze his observations of planetary positions, particularly Mars
Greatest theorist of his day
Believed that “forces” made the planets move
Developed his three laws of planetary motion

4. Kepler’s First Law
Each planet’s orbit around the Sun is an ellipse, with the Sun at one focus.

5. Ellipse: defined by points located such that the sum of the distances from the two foci is constant
Animation by Michael Kossin

6. The circle is a special form of an ellipsey
x2/a2 + y2/b2 = 1
focus
Semimajor axis = a X
Semiminor axis = b
Eccentricity
e2 = 1 - b2/a2

7. Kepler’s Second Law
A planet moves along its orbit with a speed that changes in such a way that a line from the planet to the Sun sweeps out equal areas in equal intervals of time.
Consequence: planets move faster when they are closer to the sun and, conversely, planets spend more time in the more distant parts of their orbits
A good animation demonstrating this law can be found at:

8. Kepler’s Third Law a3 / P2 = constant
The constant is the same for all planets
The ratio of the cube of a planet’s average distance from the Sun “a” to the square of its orbital period “P” is the same for each planet.
Consequence: Planets with larger orbits have longer orbital periods.
A good animation demonstrating this law can be found at:

9. a3 / P2 = constant Earth: a = 1 AU, P = 1 year
So, if we measure the size of a planet’s orbit in AU and its orbital period in Earth years, then constant in the 3rd Law is 1 AU3 yr-2
Jupiter: a = AU,
P = years

10. Kepler's Laws
1. The Law of Orbits: All planets move in elliptical orbits, with the sun at one focus.
2. The Law of Areas: Planets move faster in their orbit the closer they are to the Sun.
3. The Law of Periods: Planets on larger orbits take longer to complete an orbit than planets smaller orbits.

11. Kepler’s Laws are extremely accurate in their predictions of planetary motions.
They are “empirical”, i.e., they are derived from experiment, experience, and observation rather than from theory or logic
Isaac Newton subsequently demonstrated that Kepler’s laws are the natural outcome of gravity.

12. GROUP ACTIVITY Schmooze: (from a Yiddish word meaning to chat)
To converse idly or casually and in a friendly manner, especially in order to make a social connection.
(2) The act or an instance of schmoozing.
GROUP ACTIVITY
Assemble into groups of 5 or 6 students
Introduce yourselves & “schmooze” for a couple minutes
Discuss why you are taking the class
Create a name for your activity group
After a few minutes, we will have an exercise

13. Group Activity
The moderator’s job is:
Record the response of the group to the activity
Printed the names of each group member participating (if a member does not participate, omit their name)
Record the group’s name
At the end of the activity, each participant should sign their name following their printed name. DO NOT SIGN FOR SOMEONE ELSE!!

14. Kepler’s laws were determined empirically, i. e. , by observation
Kepler’s laws were determined empirically, i.e., by observation. No theoretical basis existed for these laws. Now, we will determine an A103 analogue:
Consider a phonograph record that is spinning. Inspired by Kepler’s 3rd Law, determine the relationship between the distance from the center of the record (“a”) and the length of time it takes for that point to make one complete circuit around the center (“P”). a
Think!!

15. Kepler’s First Law of planetary motion states that
A) an imaginary line joining the Sun and planet sweeps out equal areas in equal times
B) the further a planet is from the Sun, the faster it moves in its orbit
C) the orbits of planets are ellipses
D) the further a planet is from the Sun, the slower it moves in its orbit

16. Kepler’s First Law of planetary motion states that
A) an imaginary line joining the Sun and planet sweeps out equal areas in equal times
B) the further a planet is from the Sun, the faster it moves in its orbit
C) the orbits of planets are ellipses
D) the further a planet is from the Sun, the slower it moves in its orbit

17. Kepler’s Second Law of planetary motion states that
A) as a planet orbits the Sun, it moves faster the closer it is to the Sun
B) a planet on a larger orbit orbits the Sun more slowly than a planet with a smaller orbit
C) the orbits of planets are ellipses

18. Kepler’s Second Law of planetary motion states that
A) as a planet orbits the Sun, it moves faster the closer it is to the Sun

19. Kepler’s Third Law of planetary motion states that
A) the further a planet is from the Sun, the faster it moves in its orbit
B) an imaginary line joining the Sun and planet sweeps out equal areas in equal times
C) the further a planet is from the Sun, the longer it takes to complete a full orbit
D) the orbits of planets are ellipses

20. Kepler’s Third Law of planetary motion states that
A) the further a planet is from the Sun, the faster it moves in its orbit
B) an imaginary line joining the Sun and planet sweeps out equal areas in equal times
C) the further a planet is from the Sun, the longer it takes to complete a full orbit
D) the orbits of planets are ellipses

21. Which of the following is a contradiction of Kepler's Laws of planetary motion?
A planet in a highly eccentric orbit spends most of its time in the outer parts of its orbit.
A planet orbiting in a circular orbit.
An inferior planet having a shorter orbital period than the Earth's orbital period.
Planets have their smallest velocity when they are nearest the sun.

22. Which of the following is a contradiction of Kepler's Laws of planetary motion?
A planet in a highly eccentric orbit spends most of its time in the outer parts of its orbit.
A planet orbiting in a circular orbit.
An inferior planet having a shorter orbital period than the Earth's orbital period.
Planets have their smallest velocity when they are nearest the sun.

23. Two models of the Universe
Geocentric
Heliocentric

24. Which model more accurately depicts nature?
Both make predictions for the apparent motions of planets and stars.
Heliocentric model, with modifications incorporating Kepler’s Laws, gives more accurate predictions
But, the Geocentric model might be made more accurate through appropriate modifications.
Need additional predictions that clearly differentiate between the two models.

25. Contemporary with Kepler was the “founder of experimental science”
Galileo Galilei ( ),
the “founder of experimental science”
First person known to point a telescope at the sky
He wanted to connect the physics understood on earth with objects in the heaven
His work got him in trouble with the Church and led to his house arrest for many years.

26. (Some of) Galileo’s Observations
Galileo saw craters and shadows cast by the mountains on the Moon (Moon had a landscape; it was a “place”, not a perfect heavenly body)

27. (Some of) Galileo’s Observations
Galileo saw craters and shadows cast by the mountains on the Moon (Moon had a landscape; it was a “place”, not a perfect heavenly body)
Sunspots (sun not “perfect”)

28. (Some of) Galileo’s Observations
Galileo saw craters and shadows cast by the mountains on the Moon (Moon had a landscape; it was a “place”, not a perfect heavenly body)
Sunspots (sun not “perfect”)
Rotation of sun

29. (Some of) Galileo’s Observations
Galileo saw craters and shadows cast by the mountains on the Moon (Moon had a landscape; it was a “place”, not a perfect heavenly body)
Sunspots (sun not “perfect”)
Rotation of sun
Moons of Jupiter (Heavenly bodies existed which did not orbit the earth)

30. (Some of) Galileo’s Observations
Galileo saw craters and shadows cast by the mountains on the Moon (Moon had a landscape; it was a “place”, not a perfect heavenly body)
Sunspots (sun not “perfect”)
Rotation of sun
Moons of Jupiter (Heavenly bodies existed which did not orbit the earth)
Phases of Venus: the two models of the Universe made two very different predictions.

31. Phases of Venus

32. Galileo observed all phases!
Galileo’s observation of the phases of Venus was the final evidence that buried the geocentric model.
Geocentric
Heliocentric
No gibbous or full phases!
All phases are seen!
Galileo observed all phases!