Announcements Homework due on Sunday at 11:45pm. Thank your classmate! You should have finished reading Chapter 3, and started on chapter 4 for next week. Don t forget your out of class planetarium show on Friday evenings or Saturday afternoon. Observing at Brooks Observatory starts next Monday. Come to the 5th floor of this building at 9 10pm. Bring your filled-out blue ticket!
The Raw Exam Distribution 40 30 20 10 0 0-9 10-19 20-29 30-39 40-49 50-59 60-69 70-79 80-89 90-100
The Raw Exam Distribution 40 30 20 10 0 0-9 10-19 20-29 30-39 40-49 50-59 60-69 70-79 80-89 90-100
The Raw Exam Distribution 40 30 20 10 0 0-9 10-19 20-29 30-39 40-49 50-59 60-69 70-79 80-89 90-100
Grades Your anonymously coded grades are on the course website:
Buy-Back Congratulations: as a class, you bought back 387 points! Remember: Write out the question, the text of the answer you chose, why you chose it, the text of the correct answer, and why. If you didn t circle your answers on your exam and take it with you... do so next time!
How to Buy-Back Incorrect: On #23 I Chose E but I just guessed, I now know it s B, cause that s the answer, dude. Correct: Question 23: For how many days was this planet in retrograde motion? I Chose E, 32 days, since that s how long the planet spent in the loop on the sky. Now I understand that it is in retrograde motion only when moving from East to West, which happened from March 31st to April 12th, over the course of 12 days. So the correct answer is B, 12 days. Also: you get no credit for picking one you already got correct!
The Adjusted Exam Distribution with Buy Back 60 45 30 15 0 0-9 20-29 40-49 60-69 80-89 100-110
The Adjusted Exam Distribution with Buy Back 60 45 30 15 0 0-9 20-29 40-49 60-69 80-89 100-110
Do your homework! Exam #1 Grade (Raw) Homework #1 Grade
Do your homework! Exam #1 Grade (Raw) Homework #1 Grade
18. You observe a full moon rising in the east. Which image shown below best represents how the Moon will appear when it sets? 19. A planet is moving in normal ( prograde ) motion. Over the course of several nights, how
18. You observe a full moon rising in the east. Which image shown below best represents how the Moon will appear when it sets? 19. A planet is moving in normal ( prograde ) motion. Over the course of several nights, how
18. You observe a full moon rising in the east. Which image shown below best represents how the Moon will appear when it sets? 19. A planet is moving in normal ( prograde ) motion. Over the course of several nights, how
18. You observe a full moon rising in the east. Which image shown below best represents how the Moon will appear when it sets? 19. A planet is moving in normal ( prograde ) motion. Over the course of several nights, how
34. Which of the following is smallest? A. size of a typical planet B. 1 light-second C. 1 AU D. size of a typical star Light would travel 7 times around Earth in 1 second!
34. Which of the following is smallest? A. size of a typical planet B. 1 light-second C. 1 AU D. size of a typical star Light would travel 7 times around Earth in 1 second!
Jupiter is 3 light-seconds in circumference!
29. Earth is always precisely 1 astronomical unit from the Sun. A. True B. False
29. Earth is always precisely 1 astronomical unit from the Sun. A. True B. False http://www.windows2universe.org/physical_science/physics/mechanics/orbit/orbit_shape_interactive.html
Last Time Ancient peoples: structures to mark progression of sun/moon/planets.
Last Time Greeks: Earth is round, at center of real celestial spheres.
Last Time 1500 years of Ptolemaic model before earth was displaced as center of universe.
Last Time Copernicus: first to gain traction with a suncentered universe.
Last Time Brahe/Kepler: measured and refined the model of motions: not circles but ellipses!
Last Time Galileo: Cemented heliocentric model using a telescope. Moons of jupiter, sunspots, etc.
Last Time Retrograde motion the key: very complicated epicycle models required to account. Simple to explain when all planets orbit the sun!
Kepler s Laws of Planetary Motion Kepler s First Law: The orbit of each planet around the Sun is an ellipse, with the Sun at one focus.
Kepler s Laws of Planetary Motion Kepler s Second Law: As a planet moves around its orbit, a line from the planet to the Sun sweeps out equal area in equal time.
Kepler s 2 nd Law Equal area law implies that planets move: Faster when closer to sun Perihelion = planet closest to sun Slower when farther from sun Aphelion = planet farthest from sun
Kepler s Laws of Planetary Motion Kepler s Third Law: The ratio of the cube of the average distance of the planet from the Sun (a=semimajor axis) to the square of the orbital period (p) is the same for each planet. P 2 =A 3 p in units of years a in units of Astronomical Units
What is an Astronomical Unit? It is Earth s distance from the Sun (or more technically, it is the Earth s semi-major axis) 1 A.U. = 1.5 x 10 11 m 499 light seconds!
Does the third law work for the Earth? Earth: P = 1 year, a = 1 A.U. P 2 = a 3 so 1 2 = 1 3 or 1 = 1 It works!
Graphical Version of Kepler s Third Law The farther you are from the Sun, the longer your orbital period The farther you are from the Sun, the slower you orbit the Sun p 2 = a 3
One year of time (Earth is green)
An asteroid orbits the sun at an average distance of 4 A.U. What is it s orbital period? A) 1 year B) 4 years C) 8 years D) 64 years A C B D
An asteroid orbits the sun at an average distance of 4 A.U. What is it s orbital period? A) 1 year B) 4 years C) 8 years A B D) 64 years C D
An asteroid orbits the sun at an average distance of 4 A.U. What is it s orbital period? A) 1 year B) 4 years C) 8 years A B D) 64 years A = 4 A.U. P 2 = A 3 = 4 3 = 64 P = 8 years! C D
Consider a planet orbiting the Sun. If the mass of the planet doubled but the planet stayed at the same orbital distance, then the planet would take A C B D A) more than twice as long to orbit the Sun. B) exactly twice as long to orbit the Sun. C) the same amount of time to orbit the Sun. D) exactly half as long to orbit the Sun.
Consider a planet orbiting the Sun. If the mass of the planet doubled but the planet stayed at the same orbital distance, then the planet would take A C B D A) more than twice as long to orbit the Sun. B) exactly twice as long to orbit the Sun. C) the same amount of time to orbit the Sun. D) exactly half as long to orbit the Sun.
A 3 = P 2
A B If a small weather satellite and the large International Space Station are orbiting Earth at the same altitude above Earth s surface, which object takes longer to orbit once around Earth? A) the large space station B) the small weather satellite C) the same amount of time to orbit the Sun. C D
A B If a small weather satellite and the large International Space Station are orbiting Earth at the same altitude above Earth s surface, which object takes longer to orbit once around Earth? C D A) the large space station B) the small weather satellite C) the same amount of time to orbit the Sun.
A B Which of the following best C D describes what would happen if Mercury and Jupiter were to switch places in their orbits about the Sun? A) Jupiter, the larger planet, would have a shorter orbital period than before. B) Mercury, the smaller planet, would have a shorter orbital period than before. C) Neither of the two planets would have any change in their orbital periods.
A B Which of the following best C D describes what would happen if Mercury and Jupiter were to switch places in their orbits about the Sun? A) Jupiter, the larger planet, would have a shorter orbital period than before. B) Mercury, the smaller planet, would have a shorter orbital period than before. C) Neither of the two planets would have any change in their orbital periods.
Where do Kepler s laws work? Everywhere!
Why do Kepler s Laws work everywhere? Gravity... which brings us to... Sir Isaac Newton
Gravity, Energy, and Motion
Describing Motion speed = rate at which an object moves. Distance/Time example: 10 m/s velocity = speed + direction. example: 10 m/s due West acceleration = change in the speed or direction Example: 10 m/s 2
The Acceleration Due to Gravity All falling objects accelerate at the same rate (not counting air resistance) independent of mass. On Earth, g 10 m/ s 2 : speed increases 10 m/s with each falling second 10 m/s per second or 10 m/s 2
A C B D If you drop a hammer and a feather at the same time on the moon: A) the hammer will hit the ground first B) the feather will hit the ground first C) they will hit the ground at the same time
A C B D If you drop a hammer and a feather at the same time on the moon: A) the hammer will hit the ground first B) the feather will hit the ground first C) they will hit the ground at the same time
Gravity The acceleration due to gravity is the same for any object on the surface of the earth. Hammer and feather fall at the same rate (neglecting air resistance).
For Next Time Start Reading Chapter 4. Remember: First week of Evening observing at Brooks Observatory starts Monday. HW#2 Due Sunday Evening