Copernican model
- Stars can now be fixed
- Earth rotates and orbits, just like the other planets
- Eventually, this idea was accepted
- Galileo finally pardoned by Catholic Church in 1980
- Note: Copernicus couldn’t predict planetary positions any better than Ptolemy -- his argument was based on simplicity and beauty.
- Speed of earth in orbit (calculate) ~ 72,000 mph
- why don’t we notice this?
- we’re all moving together in an inertial frame (Ast 102)
- i.e. if you travel on a smooth and quiet plane or train, and you don’t look out the window, there is no sensation of motion at 600 mph.
Critics complained that moving earth --> parallax
- Earth travels 2 AU, stars should appear to move (parallax)
- no stellar parallax could be detected