Copernicus: A Sun-Centered Model: Practice Problem Solutions

1. Sun-centered.

2. Mercury, Venus, Earth, Mars, Jupiter, Saturn.

3. Earth, on a faster inside orbit, overtakes a slower outer planet, which makes the planet seem to slide backward for a while, like a slower car you pass on the highway.

4. His model was no more accurate than Ptolemy's (it still used circles), no star parallax could be seen, and the physics of a moving Earth was not understood yet.

5. The apparent shift of a nearby star against more distant stars as Earth moves around its orbit. Friedrich Bessel first measured it in 1838.

6. He was a canon (church administrator), and also trained in medicine and law.

7. Their orbits are inside Earth's orbit, so seen from Earth they can never get far from the Sun.