If the Earth were stationary, a given line joining point A on the Earth, a nearby star C and any given distant star would never vary. However, if the Earth changed its position in space and moved from A to B, this alignment would also change. Thus, in the background of more distant stars, the hearby star would apwar to shift from C1 to C2 as the Earth moved from A to B. This apparent shifting of nearby stars against the background of more distant ones has been observed, and the phenomenanis called Stellar parallax. It is a periodic kind of a chahge. A given star first shifts one way and then the other, during the course of one year, hence it must be due to the fact that the Earth is moving around the Sun.
The change is small, less than a second of an arc. It was only in 1838 that Friedrich Bessel, a German astronomer, could measure the stellar parallax of a star. -1 he nearest star, the Sun when viewed against distant stars appears to shift approximately 1" per day.