Astronomy in-class activity: planetary motion models, first principles versus scientific models

Astronomy 210 In-class activity 7 v.15.08.16, fall semester 2015
Cuesta College, San Luis Obispo, CA

Students find their assigned groups of three to four students, and work cooperatively on an in-class activity worksheet to analyze how the Ptolemaic and Copernican models reproduce prograde and retrograde motion of planets, and to distinguish between first principles and scientific models.

GIF animation: teacup epicycle

"070526 Teacup Epicycle"
http://flic.kr/p/oJYjtb
Originally uploaded by Waifer X

Street carousel, K Street Mall, Sacramento, CA. Video by Cuesta College Physical Sciences Division instructor Dr. Patrick M. Len.

Astronomy quiz question: heliocentric model of retrograde motion

Astronomy 210 Quiz 2, Fall Semester 2008
Cuesta College, San Luis Obispo, CA

[4.0 points.] How does Copernicus' model explain the retrograde motion of a planet?
(A) The only perfect shape is a circle, and the only perfect motion is uniform motion.
(B) A planet slows down in its orbit when it is further from the sun, and speeds up in its orbit when it is closer to the sun.
(C) A planet moves around a circle that itself moves along an orbit around the Earth.
(D) A planet has a different orbital distance and speed around the sun from the Earth's orbital distance and speed around the sun.

Correct answer: (D)

Copernicus' model of planetary motion explains retrograde motion as a "lapping illusion" when planets in different orbits traveling at different speeds move past each other. Response (A) is Ptolemy's model of retrograde motion; response (B) is Kepler's second law; response (C) is based on Aristotle's first principles, but does not explain retrograde motion.

Student responses
Section 70158
(A) : 9 students
(B) : 11 students
(C) : 14 students
(D) : 18 students

"Difficulty level": 39%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.35

Astronomy quiz question: geocentric model of retrograde motion

Astronomy 210 Quiz 2, Fall Semester 2008
Cuesta College, San Luis Obispo, CA

[4.0 points.] How does Ptolemy's model explain the retrograde motion of a planet?
(A) The only perfect shape is a circle, and the only perfect motion is uniform motion.
(B) A planet has a different orbital distance and speed around the sun from the Earth's orbital distance and speed around the sun.
(C) A planet moves around a circle that itself moves along an orbit around the Earth.
(D) A planet slows down in its orbit when it is further from the sun, and speeds up in its orbit when it is closer to the sun.

Correct answer: (C)

Ptolemy's model of planetary motion used epicycles moving along deferents to explain the retrograde loops of planets. Response (A) is based on his (and Aristotle's) first principles, but in and of itself is not a model of retrograde motion; response (B) is Copernicus' heliocentric explanation of retrograde motion; and response (D) is Kepler's second law.

Student responses
Section 70160
(A) : 1 student
(B) : 2 students
(C) : 22 students
(D) : 8 students

"Difficulty level": 69%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.89

Carousel teacup epicycle movie

070526 Carousel Teacup Epicycle
Venetian Carousel, K Street Mall
Sacramento, CA
http://www.youtube.com/watch?v=FIsiezgo7nY

Astronomy 10 learning goal Q3.2

Dramatization of planetary motion in the Ptolemaic model. Watch the girl in the teacup (planet on epicycle) as the merry-go-round (the deferent), well, goes around and around.

Geocentrism, redux

"Something's going wrong. Stop the global warming."

Dogal Hayati Koruma Dernegi (Turkish Nature Life Protection Association), www.dhkd.org
(Via shedwa.blogspot.com)

Astronomy 10 learning goal Q3.2

Ignorance of global warming is equated with the antiquated geocentric model of planetary motion.