Announcement... Extra Credit!

Announcement... Extra Credit! • See a planetarium show at Museum of the Rockies: • Sky Quest • Current Sky • Not a laser show or a kid’s show! • Sign in at the front desk. • Free admission! • 20 points — same as an activity! • One time only. By the last day of classes!

Announcement... Extra Credit! Taylor Planetarium current schedule:

Review: Spherical Earth Motion of the stars Motion of the Sun & Moon Solar System: Geocentric models Aristotle Ptolemy Copernicus Developing a model of the solar system

Models of the solar system • Stars move each night • Sun moves through the stars throughout the year • Planets • move slowly through the stars • planet means “wandering star” • Earth-centered or Sun-centered

Aristotle’s model (384-322 BC)

Problem: retrograde motion • Planets sometimes back up! • Aristotle’s model doesn’t do that.

Retrograde motion of Mars http://www.lasalle.edu/~smithsc/Astronomy/retrograd.html

Retrograde motion of Mars

Earth is at the center Earth is imperfect, celestial sphere is perfect Circles govern heavenly motions Cladius Ptolemy (85-165)

Ptolemy’sgeocentric model

Retrograde motion (Ptolemy) http://www.lasalle.edu/~smithsc/Astronomy/retrograd.html

Retrograde motion (Ptolemy)

Epicycle Ptolemy’s model was actually even more complicated.

Copernicus’ heliocentric model • Ptolemy’s model was used for almost 1400 years. • Copernicus proposed a very different model in 1543: • Planets, including Earth, move around Sun. • Retrograde motion is explained without epicycles.

Retrograde motion

Retrograde motion (Copernicus) http://www.lasalle.edu/~smithsc/Astronomy/retrograd.html

Announcement... Extra Credit!