Lecture 3e. Copernicus & Heliocentric Picure
1. Copernicus hypothesized the Earth and the planets orbit the Sun.
So
Earth was no longer the center of the universe!
2. This assertion had a number of consequences, which could be
used to make predictions that observers could check:
- variation in the Sun's illumination of Venus should cause the planet to go through
phases similar to phases of the Moon
- as discussed above, the Earth had to be rotating for day/night cycles, etc.
- as discussed above, stellar parallax should be observed
Each of these would eventually be observed, but none were seen in Copernicus' lifetime.
3. BUT this cosmology also cleared up some difficulties:
- Mercury and Venus always lying close to the Sun was understandable
- Sun's lack of epicycles in Ptolemaic theory was now explained
- errors in predictions made with Ptolemaic models were not surprising