Question

The geocentric model could not explain which of the following observations made by early astronomers? Select the two correct answers.
Responses

Mercury and Venus changed in appearance throughout the year.
Mercury and Venus changed in appearance throughout the year. - no response given

The planets had epicycles.
The planets had epicycles. - no response given

Mars and Jupiter appeared to move backwards for some period of time.
Mars and Jupiter appeared to move backwards for some period of time. - no response given

The stars appeared to move.

Answer 1

- Mercury and Venus changed in appearance throughout the year.
(The full set of phases and changing apparent size—especially Venus showing gibbous/full phases—contradicted a simple Earth-centered arrangement.)

- Mars and Jupiter appeared to move backwards for some period of time.
(Retrograde motion could only be forced into the geocentric picture with complex epicycles; the heliocentric model explains it naturally.)