Gerald Kelleher wrote:
Proof of the Earth's orbital motion is that the background stars appear
to move parallel to the orbital plane and eventually behind the Sun's glare for a period.

http://solar-center.stanford.edu/AO/dawn-rising.html

A solar eclipse abruptly alters when a star comes into view close to the
central Sun but this information is lost to those who unfortunately are
stuck with a rotating celestial sphere.



So you are using the fixed reference of the background stars to demonstrate
orbital motion.
Works just as well for the Earths rotation - that's how we know the
sidereal day.