A student made the following observations about astronomical bodies.

Observation 1: Mars reverses its direction of motion in the sky.
Observation 2: The stars appear brighter at different times of the year.

Which observation(s) can be explained using the heliocentric model?

A. Only observation 1
B. Only observation 2
C. Both observation 1 and observation 2
D. Neither observation 1 nor observation 2